Contents | Install | Terminology

# The SRE-http Web Server

## version 1.3g

## Introduction

SRE-http is an http/1.1 compliant WWW Server for OS/2. Written in REXX, SRE-http is designed to run as filter under GOSERVE, an IBM EWS Internet Server.

SRE-http provides a number of useful features including:

- Support for multiple hosts
- Remotely configurable (with complete on-line documentation)
- Common-log auditing
- Request-selector-specific and file-specific (HTACCESS) access controls
- Several types of document redirection are easily specified.
- A wide variety of cachable server side includes can be dictated by including the well-known NCSA-style elements in your HTML documents
- Easy to configure support for mappable images and searchable indices
- Client-specific and browser-specific documents are readily specified
- Support for server-side-processing using SRE-http addons and CGI-BIN scripts; with numerous tools to help programmers create their own web aware applications.
- Bundled accessories include a cachable dynamic directory display facilty, a text search facility, and a simple message-box facility.
- Available addons include a BBS sytem, a discussion-group package, and a directory-indexer/search-engine

  This document describes how to use `SRE-http.` While not necessary, the reader should first examine the documentation that comes with GoServe (GOSERVE.DOC). Knowledge of the REXX programming language would also help. However, you can still do a lot of nice stuff with only a rudimentary understanding of GoServe, or of REXX. Lastly, if you don't know HTML, the "markup language" of the world-wide web (WWW), then it's going to be hard to do anything interesting!

  Before reading this manual, we strongly recommend that you peruse the SRE-http users guide -- it's a much easier read!

  Other useful documentation files include:

- The 1 Page Introduction summarizes SRE-http.
- The SRE-http outline describes the steps that SRE-http follows when processing a request.
- The description of SRE-http parameters gives a detailed description of SRE-http's user configurable parameters.
- The list of help files summarizes the various help documents supplied with SRE-http.

  ### Other GoServe filters.....

  > An older alternative to this filter is Don Meyer's GoHTTP HTTP filter system.
  > GOHTTP offers CGI-BIN, HTACCESS compatability, common-log auditing, and rudimentary support for server side includes.

  > Another alternative is the InterFilt filter of Derek Sims. It has good support for multiple realms and multiple hosts, but lacks server side includes and other features.

  ### Notes to upgraders

  > For most sites, upgrading SRE-http from version 1.2 should present few difficulties -- most of the user-configurable options have not changed. However, there have been a few changes to minor features (and a few rarely used features have been dropped). Furthermore, SRE-http addons should be upgraded; current versions of the addons will work, but will not be http/1.1 compliant.

  > Please read the HISTORY.TXT file for a complete listing of these changes.

  ## Table of Contents

- 1) Installation notes
- 1.a)Description of files
- 1.b)A note on SRE-http program structure.
- 1.c)Variables and Parameters
- 1.d)Some basic terminology
- 2)Multiple hosts, logon rights, and other access controls
- 2.a) Support for multiple hosts
- 2.b)Setting logon requirements
- 2.c)Providing open access, to selected resources, using PUBLIC_URLS
- 2.d)Assigning client privileges
- 2.e) Restricting access to selected server resources
- 2.f)Restricting access to directories using HTACCESS files
- 3)Modifying the request
- 3.a)Specifying the home page.
- 3.b)Specifying default documents, and generating directory listings
- 3.c) Using ~ to specify a home directory
- 3.d)Establishing virtual directories
- 3.e)Specifying ALIASES
- 3.e.i)To modify simple requests (local redirection)
- 3.e.ii)To implement searchable indices
- 3.e.iii)To redirect requests for moved documents
- 3.e.iv)To specify the location of a CGI-BIN script
- 3.e.v)To indicate a negotiable resource
- 3.e.vi) Notes about ALIASES
- 3.f)What to do if the document is not found.
- 4) Server Side Includes
- 4.a)Headers and Footers
- 4.b)SRE-http style server side includes
- 4.b.i)Dynamic REPLACEments and string REPLACEments
- 4.b.ii)File INCLUDES
- 4.b.iii)Using OPTIONs (as incorporated into a request) as string replacements
- 4.b.iv)INTERPRETing pre-defined REXX-code
- 4.b.v) SELECTive excludes
- 4.b.vi) CACHE control
- 4.c) NCSA HTTPD style server-server side includes
- 4.c.i)Details on NCSA ssi's
- 4.d) Order of execution of keyphrases
- 5) Image Maps, CGI-BIN and SRE-http Addons
- 5.a) Processing image maps
- Types of regions
- 5.b)Creating SRE-http addons
- 5.b.i)Calling Syntax
- 5.b.ii)Return Values
- 5.b.iii)Notes
- 5.c) Support for CGI-BIN scripts.
- 5.c.i) CGI-BIN scripts in other directories.
- 5.c.ii) Notes on creating CGI-BIN scripts.
- 5.c.iii) Using PERL CGI-BIN scripts.
- 6) Miscellaneous SRE-http features
- 6.a) Special directives and special commands
- 6.a.i)Special directives
- 6.a.ii)Special commands
- 6.b)Common-log, browser, and referer audit files; and scheduled events
- 6.c)The RECORD_ALL_FILE running-count
- 6.c.i)Suppress recording of repetitive requests
- 6.d) Load balancing
- 6.e)Creating a user written pre-filter.
- 6.e.i) Running the GoRemote package
- 6.f)Creating a user written post-filter
- 6.f.i)Mailing event specific alerts
- 6.g) Uploading and deleting files
- 6.h) Automatic creation of response headers.
- 6.i) User defined MIME media types
- 7) Some useful built-in facilities
- 7.a)DOSEARCH : Search files for a text string
- 7.b)SENDFILE : A file transfer facility
- 7.c)Write to, and read from, message boxes
- 7.c.i)The message writer
- 7.c.i)Viewing message boxes
- 7.c.i)MESSBOX privileges
- 7.d)The SRE-http procedure library : A macrospace library of useful routines (for the ambitious REXX programmer).
- 7.e) Client-specific and browser-specific customization
- 8) Addons: A list of several useful SRE-http addons.

- Appendix 1: Description of various SRE-http parameter/control files.
- Appendix 2: Summary
- A2.a)Limitations of SRE-http
- A2.b)Summary of SRE-http Features
- Appendix 3: Terminology

  ## 1) Installation Notes

  SRE-http consists of a `filter` program (SREFILTR.80 or SREPROXY.80), numerous support procedures and daemons (such as SREFMON.CMD), sample pages, and various and sundry documentation files. As noted above, you'll need the latest version (2.52) of the GoServe package (note that earlier versions of GoServe lack several features that are needed to fully implement http/1.1)

  1. For convenience, let us assume that the GoServe package has been installed in the \GOSERVE directory (your GoServe working directory), and the GoServe data directory is set to \WWW.
  2. Copy SREV13F.ZIP to a temporary directory and then unzip it in the usual manner (i.e.; `UNZIP SREV13F)`. From an OS/2 prompt, run INSTALL (a REXX program bundled with SRE-http), and follow the on-line instructions. You will be asked to provide the names of several directories.

     If you select the defaults, INSTALL will create a number of directories. You will be asked to provide names, we recommend accepting the defaults.
     You will also be given the opportunity to set several SRE-http parameters, and to setup a SUPERUSER. We strongly recommend that you take this opportunity. In particular, setting up a SUPERUSER can help avoid later configuration headaches (though if you are very security conscious, you can skip this without terrible consequence).

     After running INSTALL, you can delete the contents of this temporary directory.

  3. Set up GoServe to run SRE-http:
     - Set the `filter` to be SREFILTR.80. To do this, you can insert http filter srefiltr.80 in the optional parameters line in GoServe's settings window (right-mouse click on the GoServe icon ...)
     - In certain cases, throughput can be markedly improved by using the SREPROXY.80 variant of SREFILTR.80.
     - For less complicated sites, the sreLite variant of SRE-http can yield significant improvements
     - You can start GoServe now ...
     - If you intend to run "server-side" programs, you might want to increase the following `Limits`:
     - `End client after inactive`
     - `End client after total`
     - Double check that the `DataDir` option points to the directory containing your HTML files (for example, \WWW).
     - It is HIGHLY recommended that the Data Directory and the GoServe Working Directory be different!
     - You must set the Options-Limit-Connection_Maintain value to be greater then 0 (a value between 10 and 30 seconds is reasonable).
     - You must have a properly defined TZ variable (it defines the time zone) in your OS/2 CONFIG.SYS file.
     - To view a running log of SRE-http's actions, run the PMPRINTF program.
  4. At this point, the default version of SRE-http is running! You'll probably want to change the values of a number of SRE-http's parameters. Although you can do this by editing the various parameter files (such asINITFILT.80) with a text editor, for the new user it is probably easier to run CONFIGUR.HTM -- a HTML front-end to SRE-http's built-in configurator.

     The most straightforward way of doing this is:

     - Make sure that GoServe is running on your server, with SREFILTR.80 as it's filter.
     - Fire up your favorite web browser
     - Point it at http://your.server/CONFIGUR.HTM (where your.server is the address of your http server).
     - You will be given the choice of a simple, intermediate, and expert mode configurator. The simple mode is best suited for new users; it's a bit cumbersome when making large changes, but is very well documented.
     - Hint: If the configurator won't let you in (due to insufficient privileges), you might want to check the OWNERS variable (in INITFILT.80) to be sure it points to your IP address. Alternatively, you can use the SUPERUSER username/password you created during the installation process.
  5. If you need to use a port other then 80, you should:
     - Change the names of all SRE-http files that end with .80 to be the .nnn, where nnn is the desired port (nnn can be greater then 3 digits if HPFS is being used). In particular, change `SREFILTR.80, INIT_STA.80 and INITFILT.80`
     - Enter http PORT nnn FILTER SREFILTR.nnn in the `optional parameters` setting of GoServe.
     - Note that it is possible to run multiple instances of the GoServe and SRE-http; using different ports, different GoServe working directories (and possibly different data, etc. directories), and different copies of the user-configurable files (the .IN, .CNT, and INITFILT.nnn files).
     - Remember, when using a port other then 80, clients will need to include `:nnn` in the IP address of your server.
  Now, all you have to do is create some informative, efficiently organized, and eye-catching HTML documents, paste them together, and add links to the rest of the net. But that's the fun part.

  > A note to upgraders As of ver 1.3d, SRE-http will be using configuration files located in a CFGS\ directory. For information on these new files, and on how to migrate older configuration files, please see USE_CFGS.DOC

  ### 1.a) Description of the files that comprise SRE-http

  The SRE-http package consists of a number of files. These include the SRE-http REXX programs, the macrospace procedure library, several user-configurable parameter files, samples of "counter and control" files, and some sample HTML files. A complete description of these files is contained in the file list.

  #### 1.a.i)On changing file and directory names

  Many of the directories, and files, mentioned above can have their names changed by modifying variables that are located in INITFILT.80 (the INITFILT_FILE); either by editing the file with a text editor, or by using the intermediate configurator. In this documentation we usually refer to files and directories by their "titles" (such as GoServe working directory), but occasionally the "default name" is used (such as \GOSERVE).

  If you change the names of your directories, keep the following in mind:

  - If you intend to make temporary files available to clients, the TEMPFILE_DIR directory should be a subdirectory of the GoServe data directory.
  - For SRE-http's documentation and examples to work properly, the IMGS and SAMPLES sub-directories should be directly under the GoServe data directory

  > New addition: You can now specify host & port specific configuration files in the CFGlist.CFG configuration file.

  ### 1.b) SRE-http structure: multi-threading and macrospace

  To speed up processing, and to facilitate modularization, SRE-http makes extensive use of REXX macrospace.

  Of greater import, SRE-http uses several daemons ("helper" threads) to handle a number of tasks (such as username lookup, alias matching, and SSI-document caching). These daemons are launched upon the first request to SRE-http. In addition, SRE-http stores a number of variables in the local (GoServe) environment.

  > For most users, these implementation details are unimportant. However, these threads do use system resources (queues) which remain alive even after GoServe has been turned off. To free these resources, you can use the FREEUP.CMD program that is shipped with SRE-http.

  > Citation: SRE-http uses the REXXLIB library to access macrospace and to generate/communicate between threads. A `distribution` copy of REXXLIB is supplied with SRE-http, and may be used freely with SRE-http. If you wish to use REXXLIB in other REXX programs, contact Quercus Systems for licensing information.

  Lastly, SRE-http monitors the parameter files, including INITFILT.80. Changes to these files will be incorporated into SRE-http's parameters about every 10 seconds.

  ### 1.c) Variables and Parameters

  Throughout this documentation reference is made to variables (aka "parameters") used to change SRE-http's options and features.

  > In the interest of thoroughness, this manual discusses the multitude of SRE-http options in terms of directly modifying these parameters. However, most individuals will probably never need to actually edit a file. Instead, almost all of the parameters mentioned herein can be modified using the intermediate-mode configurator (CONFIG2.HTM). In fact, in most cases the simple-mode configurator (CONFIG0.HTM) will do the job -- where appropriate, links to the appropriate section of the simple-mode configurator will be made available for your browsing pleasure .

  If you are a hands-on kind of administrator, feel free to directly modify these parameters. If so, you might also want to read the detailed descripton of INITFILT.80.

  ### 1.d) Some basic terminology

  The SRE-http documentation uses some not-necessarily-intuitively-obvious terms. The following lists a few of the more important ones. For a more complete list, see the terminology appendix.
  URL
    Universal Resource Locator (URL) is a scheme for specifying Internet resources using a single line of printable ASCII characters. A URL should contain a protocol, domain name, port number (optional), the location of the resource, and an (optional) option list (following a ?).
    Examples:
- `http://your.server.net/dir1/sample.htm`
- `http://pet.store.com/prices?type=mammals&class=retail`
  Request string
    When a client asks for a URL (say, by clicking on a link), a request string (along with request headers and a request body) is sent to the server (at the domain name and port listed in the URL). The request string consists of three tokens: the http method, the location of the resource on the server, and the http protocol.
    Examples (assuming the above URLs):
- `GET /dir1/sample.htm HTTP/1.0`
- `GET /prices?type=mammal&class=retail HTTP/1.0`
  Selector (also referred to as the request selector )
    The selector is the location of the resource on the server. Specifically, it's the (slightly modified) second term in the request string.
    Examples (assuming the above request strings):
- `dir1/sample.htm`
- `prices?type=mammal&class=retail` Note that the "slight modifications" consist of:
- dropping the leading /
- decoding URL-encoded characters (note that the above examples do not include any URL-encoded characters).

  In many cases, the connection between the selector and server resource it refers to is simple (such as when the selector is a filename relative to the GoServe data directory). In other cases, it's completely virtual (as when the resource consists of `the output of a program that's run using information provided by the client`).

  Selector-specific (usually written as SEL-specific )
    SEL-specific refers to SRE-http configuration information that is specific to a selector -- such as resource privileges, or a virtual directory.

    > The selector is a pointer to a web-server resource. Typically, this would be a file; but it might refer to the output of some program run just for this request. In either case, SRE-http has to match the selector to the actual resource (an activity that can become rather convoluted!).

    In much the same way that OS/2 `extended attributes` contain additional information about a file, SRE-http's SEL-specific information contain additional information about a selector (needless to say, this information is only used by SRE-http).

    Return to table of contents

    ## 2) Multiple hosts, logon rights, and other access controls

    A summary of this section:
    - SRE-http supports multi-hosting. Multiple hosting can occur in two different manners:
      1. When multiple numeric IP addresses are handled by a single computer
      2. When multiple aliases exist for a single numeric IP address; and the HOST: request header is provided by the client's browser.
    - SRE-http offers a number of logon controls. These are used to control basic access to any of the resources on your server.
    - A set of PUBLIC_URLS can be made available to the general public.
    - User specific privileges are used to permit (or deny) access to your server's resources.
    - SEL-specific and directory-specific access controls can be used to institute more refined access controls.

    ### 2.a) Multiple hosts

    To use SRE-http in a multi-host environment, you must specify host-specific entries that assign a data-directory and a host-nickname to a specific IP address.

    > The host-nickname is used throughout SRE-http's configuration files. It identifies parameters that apply only to requests directed to one (of possibly many) hosts being served by SRE-http.

    There are two ways of specifying host-specific entries:
    1. Creating HOSTS. "stem variables" in the INITFILT.80 file.

       The simple-mode configurator can be used create and modify these host-specific entries.

    2. Creating HOST "definitions" in the CFGLIST.CFG file. This is the recommended method (new as of March 1999) -- though at this time the on-line configurators will not modify CFGLIST.CFG.

    In either case, for each host entry you need to define an IP address (or alias), a host-nickname, and a default data directory. the hosts (either IP addresses

    For example, HOST. stem variables (in INITFILT.80) should contain the following information (in a comma delimited list):

         HOSTS.n ='ip_address, host_nickname,default_dir'

    Where:
- `ip_address` is a IP address (integer or numeric)
- `host_nickname` is the "nickname" you will use when referring to this host. The `host_nickname` must not be a number, it must contain at least one non-digit character. Thus, a host nickname of `1234` is invalid, but `1234X` is okay.
- `default_dir` is the default directory for this host (it is used instead of the GoServe default data directory).

  > A note on superceding hosts: As of ver 1.3g, there are three kinds of Hosts:`strict-superceding`, `superceding` and `non-superceding`. The basic difference is how and when non-host specific parameters are used to resolve requests to a defined host. See IN_FILES.DOC for the details.

  If your server recieves request from a host which does not have a matching HOSTS. entry, it will be treated as "generic" request; that is, the standard (single host style) default directory, etc. will be used with such requests.

  > Thus, if all requests (regardless of intended host) have identical access to your server's resources (it's files and programs) you can ignore this entire section!

  Given that you do want to have different resources available to different hosts, almost all of the SRE-http variables and parameters can be specified on a "host specific" basis

  - To specify "host specific" parameters in the .IN and .CNT files the host nickname, followed by //, is used.
    For example, for a virtual directory entry that maps TIGERS/ to D:\ANIMALS\TIGERS, but only for requests to ZOO.OURISP.NET; you might specify:

    > `ZOOSITE// TIGERS/ D:\ANIMALS\TIGERS`

    where ZOOSITE is the host nickname for ZOO.OURISP.NET, and a space separates the ZOOSITE// from TIGERS/.
  - For parameter names (defined in INITFILT.80), host-specific results are defined by appending a .HOST_NICKNAME to the variable name. For example, `CHECKLOG.ZOOSITE='NO'` refers to this "ZOOSITE" host.
  - A few of SRE-http's parameters are not host specific; such as the DISPLAY_ENV parameter.

  #### Notes

  - You can define Hosts using both the HOSTS. variables (in INITFILT.80) and by host-definitions in CFGLIST.CFG.
  - Superceding-hosts are identified by using `_!` as the first two characters in the host_nickname.

    Strict-superceding-hosts are identified by using `_!!` as the first three characters in the host_nickname.

  - CFGLIST.CFG is in the CFGS\ subdirectory of the GoServe working directory.
  - The host specific default directories are defined in the HOSTS. stem variables.
  - Requests to IP addresses not represented by a HOSTS. entry are treated as "generic" requests; that is, the standard (single host) variables apply.
  - In general, if a SRE-http variable/parameter does not contain host nickname information, then it applies to all hosts. In other words, if a host specific value of a parameter does not exist, the "generic" value is used.
  - INITFILT.DOC discusses in greater detail which SRE-http parameters may be host specific.
  - Be careful when using shorthand IP names (say, in a mixed Internet/Intranet environment).

  ### 2.b) Logon Controls

  > The simple-mode configurator can be used to enable LOGON, to add users to the USER_FILE, to add/remove IN-HOUSE clients, and to enable the LOGON_FAIL_FILE.

  #### Setting LOGON requirements with the CHECKLOG variable

  CHECKLOG should have one of the following values:
  NO
    No logon required; unencumbered entry for all clients.
  YES (or ALWAYS)
    Logon required for all requests.
  INHOUSE
    Entry allowed only to clients with INHOUSE or SUPERUSER privileges.

  #### Allowing unencumbered access to IN-HOUSE users

  The INHOUSEIPS. stem variable can be used to specify the numeric IP addresses of clients who are to be given "IN-HOUSE" status. IN-HOUSE client do not have to enter logon information, and they are automatically granted the privileges stored in the INHOUSE_PRIVS variable.

  ##### Notes

  - INHOUESIPS must be host-specific; INHOUSEIPS.1.ZOO='151.121.65.143' (see INITFILT.DOC for details).
  - The * character can be used as a "wildcard" in the INHOUSEIPS. stem variables.
  - Each INHOUSEIPS. value can include a client specific list of privileges (place it after the IP address).

  #### Owners have SUPERUSER status

  You can give SUPERUSER privileges to a set of numeric IP addresses by changing the value of the OWNERS variable.
  Notes:
- Wildcards are not allowed in the OWNERS variable
- OWNERS are given INHOUSE_PRIVS privileges, as well as SUPERUSER privileges.
- The OWNERS variable must be host-specific (see INITFILT.DOC for details).

  #### Logon for non IN-HOUSE users.

  If a logon is required, an authorization string (containing a name and password) is obtained from the client. SRE-http then examines the USER_FILE for a match. If a match is found, the request is honored (abstracting from SEL-specific or directory-specific access controls). Otherwise the client is asked to re-enter her name and password. Note that entries in the USER_FILE may be "host specific".

  Be aware that ...

  - SRE-http ver 1.3g supports both "basic" and "digest" authentication scheme.

    > Basic authentication is a very simple means of encoding the username and password, and is easily broken. Digest authentication is much more difficult to break -- the password is encrypted using an MD5 algorithim. See ENCRYPT.DOC for a dicussion of SRE-http encryption capabilites

  - Once asked for an authorization, most browsers will include an "authorization field" in subsequent requests to the same site. Thus, even if `CHECKLOG=ALWAYS`, the client will only need to enter his username and password once (that is, she won't need to reenter it each time a different document is requested).

  #### Keeping out known pests, and detecting fake IP addresses

  There may be particular clients (or sets of clients) that must be harshly denied all access to your site. This can be accomplished by recording the numeric IP addresses of these "unwanted clients" in the UNALLOWEDIPS.n stem variables (wildcards are permitted).

  Note that the OWNERS and INHOUSEIPS.n stem variables are checked first. If the client's numeric IP address appears in either of these lists, UNALLOWEDIPS.n is not checked. Thus, by setting `UNALLOWEDIPS.1="*"`, you can deny entry to everyone except OWNERS and IN-HOUSE users.
  Also note that on multi-hosted sites, UNALLOWEDIPS. entries must be "host-specific" (see INITFILT.DOC for details).

  For additional security, you can set the DNS_CHECK variable (to YES). When set to YES, SRE-http will lookup the client's IP name; and if it does not exist (there is no DNS entry), logon will be denied. This provdes some security against "spoofers", but it also slows down response time, and may keep out legitimate users using dynamic (and possibly unnamed) numeric IP addresses.

  > Caution: Use of either DNS_CHECK or UNALLOWEDIPS. will cause "cache busting" -- proxy servers out there on the web will not cache your documents. Since this can reduce throughput (both for your site's material, and for the entire web), enabling either of these options is not generally recommended.

  #### The LOGON_FAIL_FILE

  If the client does not have "logon rights", SRE-http will use the value of the LOGON_LIMIT and the LOGON_FAIL_FILE to determine the response.
  - LOGON_LIMIT is used to limit the number of attempts-per-minute.
  - If LOGON_LIMIT is exceeded, or the username/password is incorrect, you can then send the LOGON_FAIL_FILE as a "response" (rather then continually asking for the username and password).
  For further details, see the description of LOGON_LIMIT and LOGON_FAIL_FILE in INITFILT.DOC.

  #### Creating your own username/password databases

  In many circumstances you may wish to access some other database of usernames and passwords; say, a database maintained by a bulletin board system, or a database that is encrtyped. Although a direct means of accessing such databases is not offered, youa can instruct SRE-http to user your own custom procedure.

  To do this, set the USER_LOGON_PROC parameter (in `INIT_STA.CFG`) to point to a REXX program file that contains this custom procedure (or, that contains a procedure that calls a database manager or some other executable). For more details, see the discussion of USER_LOGON_PROC in INITFILT.DOC

  ### 2.c) PUBLIC_URLS

  There may be cases where you generally do not want to allow public access to your site, except for a set of clearly delimited public areas. For example, you may have a private site, except for a set of "who we are" documents. Although one could use selective access controls to accomplish this, the use of PUBLIC_URLS provides a simple and direct alternative.

  These PUBLIC_URLS (which are specifined in CFGS\PUBURLS.IN) are used to identify server resources that are "open to the public" -- that can be accessed by clients who have no logon rights and no access privileges.

  Basically, SRE-http compares the request (using wildcard matching with substitution) against the entries in PUBURLS.IN.

  All requests that match an entry in PUBURLS.IN:

  - will be examined for ALIASES and for virtual directory matches
  - will be checked for an extension, and will be examined for AUTO_NAME match (if needed).
  - server side includes, and server side processing, will be performed (provided the NO_INCLUDE and NO_PROCESSING variables are not in force).
  - Caching will not be suppressed.
  - The PUT and DELETE methods will not be permitted /permi
  - The clients privileges are set to:
  - `PUBLICFILES PUBLIC`,
  - plus the privileges in the PUBLIC_PRIVS SRE-http parameter,
  - plus possible In-house privileges,
  - plus privileges that might be associated with a username/password sent with this request
    ... even though this username/password is not required, the browser might have used it to gain access to a different resource on your server.
  PUBLIC_URLS can also specify literal public_urls. When a request selector matches one of these literal public_urls; file transfer is expedited by:
  - Not performing aliasing
  - Not using virtual directories and AUTO_NAME
  - Not attempting server side includes
  - Not attempting AUTO-HEADER.

  Notes:

  - To speed up processing, you can disable the ALWAYS_CHECK_PRIVS parameter (in-house and username privileges will not be available).
  - In a multi-host environment, the PUBLIC_URLS must be host specific (that is, "non-host specific" values of PUBLIC_URLS are not not used as defaults).
  - If you do not use PUBLIC_URLS, setting NEVER_PUBLICURLS=1 (in INIT_STA.80) can slightly speed up processing.
  - For a more detailed description of how to use PUBLIC_URLS, see PUBURLS.DOC.

  ### 2.d) Assigning client privileges

  In several circumstances, SRE-http will check the "client privileges" before transferring information. In particular, file transfer when SEL-specific access controls are in place (i.e.; when `ALLOW_ACCESS='NO'`) requires that the client have appropriate privileges.

  > In a sense, privileges offer a convenient shorthand for identifying sets of users.

  Privileges are set automatically for:
- IN-HOUSE clients are granted privileges stored in their INHOUSEIPS. variable,
- OWNERS are granted SUPERUSER privileges.

  > In addition, IN-HOUSE clients and OWNERS will be granted the privileges that are listed in the INHOUSE_PRIVS "space delimited list" variable. It is recommended that INHOUSE_PRIVS always include the INHOUSE privilege.

  For everyone else:
- If a logon is required, the privileges are read from the USER_FILE. Last of all ..
- Privileges listed in the the PUBLIC_PRIVS "spaced delimited list" variable are given to everyone.

  #### Special Feature: Dynamic privileges

  In addition to the above "static" privileges, clients can be assigned "dynamic" privileges. These dynamic privileges are typically set by prior actions (say, filling out a registration form, or requesting an introductory file), and have a short life expectancy (measured in minutes). For further discussion of these "dynamic" privileges, see ADDPRIVS.DOC, and the discussion of the CHECK_ADD_PRIVS and ADD_PRIVS_PREFIX variables in INITFILT.DOC.

  #### Special Feature: Secret privileges

  If you start a client privilege with a ? (say, `?PXX12`), then it will be treated as a "secret privilege". Secret privileges are not used in access controls, and SRE-http utilities should NOT reveal their values. They are designed to be by used by addons, such as the DYN_PWD "dynamic password" addon.

  ### 2.e) Accesss control on a selector-specific basis.

  > The simple-mode configurator can be used to enable selector-specific access controls, and to add/remove selector-specific access control entries

  There may be cases where you want clients to have unencumbered access to some, but not to all, the resources of your server. One way to do this is to assign access privileges on a which selector specific basis. The ACCESS_FILE, and the ALLOW_ACCESS variable, are used to construct these selector-specific (SEL-specific) access controls.

  ALLOW_ACCESS can take the following values:

  YES
    No limits -- all clients (with logon rights) are automatically given access rights to the server resource.
  INHOUSE
    IN-HOUSE users (and SUPERUSERs) are given automatic access rights, all others must have appropriate privileges.
  NO
    No one (except SUPERUSERs) is given automatic access rights, all others must have appropriate privileges.
  When ALLOW_ACCESS is enabled, SRE-http will examine the ACCESS_FILE for an entry that matches the request selector .
  - If a matching entry is found, SRE-http will then extract a SEL-specific resource privileges list. This is used (along with the client privileges) to determine if the client is authorized to access the resource.
  - If a matching entry is not found, the request will not be honored.

  #### Additional Features of the Access Control File

  In addition to general access rights (do you have any rights to the server resource), the ACCESS_FILE contains several additional pieces of SEL-specific information:
  - a permissions list,
  - the Realm Name
  - the name of a access failure file ,
  - the name of an advanced options file

  Permissions
  The permissions list includes information on:

  - suppression of server side includes and server side processing
  - PUT and DELETE permissions
  - CACHE enabling
  - suppression of aliasing, directory-specific access controls, virtual directory lookup, and post-filtering

  The Realm
  When ALLOW_ACCESS is enabled, and the client does not have appropriate privileges, SRE-http will query the client for a new username/password. When querying, the SEL-specific realm is displayed (if available). If there is no SEL-specific realm, the THE_REALM realm is displayed.

  ACCESS_FAIL_FILE
  If the client does not have access to the server resources represented by the selector, SRE-http will use the value of ACCESS_FAIL_FILE to dictate the response. If ACCESS_FAIL_FILE=0, a username/password will be re-requested. Otherwise, the ACCESS_FAIL_FILE, or a SEL-specific access failure file, will be returned. For details, see the discusion of ACCESS_FAIL_FILE in INITFILT.DOC.

  Advanced Options
  The SEL-specific advanced options file allows you to specify several SEL-specific advanced options, including:

  - Execution of external REXX procedures prior to returning a requested document
  - Customizing the response headers
  - Suppressing specific server-side-includes (such as the header and footer).
  - Selector specific mime type
  - Specifying selector-specific replacement rules

  #### Notes: Two types of resource privileges

  There are two types of resource privileges :
  ONE_OF (the default type).
    The client must have "one of" the ONE_OF privileges.
  MUST_HAVE (start with the & character)
    The client "must have" all the MUST_HAVE privileges.

    ..... if only one privilege is specified, these two types are equivalent.

  #### Notes: Matching client privileges to resource privileges

  SRE-http's privilege matching algorithim is quite simple:
  1. If a MUST_HAVE privilege appears in the SEL-specific resource privileges list, then it must also appear in the client privileges list. If not, access is denied.
  2. After checking all of the MUST_HAVE privileges, SRE-http then compares each ONE_OF privilege to the client privilege list. If any of these ONE_OF privileges appear, then access is permitted. Otherwise, access is denied.
  3. Reiterating: access is denied if there is no overlap between the client's privileges and the ONE_OF resource privileges

  #### Notes: SEL-specific permissions

  SEL-specific permissions are used to provide SEL-specific control of the features of SRE-http. That is:
- SEL-specific privileges are used to control access to a resource
- SEL-specific permissions are used to control SRE-http features, assuming that the SEL-specific privileges have been satisfied!
  Currently, the following permissions are available:
- Suppressing server-side actions You can suppress server-side-includes, and server-side-processing on a "SEL-specific" basis by including NO_SSI and NO_SSP permissions (respectively). You can also suppress "in-document" server-side processing (the SELECT and INTERPRET CODE keyphrases) by including a NO_CODE permission (note that NO_SSP implies NO_CODE).

- Permitting the PUT and DELETE methods SRE-http understands the PUT and DELETE HTTP methods. The PUT method is used to upload a file to your server, and save it using the location specified in the request. The DELETE method is used to delete a file, as specified by the location specified in the request.

  For security reasons, PUT and DELETE requests will only be honored if the appropriate permssion (PUT or DELETE respectively) appears in the permissions list .
  Furthermore, when using the PUT_FILE or GET_URL facilities to upload to a non-upload_directory subdirectory (that is, to a virtual directory), the PUT permission must apply (to the "selector" that matched the virtual directory).

- Suppressing examination of HTACCESS files To suppress the use of HTACCESS files for selected server resources, include a NO_HTACCESS permssion. Note that this will not effect the SHOWDIR dynamic directory list processor.

- Suppressing virtual directory, post-filter, and aliasing The NO_VIRTUAL, NO_POSTFILTER, and NO_ALIAS permissions will suppress virtual directory lookup, post-filtering and file recording, and alias lookup (respectively) on a SEL-specific basis.

- Allowing a file to be cached Whenever there is a possiblity that access to a resource will be denied to a client, SRE-http will disable caching of the file invoked by the request selector . In particular, if CHECKLOG is not equal to "NO", or if ALLOW_ACCESS is not equal to "YES", then caching will be suppressed.
  While an important security feature, there may be cases where you are willing to sacrifice some access control in order to speed up request processing. To achieve this, you can enable caching (on a URL specific basis) by including CACHE in the permission list.

  > Caching a response means: allow proxy servers (anywhere on the web) to store (and resolve) this response (and it's associated selector).

  Note that CACHE does not permit the GoServe cache. If you want to allow the GoServe cache to handle this selector, then use CACHE*. Please be aware that the GoServe cache is not http/1.1 compliant. When the GoServe cache answers a request, it will claim to be an http/1.0 server, and it will not include cache-control, etag, and other such http/1.1 response headers. While not necessarily a serious problem, it is a bit strange. Therefore, you may wish to use CACHE* only for unimportant resources, and to not check the "call filter anyways" GoServe option. That is, use CACHE* when SRE-http auditing (and other post-filter actions) are not needed (for example; for icons and background images).

  #### Notes: Miscellaneous

  - Advanced user option: You can specify REALM-specific resource privileges which will be added to the explicit SEL-specific resource privileges list (every selector identified as belonging to a given realm will have the same list of REALM-specific resource privileges).
  - Entries in the ACCESS_FILE can be "host specific".
  - The default ACCESS_FILE is ACCESS.IN.
  - Permissions are examined even when ALLOW_ACCESS=YES
  - Files requested by server side includes are not subject to access controls.
  - If the ACCESS_FILE does not exist, then access is disallowed to clients for whom ALLOW_ACCESS is enabled. The idea is that if there is no matching entry (in the ACCESS_FILE) for a selector, then the server resources associated with the selector should not be accessible. (... and if the ACCESS_FILE is unavailable, then there can't be a match).
  - Wildcard matching is supported.
    Note that global values of NO_INCLUDE=YES and NO_PROCESSING=YES take precedence over the SEL-specific SSI and SSP permissions!
  - Warning: use of the CACHE or CACHE* permission can inadvertently subvert access control!
  - You might want to include a global wildcard match. For example:
    - `* NO` -- if not explicitily mentioned, do NOT allow access
    - `* *` -- if not explicitily mentioned, allow access

  Return to table of contents

  ### 2.f) Directory-specific access control, using HTACCESS files.

  To provide compatability with HTTPD style servers (such as Don Meyer's GOHTTP), SRE-http supports the HTACCESS method of access control. This support uses code graciously loaned to us by Don Meyer, suitably modifed for SRE-http.

  Briefly, the HTACCESS method utilizes special HTACCESS files that are placed in your various directories (usually with the name `HTACCESS.`, or `.HTACCESS`). These files (there may one in each of several directories) contain entries pointing to password files, user-group files, and other parameters that are used to ascertain who shall be given access to the files in the directory (and it's child directories).
  HTACCESS control will be checked for all requests. Note that the presumed location of the HTACCESS file depends on the type of request:

  - Request for documents (including PUT and DELETE method requests) == In the directory of the document
  - File uploads == In the target directory of the upload (typically the UPLOAD_DIR directory)
  - CGI-BIN requests == In the CGI-BIN directory (or appropriate subdirectory)
  - SRE-http's built-in and included facilties == In the GoServe directory
  - Other server side processing requests == In the directory containing the requested program.
  In all these cases, the "parent" directories are also checked for HTACCESS files.

  #### Notes on the use of the HTACCESS method

  - Both methods of access control CAN be active: the "native" SRE-http "SEL-specific" access is checked first, and then the "HTACCESS" method of "directory specific" access is checked.
  - Since just about all the options provided by the "HTACCESS" method can be provided by the "native" SRE-http methods:

    > on speed of throughput grounds we recommend using the "native" SRE-http methods (that is, the SEL-specific method) whenever possible.

  - For details on enabling SRE-http's support of HTACCESS controls, see the description of the DO_HTACCESS and HTACCESS_FILE variables in INITFILT.DOC.
  - HTACCESS lookups are suppresed when the request matches a PUBLIC_URLS (that is, HTACCESS controls, redirection, etc. will not be attempted).
  - The HTACCESS files may also contain:
  - URL "redirection" information,
  - directory-specific default index information,
  - dynamic directory list processor parameters

  ## 3) Modifying the request

  URL's can get long and nasty, documents are often moved, people often mistpye URLs or don't ask for an exact filename, and sometimes it's just nice to use shorthands when specifying the location of your server resources. These actions are examples of modifications to the request.

  This section discusses ways you can conveniently modify & redirect a request (as recieved from the client).

  ### 3.a) Specifying the home page (the default)

  When the client sends an empty request, a `/`, or `"/?some+options"`, SRE-http assumes that the client desires the "home page" (the default document). By tradition (but not necessarily) the default document is a file named INDEX.HTM located in the root of the data directory.

  The default can be set using the `DEFAULT or DEFAULT.HOST_NICKNAME` variable (that is, DEFAULT may be host specific).

  > You can use the simple-mode configurator to set the home page and the directory-specific default document(s)

  Return to table of contents

  ### 3.b) Specifying default documents for directories

  Often, a request may arrive that specifies a directory, but does not specify a file. For example, a request for `COOLJUNK/JOKES/` does not specify a particular file, but instead implies "give me the default document for the COOLJUNK/JOKES subdirectory of the data directory". In these cases, the AUTO_NAME variable is examined.

  AUTO_NAME should contain a space delimited list of filenames to use when a request for a "directory" is recieved. SRE-http will attempt to find these files in this "requested" directory -- starting with the first name in the AUTO_NAME list. To assist in this search, a special name, consisting of *.HTM (or *.HTML) means use the directory_name.htm file.

  Lastly, an entry of !CREATE instructs SRE-http to generate a directory listing of files and subdirectories in the requested directory. This listing is generated with SRE-http's !DIR special action. By default, a <PRE> formatted table is generated, containing (for each file):

  - a descriptive icon
  - a link to the file
  - the file creation date
  - the size of the file
  If you are interested, it is fairly easy to modify these display options -- you can even tell SRE-http to automatically generate a description for each file.

  #### Example

  `AUTO_NAME=" *.HTM INDEX.HTM "`
  If the request is for `/INFO/MAINE/`, and your data directory is `D:\WWW`, then ...
- `*.HTM` is interpreted as: `D:\WWW\INFO\MAINE\MAINE.HTM`
- `INDEX.HTM` is interpreted as: `D:\WWW\INFO\MAINE\INDEX.HTM`

  #### Notes

  - AUTO_NAME has no effect on calls that do not specify a directory name --that is, the document specified in the DEFAULT variable is used in response to an empty (or /) request.
  - AUTO_NAME, and other forms of "local redirection" can cause problems when the client's browser resolves "partial URLS" -- see INITFILT.DOC for further discussion!
  - If you start a filename (in the AUTO_NAME list) with a /, is is assumed to be relative to the data directory (or to a virtual directory).
    Otherwise, the file is assumed to be relative to the current URL (you can include additional path information).
  - Instead of *.HTM, you can use *.`ext`, where `ext` can be any other extension (say, `HTML`, or `SHT`
    For example: `auto_name=" *.HTM *.SHT INDEX.HTML PUBS/INDEX.HTM "` (note that PUBS/INDEX.HTM refers to the PUBS directory relative to the current URL).
  - !CREATE should always be the last item in AUTO_NAME (anything following it will never be reached).
  - !SHOWDIR can be used as an alternative to !CREATE -- see SHOWDIR.DOC for details.
  - For a full featured directory lister, you might want to examine the GETAFILE addon for SRE-http!

  In contrast to explicit request to the root of a directory (that is, requests that end with a /); requests:

- that do not end in a /,
- than do not contain a ?, and
- that do not have a .extension can be interpreted in several manners. The NOEXT_TYPE variable is used to select how such requests are interpreted.

  NOEXT_TYPE can take any mixture of the following values (in a space delimited list):

  - `DIR` or `REDIR`: A / is appended to the end of the request, and the client is redirected back to the modified URL (that is, a remote redirection is attempted).
  - `HTM or HTML` : Interpret as an abbreviation for an HTML file (with extensions of .HTM or .HTML respectively).
  - `NONE`: Interpret as is.
  - `other_string`: The other_string is added. For example, if `NOEXT_TYPE=.GIF`, then `.GIF` will be added to these "no extension" requests.
  Note that a DIR (or a REDIR) should be the last item in the NOEXT_TYPE list.

  Return to table of contents

  ### 3.c) Using ~ to specify the home directory

  > You can use the simple-mode configurator to set the home-directory

  As a convenience, SRE-http will replace occurences of ~ characters in request selector with a string. Since the ~ is often used to point to a set of individual "home directories", this replacement string is stored in the HOME_DIR variable.

  To select the home directory , change the value of the HOME_DIR (or HOME_DIR.HOST_NICKNAME) variable.

  ##### Example

  If ...
- HOME_DIR="BRANCH/STAFF/PERSONAL/" and
- The request is `~JOES/PAGE.HTM`, .. then
- SRE-http will look for: `BRANCH/STAFF/PERSONAL/JOES/PAGE.HTM` (under your data directory, or in a virtual directory).

  ##### Notes

  - This HOME_DIR "string replacement" does minimal syntax checking (// are replaced with /). Thus, one should be careful that the definition of HOME_DIR, and it's use in the the links included in your HTML documents, is consistent.

  #### Advanced Option: Specifying User Subdirectories

  In many cases, you may wish clients to limit access to particular subdirectories of your `HOME_DIR` directory. For example, suppose all "students" have space on the `HOME_DIR` directory of your web server; or `HOME_DIR` may be on a LAN drive accessible as a virtual directory from the web server. These "student" directories may contain several subdirectories; one of which is intended for WWW use, while the others are for personal use.

  > The goal is to give clients direct access to the "web" related directories but not to the "personal" directories.

  This goal can be achieved by including a $ in the `HOME_DIR` parameter. Specifically, the $ is replaced by the portion of the request between the ~ and the first / following this ~

  For example: If:

  - `HOME_DIR=USERS/$/WWW`
  - the request is `/~GERALD/RESUME.HTM`
  Then SRE-http will use: /USERS/GERALD/WWW/RESUME.HTM

  For futher details, see the discusssion of the `HOME_DIR` parameter in INITFILT.DOC.

  ### 3.d) Establishing virtual directories

  > You can use the simple-mode configurator to add/remove virtual directories.

  By default, SRE-http will match the request selector to a file in the `data directory`; or if the request is for server side processing (such as an SRE-http addon, or a CGI-BIN script), to a file in the `addon directory` or `CGI-BIN directory`. While a good security feature (files not in these directories are inaccessible), this can be an inconvenience. To remedy this inconvenience, one can define "virtual directories" using the VIRTUAL_FILE. Basically, SRE-http will compare the starting portion of a URL to see if it matches an entry in VIRTUAL_FILE. If it does, the directory listed in the entry is used (instead of the data directory or addon directory).

  Thus, you can make available a wide, but controllable, set of "local" directories (on or LAN accessible from) your server.

  In addition, "virtual directories" can point to "remote" directories on other http servers -- SRE-http will attempt to retrieve the file from the remote server; without using a redirection.

  To clarify: to the client, remote virtual directories are indistinguishable from "local" virtual directories.

  > In particular, HTML files with server side includes can be remotely located -- and if the remote server makes no attempt to process these server side includes, SRE-http will!

  For details on the use of the virtual directories, see the description of the VIRTUAL_FILE .

  Note that entries in the VIRTUAL_FILE may be "host specific"

  Return to table of contents

  ### 3.e) Using "aliases" when responding to requests

  ALIASES are used in SRE-http to redefine and redirect requests
  Along with the ALIAS_FILE, the CHECK_ALIAS parameter controls whether and when ALIAS checking occurs.

  CHECK_ALIAS should have one of the following values:

- NO = Suppress ALIAS checking
- YES = Enable ALIAS checking

  #### Major uses for ALIASES

  #### 3.e.i) Local redirection

  - To modify simple URLs's. For example:
  - You may want to convert a request for `GETINFO` into: `INFODIR/GETINFO.HTM`.

  #### 3.e.ii) Processing searchable indices

  - The DOSEARCH SRE-http addon (available from the SRE-http home page), when combined with an ALIAS, provides a simple means of implementing text-based searchable indices.

    To use SRE-http's searchable index facility, one should create an alias of the form:
    `INDXFILE.HTM?* DOSEARCH?FILE=FILE.NAM&TARGET=*`
    Where

    - `INDXFILE.HTM` is the name of a searchable index (that is, an HTML document containing an <ISINDEX> element).
    - `DOSEARCH` instructs SRE-http to "execute the DOSEARCH addon."
    - `FILE.NAM` is the name (relative to the data directory, or in a "local" virtual directory) of the ASCII text file to be searched.
    Note that the alias will not be activated on the first request for INDXFILE.HTM -- only upon return (when a ? is appended to the request selector by the browser) will this alias match occur.

    If you want to use some other text search program, you could set up an alias of the form:
    `SEARCHIT.HTM?* SRCHREXX?*`

  - SEARCHIT.HTM is invoked at first (since the request does not contain a ?).
  - The SRCHREXX procedure is called after the client enters the search string (and the client appends a ? to SEARCHIT.HTM). SRCHREXX should be a REXX procedure located in the SRCHREXX.CMD (or SRCHREXX.80) file in the ADDON directory; and it might call a powerful search engine.

  #### 3.e.iii)Remote redirection

  - There are 4 ways of using an alias to indicate that a document has been moved to a new server (or you can use the simple-mode configurator to add/remove remote redirections).
    `target http://new.site.org/newname`
      If the request selector matches `target`, a "temporary" (HTTP status code 302) redirection to the new URL (i.e.; http://new.site.org/newname) will be returned to the client. A full URL must be specified (starting with http://).
    `target !TEMP http://new.site.org/newname`
      Same as above, but you can use short-hand's URLS (i.e.; without the http://). If you do not include an ip address, redirection will be back to your site.
    `target !MOVED http://new.site.org/newname`
      Same as above, but the redirection is permanent (HTTP status code 301).
    `target !NOTIFY http://new.site.org/newname`
      A "message has been moved" document will be returned to the client, which will contain a link to it's new location. Techincally speaking, this is not "redirection". Rather, it's a "notification of redirection", with the intention that the client will change the appropriate links (or bookmarks). Citation: The code for this is courtesy of Don Meyer!
    Examples:
  - `PROJ/P48.HTM http://www.prez.edu/truman.htm`
  - `PROJ/LINCOLN/* !MOVED civ.war.org/p1/alinc.htm` Notes:If you do not use !TEMP or !MOVED, you must specify a full URL-- do not forget the http://.

  #### 3.e.iv) Redirecting requests for CGI-BIN scripts

  > This usage of alias is somewhat obsolete, use of CGI-BIN virtual directories is now recommended).

  If you want to run a CGI-BIN script that is not in your CGI_BIN_DIR directory, you can use the ALIAS file to provide path information. In this case, the alias should consist of the CGI-BIN script name (without any slashes or other path information), followed by the drive and directory where it can be found.
  For example:
- If ..
  - a selector of `CGI-BIN/MAKEMAP/?NEB+IOWA` is recieved
  - The ALIAS file contains a `MAKEMAP D:\EXES\GIS` entry
  - MAKEMAP.EXE is a CGI-BIN script located in D:\EXES\GIS
- then...
  - D:\EXES\GIS\MAKEMAP.EXE will be invoked, with NEB+IOWA placed into standard input (along with all the other CGI-BIN variables stored in the environment).

  Note that if this `MAKEMAP D:\EXES\GIS` entry did not exist, SRE-http would look for a MAKEMAP program (such as MAKEMAP.CMD) in your CGI_BIN_DIR directory.

  #### 3.e.v) Content Negotiation

SRE-http supports both server-side and client-side content negotiation. In either case, you use a special ALIAS to indicate that a given selector is "negotiable".

The basic syntax of this alias is:
`sel !NEGOTIATE`
where `sel` is a selector, and `!NEGOTIATE` indicates that `sel` is a "negotiable" resource.
For example: `VARTEST/VAR3.VV !NEGOTIATE`

> Actually, `sel` should be a "variant list" -- SRE-http uses "variant lists" to determine which "alternate" (of several possible variants) to use.

Alternatively,you can use:
`sel !NEGOTIATE variant_file`
where sel is a * wildcard containing selector, and variant_file is a valid selector pointing to the variant file.
For example: `INFO/* !NEGOTIATE INFO/MANUALS.LST`

> INFO/MANUALS.LST would be the "variant file" -- it would be used for all request selectors that match INFO/*. If you use this "wildcard" construct, be sure to include an appropriate PATTERN: in the variant file.

For details on SRE-http's support for content negotiation, including support for custom "remote variant selection algorithims", see NEGOTIAT.DOC.

#### 3.e.vi) Notes about Aliases

- Entries in the ALIAS_FILE may be "host-specific"
- Host-specific aliases are checked first. If there is no host-specific alias that matches the request, then the default (non-host-specific) aliases are checked.
- The use of aliases as a means of identifying the location of a CGI-Bin script is "not spec", so should be used with caution.
- "Local redirection" using aliases can cause problems when the client's browser resolves "partial URLS" -- see INITFILT.DOC for further discussion!
- You can use wildcard matches and wildcard matches with substitution in your aliases (note the LINCOLN example above). This is useful if you want to redirect all request for files that used to be in a subdirectory to some new location.
- ALIASES are processed before the AUTO-NAME replacement is attempted. Keep this in mind when considering how to handle requests that arrive with no extension, no ?, and that do not end with a /.

Return to table of contents

### 3.f) What to do if no document can be found

Sometimes, despite the use of aliases et al., it may not be possible to map the request to a file (or other resource) on your server. In those cases, a `404 Not found` response is returned to the client, along with a short description. You can put a customized message in this short description. In particular, you can put a link to your "home page".

The NOT_FOUND_URL variable contains this customized message. By default, it's value is:
`<a href="/"> Visit the HOME_NAME home page? </a>`
Note that `HOME_NAME` will be replaced by the current (possibly host specific) value of the HOME_NAME variable.
Thus, the befuddled client merely needs to click on this link to get some kind of access.

Notes:

- For greater customizaton, you can set NOT_FOUND_URL to point to a could not find document response file. This should be either be a fully qualified file name (this file will be returned whenever the requested resource can not be found); or, it can be a pathless filename, in which case the file is assumed to be relative to the selector's directory.
- HOME_NAME should contain a short description of your domain; say:
  `BIG/SERVICE: Your Friendly Government Agency!`.
  Or, you can set `HOME_NAME`=" " to send a generic message.
- Note that HOME_NAME and NOT_FOUND_URL can be HOST specific.
- For further discussion of HOME_NAME and NOT_FOUND_URL, see INITFILT.DOC.
- Hint: in conjunction with NOT_FOUND_URL you can use the MTCHFILE.RXX to present the user with a list of possible matches to your misspelled request.

Return to table of contents

## 4) Using Server Side Includes

One of the primary advantages of SRE-http is the extensive support for a variety of server side includes. These server side includes (SSI's) let you easily create dynamic documents. In particular, inclusion of files, text strings, and transient variables (such as the time, date, and number of requests) are easy to accomplish, requiring modifications to your HTML documents, and not to the server software.

SRE-http supports two sets of SSIs -- the NCSA set of SSIs, and a set of SRE-http-style SSIs. Both sets require the inclusion of special keyphrases in one's HTML documents. When an HTML document is requested, SRE-http will (optionally) detect these keyphrases, and perform some sort of textual substitusion.

The basic structure of a keyphrase is:

- <!-- KEYWORD `` argument `` --> where:
  - KEYWORD can be one of several phrases:
    - SELECT -- used to selectively include blocks of HTML code
    - REPLACE -- used to "replace strings"
    - INCLUDE -- used to "include files"
    - OPTION -- used to "include options sent by the client"
    - INTERPRET -- used to "include the results of a custom-designed REXX routine"
    - CACHE -- controls SRE-http's server side include CACHE
    - #cmd -- NCSA HTTPD style server side includes
  - argument is a string containing "arguments" that are used, in conjunction with the keyphrase, to dictate how SRE-http should modify this document.
  Examples:
- <-- REPLACE CREATION_DATE --> :
- <-- INCLUDE ADDLIST.HTM -- >
- <-- #FLASTMOD FILE="srehttp.htm" -->

  #### Alternate keyphrases

  In the interests of brevity, and to help avoid conflicts with other html comments that aren't comments , there are several modifications you can make to these KEYWORDS.
  1. If desired, you can add a "preface" (such as the ! character) to the definitions of the first six keywords (i.e.; !REPLACE is used instead of REPLACE). For further details, see the description in INITFILT.DOC of the KEY_PREFACE variable.
  2. You can use several shorthands:
     - `%` instead of `REPLACE`
     - `$` instead of `INTERPRET FILE`
     - `#` instead of `INTERPRET CODE`
     For further details, see the descriptions in INITFILT.DOC of the QUICK_INTERPRET, QUICK_INTERPRET_CODE, and QUICK_REPLACE variables.

  #### Miscellaneous Notes

  - When SRE-http finds a keyphrase, it will ALWAYS remove the keyphrase, and replace it with the file or string dictated by the KEYWORD argument . This replacement occurs at the position in the document that was occupied by the keyphrase. If a faulty keyphrase is encountered (i.e.; a non-supported argument is used), SRE-http will remove it.
  - The SELECT keyphrase is a little different: it dictates whether the "block of HTML code" that follows the SELECT keyphrase is to be retained. Thus, it is best thought of as a "server side exclude" -- the keyphrase is always removed, but sometimes so is a lot of other stuff!
  - The CACHE keyphrase is used to control SRE-http's caching of documents that contain server side includes (it is not used to control the GoServe, SREPROXY, or external proxy caches).
  - The NSCA HTTPD style server side includes are provided for completeness sake; some of them are redundant with REPLACE and INCLUDE.
  - You can instruct SRE-http to perform server side includes only on files that have a .SHT or .SHTML extension. See the description of the SSI_SHTML_ONLY and SSI_EXTENSIONS parameter (in INITFILT.DOC) for details. Or, you can use the simple-mode configurator.
  - Instead of using <!-- and --> as keyphrase delimiters, you can specify your own set(s). See the description of DELIM_1 and DELIM_2 in INITFILT.DOC for details.
  - As a more general type of "server side include"; you can use REPLACE_RULES. -- these perform textual replacements over your entire document; and may be specified generically (see INITFILT.DOC), or on a selector specific basis (see ADV_OPTS.DOC).

  ### 4.a) Headers and Footers

  In addition to server side includes using keyphrases, a multi-line header and footer can be automatically added to all HTML documents. The header is added just after the (first) <BODY > tag in the document (see the notes for an exception to this rule); and the footer is added just before the (last) </BODY > tag.

  To set these, just change the values of the HEADERS. (for headers) and the FOOTERS. (for footers) stem variables located in INITFILT.80. Or, you can use the simple-mode configurator.

  #### Header and Footer Notes

  - Headers and Footers can contain keyphrases.
  - To suppress addition of a header and/or a footer, set HEADERS.1=0 and/or FOOTERS.1=0.
  - If the HEADER starts with <BODY>, then the HEADER will replace the first <BODY> element.
  - The various server-side includes are only attempted for HTML files.
  - If you will NEVER have server-side includes, you can set the NO_INCLUDE variable to equal "YES". This will speed up request processing a bit.
  - HEADERS., FOOTERS., and NO_INCLUDE can be host specific (see INITFILT.DOC for details).

  Return to table of contents

  ### 4.b) SRE-http style server side includes

  #### 4.b.i) The REPLACE keyphrase

  Syntax: `<!-- REPLACE Varname -->` , where `Varname` is the name of a static or dynamic variable. Note that you can use % instead of REPLACE.

  The REPLACE keyword is used to insert dynamically determined information and short (static) strings into a document. SRE-http recognizes the following "built-in" `Varnames` (the underlined variables are user-configurable, possibly host-specific, "static" variables that can be modified by editing INITFILT.80): :

  - DATE : todays date (i.e.; 27 Aug 1988)
  - TIME : current time (local) (i.e.; 4:54pm)
  - DATEGMT : current date (at GMT)
  - TIMEGMT : current time (GMT) -- a GMT is appended
  - CREATION : Short message stating (local) creation time and date of the document
  - CREATION_DATE : Creation date of document
  - CREATION_TIME : Creation time of document
  - SERVERNAME : The IP name of the server (i.e.; WWW.MYORG.NET). If multiple hosts, this will be the IP name of the server to whom the request was directed.
  - SERVER : the server software (i.e. GOSERVE ver. 2.52 )
  - WEBMASTER : The Webmaster's address
  - USERNAME : The client's name, i.e. johndoe.somewear.net (or his numeric ip address if a name is unavailable)
  - HOME_NAME : The host specific colloquial (not necessarily IP) name of this domain
  - URL : The current URL (includes the servername and serverport)
  - BROWSER: The name of the web browser the client is using (sometimes referred to as the 'User-Agent')
  - FILTER_NAME : The name of the filter (i.e.; SRE-http ver 1.2).
  - REFERER : The address of the server that refered the client to your site (often unavailable).
  - INHOUSE.n : n = an integer. If the user has INHOUSE privileges (but does not have SUPERUSER privileges) then replace with the INHOUSE.n variable
  - SUPERUSER.n : n = an integer. If the user has SUPERUSER privileges then replace with the SUPERUSER.n variable
  - HITS and HITS_FILE: A string stating the number of hits for the "URL" or the file (respectively), being requested (the number of hits is stored in the COUNTER_FILE ).
    Note that a given document may be reached via several different selectors (say, due to several aliases pointing to the same file), each of which will have a seperate counter. In contrast, each FILE has a unique counter. Also note that on multiple host servers, otherwise similar selectors (that may even point to the same file) will have seperate URL counter entries -- but (if they do point to the same file) will have only one FILE entry.
  - COUNTS and COUNTS_FILE: Same as HITS, but just the number is displayed.
  - OPTION_COUNTS.n and OPTION_HITS.n : Normally, the same as COUNT and HITS. But, if an option has been recieved, use the value of the nth option (rather then number of hits).
  - READ_HEAD or HEADER : Displays (using a <PRE>> format) the "request header". This can be a handy debugging tool.
  - PREFILTER_RESULT : Displays "status" message returned by the PREFILTR routine. If the PRE_FILTER variable equals NO, PREFILTER_RESULT will be an empty string.
  A special argument can be used to extract variables from the GoServe environment, which // contains many variables created by SRE-http.
  - VARIABLE.varname will extract the varname variable, where varname is either in the GoServe/SRE-http environment, or a value hard coded in INIT_STA.80. For example, VARIABLE.HOST_NICKNAME refers to "host nickname" (if available) to whom this request was directed.

  Last of all, if none of the above matches argument , the custom REPLACEments are searched for a match (which might be host specific). If a match is found, the information from this custom REPLACEment is used.
  You can even include `argument placeholders` to this custom replacement; they will be replaced by `arguments` included in the REPLACE keyphrase.
  To create custom REPLACEments, you should edit the REPSTRGS.IN file, or the ATTRIBS.CFG file (or you can use the simple-mode configurator).

  ##### Examples

  <!-- REPLACE TIME -->
  <!-- % URL -->
  <!-- % ODOM MYDOC1 -->

  ##### Notes

  - To create a host-specific "static" variable, you should include a .HOST_NICKNAME. For example, for a host with a nickname of ZOO, the WEBMASTER should be specified (in INITFILT.80) using:
    `WEBMASTER.ZOO='MANAGER@ZOO.YOURSTATE.ORG'`.
    If a matching host-specific entry does not exist, the "generic" entry (in this case, WEBMASTER) would be used.
  - Both "built-in" and "user-defined in the ATTRIBS.CFG and REPSTRGS.IN file" variables can be host specific (using the above syntax in both cases).
  - When including static variables in your HTML documents, the .HOST_NICKNAME should not be appended!
    For example, if the ZOO host is asked for INDEX.HTM, and INDEX.HTM containsthe tag: <!-- REPLACE WEBMASTER -->; SRE-http would look up the value of the WEBMASTER.ZOO variable.
    In contrast, if the tag were: <!-- REPLACE WEBMASTER.ZOO --> SRE-http would look for WEBMASTER.ZOO.ZOO.
  - Dynamically determined information consists of variables that are determined at the moment the request is recieved. For example:
    <!-- `REPLACE TIME` -->
    will cause the current (local) time to be placed in the document.
  - Static information is the same for all requests (to a given host). Inclusion of static variables can be a great convenience when writing sets of HTML documents, especially if phrases that occur in all these documents are subject to frequent change (say, a daily message).
  - The HIT_CACHE_LEN and HIT_OWNER_SUPPRESS variables can be used to reduce the number of false hits.

  Return to table of contents

  #### 4.b.ii) The INCLUDE keyphrase

  Syntax: `<!-- INCLUDE FileName -->` , where FileName is the name of the File to be included.

  The INCLUDE keyphrase instructs SRE-http to include the contents of a file into the requested document (where argument is the file-to-be-included). For example, `INCLUDE PHONE.LST` would cause the contents of the file `PHONE.LST` (in your data directory) to be inserted into the document.

  ##### Examples

  <!-- include buttons.bar -->
  <!-- include newtoday.txt -->

  ##### Special Feature: Browser and Client Specific File Includes

  You can use the ByBROWSR.RXX INTERPRETable utility to selectively include browser-specific files into your documents. These can be complete documents (with the "requested document" containing only a stub); or you can include smaller browser specfic components in an otherwise all purpose document.

  In a similar vein, the ByCLIENT.RXX INTERPRETable utility can be used to selectively include files on a "client-specific" basis, where clients can be identified with cookies, privileges, or their IP address.

  ##### Notes

  - It is recommended that INCLUDE keyphrases appear on seperate lines of a file (with no other HTML statements or text).

    > The file is treated as a long string (that contains linefeeds) and replaces the keyphrase -- anything before or after the keyphrase (on the same line) will be placed just before and after the contents of the file.

  - FileName is interpreted relative to the Data Directory, or to a "local" virtual directory .
  - The INCLUDE keyphrase will check for potentially fatal, recursive file INCLUDES, and disallow them. Since this check is very primitive, it will also disallow multiple INCLUDEs of the same file. If you need to include a file multiple times (say, to position a button bar at the top and bottom of your document), you can use the #INCLUDE keyphrase.
  - INCLUDE, in combination with the INTERPRET keyphrase, facilitates customization of your documents , based on client specific informaton (such as the `user agent` )!
  Return to table of contents

  #### 4.b.iii) The OPTION keyphrase

  Syntax: `<!-- OPTION n -->` , where n is an integer.

  The OPTION keyphrase instructs SRE-http to insert the contents of the n'th OPTION into the document.
  OPTIONs are contained in the portion of the request following the ? character.

  ##### How to pass OPTIONs to a document

  To pass OPTIONs to a document, the selector portion of the request should have the form:
  `HTMLFILE.HTM?Your+OPTION+1&OPTION2`
  - In this example ....
  - `OPTION 1` keyphrases in HTMLFILE.HTM would be replaced with the string `Your OPTION 1`
  - `OPTION 2` keyphrases in HTMLFILE.HTM would be replaced with `OPTION2` .
  - `OPTION 3` keyphrases in HTMLFILE.HTM will be removed (since only two options appear in the request).
  - URL character decoding is done on the string following the ? character.
  - You can have as many OPTIONs as you like, each seperated by a &.

  ##### OPTIONs and searchable indices.

  > When a browser responds to document containing the <ISINDEX > element, the request will have the same `HTMLFILE.HTM?word1+word2` format. In order to properly respond to such "searchable index generated" responses, you should set up an ALIAS

  ##### Examples

  <!-- Option 1 --> <!-- Option 3 -->

  ##### Notes

  - The OPTION keyphrase is somewhat obsolete -- the use of cookies may be more appropriate (see SAMPCOOK.SHT for an example).
  - OPTIONs can be useful as a simple means of keeping track of where the client came from. For example, you can use the OPTIONs keyphrase to include message about "where you came" from in linked documents.

    > The SAMPOPT1.SHT and SAMPOPT2.SHT files bundled with SRE-http demonstrates this use of OPTION (careful, it causes problems if disable SSI).

    Another example (albeit trickier), is to use OPTION keyphrases to customize URLS, with the goal of helping the client return to one of several potential "invoking" documents.
  - The OPTIONs are stored in the OPTLIST. "stem" variable, with OPTLIST.0 containing the number of OPTIONs recieved. This information can be used in INTERPRET keyphrases to help customize documents.

  Return to table of contents

  #### 4.b.iv) The INTERPRET keyphrase

  Typical syntax: `<!-- INTERPRET FILE xxx.RXX -->`

  INTERPRET provides a means of including and executing a REXX-code-block

  There are two major variants of the INTERPRET keyphrase:

  1. `INTERPRET CODE statment 1 ; statement 2 ; ...` ; where each `statement n` is a valid REXX statements (and each statement is seperated by a semi-colon). For example:
     `INTERPRET CODE tmp1=server() ; interpret.result=tmp1`
     A Shorthand: You can use # instead of INTERPRET CODE
  2. `INTERPRET FILE Filename arg_list` , where:
  3. `Filename` is a file containing REXX code (`filename` is assumed to be relative to the SRE-http addon directory, or to a "local" virtual directory).
  4. `arg_list` is an optional comma delimited list of "arguments" A Shorthand: You can use $ instead of INTERPRET FILE

  ##### Example

  If your document contains the keyphrase:
    <!-- INTERPRET FILE GOBED.RXX-->
    (`or, equivalently, <!-- $ GOBED.RXX-->` )
  and GOBED.RXX contains:
    tmp1=time('h') ; if tmp1<6 | tmp1>23 then interpret.results=" <em> It is late, GO TO BED! </em> " ;
  then the phrase It is late, GO TO BED! will appear in your document whenever your local time is between 11:00 P.M and 6 A.M.

  In general, the INTERPRETed REXX-code-block should include one or more of the following:

  1. A SAY or AUDIT command (for writing status messages)
  2. Assignment of a (possibly multi-line) string to the INTERPRET.RESULTS variable. The contents of INTERPRET.RESULTS is written into the document (at the location the keyphrase occupies).
  3. A QUEUE (or PUSH) command -- with each QUEUEd (or PUSHed) string automatically appended to INTERPRET.RESULTS (see the discussion of the USE_STDOUT variable in INITFILT.DOC for more details on this #EXEC-like feature)
  4. RETURN 'stuff to include'

  ##### Notes:

  - When processing a REXX code-block, syntax checking is turned on -- coding errors will cause the code-block to fail, but will not crash GoServe.
  - `INTERPRET FILE` blocks are "interpreted" by SRE-http -- they are not called as external procedures.

    > Therefore: an INTERPRET FILE code-block can not contain procedures or subroutines

    This inconvenience can be partially ameliorated by calling "external" procedures from within the INTERPRET FILE code block.
  - If a `RETURN` is encountered in an INTERPRET file, the "returned" string is used as the server side include (the value stored in INTERPRET.RESULTS, and output from PUSH and QUEUE statements, are ignored).
  - The comma delimited `arg_list` can be accessed using the usual REXX syntax (i.e.; `parse arg aval1,aval2` ). You can include up to 10 arguments.
  - The following functions and variables can be accessed by a REXX code block:
  - `servername` : IP name of the server (useful on multi-host servers)
  - `host_nickname` : SRE-http's host nickname (for this `servername`)
  - `optlist.` : The option list stem variable (the "options" following a `?` in the request).
  - `privset` : A list of the client's privileges (not including secret privileges).
  - `verbose` : The VERBOSE variable (higher values for more PMPRINTF output)
  - `docname` : The "action" portion of the request
  - `ddir`: The "default data directory" (may be host specific)
  - `usedfile` : The fully qualified name of the requested file
  - `Get_value(env_var)` : The `GET_VALUE` function will return the value of an SRE-http "environment" variable.

  - If you wish to have INTERPRET CODE conditionally include a ssi keyphrase (say, an <!-- INCLUDE filename.ext --> keyphrase), you should use the special MKSSI function. MKSSI will wrap the keyphrase with <!-- and -->, thereby avoiding confusion (since SRE-http uses the first --> it finds as an `end of keyphrase` delimiter). For example:

        <!-- INTERPRET CODE if SREF_BROWSER_INFO('TABLES')='YES' then ;
                                     return mkssi('INCLUDE TABLEVER.HTM') ;
                               else ;
                                     return mkssi('INCLUDE TEXTVER.HTM ');-->

  - You can use the REDIRECT function to conditionally redirect. For example:

        <!-- INTERPRET CODE if extract('clients')>3 then ;
                   interpret.result=redirect('http://foo.bar.net/busysite.txt') ;
                 else ;
                   interpret.result=redirect('pages1/oksite.html',302);-->

    Note that a second argument can be included: 301 (permanent redirection), 302 (temporary redirection), and 200 (text message redirect); the default is 301 (permanent redirection). Also, relative URLs (selectors) are interpreted relative to your server (and port).
  - You can access the GoServe functions (such as the REQFIELD function).
  - There are several SRE-http procedures, including string manipulation routines, that you may find useful.
  - If you have multiple `INTERPRETs` in a document, you can use the GLOBALS. stem variable to retain variables. All other variables are local to each `INTERPRET` keyphrase.
    For example, you could set GLOBALS.ATIME=time() in an early `INTERPRET` , and reference GLOBALS.ATIME later in the document (say, to compute the time it takes to process some intermediate steps).
  - `INTERPRET` will be ignored if NO_PROCESSING='YES', or if a NO_SSP permission applies to this selector.
  - `INTERPRET CODE` keyphrases will be ignored if NO_INTERPRET_CODE='YES', or if a NO_CODE permission applies to this selector.
    Note that INTERPRET FILE keyphrases are not effected by NO_INTERPRET_CODE
  - When using `INTERPRET CODE` : each statement must end with a semi-colon.
  - If your needs are complicated, you might want to write your own SRE-http addon; typically this would be a REXX routine that would generate an HTML document that SRE-http would then return to the client
    However, when combined with the other keyphrases, the INTERPRET keyphrase can accomplish quite a bit of customization!
  - DIRINFO.RXX, USETABL2.RXX, BYBROWSR.RXX, MTCHFILE.RXX, and ADDPRIVS.RXX are samples of `INTERPRET FILE` files (ADDPRIVS.RXX uses the `arg_list`).
  - Obsolete: An INTERPRET_FILE can be used to store small rexx-code-blocks using a "label" system. However, we no longer recommend this method.

  Return to table of contents

  ### 4.b.v) The SELECT keyphrase

  The SELECT, and the #IF, keyphrases are qualitatively different from the other keyphrases -- they act as a "conditional server side include" of HTML code that is already in your document. The power of SELECT is the ability to check dynamic variables (such as the client's IP address, or his user agent), and retain or exclude a portion of the HTML document accordingly.

  A SELECT keyphrase expects an argument containing a block of REXX code, just like the code blocks used in the INTERPRET keyphrase. This block of code will be `interpreted`. The code block should "exit" with either a `RETURN 1` or `RETURN 0` , where:

- `RETURN 1` : the subsequent HTML text block is retained
- `RETURN 0` :the subsequent HTML text block is deleted. The "subsequent HTML text block" is delimited by a `SELECT END` keyphrase, and can be of any length (if no `SELECT END` keyphrase is encountered, the remainder of the file is dropped). Lastly, if there is no RETURN, the code block is retained (i.e.; the default is RETURN 1).

  Example:

         <!--SELECT
            tmp.1=extract('clientaddr') ;
            tmp.2=sref_value('OWNERS',,'INI');
            tmp.3=wordpos(tmp.1,tmp.2); ;
            if tmp.3=0 then return 0
         -->
               <em> Hello!  You have SuperUser Privileges !! </em>
         <!-- SELECT END -->

  Note that `RETURN 1` is assumed by default, hence when the clients IP address is listed in the an OWNER variable (and the code block ends without a return) the `Hello! ...` message will not be deleted.

  #### Notes

  - The following variables are available to a SELECT "code block": host_nickname, optlist., privset, servername, verbose, ddir, docname, and usedfile
    In addition, you can
  - access the "GoServe" variables (such as clientaddr, selector, and serveraddr) using the EXTRACT function.
  - access other GoServe functions, such as clientname()
  - access SRE-http variables using SREF_VALUE(). In particular, the initialization variables (set in INITFILT.80) can be accessed by using avar=SREF_VALUE(varname,,'INI')
  - SELECT will not be done if:
    NO_PROCESSING='YES', NO_INTERPRET_CODE='YES', or if either a NO_CODE or a NO_SSP permission applies to this selector.
  - SELECT blocks can not be nested. They may contain other keyphrases.
  - Older versions of SRE-http used SELECT.RESULT=1 and `SELECT.RESULTS=0` instead of `RETURN 1` and `RETURN 0` (respectively). This is still supported, but it is not recommended.
  - SELECT keyphrases are processed somewhat more slowly then other keyphrases -- for small replacements, you might want to use INTERPRET keyphrases instead. Notes:
  - The XSSI #IF ssi element can also be used for conditional includes. #IF can be nested, but the test conditions (string comparisons) are simpler.
  - If you've played around with the DELIM_1 and DELIM_2 parameters: when entering the beginning and end SELECT keyphrases, you must use the same set of delimiters.

  Return to table of contents

  ### 4.b.vi) The CACHE keyphrase

  > You can use the simple-mode configurator to enable caching of server side includes

  To improve performance, SRE-http will "cache" HTML documents that have server side includes (SSI). This caching is of the document after the SSIs have been performed. In simple cases SRE-http can send this cached file, without having to repeat the actual process of SSI lookups, etc. Needless to say, this can greatly improve server performance.

  > Note: SSI caching is not the same as allowing proxy servers (or the GoServe cache, or SREPROXY) to cache a response

  For a complete description of SRE-http's SSI-caching algorithim, and of the various options available for the CACHE keyphrase, please read SSICACHE.HTM . What follows is a very brief description of the options available for the CACHE keyphrase.

  <!-- cache no -->
    Do not cache this document
  <!-- cache asis -->
    Use a cached version "as is"
  <!-- cache notrigger -->
    Do not check the trigger files; but do check the own file.
  <!-- cache duration nnn -->
    Set the lifespan for this file's cache entry, where nnn is the number of (possibly fractional) days.
  <!-- cache trigger file1 file2 .. -->
    Check the file-stamps of these fully qualified files.
  <!-- cache trigger_type stamp -->
    Selects which field(s) of the trigger file-stamps to check.

  Return to table of contents

  ### 4.c) Support for NCSA HTTPD server side include

  With only minor exceptions, the server side include syntax of the NCSA HTTPD server is fully supported by SRE-http. These are invoked with a keyphrase of:

  > `<!-- #cmd option="value" -->`

  Where `cmd` can be: CONFIG ECHO EXEC FLASTMOD FSIZE IF INCLUDE SET

  #### 4.c.i) Details on NCSA HTTPD server side includes

- #INCLUDE: Include a file.
  `option` can be VIRTUAL or FILE. If VIRTUAL then value should be a relative file name (relative to the data directory or to a "local" virtual directory). If FILE, then value is interpreted relative to the directory containing the "requested file" (the file that contains this server side include).

  > Note: #INCLUDEd files will not be checked for recursive includes. To check for recursive includes, use the <!-- INCLUDE filename --> keyphrase.

  Examples:

            <!-- #include virtual="/samples/intro.doc" -->
                If your data directory is D:\WWW,
                then D:\WWW\SAMPLES\INTRO.DOC will be included.
            <!-- #include file="intro.doc" -->

  If your data directory is D:\WWW, and if the selector containing this SSI is /SAMP2/INDEX.HTM then D:\WWW\SAMP2\INTRO.DOC will be included. <!-- #include file="/samples/intro.doc" --> If your data directory is D:\WWW, and if the selector containing this SSI is /SAMP2/INDEX.HTM then D:\WWW\SAMP2\SAMPLES\INTRO.DOC will be included.
- #CONFIG: Configure some options.
  `option` can be:
  - ERRMSG: Error message to display when a bad request is made
  - SIZEFMT : If `value=ABBREV`, will display kilobytes or megabytes (as appropriate). Otherwise, displays exact byte count (with commas added).
  - SRE-http modification: ABBREV will generate `nnn.nnM` style abbreviations (i.e.; `3.12M`); the standard seems to be `nnnM` (i.e.; `3M`). If you prefer this terser standard, use MABBREV instead of ABBREV.
  - TIMEFMT: A set of instructions on how to display time and date. These are based on the strftime C function -- see TIMEFMT.DOC for a description of the various options.
  Examples:

            <!-- #config sizefmt="abbrev" -->
            <!-- #config timefmt="%A , %c  (%r) ==is %j day of year" -->
            <!-- #config errmsg=" Sample error message " -->

- #FLASTMOD: Modification date of a file.
  The `option` and `value` are the same as for #INCLUDE

  Examples:

            <!-- #flastmod virtual="/samples/intro.doc" -->
            <!-- #flastmod file="intro.doc" -->

- #FSIZE: Size of a file
  The `option` and `value` are the same as for #INCLUDE

  Examples:

            <!-- #fsize virtual="/samples/intro.doc" -->
            <!-- #fsize file="intro.doc" -->

- #EXEC: Execute a CGI script.
  `option` should equal CMD, and `value` should be a file name (in the CGI_BIN_DIR directory) of a CGI script (typically a REXX program or an executable). Note that the EXEC server side include captures the output of the script, and includes this output in the requested document. EXEC will not be done if NO_PROCESSING=YES, or if a NO_SSP permission applies to this selector.

  Example:

          <!-- #exec CMD=jcount?index.htm -->

- #ECHO: Value of a variable
  `option` should be VAR, `value` should be a variable name. This is equivalent to the REPLACE keyphrase, but with different variable names (although many of them overlap).

  The supported variables are:

  > DOCUMENT_NAME, DOCUMENT_URI, DATE_LOCAL, DATE_GMT, LAST_MODIFIED, SERVER_SOFTWARE, SERVER_NAME, GATEWAY_INTERFACE, SERVER_PROTOCOL, SERVER_PORT, REQUEST_METHOD, SCRIPT_NAME, QUERY_STRING, REMOTE_HOST, REMOTE_ADDR, AUTH_TYPE, AUTH_NAME, HTTP_ACCEPT, HTTP_REFERER, HTTP_USER-AGENT

  Unsupported variables are (they really aren't relevant to server side includes):

  > PATH_INFO, PATH_TRANSLATED, REMOTE_IDENT, CONTENT_TYPE, CONTENT_LENGTH

  Examples:

         Server Software: <!-- #echo var="SERVER_SOFTWARE" -->
         GMT date and time: <!-- #echo var=DATE_GMT" -->
         Http accept: <!-- #echo var="HTTP_ACCEPT" -->
         Http user_agent: <!-- #echo var="HTTP_USER-AGENT" -->

- #IF: Conditional inclusion of HTML
  The #IF element has the following syntax:

          <!--#if expr="test_condition" -->
              some html
          <!--#elif expr="test_condition" -->
              some other html
          <!--#else -->
              some default html
          <!--#endif -->

  The `if` element works like an if statement in a programming language. The test condition is evaluated and if the result is true, then the text until the next `elif`, `else`. or `endif` element is included in the output stream.

  The `elif` or `else` statements are used if the original test_condition is false. These elements are optional. Note that the first true statement is used, and `else` is always true (it does NOT take an `expr`).

  EXAMPLE: the below example will print "in foo" if the DOCUMENT_URI is /foo/file.html, "in bar" if it is /bar/file.html and "in neither" otherwise:

          <!--#if expr="\"$DOCUMENT_URI\" = \"/foo/file.html\"" -->
          in foo
          <!--#elif expr="\"$DOCUMENT_URI\" = \"/bar/file.html\"" -->
          in bar
          <!--#else -->
          in neither
          <!--#endif -->

  Notes:
  - #IF ... #ELIF ... #ELSE ... #ENDIF blocks can be nested.
  - The SRE-http SELECT ssi element can also be used for conditional includes. SELECT can not be nested, but the test conditions can be far more elaborate (given that you understand REXX).
- #SET: Define a variable
  The #SET element has the following syntax:
  `<!-- #set var="varname" value="a value" -->`
  These variables can be used (as a textual substitution) in any HTTPD-style server side include -- just prepend a $ before the varname. For example:

  > `<!-- #set var="foobar" value="hello world" -->
  > <!-- #echo var="$foobar" -->`

Need more information on NCSA HTTPD server side includes (and the XSSI extensions)

Return to table of contents

#### 4.d) Order of execution of SSI keyphrases

Server-side includes are processed in the following order:

1. The requested document is read into memory.
2. Headers and Footers, if specified, are included.
3. The document, (that now includes headers and footers), is scanned for keyphrases.
4. When a keyphrase is encountered, the appropriate server side include is performed; or if a SELECT keyphrase is encountered, a server side "exclude" may be conducted.
5. After each keyphrase is processed, step 4 is repeated (from the beginning of the file).
6. This process continues until there are no more keyphrases.
7. If you've specified more then one set of keyphrase delimiters, step 3 will be repeated for each set.

Note that the keyphrases in the latter part of a document are processed after freshly included keyphrases. While not the most efficient algorithim (long documents with many server side includes will cause a lot of string comparisons), it does enable recursive processing of all keyphrases

This recursive feature allows for some powerful document manipulation strictly through the use of keyphrases. In particular, the INTERPRET keyphrase can examine variables such as the "referer", the "client name", or the "OPTION list", and generate inclusions that incorporate other keyphrases (which will be processed on the next cycle of keyphrase interpretation).

There are several caveats:

- SRE-http will check for potentially fatal recursive includes, and disallow them. If this should occur, a simple error comment is added to the document that is sent to the client. See the description of the INCLUDE and #INCLUDE keyphrases for some important provisos.
- If you use the AUTO_HEADER feature, you should not place server side include keyphrases in the <HEAD> portion of your HTML documents.
- In general, we do not recommend use of the DO_SEND_PIECE (the send pieces as they become available) SRE-http option. If you do use it, note that:
- SSI-caching will be suppressed ,
- You will not be able to dynamically add cookies (say, with an INTERPRET keyphrase)
- DO_SEND_PIECE is suppressed if:
- there is more then 1 set of keyphrase delimiters, or
- the FIX_EXPIRE option is being used.

Return to table of contents

## 5) Imagemaps, CGI-Bin Scripts, and SRE-http addons

The modern web site is apt to provide an array of service to it's clients. These services, which imply more then just the delivery of documents and images, are based on an interaction between the client and the server; with the server using information recieved from the client, recording and otherwise manipulating this data, and returning some results.

Delivery of this server side processing typically requires installation of some sort of program that adheres to an application programming interface (API) for communicating to web clients via a web server. SRE-http supports several such API's, including:

- NCSA and CERN server side imagemaps
- GoServe/SRE-http addons
- The Common Gateway Interface (CGI-BIN)

  ### 5.a) Using imagemaps

  SRE-http provides a simple means of responding to image maps, using NCSA or CERN style "MAP" descriptor files. The key is to include a map-image indicator substring in the the "resource location" of a URL that points to a .MAP file.

  More specifically, when a MAPIMAGE/ substring is encountered in the action portion of the request, SRE-http will remove MAPIMAGE/, and assume the remaining portion of the action refers to a NSCA MAP file (similarly, a MAPCERN/ substring refers to a CERN MAP file).

  For example, if the request selector is:

  > `MAPIMAGE/PROJECTS/BRANCH1.MAP?55,123`

  then the "mappable image" handler would look for `PROJECTS\BRANCH1.MAP` (under the data directory, or a "local" virtual directory), and use the instructions therein (in conjunction with the pixel location 55,123) to "redirect" the client.

  #### 5.a.i) Type of regions recognized.

  There are four types of regions recognized by SRE-http:
  1. `Circles`
  2. `Rectangles`
  3. `Polygons`
  4. `Points`
  5. and you should always specify a default URL
  The selected pixel will be assigned to the URL associated with the first `Circle`, `Rectangle`, `Polygon`, or 'exactly-hit' `Point` it matches. If there is no such match, and there are `Points` specified in the MAP file, then the URL associated with the closest `Point` is used.

  > However, if the distance to this closest `Point` is greater then the value of the MAX_POINTDIST variable, or if there are no `Points` specified in the MAP file, the default URL is used.

  #### Notes:

  - To modify the map-image indicator substrings used to indicate a CERN and NCSA imagemap, see the description of the NCSA_ISMAP and CERN_ISMAP variables in INITFILT.DOC
  - The MAP file must be in your data directory, or a "local" virtual directory (i.e.; if your data directory is E:\WWW, then the above example refers to E:\WWW\PROJECTS\BRANCH1.MAP)
  - There are several handy "map" making tools available, such as MAPEDIT.
  - HTACCESS is never checked for image map requests (but HTML documents that contain clickable images are subject to HTACCESS controls).
  - The SAMPMAP.HTM file that comes with SRE-http (which uses SAMPMAP.MAP and SAMPMAP.GIF) provides a simple example.
  - Your MAP file should, but need not, contain fullly specified URLS. The http:// will be added if missing; and if there is no IP address, your server's address (and port) are added.
  - If the selected URL (the URL corresponding to the selected point) is a "virtual URL" (contains no IP address, and does not start with a /), then the invoking URL (minus the MAPIMAGE/) is used.
    Thus,
  - if the selected point is associated with ANIMALS/TIGER.HTM,
  - the .MAP file was /ZOO/GUIDE/CAGES.MAP,
  - THEN ...
  - the selected URL will be /ZOO/GUIDE/ANIMALS/TIGER.HTM.
  - SRE-http's MAPIMAGE procedures are borrowed from Don Meyer's GoHTTP package!

  Please remember that the MAPIMAGE/ "indicator string" does not refer to the MAPIMAGE/ directory!

  Return to table of contents

  ### 5.b)Creating SRE-http addons

  As an alternative to CGI-BIN scripts, SRE-http addons can provide a faster (and less convoluted) REXX based method of creating web aware applications. The basic idea is to write an "external" REXX procedure which will do the processing, or which calls some other executable program (such as a database manager) -- and then tell SRE-http to call this procedure.

  The following steps outline how to do this:

  1. Create an HTML document that returns an `action` that invokes a Server Side Processing request. For example, you might include a FORM element with an ACTION attribute of "/XXX".
  2. Create a file (that contains your REXX procedure), with the name xxx.CMD (or xxx.80) , where xxx is the action name. Note that the xxx file is relative to the ADDON directory (or a "local" virtual directory).
     For example, if the action name is /PROGS/FAST2, and \GOSERVE\ADDON is your addon directory, SRE-http will look for \GOSERVE\PROGS\FAST2.CMD.
  3. This REXX procedure should process the request (using information passed to it by SRE-http), and it may call other programs (not necessarily REXX programs).
  4. xxx should issue GoServe completion codes (such as VAR, FILE, and STRING).

  ### 5.b.i) Calling Syntax

  SRE-http will call your addon with several arguments. The addon can read these arguments using:

      parse arg  ddir, tempfile, action,list,verb ,uri,user, ,
                basedir ,workdir,privset,env_id,transaction,verbose, ,
               servername,host_nickname,home_directory,param1,semqueue, ,
               prog_file,request_num

  The following describes these arguments (note that several of these arguments are rather arcane or are nearly obsolete):
  ddir
    The data directory, may be host specific (typically, x:\WWW)
  tempfile
    The temporary, "transaction specific" file (i.e.; D:\GOSERVE\TEMP\$341.80) being used by this request
  action
    The action portion of the request (the portion of a request before a ?)
    Example (assuming the GET HTTP method was used by the client)
- If the request selector is: `/sports/getscore?city=boston&date=July+5+1994`
- then the action is sports/getscore
  list
    - If verb=GET: the partially cleaned up portion of the request selector after the ? (URL decoding is performed).
      In the above example, list would be `city=boston&date=July+5+1995`
    - If verb=POST: the body of the request -- without URL decoding.
  verb
    Either GET or POST
  uri
    The "universal resource indicator" -- the `request-line` portion of the original request string, as sent by the client to the server -- without cleanup or encoding (but with "special ! directives" removed). This can be useful if & (and other special characters) may be text returned by GET method client requests -- in which case the partial processing done to the list may cause trouble.
    Note: http `GET` requests have 3 components: a verb, a request line, and a protocol.
  user
    The numeric IP address of the client
  basedir
    The "base directory", where SRE-http (and probably GoServe) are located.
  workdir
    The fully qualified name of a directory that the addon can use for "temporary" files. (set in the TEMPFILE_DIR variable).
  privset
    The list of user privileges granted to this client. This will be divided into two sections (seperated by a comma). The first section contains the regular privileges, and the second section contains the secret privileges (the privileges that start with a `?`). These secret privileges are reported without the leading ?.
  env_id
    A substring that can be used when directly accessing the innards of SRE-http (rarely used)
  transaction
    The transaction number
  verbose
    The verbose instruction (1 signifies "say intermediate results").
  servername
    The IP name of the "host" this request is addressed to. This is derived from a HOST: request header, or from the numeric ip address.
  host_nickname
    The SRE-http nickname for the "host".
  home_directory
    The "home directory" (used in ~ replacment)
  param1
    A parameter used for by some older addons (rarely used)
  semqueue
    Semaphore/queue information -- used by the daemon manipulation procedures (as described in DAEMONS.DOC)
  prog_file
    Fully qualified name of the file (containing this addon). If addon was "loaded from macrospace", this will be an empty string.
  request_num
    The request number. Note, that in the maintain-connection world of http/1.1, there may be multiple requests per transaction.

    ### 5.b.ii) Return Values

    The xxx.CMD procedure should return a simple status message of the form:
    `response_code bytes_returned Description Message , file_used`
    Where:
- `response_code` : the http response code (typically, 200 for GET requests and 201 for POST requests)
- `bytes_returned` : the number of bytes transfered (should not include response headers)
- `Description message` (optional) : a descriptive message (it's transferred to the post-filter)
- `file_used` (optional) : The program that was run (must follow a comma) Examples:
- `200 12515 Message Succesfully Recieved, D:\GOSERVE\MESSAGES`
- `401 302 Unauthorized access of PRIVATE DATABASE`

  ### 5.b.iii) Notes

  - For further hints on programming to the SRE-http API, see MK_ADDON.HTM and the documentation for the SRE-http procedure library
  - How does SRE-http recognize a request to run an addon or a CGI-BIN script?
    - If VERB=GET
      ... SRE-http looks for a ? character in the request selector , and also checks that the request is not for a text/html file.
    - If VERB=GET and the action portion of the request selector contains a `CGI-BIN/`, then it's assumed to be a request to run a CGI-BIN script.
    - If VERB= POST
      ... SRE-http assumes it is a request for an addon (or a CGI-BIN script)
  - Caution: As a probably-unwise-but-too-late-too-change-now convenience, on GET method requests the `LIST` parameter has been URL decoded. While saving programmers a step, this does make it difficult to detect & and = signs.
    Therefore, `careful programmers may wish to use the `URI` variable when processing GET method requests. Alternatively, you may wish to suppress this decoding by changing the value of the GET_DECODE_OPTIONS parameter in INIT_STA.80

    `
  - STATUS.CMD, and STATUS.HTM, contain an example of how to request Server Side Processing using a REXX procedure.
  - If a syntax error occurs, SRE-http will trap it and return a simple error message to the client.
  - To call an external, non-REXX program from within an external REXX procedure, use the `address cmd` REXX command.
  - If you write HTML code to TEMPFILE (for return to the client), you should return from your external REXX procedure using:
    `foo=SREF_GOS('FILE ERASE TYPE text/html NAME ' TEMPFILE )
    return response_code #_bytes a message here`
  - When using an HTML FORM to invoke an SRE-http addon, we recommend that the "action" contain a leading / character (this avoids incorrect path assignment by the browser).
  - If the NO_PROCESSING variable equals YES, or the NO_SSP permission is enabled, then server side processing will not be permitted.

  Return to table of contents

  ### 5.c)Support for CGI-BIN scripts.

  SRE-http supports CGI-BIN scripts (using procedures adapted from Don Meyer's GoHTTP package). To run CGI-BIN scripts, you'll need to:
  - Make sure that the CGI_BIN_DIR points to an existing directory (i.e.; \GOSERVE\CGI-BIN).
  - Copy the CGI-BIN script (such as a REXX file, a binary .EXE file, etc.) to the CGI_BIN_DIR directory.
  - Invoke it using a standard CGI-BIN request selector . For example:
    `href=http://foo.bar.net/cgi-bin/test-cgi/morepath/?a+message`.
  SRE-http's implementation of CGI-BIN has one major improvment: the ability to send pieces of the output as they are created. That is, one can:
  1. wait for the CGI-BIN script to end, and then send all the output it generated
     ... or
  2. send output as it is generated
  The second option is especially useful when large amounts of output are being generated (it avoids some troublesome server-timeout & client-impatience problems). For details see the discussion of the CGI_BIN_PIECES variable in INITFILT.DOC

  SRE-http's implementation of CGI-BIN also includes a few minor modifications:

  - A few additional environment variables are created. The most important one is SREF_PRIVSET -- it contains a list of the client privileges (but not the secret privileges).
  - SRE-http comes with a few sample CGI-BIN scripts (written in REXX). The TEST-CGI.CMD file (which is copied to your CGI_BIN_DIR) will display the values of the CGI-BIN variables (invoke it using /CGI-BIN/TEST-CGI).
  Need more information on CGI-BIN ?

  ### 5.c.i) Using CGI-BIN scripts in other subdirectories

  By default, CGI-BIN scripts are assumed to be in the CGI_BIN_DIR directory (say, \GOSERVE\CGI-BIN). Obviously, this can become inconvenient once you acquire a greater-than-small set of scripts. The obvious solution is to place the script files in subdirectories.

  Unfortunately, there does not seem to be a clearly specified method of doing this. With this in mind, SRE-http offers two means of specifying subdirectories containing your CGI-BIN scripts:

  1. Using "aliases".
     This does not require changes to the standard syntax of CGI-BIN request selectors; i.e.; CGI-BIN/ASCRIPT/PATHINFO/?args ). The disadvantage is that a seperate alias is need for each script -- even for scripts in the same subdirectory.
  2. Using the portion of the request selector before the `CGI-BIN/`
     The notion is to include subdirectory information before the `CGI-BIN/` (the "this is a CGI-BIN script" indicator). SRE-http will interpret this starting portion as a subdirectory of the CGI_BIN_DIR, or as a virtual directory (in both cases,the usual HTACCESS controls may apply). This permits a powerful division of scripts into directories. The disadvantage is that it doesn't seem to be "spec" (hence may be cumbersome to port).

     > Requests for CGI-BIN scripts are often followed by /PATHINFO/. This is typically used by the script (it does not point to the script).

     Example:`KIDSTORE/INVENTORY/CGI-BIN/TOYCT?toddler`
     This invokes the TOYCT program (with an argument of `toddler`),
     which is located in (perhaps) \GOSERVE\CGI-BIN\KIDSTORE\INVENTORY\.

  ### 5.c.ii) Notes on creating CGI-BIN scripts

  - When writing CGI-BIN scripts, keep in mind that a number of variables are available in the enviroment.
  - You can output results with SAY statments.
  - Your first SAY statements should declare the MIME type. For example: `
    Say "Content-type: text/html"
    Say`

  ### 5.c.iii) Using PERL scripts with SRE-http

  In order to take advantage of a broad spectrum of CGI-BIN scripts, SRE-http can use "non-REXX" processors to interpert CGI-BIN scripts.

  As long as you have the appropriate interepreter installed on your server, it's quite easy to do this. All that you need to do is tell SRE-http (using the INTERPRET_TYPES parameter) which interpeter to associate with different file extensions -- see INITFILT.DOC for a details on how to change the INTERPRET_TYPES parameter.

  Of particular interest is the use of one of the OS/2 PERL interpreters; since there are a slew of PERL scripts out there. In fact, it's not that hard to obtain a PERL interpreter -- see PERL.DOC for details on one we've had some success with.

  Return to table of contents

  ## 6)Miscellaneous SRE-http features

  SRE-http has numerous features that allow you to selectively record and audit requests, upload files, perform "pre-filter" and "post-filter" actions, and sundry trickery and sleight of hand.

  ### 6.a) Special commands, and directives, recognized by SRE-http

  SRE-http offers a set of special commands, and special directives for performing TCP/IP actions, computing statistics on the status of GoServe, and requesting special server actions. These command all start with an exclamation point (!), followed by a word or a phrase.

  > The special commands are basically built-in "server side programs". In contrast, the special directives are used to modify SRE-http's logic.

  ### 6.a.i) Currently available special directives

  !force/selector
    The `!FORCE` special directive instructs SRE-http to suppress the LOGON_FAIL_FILE (and ACCESS_FAIL_FILE) feature when considering the `selector`. This guarantees that unauthorized clients will be presented with a username/password screen.
    `!FORCE` is meant to be used in the LOGON_FAIL_FILE and ACCESS_FAIL_FILE, where it provides a means by which a client can try again with a different username/password.

    It is also used to force re-compilation of an HTML document with server side includes (in other words, it suppresses use of the SSI-Cache).

    > Hint: To avoid problems with NetScape, use `!FORCE/xxx` instead of `!FORCE?xxx`

    Examples:
- !FORCE/DIR1/INDEX.HTM
- !FORCE/DIR2/INCS/INDEX.SHT
  !NOBALANCE/selector
    `!NOBALANCE` will suppress all attempts at load balancing -- the recieving server will process the request.
  !CGI-BIN_n (n=0,1,2, or 3)
    Overrides the `CGI_BIN_PIECES` and `EMPTY_PATH_OK` parameters on a selector specific basis.
    - 0 : Sets `EMPTY_PATH_OK=0` and `CGI_BIN_PIECES=0`
    - 1 : Sets `EMPTY_PATH_OK=1` and `CGI_BIN_PIECES=0`
    - 2 : Sets `EMPTY_PATH_OK=0` and `CGI_BIN_PIECES=1`
    - 3 : Sets `EMPTY_PATH_OK=1` and `CGI_BIN_PIECES=1`
    Notes:
- `EMPTY_PATH_OK` controls how CGI-BIN PATH_INFO is saved to the OS/2 Environment.
- `CGI_BIN_PIECES` enables the the send CGI-BIN (stdout) output as it becomes available mode
- For further details on `EMPTY_PATH_OK` and `CGI_BIN_PIECES`, see INITFILT.DOC.

  Examples:

- http://foo.bar.net/!CGI_BIN_0/CGI-BIN/TEST-CGI
- http://bar.foo.gov/!CGI_BIN_2/CGI-BIN/WWWPAGE.EXE?Status
  !RANGE
    The !RANGE special directive instructs SRE-http to send a range of a resource. !RANGE can be used to send selected bytes, lines, and sections of a resource to the client. This can be a convenient way to subset a resource (say, instead of having multiple files).

    Examples:

    - `<A href="!range:bytes=100-1000,10000-120000/outline.doc"> Useful Tools</a>`
    - `<A href="!range:lines=-50,200-500,1200-/prices.cur"> Fruit Prices</a>`
    For further details on the syntax of the !RANGE directive, see RANGE.HTM

  !RUN
    The !RUN special directive is used to expedite processing of SRE-http addons. In particular, it is meant to be used with SRE-http addons that have been referenced in one of the `KEEP_ADDON.` entries.

    Examples:

- <a href="/!RUN/GIF_TEXT&font=enviro&text=hello">
- <a href="/!RUN/STATUS?"> When !RUN is used, SRE-http assumes the addon has been preloaded into macrospace (hence the `KEEP_ADDON.` requirement). With this assumption, it is possible to not bother with a fair amount of overhead -- thereby expediting loading and execution.
  For more details, see the description of KEEP_ADDONS. in INITFILT.DOC.
  !norecord?selector
    Instructs SRE-http to NOT record this request. It has the same effect as a NO_POSTFILTER permission. You can disable this option by setting the NO_NO_RECORD parameter.
  !sendas_mimetype_mimesubtype/dir/filename.ext
    The `!sendas` special action is used to force the server to send the requested file as mimetype/mimesubtype. This can be useful if you wish to create links to unusually named text, or html, files. For example, if you have a series of html documents named CHAP.1, CHAP.2, etc.; you could use links of the form:
    <a href="/!sendas_text_html/mybook/chap.3">Get chapter 3 </a>

    Technical note: `!sendas` suppresses SRE-http's extension mapping method of determining the mime type (and subtype); and uses the explicitly coded `mimetype` and `mimesubtype` instead.
    For information on customizing SRE-http's extension mapping, see the description of MEDIATYP.RXX.

    Special feature If `!SENDAS_CHECK_TYPE` is used, then if no explicit match can be found, the file will be checked for "all text characters", and if such is the case, will be returned as text/plain. `!SENDAS_CHECK_TEXT` is simliar, except it checks the file before using the explicit extension (the explicit extension is used if only the file contains non-text characters).

  !delsend/filename.ext
    !delsend is used to send a file from the SRE-http TEMPFILE_DIR "temporary file" directory. More precisely, !delsend will look for `filename.ext` in the TEMPFILE_DIR, send it (if it exists), and then delete it.

    !delsend is provided to facilitate writing server side programs that generate several output files -- the client would be sent back a response containing !delsend links to these several files.

    #### Notes

    - When a `!force` , `!norecord` , `!sendas` or `!delsend` request is recieved, the !cmd portion (i.e.; the !sendas_xxx_yyy/, or the !delsend/) are immediately stripped off. Thus, SRE-http's various "SEL-specific" operations (such as access control, or aliasing) are performed on this "stripped" request selector .
    - You can end the `!cmd` portion with either a ? or a /. For example, the following two request selectors are equivalent:
    - `!sendas_text_plain/hello.lst`
    - `!sendas_text_plain?hello.lst` Hint: NetScape's redirection can do odd things if you use a ?.

    ### 6.a.ii) Currently available special commands

    !authorize
      SRE-http will send back an "authorization" request. The primary users of this will be server administrators -- since a !AUTHORIZE link will repetitively ask for the client's username/password.
    !ping
      'PINGS' the client.
    !statistics
      View current GoServe statistics.
    !HOST?xxx.yyy.zzz.aaa
      Get information on IP address xxx.yyy.zzz.aaa
    !reset
      Resets various GoServe statistics, and instructs SRE-http to re-read parameter files immediately (only available to OWNERS, or clients with SUPERUSER privileges).
- If !reset?params, then statistics will not be reset.
  !save
    Saves various GoServe statistics to the GOAUDIT.80 audit file. This is only available to SUPERUSERs, or to users with a CONTROL privilege.
  !ssi
    Used to access information on the SSI-cache. The following sub-options are recognized:
- !ssi?status : writes a (fairly technical) status report to the PMPRINTF window.
- !ssi?status=short : writes a brief status report to the PMPRINTF window
- !ssi?status=fully_qualified_file_name : writes a report on the SSI-Cache entry (if it exists) for the `fully_qualified_file_name`
- !ssi?reset = Resest (clear) the SSI-cache
- !ssi?remove=fully_qualified_file_name : remove the SSI-Cache entry (if it exists) for the `fully_qualified_file_name`
- !ssi?cleanup = Cleans up the SSI-Cache Notes:
- The client must have SUPERUSER privileges to invoke these !SSI options.
- After completion of the !SSI request, a short status report (in plain-text format) will be returned to the client.
- For an illustration of the use of `!SSI`, see SSICACHE.HTM
  !variable?var1&var2..
    Returns the value of environment variable var1, etc. (client must have SUPERUSER privileges to use this).
  !write_cache
    saves the `record_all_file` cache to the `record_all_file`
  !dir?`dirname`
    Invokes SRE-http's built in directory lister; which will create a list of all files (and subdirectories) of `dirname`.
    To modify the various display parameters used by !dir, see the DIR.DOC file, or see the description of the DIR_EXCLUSION, DIR_ACCESS, and DIR_OPTIONS parameters in INITFILT.DOC.

    Notes:

- The !CREATE option of the AUTO_NAME parameter also uses `!dir` to generate a directory listing.
- For a more richly featured directory lister, try the Get-a-File SRE-http addon.

  Return to table of contents

  ### 6.b) Common-log, browser, and referer audit files; and scheduled events

  In keeping with http server standards, SRE-http will maintain a common-log format audit file. Entries in common-log format audit files have the following structure:

      aclient.somehere.org - username [18/Mar/1996:16:24:08 -0500] "GET /SAMPLES/HELLO.HTM HTTP/1.0" 200 1251

  Besides offering a compact synopsis, a number of tools exist to help you analyze common-log files.

  Furthermore, as an adjunct to the common-log audit file SRE-http can also record the browser used by each request (as well as the referer) in seperate log files.

  #### Notes

  - The WRITE_LOGS parameter is used to enable SRE-http's common-log, browser, and referer audit files (see INITFILT.DOC for details).
  - If post-filter processing has been suppressed (with the NO_POSTFILTER permission), the request will not be recorded to these audit files.
  - The SREFLOGS.INI file contains log-file control parameters. For example, you can select seperate log-files for each of several hosts, you can suppress any of these log-files, and you can suppress auditing of 400 (failure) or 300 (moved) requests.
  - The SCHEDULE.CFG file (in the CFGS directory) can be used to run scheduled programs on an hourly, daily, weekly, or monthly basis. RENLOGS.CMD (an alternative to the LOGFILE_MAXSIZE parameter) is an example of such a scheduled-events program.

  Return to table of contents

  ### 6.c) Recording ALL requests for files

  > You can use the simple-mode configurator to enable the common-log audit file and the RECORD_ALL_FILE running count.

  As an alternative to the common-log audit file, SRE-http maintains a running count of requests in the RECORD_ALL_FILE . This file contains a count of requests, broken down by selector or by filename.

  > Record refers to updating a count of the number of times a resource has been requested.
  > It does not mean keeping a record of each hit! If you need such detailed accounting, you should use the common-log file (or you can use GoServe's GOAUDIT.80 file).
  > For customized auditing needs, you can add your own procedure using the post-filter option (POSTRCRD.80 is an example of such a procedure).

  To enable the RECORD_ALL_FILE, you need to set the RECORD_OPTION parameter. RECORD_OPTION can take the following values:
  NO
    Do not maintain a running count
  YES
    Record requests, but remove the the argument list from the selector (for example; remove `?hi+there` in `ANIMALS/MONKEY.HTM?hi+there` selector
  YES_ALL
    Record requests, do not remove an argument list.
    Caution: Use of YES_ALL can lead to a very large RECORD_ALL_FILE
  FILE
    Record requests by fully qualified file name. In contrast, when YES or YES_ALL are specified, requests are recorded by selector
    Caution: Use of FILE can lead to a very large RECORD_ALL_FILE -- careful use of wildcard entries is recommended.

  #### RECORD_ALL_FILE: Implementation details

  To speed throughput, SRE-http caches the RECORD_ALL_FILE in memory, with a single thread responsible for updating it (the POSTFCHK thread). This raises several issues:
  1. The cache is written to disk on a regular basis (about once every five minutes). Thus, it is possible for the file version to be somewhat out of date; and it is possible to loose entries (say, if the server crashes).
  2. If you "hand edit" the RECORD_ALL_FILE (say, to add wildcard entries), SRE-http will read it into the cache, overwriting any changes that have been recently made. That is, any requests recieved while you were editing the file will not be recorded.
  3. If the cache grows large (over 1000 entries), SRE-http will start over -- and save the old RECORD_ALL_FILE (you won't loose information, but it will be spread over a few files). There is one exception: SRE-http will retain "wild card" entries (but will reset their count to 0).
  Given the above: the RECORD_ALL_FILE should be treated as an approximate (albeit probably very accurate) count of requests.

  > To avoid loosing a few minutes of entries that will occur when you shut down GoServe, you can issue a !WRITE_CACHE request just beforehand

  #### Notes

  - Wildcard matching of entries is supported, both by "selector " and by "FILE".
  - By default, results are written to RECRDALL.CNT -- this can be modified by changing the RECORD_ALL_FILE variable.
  - Entries in the RECORD_ALL_FILE may be "host specific". However, when FILE is specified, host information is not used.
  - For YES and YES_ALL, each entry in the RECORD_ALL_FILE contains the request selector (minus the argument list if RECORD_OPTION=YES), the number of "honored" requests, and the date of the most recent request.
  - For FILE, each entry contains the fully qualified file name, the number of times the file was requested, and the date of the most recent request. Note that when FILE is used, information after the ? is ignored (there is no FILE_ALL option!).
  - Only "honored" requests are recorded -- requests for actions that are not honored (when ALLOW_ACCESS is enabled) are not recorded.
  - If an entry matching the request selector is not found in RECORD_ALL_FILE, a new entry will be created!
  - ... however, a wildcard match is always attempted. The use of "wildcard matching" is recommended if many temporary files are likely to be requested. For example, one should include a "wildcard" for the "temporary" directory in your RECORD_ALL_FILE
  - The size of the RECORD_ALL_FILE cache can be increased or decreased by changing the RECORD_CACHE_LINES variable. Or, you can suppress this caching by setting RECORD_CACHE_LINES=0. See INITFILT.DOC for details.
  - The differences between the RECORD_ALL_FILE method, and placing a REPLACE HITS (or REPLACE HITS_FILE) keyphrase in all documents, are:
    - Nothing is written to the requested file (the client is not given info on # of hits)
    - The RECORD_ALL_FILE is updated, not the COUNTER_FILE.
    - All requests are tracked: including transfer of HTML documents and.GIF files, and Server Side Processing requests.

    > Thus, if a `REPLACE HITS` keyphrase is included in a document, and RECORD_OPTION is enabled , a "count of requests" will be updated in the COUNTER_FILE and in the RECORD_ALL_FILE

  - For viewing the RECORD_ALL_FILE, we recommend the NUSTATUS SRE-http addon.

  Return to table of contents

  ### 6.c.i) Suppress recording of repetitive requests

  To reduce the number of false hits from clients re-requesting a URL after a short absence (often caused by the use of a browser's "back" key), a list of current hits can be maintained. If a request selector matches a request in this list of current hits (where the request selector and the client's IP address are both used), the "count of hits" will not be augmented. Specifically, the COUNTER_FILE and the RECORD_ALL_FILE will not be augmented.

  In addition to "re-requests", you may also wish to not record requests from OWNERS (such as the webmaster) -- since these are likely to be due to site maintenance activity, and not due to interest in the content of the requested files.

  INITFILT.DOC contains details on both of these options: see the descriptions of the HIT_CACHE_LEN, HIT_CACHE_DURATION, and HIT_OWNER_SUPPRESS variables (or you can use the simple-mode configurator).

  #### Notes

  - You can control the size and duration of the list of current hits by modifying the HIT_CACHE_LEN and HIT_CACHE_DURATION variables
  - You can not record requests from OWNERS by enabling the HIT_OWNER_SUPPRESS variable.
  - Similar request suppression options exists for the COUNTER.RXX hit-recorder.

  Return to table of contents

  ### 6.d) Load balancing requests across several servers

  SRE-http is shipped with support for a simple form of "load balancing". When load balancing is active, the server will first check the number of active clients. If this exceeds the number specified in the LOADTHRESHOLD variable, then the client is redirected to one of the servers listed in the BackupServerList variable.

  For details on how to invoke load balancing, see the description of LOADTHRESHOLD in INITFILT.DOC

  > Suggestion: If you are interested in "dynamic" load balancing (that uses real-time server-load information); you might be interested in the Balancer dynamic load-balancer.

  Return to table of contents

  ### 6.e) Creating user written pre-filter(s)

  In certain cases, you may wish to have a set of custom written REXX routines examine the request before yielding control to SRE-http. For example, you may wish to shunt some special requests to a variety of different filters.

  To do this, set the PRE_FILTER variable:

  - PRE_FILTER=NO: no pre-filtering will be attempted.
  - PRE_FILTER=YES: a pre-filter (a REXX procedure) will be called. The pre-filter will be called after logon privileges have been determined; when individuals do not have logon privileges, the pre-filter will not be called.
  - PRE_FILTER=FIRST: same as PRE_FILTER=YES, except the pre-filter is called as the very first action (before logon privileges are ascertained).
  You can specify the name(s) of the pre-filter procedure file(s) by setting the PREFILTER_NAME variable. By default, PREFILTER_NAME="PREFILTR" (which refers to PREFILTR.80).

  When a pre-filter is called, several arguments will be passed. The first three are generated by GoServe, the second to last is generated by SRE-http and is not passed when PRE_FILTER=FIRST, and the last offers a means of transfering results from earlier to later pre-filters. parse arg source,request,sel,privs,servername,otherargs

- `source:` myaddr port transaction who whoport
- `request:` verb selector protocol
- `sel:` action '?' awords
- `privset`: list of privileges (including the secret privileges, which will be seperated from the regular privileges by a comma).
- `servername` -- ip name of server (useful in multi-host environments).
- `Other_args` -- results from prior pre-filter. The pre-filter should return a comma delimited list:
  `status , status message`
  Where status is either 0 or 1:
- 0= No response to client, SRE-http should continue processing.
- 1=Response to client, SRE-http should exit (perhaps with response recording) The Status message will be stored as PREFILTER_RESULT. Note that the `REPLACE PREFILTER_RESULT` keyphrase can be used to display this status message.

  #### Notes

  - If more then 1 pre-filter is called, the PREFILTER_RESULTS will be from the last pre-filter specifed in PREFILTER_NAME
  - If an earlier pre-filter issues responds to the client (and issues a GoServe "completion code"), the remaining pre-filters are skipped.

  Return to table of contents

  #### 6.e.i) Using a pre-filter to invoke the GoRemote package

  The PREFILTR.80 file that comes with SRE-http contains a pre-filter that enables support for the GoRemote package. GoRemote (the "server remote control" package bundled with GoServe) is typically called as a special filter. By using this pre-filter, GoRemote will automatically be called (instead of SRE-http) when a GoRemote specific action is requested.

  To do this, you'll need to:

  1. Make sure you have the GOREMOTE package (GOREMOTE.ZIP), and unarchive it to either the root of your data directory, or to the GOREMOTE/ subdirectory of your data directory. You'll need GOS32.GIF, GORM*.HTM and GOREMOTE.* files. Since there are about a dozen GORM* files, placing them in a subdirectory is asthetically preferable.
  2. Copy GOREMOTE.80 to your GoServe working directory. If GOREMOTE was installed in a GOREMOTE/ directory, copy GOREMOTE.HTM, GOS32.GIF and GORMOK.HTM to the root of your data directory
  3. Make sure that PREFILTR.80 (the one that comes with SRE-http) is also in your GoServe working directory.
  4. Using CONFIG2.HTM (or by direct modification of the INITFILT.80 file), set the PRE_FILTER variable to:
     - YES = If you want to limit access to GoRemote:
     - Clients with SUPERUSER or INHOUSE privileges will be able to view filter settings and statistics.
     - Clients with SUPERUSER privileges will be able to change settings.
     - FIRST = If you want all clients to have access to GoRemote
     You should also set PREFILTER_NAME='PREFILTR.80'
  5. Set up a link to GOREMOTE (or GOREMOTE/GOREMOTE if you installed GOREMOTE in a GOREMOTE subdirectory).
  6. You do not need to make any other modifications, either to SRE-http, or to the GoRemote files!
  Notes:
  - This pre-filter works by capturing all calls to GOREMOTE.*, GOS*.*, and GOR*.* (or to these files in the GOREMOTE/ directory). So, if you use this pre-filter, don't create files with these names (though you can create files with these names in different subdirectories).
  - When requesting GOREMOTE, do not use GOREMOTE.HTM (the GoRemote filter is not expecting to see an extension).

  Return to table of contents

  ### 6.f) Creating a user written Post-Filter

  In certain cases, you may wish to execute some additional actions after responding to a client's request. For example, you may wish to record client specific information in a custom designed audit file. Or, you may wish to e-mail responsible parties when certain events occur (such as a file upload). Or you may wish to do both!

  To accomodate such needs, SRE-http can be told to call a series of "post-filters". As with the "pre-filter", these post-filters are custom designed REXX procedures.

  To enable post-filter calling, set the POST_FILTER variable:

  - POST_FILTER=NO: post-filter(s) are not be called.
  - POST_FILTER=YES: post-filter(s) are called.
    Note: The post-filter(s) are called after a response has been sent to the client.

    > Therefore, you can not use a post-filter to modify the response sent to the client!

  You can specify the names of the (possibly several) post-filter procedure files by setting the POSTFILTER_NAME variable. By default, POSTFILTER_NAME="POSTFILT".
  To specify several post-filters, just enter a space delimted list. For example `POSTFILTER_NAME="POSTMAIL.80 POSTRECRD.80 "` -- they will be executed in the order of appearance.
  Note that if there is no extension, and no ending period, an extension of .80 is assumed (or .nnn if you are using a non-80 serverport).

  When a post-filter is called, several arguments will be passed:

  - `amessage` : a short SRE-http status message
  - `source` : The server address and client address
  - `request`: The request string; the verb, the selector , and the http protocol
  - `sel`: The selector
  - `tempfile`: The temporary file used by this transaction
  - `servername`: The host to whom the request was directed (the servername)
  - `host_nickname`: The "host nickname" corresponding to the `servername` (or blank, if there is no HOSTS. variable for `servername`)
  - `USED_FILE`: The fully qualified file used by the request: such as the HTML file requested by the client, or the CGI script executed by the server.
  - `TheReferer`: The value of the 'referer' request header -- if set, it contains the fully qualified URL which contained the link which invoked this request.
  - `Request_specfic_cache`: A pointer to a set of request specific information. This can be used by the SREF_READ_STATE macrospace procedure (note that post-filter actions can not issue GoServe commands).
  - `RESPONSE_STATUS`: The `response code` and the `number of bytes returned`. For example: `200 19218`.
  - The `list of privileges`
  - The list of `secret privileges`
  For a simple example of a post-filter, see the POSTFILT.80 file that comes with SRE-http. For more useful examples, see POSTMAIL.80 (an e-mail alert routine) and POSTRCRD.80 (a client info recorder).

  #### 6.f.i) Using SREF_MAILIT to issue "event specific" alerts

  The POSTMAIL.80 that comes with SRE-http uses a version of the SREF_MAILIT procedure (contained in the SREFPRC macrospace procedure library) to e-mail "event specific" alerts through an SMTP Gateway. A different (set) of individuals can be notified for each of a set of events, where events are identified by the request selector (with wildcard matching supported), or by the requesting client's IP address. POSTMAIL.80 contains detailed instructions on how to generate these e-mail alerts. POSTMAIL.80 also contains a useful discussion on the use of OS/2's SENDMAIL as an SMTP gateway).

  Notes:

  - To use this facility, you must set the SMTP_GATEWAY variable to be the address of your SMTP server. If you do not have access to an SMTP server, you might be able to use OS/2's SENDMAIL program to set up your server machine as a SMTP server (see the OS/2 TCP/IP Command Reference for more information on SENDMAIL).
  - Ambitious programmers can use SREF_MAILIT for more advanced e-mail purposes.

  Return to table of contents

  ### 6.g) Uploading and deleting files

  SRE-http provides two built-in "actions" for uploading files, one HTTP method for uploading files, and one HTTP method for deleting files. Each of these has it's own advantages and disadvantages:
  1. GET_URL: A built-in action for uploading files from another HTTP server
     - Requires that the client has ready access to an HTTP server.
     - Given this access, uploading is quick and easy.
  2. PUT_FILE: A built-in action for uploading files from the client's own machine
     - Requires that the client be using a browser that supports the `type=file` FORM attribute (such as NetScape 2.01 and above).
  3. The PUT method.
     - Requires that the browser (or other software) know how to issue a PUT method HTTP request. The DOPUT.CMD program illustrates the use of the PUT method.
  4. The DELETE method. This can be used to delete files from your server. As with the PUT method, it requires a browser that knows how to issue DELETE method HTTP requests.
  General Usage notes:
  1. GET_URL.

     Set up a URL with the GET_URL action, followed by the URL of the file you want to get, and the "local name". The request selector should look like: `GET_URL?url=http://a_url&file=relative_file_name`

     For example:

     - `GET_URL?url=http://www.pc.com/price.lst&file=pcprice.1`
     will copy `price.lst` (on the server at `www.pc.com` ) to a file named PCPRICE.1 (in the `upload directory`).
  2. PUT_FILE.

     Create an HTML FORM with a `type=file` attribute. For example:

         <FORM enctype="multipart/form-data" ACTION="/put_file" METHOD="post">
           Send this file <INPUT TYPE="file"  name="relative_filename">
           <INPUT TYPE="submit" VALUE="send file">
         </FORM>

  3. The PUT and DELETE HTTP methods are, by default, not permitted. To allow PUT or DELETE methods, you must include a PUT or a DELETE permission in the permission list of the appropriate entry (for the requested selector ) in the ACCESS_FILE.
  4. As with the more commonly used GET and POST methods, selectors in PUT and DELETE method requests are relative to the data directory (or to a local virtual directory).
  5. You can allow PUT to overwrite preexisting files by setting PUT_NO_OVERWRITE=0 (in INIT_STA.80). If PUT_NO_OVERWRITE=1, then if the selector maps to a pre-existing file, an error message will be sent back to the client.
  6. PUT and DELETE will not be permitted if ACCEPT_RANGES='NO' (ACCEPT_RANGES is set in INITFILT.80).

  #### PUT_FILE and GET_URL usage Notes

  - PUT_FILE and GET_URL store results in files relative to the UPLOAD_DIR directory, or to a "local" virtual directory. Note that if the target is a virtual directory, a PUT permission must exist for the specified file.
    For example, if the relative file name is TODAY/OUTPUT.1, and TODAY has a virtual directory match, then access controls for TODAY/OUTPUT.1 will be examined for a PUT permission. In contrast, if TODAY has no virtual directory match, then output is assumed to be to the TODAY subdirectory of the UPLOAD_DIRECTORY -- and the PUT permission is not needed.
  - Files must be less then UPLOAD_MAXSIZE in kbytes size; and there must be UPLOAD_MINFREE kbytes free (in the UPLOAD_DIR directory) after the file is uploaded. If either condition can not be met, the file will not be uploaded.
  - If the filename (after resolving for is directory) exists, an error message will be returned.
  - If you do not specify a local file name, SRE-http will create a "unique" file name in your UPLOAD_DIR directory.
    You can specify "partially random" filenames by including ? characters in the filename. SRE-http will attempt to create a unique file name by appropriate substitutions of the ? character. For example:
    - if filename=ABC??.TXT,
    - and ABC01.TXT exists,
    - then SRE-http will use ABC02.TXT.
  - For GET_URL: You must completely specify the URL (including the http:// portion).
  - A short status report on success of the upload operation is written to the UPLOAD_LOG file.
  - For PUT_FILE: Browsers that do not support the `type=file` FORM attribute will send back garbage (that will be ignored).
  - UPLOAD.HTM contains an example of the use of GET_URL and PUT_FILE.

  - For PUT method uploads, size limits are not imposed.

  Return to table of contents

  ### 6.h) Automatic generation of response headers

  If desired, SRE-http will parse a requested document, extract all LINK and META HTTP-EQUIV elements found in the <HEAD>, and create the appropriate response headers. This is especially useful in response to HEAD requests.

  To do this, set the value of the AUTO_HEADER variable:

  - NO : Do not create response headers
  - HEAD: Create response headers when a HEAD HTTP method request is recieved for an HTML document.
  - ALWAYS: Create response headers whenever a GET or HEAD request is recieved for an HTML document.

  #### Notes

  - GoServe automatically generates several response headers (such as content-length and file-creation-date).
  - Server side includes (that might be in the <HEAD>) are not processed when a HEAD request is recieved. Furthermore, server side includes are not processed when response headers are created, but are processed when the <HEAD> is returned as part of the document.

    > Thus, if you intend to use AUTO_HEADER, we recommend not using server side includes in the <HEAD> portion of your HTML documents!

  - From an HTTP purist basis, the use of AUTO_HEADER="HEAD" would be discouraged, since the response headers returned by a GET and a HEAD request would be different. However, since many browsers understand that LINK and META EQUIV elements (in the <HEAD> section of an HTML document) are equivalent to response headers, this may not be a serious drawback.

  Return to table of contents

  ### 6.i) Defining new media types

  SRE-http recognizes a list of the most frequent MIME media types (using the extension of the requested file). If you want to add to this list, you can do so by editing the `MEDIATYP.RXX` file located in your GoServe directory.

  Additions to MEDIATYP.RXX may be new media types (say, an experimental MIME type), or they may be assignations of a non-standard extension to a common MIME type (say, .DOCUMENT to text/plain).

  #### Notes

  - MEDIATYP.RXX is checked only when the requested file has an extension that does not match one of SRE-http's pre-defined mime types. Therefore, it can not be used to redefine a built in mime type.
  - Instructions on how to modify MEDIATYP.RXX are contained in the copy of MEDIATYP.RXX that ships with SRE-http.
  - If you add new text/html entries, and you want these to be equivalent to SHTML entries (that is, html entries with server side includes permitted), you should edit the SSI_EXTENSIONS variable in INIT_STA.80 (see INITFILT.DOC for details).

  Return to table of contents

  ## 7) Some useful facilities provided with SRE-http

  SRE-http comes packaged with several useful tools: a speciallized file-transfer utility, a message box utility, and client customization tools.

  ### 7.a)The DOSEARCH facility

  In the interests of space, DoSEARCH is no longer packaged with SRE-http. However, DOSEARCH is available as an addon from the SRE-http home page

  Return to table of contents

  ### 7.b)The SENDFILE facility

  SENDFILE is an SRE-http facility that transfers files to a client. It can record the number of times this file has been completely sent. In addition, it can be used to sequentially send a set of files.

  SENDFILE is invoked with a request selector of:
  `SENDFILE?file=selector&forcetext=1&COUNTER=option_list&header=response_header`
  (the &forcetext=1 and &COUNTER=option_list are optional)

  SENDFILE will ...

  1. Check for the existence of a file corresponding to the `selector` (the file that the `selector` maps to is assumed to be relative to the data directory or relative to a "local" virtual directory).
  2. Look in the SENDFILE_FILE for an occurence of the `selector`. If none exists, create an entry.
  3. If the `selector` exists (and the entire file was sent), the "count of requests" for this `selector` is augmented. That is, if the client killed the connection half way through, the count will not be augmented.
  4. If a COUNTER=... options is present, COUNTER.RXX will be used (with the option_list).
  5. The values of HEADER= options are used as additional response headers. Examples:
  6. `SENDFILE?file=foo.bar&HEADER=refresh:+2+;+url=/sample/thanku.htm`
     would cause a `Refresh: 2 ; url=/sample/thanku.htm`
     response header to be sent (2 seconds after SENDFILE transmits the file, the browser will then request /sample/thanku.htm )

  7. `&HEADER=content-disposition:+attachment;+filename="spiffy.2"&file=foo.bar`
     would cause a `Content-disposition: attachment; filename="spiffy.2"` to be sent (the "save file as" box will offer spiffy.2 as the default filename)
     Note that the value of a HEADER= option must be URL encoded (i.e.; + characters used for spaces).

  8. If more then one `FILE=selector` option appears, then SENDFILE will attempt to send each of the files (that the `selector`s map to) to the client without requiring further mouse clicks. In other words, you can simulate a FTP MGET command!

     This does require a browser that can handle multipart-mixed documents -- for example, Netscape 2.0 and above.

     > Example:`/SENDFILE?file=/dir1/hello.htm&file=/download/spiffy.zip&file=/dir1/thanks.htm`.

     > First, `/dir1/hello.htm` is sent to the client; which is immediately followed by `/download/spiffy.zip` (the client will almost certainly be asked to provide a name to save spiffy.zip as). After spiffy.zip has been transmitted, `/dir1/thanks.htm` will be sent.

  9. As a shortcut, you do not need to specify the `FILE=` -- an option with no = is assumed to be a FILE= option. For example, `SENDFILE?samples/intro.doc` is equivalent to `SENDFILE?file=samples/intro.doc`

  ##### Notes

  - If the client breaks the connection before the a file is completely sent, the SENDFILE_FILE is not modified (the request is not recorded).
  - By default, SENDFILE_FILE is SENDFILE.CNT.
  - When ACCESS_ALLOW is enabled, the ACCESS_FILE should contain an entry of the form
    SENDFILE?*
  - The SENDFILE_FILE supports wildcard matching.
  - For details on the COUNTER= option_list, see COUNTER.DOC .
  - If `FORCETEXT=YES`, SENDFILE will assume that all files are of "mime-type text/plain". This can be a useful trick (it tricks the client into displaying everything as a text file), but if .GIF (or other non-text files) are chosen, garbage will be displayed ( use this option with discretion)!
  - Entries in the SENDFILE_FILE may be "host specific".
  - SRE-http will check that the browser understands multipart-mixed documents (it looks for a connection: request header, or if the browser claims to be http/1.1 compliant). If the browser can not handle such documents, only the first `FILE=selector` statement is processed.
  - SENDFILE will only record (in SENDFILE.CNT) the first file sent (that is, only the file referenced by the first `FILE=selector` option).
  Return to table of contents

  ### 7.c) Using Message Boxes

  SRE Filter's built-in message box facility provides a mechanism for storing messages from clients. SRE-http provides a few simple built-in tools for manipulating these messages boxes. These include:
  1. A message writer. The message writer is invoked with a request selector of:
     `MESSAGE?messbox=messagebox&field1=value&..&fieldn=value`
  2. Two simple facilities (VIEWMESS and ASKMESSBOX) are provided for viewing an entire message box.
  3. Message box access can be controlled through the use of message box privileges.
  Of perhaps greater interest, the FORUM, READMAIL, and MAILLIST SRE-http addons make extensive use of these SRE-http messages boxes.

  #### 7.c.i) The Message Writer

  The message writer is usually invoked with an HTML FORM with ACTION="/MESSAGE" (see SAMPMBOX.HTM for an example). In addition to an INPUT element identifying the "message box", you can specify a number of fields (the field name, and it's value, are written to the message box using an e-mail type format). Several of these fields are treated specially, as explained below:
  MESSBOX (recommended)
    The particular message-box to put the note into. If a MESSBOX field is not included, the note will be put into the ANYONE message-box. If MESSBOX names a non-existent message-box, a new message-box will be create.
  NAME and SUBJECT (recommended)
    These are expected, if not included a dummy value will be created. Note that each message is automatically given a TIME and DATE stamp.
  FAX, E-MAIL, ADDRESS, and PHONE (optional).
    The name, and value of these fields are written to the message box. Note that the E-MAIL field is explicitly used by SRE-http's FORUM addon.
  PASSWORD and DURATION
    The PASSWORD and DURATION fields are used by the FORUM addon to control "delete privileges" for a given message. PASSWORD will be encrypted before being written to the message box file. Note that messages boxes are not designed for security (the encryption is weak), so don't use them when confidentiality and integrity are important.
  INDEX
    Including an `INDEX=YES` field will cause MESSAGE to update an index file (with an .IDX extension). These .IDX files are used by the FORUM addon to speed up response. Note that this .IDX file creation will occur after responding to the client (it's a post-filter type of action) -- the client will not notice any adverse impact from inclusion of an `INDEX=YES` field (but other clients may be impacted by the extra workload!)
  BROADCAST_LIST
    If included, SRE-http will simultaneously e-mail (through the SMTP gateway you set with the SMTP_GATEWAY variable) copies of your message to a list of e-mail addresses. This list, a file with name given by BROADCAST_LIST, must be in (or under)the MESSBOX_DIR. Furthermore, the client must have SUPERUSER or BROADCAST privileges, or a privilege equal to the value of BROADCAST_LIST. If not, SRE-http will send authorization request back to the client.
- Example: if BROADCAST_LIST=CLASS10.LST, then the client must have a `CLASS10.LST` client privilege.
  Note that the BROADCAST_LIST file (i.e.; CLASS10.LST) should contain valid e-mail addresses, one per line.
  BROADCAST_ONLY=YES
    Do not write to message box, just BROADCAST
  BROADCAST_NAME=My_name
    Used in the "from" field of the e-mail message.
  WRITE_TO_FILE=YES
    If included, SRE-http will write an "E-mail" like file (containing From, To, Date, and Subject fields; followed by the Contents) to your MAILBOX_DIR directory. These files are designed to be read, and processed as an "e-mail message to a list-server", by the MAILLIST (and READMAIL) SRE-http addons.

    > If you are broadcasting to many recipients, the use of WRITE_TO_FILE in conjunction with the MAILLIST addon, rather then the BROADCAST_LIST, is recommended.

  Other names (optional).
    The name, and value, of these fields will be written to the message box.

    > The difference between "other names" and the PHONE, ADDRESS, and FAX "optional" fields is merely in the order of appearance.

  RESPONSE_FILE
    The RESPONSE_FILE field is used to indicate a file contaning a "response" to a posted message. If no RESPONSE_FILE is included, a very simple generic response will be returned.
  MESSAGE (recommended)..
    The (multi-line) message. It's written last of all.

    #### 7.c.ii) Viewing Message boxes with VIEWMESS and ASKMESSBOX

    The direct means of reading a message box is to simply view it using the OS/2 TYPE command (message boxes are ASCII files, with a .LOG extension, located in the MESSBOX_DIR directory). SRE-http also provides a simple mechanism for remotely viewing these message boxes.

    > A request selector of `VIEWMESS?messbox=message_box` will cause SRE-http to transfer the message-box-file to the client.

    SRE-http also provides a simple routine that generates an HTML document that displays a list of all available message-boxes, and let's the client choose which one to view. This routine can be invoked with a request selector of
    `askmessbox?An+optional+header`
    The "optional header" is displayed as an <H2> at the top of the document.

    #### 7.c.iii) MESSBOX Privileges

    To access a message box with MESSAGE (or with the FORUM addon), the client must have "message box specific" privileges. These are specifed by including (in the client's privilege list), entries of the form:
    MESSBOX=a_message_box.
    For example: `MESSBOX=FORUM1` would give (read/write) access to the `FORUM1` message box. Note that this is in addition to any "selector and FILE specific" access controls you may have imposed.

    The `a_message_box` portion of the privilege can contain the * "wildcard" character. For example, `MESSBOX=FORUM*` would provide access to FORUM1, FORUM2, etc.

    On installation, SRE-http includes `MESSBOX=*` in the PUBLIC_PRIVS parameter (the effect of which is to allow open access all message boxes). You'll need to remove this from PUBLIC_PRIVS if you want to limit access to message boxes!

    ##### Notes

    - You can also limit access to message boxes by creating an entry in the ACCESS_FILE of the form:
      MESSAGE* resource_privilege_list
      (you may also want to create similar entries for VIEWMESS and ASKMESSBOX)

    Return to table of contents

    ### 7.d) The SRE-http procedure library

    SRE-http uses a procedure library (that is loaded into macrospace) to provide many functions. Several of these routines may be quite useful to the ambitious REXX programmer. These procedures include:
    - SREF_MEDIATYPE: Return the MIME type of a file (based on it's extension)
    - SREF_REPLACESTRG : Replace substrings
    - SREF_MULTI_SEND: Expedites the creation of multi-part documents
    - SREF_GRAB_FILE : Wait for file to become unlocked, and then read it into a variable.
    - SREF_FIX_URL : Given a local selector , and servername, and a serverport, return a legitimate URL (including the http://).
    - SREF_WILDCARD : Perform a wildcard substitution.
    - SREF_JULDATE: Return the Julian date and time (days since 0/0/0, time in fraction)
    - SREF_MAILIT : Send an E-mail message.
    - SREF_CGIVARS : Determines one of the "CGI-BIN" variables.
    - SREF_BROWSER_INFO: Check on the capabilities of the client's browser.
    See SREFPRC.DOC. for a complete description of these procedures.

    Return to table of contents

    ### 7.e) Client-specific and browser-specific customization

    SRE-http provides two addons that facilitate the creation of customized documents. Both of them are invoked with an <!-- INTERPRET FILE --> server side include:
- BYCLIENT.RXX: ByCLIENT.RXX is used to specify a set of files to be #INCLUDEd on a client-specific basis. Identification of clients is based on either a special cookie, the client privileges, or IP address.
- ByBROWSR: ByBROWSR.RXX is used to specify a set of files to include on a browser-specific basis. Browsers are identified by their user-agent; which are then matched (possibly using * wildcards) to one of several file-mapping rules.

  > Suggestion:For a highly dynamic (cookie based) means of customizing documents, check out the CUSTOMIZ addon.

  Return to table of contents

  ### 8) SRE-http addons

  In addition to all the features/options/utilities packaged with SRE-http, there are an ever-increasing number of SRE-http addons available.

  > Note that the SRE-http addons use a somewhat non-standard interface. However, given the flexibility and power of the GoServe/SRE-http API , these addons are often considerably faster then equivalent CGI-BIN scripts, and can often provide services (such as server push) that would be almost impossible with standard CGI-BIN

  You can find & download the latest SRE-http addons from the SRE-http home page.

  The following (non-exhaustive) list of currently available addons is provided to tease your appetite:
  - FORUM: A news-group and list-server discussion-group package.

    The FORUM addon consists of several components, including:

    1. FORUM: The FORUM component provides a simple, but fairly complete, multi-threaded "news group" like capability. The basic output of FORUM is a list of "links" to messages in the message box. The list is organized hierarchically, with indentation used to indicate discussion threads.

       Clinking on a link causes just that message (and it's various "fields") to be displayed. The client then has a number of options: including sending a response to the message poster (given that an e-mail address is available), posting a new message to the message box (either as a response to the message, or a as new entry in the discussion thread), or viewing the next message or the next thread.

    2. READMAIL: The READMAIL component will transfer incoming e-mail to SRE-http message boxes. This mail is read from the incoming mail directory of an SMTP-gateway running on your server; for example, the SMTP-gateway provided by OS/2's SENDMAIL daemon. By combining READMAIL, and the BROADCAST_LIST option of MESSAGE, a simple "list server with automatic archiving" can be implemented.

  - BBS: A full featured "web based bulletin board system"

    BBS is a WWW bulletin board system. BBS features include:

    - Individual file descriptions can be displayed, along with file size and creation date.
    - Directory specific inclusion files (i.e.; FILES.BBS) and exclusion files can be used to control file and sub-directory display.
    - Optional "automatic descriptions" can be generated for HTML, .ZIP, and text files.
    - .ZIP files can be "opened and displayed", with subsequent retrieval of a specific file from within the .ZIP archive
    - Netscape 2.01, and other HTML 3.0 compliant browsers, can upload files by using a FORM containing a file="type" element.
    - Uploads and downloads can be recorded on a per user basis.
    - A flexible access control mechanism allows customizaton of which file areas a user can peruse.
    - Downloads can be disallowed if a user's "download to upload" ratio grows too large.
    - Directory specific headers, footers, and "exclusion lists" can be specified.
    - Optional caching of directory-listings can greatly speed up throughput.

  - GOSWISH: A front-end (+ more) to the freeware SWISH search engine. SWISH is used to index the many directories comprising your web-site. It creates a compact index that it can search quickly for matching words.

    GOSWISH, the SRE-http front-end, enables you to search this from an HTML form. In addition, GOSWISH will automatically create a description. You can also use GOSWISH to create a "description index", which you can then search for matches.

  - GETAFILE: A directory displayer, with user-settable display features

    GETAFILE is a similar to SRE-http's !DIR dynamic directory display facility. It is somewhat easier to configure, and has a few extra bells and whistles.

  - CALC: A character-mode scientific calculator with a web interface
    CALC is a WWW-accessible scientific calculator. It uses a keyboard interface, and is based on an aging DOS program. On the other hand, it's quite feature rich: multiple equations and temporary variables can be specified, trigonometric functions are fully supported, analytic derivatives can be taken, and more...
  Did we say `non-exhaustive`? Some of the other addons include:
- Customiz: a client-customization utility (using cookies)
- GIF_TEXT: a text-to-gif converter (using numerous fancy-multi-colored fonts)
- WWWthumb: a create & deliver grahpical thumbnails utility
- and much more!

  Return to table of contents

  ## Appendix 1) User-configurable SRE-http files.

  SRE-http is managed and customized through a set of ascii (text) configuration files. In this appendix, we list these configuration files, indicating what they do and where to find more information about them.

  But first, some preliminary notes...

  1. Unless otherwise noted, these configuration files will be located in the CFGS\ subdirectory of your GoServe working directory. Note that and "audit, count, and selector-specific files" are usually in the DATA\ subdirectory of your GoServe working directory.
  2. All of SRE-http's configuration files are text-based -- you can always edit them with your favorite text editor (such as EPM). Many of the files can also be modified using the on-line SRE-http confgiurator.

  FileName | description | more info
  --- | --- | ---
  Host specific parameter files | Files that specify additional host and port specific parameter files.
  CFGLIST.CFG | CFGLIST.CFG is used to specify host-specific information, including HOST definitions (assignations of IP addresses/aliases to SRE-http HOST_NICKNAMES), and to define host (and port) specific configuration files. | USE_CFGS.DOC contains a detailed description of the CFGLIST.CFG.
  General SRE-http variables | Files that specify basic SRE-http parameters, and files used for other non-request-specific purposes.
  INITFILT.80 | INITFILT.80 contains a number of SRE-http parameters. These are parameters that are global to all requests. They are also parameters that are can be changed on the fly -- you do not need to restart GoServe. | INITFILT.DOC contains a detailed description of the various parameters contained in INITFILT.80 You can modify INITFILT.80 parameters using the intermediate configurator. Or, you can run EDITINIT.CMD (from an OS/2 command prompt on the server).
  INIT_STA.80 | INIT_STA.80 is similar to INITFILT.80 -- it contains global parameters. However, these parameters tend to be a bit more obscure. More importantly, they only are read when GoServe/SRE-http start -- so for changes to take effect, you must restart GoServe. | INITFILT.DOC contains a detailed description of the various parameters contained in INIT_STA.80 To modify INIT_STA.80, you can run EDITINIT.CMD (from an OS/2 command prompt on the server).
  USERS.IN | The SRE-http USERS.IN file is used to register users. Each entry in USERS.IN contains a username, a password, and an optional list of client privileges. | USERS.DOC contains a detailed description of SRE-http's USERS.IN file. The SRE-http manual describes SRE-http's logon controls.
  REPSTRGS.IN | SRE-https REPSTRGS.IN file is used to specify "replacement strings" for use with the <!-- REPLACE astring --> server side include. | REPSTRGS.DOC contains a detailed description of SRE-http's REPSTRGS.IN file.
  SCHEDULE.CFG | SRE-http has a simple scheduling daemon that will run programs on a hourly, daily, weekly, or monthly basis. You specify what you want to run via the SCHEDULE.CFG file, which is located in the CFGS\ subdirectory (of your GoServe working directory). | SCHEDULE.DOC contains a detailed description of SRE-http's SCHEDULE.CFG file.
  Selector-specific attributes | User-configurable, selector-specific attributes are attributes that you (the web site administrator) may wish to set on a request-selector basis. These include access requirements, controls on how SRE-http will process a request, URL redirections, and other remappings.
  ALIASES.IN | The ALIASES.IN file is used to modify and transform the request selector. This includes local and remote redirection, specifying searchable indices, and specification of negotiable resources. | IN_FILES.DOC contains a detailed description ALIASES.IN. You can modify ALIASES.IN with the intermediate configurator.
  ACCESS.IN | The ACCESS.IN file is used to control access to your server's resource on a selector specific basis. This access control is based on a comparison of a client's "privileges" and the privileges assigned to a selector. | IN_FILES.DOC contains a detailed description ACCESS.IN. You can modify ACCESS.IN with the intermediate configurator.
  PUBURLS.IN | PUBURLS.IN is used to specify "public URLS". Public-urls are defined as resources for which access (and logon) controls are not imposed. | PUBURLS.DOC contains a detailed description PUBURLS.IN.
  VIRTUAL.IN | VIRTUAL.IN is used to specify virtual directories. Virtual directories are used to allow access to files not in a default directory. The typical use is to allow requests for documents to be in a subdirectory not under the "GoServe data directory". | IN_FILES.DOC contains a detailed description VIRTUAL.IN. You can modify VIRTUAL.IN with the intermediate configurator.
  ATTRIBS.CFG | ATTRIBS.CFG is used to set selector-specific attributes using a "realm-oriented" architecture. It supplements (or replaces) ACCESS.IN, ALIASES.IN, PUBURLS.IN, and VIRTUAL.IN. ATTRIBS.CFG can also be used to specify users (as a supplement to USERS.IN), and to specify replacement strings (as a supplement to REPSTRGS.IN) | IN_FILES.DOC contains a detailed description ATTRIBS.CFG. You can modify ATTRIBS.CFG with the intermediate configurator.
  Advanced options files | SRE-http's selector-specific advanced-option files provide a set of less-frequently needed, "advanced-options" to the ambitious webmaster. These advanced-options include execution of "mid-filter" procedures, customization of response headers, specifying the Content-type, and enabling of content encryption. | ADV_OPTS.DOC contains a detailed description of SRE-http advanced options. You can modify ACCESS.IN or ATTRIBS.CFG (using the intermediate configurator) to specify these files (by default, they should be placed in the DATA\ subdirectory of your GoServe working directory).
  Counter and Audit Files | Unless otherwise specified, the various counter and audit files are located in the DATA\ subdirectory of the GoServe working directory.
  COMMON.LOG and other LOG files | SRE-http supports auditing using standard COMMON.LOG, BROWSER.LOG, REFERER.LOG and COMBINED.LOG files. | SREFLOGS.DOC contains a detailed description of SRE-http's implementation of common log files.
  RECRDALL.CNT | The RECORD_ALL_FILE (with default name RECRDALL.CNT) is used to record all actions, such as transfers of files and requests for server side processing. It is used when RECORD_OPTION is enabled. | CNTFILES.DOC contains a detailed description of the structure of RECRDALL.CNT. Note that the RECORD_CACHE_LINES parameter is used to control "caching" of RECRDALL.CNT.
  GOAUDIT.80 | GOAUDIT.80 is GoServe's audit file. It is located in the GoServe working directory. | GOAUDIT.80 is described in the GoServe documentation (GOSERVE.DOC). You can use GoServe's Option-Audit tab to control what is written to GOAUDIT.80.
  SENDFILE.CNT | The SENDFILE_FILE counter file (with default name SENDFILE.CNT) is u by the SENDFILE facility to record transferals. SENDFILE is especially useful when transfering large files, since SENDFILE will only record a "hit" if the entire file is successfully sent. | CNTFILES.DOC contains a detailed description of the structure of SENDFILE.CNT. The SRE-http manual describes how to use the SENDFILE facility.
  COUNTER.CNT | The counter file is used to record the number of requests (also known as the number of hits) for this document. It is used whenever a <!--REPLACE HITS --> or a <!-- REPLACE COUNTS --> server-side include keyphrase is processed. | CNTFILES.DOC contains a detailed description of the structure of COUNTER.CNT.
  COUNTER.RXX | COUNTER.RXX is a flexible "number of hits" generator and request-information recorder. It can be used in server side include to provide a textual counter (as an alternative to <!--REPLACE HITS -->). Or, it can be used in an in-line image to provide an odometer style, graphical counter. In contrast to <!--REPLACE HITS -->, COUNTER.RXX stores hit counts in seperate selector (or file) specific files. | COUNTER.DOC contains a detailed description of how to use COUNTER.RXX. provides a demo of COUNTER.RXX (andof <!--REPLACE HITS -->).
  XCOUNT.CMD and JCOUNT.CMD | XCOUNT.CMD and JCOUNT.CMD are two cgi-bin scripts that provide hit counter capabilities. | See CNTDEMO1.SHT for a demo.

  Return to table of contents

  ## Appendix 2) Summary

  ### AP.a) Known limitations of SRE-http

  The currently known limitations of the SRE-http package include:
  - Technically speaking, SRE-http ver 1.3 is conditionally compliant with the http/1.1 spec. Conditional compliance means that all of the features that must be supported are implemented, but not all of the should be supported options are available (though most of the more important & interesting should options are implemented).
  - SRE-http has not been tested with proxy servers (some users report good success using SRE-http with INJOY)
  - SRE-http does not support SSL. However, SRE-http ver 1.3g does support:
    - "digest" authentication, which (given that one's browser knows how to use digest authentication) provides much better password protection that the older "basic" authentication.

      > Since non-http/1.1 browsers will probably be with us for several years, SRE-http also supports a quasi-digest authentication method, that requires clients to generate dynamic passwords (using a program on their own machine).

    - A proprietary form of file encryption using a "shared secret". This requires that you distribute SRE-http decryption software to clients.
  In other words, SRE-http is designed as relatively full-featured package for non-cutting edge small-to-medium load sites being maintained by non-professionals

  ### A2.b) Summary of SRE-http Features

  The following summarizes most of SRE-http's features:
  - Multiple hosts (either unique IP addresses, or multiple aliases per IP address) are supported.
  - Seperate data directories, aliases, etc. can be specified for each supported host
  - Logon requirements may be required of no one, everyone, or the general public.
    - A set of public resources can be specifed, which will be available to all clients.
    - OWNERS (with SUPERUSER privileges) and IN-HOUSE users can be automatically detected (using their numeric IP address), with logon requirements waived.
    - A set of "unallowed" numeric IP addresses can be specified.
    - Wildcards can be used in the list of IN-HOUSE and "unallowed" numeric IP addresses
    - Custom logon procedures can be optionally used
  - Several tools for resolving and redirecting requests are provided
    - A "directory specific" document can be sent when a request selector specifying a directory, but no file is name, is recieved
    - Instead of a default document; a "directory listing" can be produced, with file descriptions generated for all plain, html, and .ZIP files. These directory listings can be cached, and used for subsequent requests.
    - ALIASes can be used to redirect requests for moved documents, to resolve commonly occuring "misspelled requests", and to transfer specific files from anywhere on your server.
    - Server-side and client-side content negotiation is supported.
    - A customized "not found" document (complete with suggested link) can be sent when the requested document is missing.
    - ...or a selectable list of nearest matches to the requested file can be returned.
    - The ~ shorthand for the "home directory" is supported. In addition, ~ can point to www-specific subdirectories of the "home directory"
    - Transfer of files from outside the "default data directory" is easily supported through the use of "virtual directories".
    - Transfer, with optional processing, of files from remote servers (without using redirection) is supported through the use of "remote" virtual directories.
    - * wild card character(s) in selectors can be used to request a "best matching" document.
  - A variety of server-side includes are easily achieved
    - Global replacment-rules, that are not dependent on HTML-like statements, can be specified on either a general or file-specific basis.
    - A special caching algorithim selectively caches documents that contain server side includes
    - Headers and Footers can be included in all HTML documents
    - Recursively processed keyphrases, that dictate server side includes, can be placed in your HTML documents
      - Dynamic and Static String REPLACEments
      - Inclusion of files (from anywhere on your system)
      - Inclusion of OPTIONs that appear in the request selector (information after a ?)
      - Execution of REXX-code blocks, and insertion of the results
      - SELECTive excludes of HTML code blocks
    - The NSCA HTTPD server side include syntax is fully implemented
    - The SET and IF..ELSEIF..ELSE XSSI Apache Extensions to the NCSA HTTPD SSI syntax is implemented.
    - Easy-to-use support for client-specific and browser-specific customization of HTML documents
  - Standard server features include:
  - NCSA style IMAGEMAPS are supported, and easily requested.
  - Searchable indices on text files are easy to setup
  - A flexible mechanism for controlling access to explicit selectors (and the files they correspond to); including definitions of realms as a set of selectors.
  - Support for the HTACCESS method of access control
  - Several mechanisms for recording hits
  - Several forms of redirection can be specified
  - A simple form of load balancing is supported
  - Support for "common-log" format audit files (as well as browser and referer log files)
  - Special SRE-http built-in features include:
  - A file display and transfer facility with easy directory traversal
  - A simple but powerful "text file" search facility
  - Dynamic assignation of "short-term" privileges to clients
  - Extraction of a range (bytes or lines) of a resource using options specified in the selector
  - Tracking of recent hits to prevent recording of repetitive requests
  - Optional limits on frequency of unsuccesful "logon" attempts, with options for custom response files in the event of "logon" or "access" denial.
  - Implementation of "byte range retrieval" (which is used by Adobe Acrobat to access subsections of documents)
  - Reponse headers can be automatially generated, using LINK and META HTTP-EQUIV elements in the <HEAD> portion of the document.
  - A Content-MD5 digest can be added to all, or to a select set, of responses
  - On-the-fly GZIP transfer-encoding is supported (both sending and recieving). GZIP and COMPRESS are also understood as content-encodings.
  - Several file upload methods are supported
  - Client directed retrieval of files from other HTTP servers
  - Browsers that support the `type=file` FORM attribute (such as NetScape 2.01), can upload files from their own machines.
  - The PUT verb, with byte ranges, can be permitted on a per selector (or per "set of selectors") basis
  - The DELETE method can be permitted on a per selector (or per "set of selectors") basis
  - User written server side processing (gateway programs) options include:
  - Support for SRE-http addons (REXX routines that return results directly to the client).
  - CGI-BIN scripts (both REXX and binary executables, and PERL scripts if you have a PERL interpreter installed) are supported (using procedures adapted from the GoHTTP package).
  - A "pre-filter" can be called prior to invoking SRE-http
  - SRE-http comes with a special pre-filter that implements the the GoRemote package.
  - A "post-filter" can be called after SRE-http has responded to the request.
  - SRE-http comes with a special post-filter that uses socket calls, to an SMTP server, to e-mail "event specific" alerts.

  Return to table of contents

  ## Appendix 3) Terminology

  The following terms are used in this documentation. Please forgive any non-standard uses you may encounter (better yet, let me know).

  You might also want to review the basic terminology for extended descriptions of a few key concepts.

  The \ and / characters
    The / character is used in URLs to "indicate hierarchical structures, such as directories". It is equivalent to the \ OS/2 (and DOS) character. Thus, / that appear in a request selector are converted into \ when SRE-http needs to find a file.
  Action
    The action is the "location" portion of a request selector.
    - If the GET method was used -- it's the part after the first / (that ends the domain name) and before the first ? (or the end of the request selector , if no ? is present).
      Examples:
      - In `http://foo.bar.org/calc/calc.htm`,
        the action woud be `calc/calc.htm`.
      - In: `http://foo.bar.net/workdir/myfile.htm?not+readyl`,
        the action would be is `workdir/myfile.htm`.
      - In:`http://young.kids.com/toys/demo?dogs+cats`,
        the action would be `toys/demo`
    - If the POST method was used, the request selector (not including a leading / character) is the action (there should never be a ? in a POST method request string). All other information is contained in the "body" of the request. SRE-http assumes that all POST method requests are for Server Side Processing.
  Addon directory
    The addon directory (with a value given by the ADDON_DIR parameter) is where SRE-http's external procedures should be stored. For example, several external procedues shipped with SRE-http (i.e; the simple and intermediate configurator) should be located in this directory.
  Alias -- converting selectors
    SRE-http uses "aliases" to perform textual substitution. Typically, an alias is used to replace a simple request selector with a more complicated one. In addition, aliases are used for several special purposes: implementing "searchable indices", document redirections, and specification of the location of CGI-BIN scripts.
  Alias -- virtual hosts
    A given IP address can be used by several hosts: including the host associated with the "canonical" name, and hosts associated with one of several aliases. Unfortunately, TCP/IP requests arrive with only the numeric IP address, making it difficult for the server to determine to which host the request is directed to. However, HTTP 1.1 compliant browsers (such as NetScape 2.01) will include a `HOST:` request header containing the host to whom this request is directed; and SRE-http can use this request header (if present) to determine the proper host.
  Client
    The Client (sometimes referred to as the requester) is the individual requesting a URL -- where the URL may point to a file, or may invoke Server Side Processing. Typically, the request was generated by someone running a Web Browser, and clicking on a link or submitting a FORM.
  CGI-BIN
    CGI (Common Gateway Interfact) - BIN is a standard by which server side ("gateway") programs can be invoked. It uses environment variables to pass data, as well as standard input and output. SRE-http supports CGI-BIN, using procedures adapted from the GoHTTP package. One nice feature of SRE-http is an ability to call alternate (non-REXX) interpreters for specific scripts (such as PERL when a script has a .PL extension).

    > Although this support should permit use of many CGI-BIN scripts, the use of the "native" SRE-http interface (using REXX procesures that are passed information in the argument list) offers advantages to ambitous programmers

  The Default Data Directory
    The Default Data Directory is the root directory of your web site -- it (and it's subdirectories) are the usual locations for the HTML documents, images. In simple cases, the GoServe data directory is used as the the Default Data Directory. On multiple-hosts server, each host can be granted it's own Default Data Directory.

    A simple example might help:

    - a request selector of MYFILES/PROJECT1/BIGTASK.HTM is recieved
    - your default data directory is E:\WWW
    then, SRE-http will look in E:\WWW\MYFILES\PROJECT1 for the BIGTASK.HTM file.

    A Note On Data Security in SRE-http

    > In general, the only files available for clients are those in (or under) the Data Directory. Exceptions to this rule include:

- Files explicitly transferred by user-supplied executable code (i.e; REXX procedures). Note that user-written Rexx code may be invoked by a CGI-BIN script or a SRE-http addon, or by INTERPRET, #EXEC and SELECT keyphrases.
- A !TRANSFER "alias" can be used to access files from anywhere on the server.
- Files specified by literal PUBLIC_URLS.
- Virtual directories can point to anywhere.
  ELEMENT
    ELEMENT's are the constituent parts of an HTML document. They dictate the structure, layout, and display characteristics of an HTML document. ELEMENTS are identified using HTML tags, where an HTML tag consists of text within < and > characters. Often, a start and stop tag are used.

    For example:

    - `<H1> Welcome </H1>` : defines a "level 1 Header"
    - `<A href="/morejunk/stuff.htm"> More info? </A>` : defines a link to a local document.
  File Names: Fully qualified and Relatve
    SRE-http can treat File Names as "fully qualified" names or as "relative" names. Fully qualified names should be fully pathed -- containing the complete path to the file (sometimes the drive letter will be missing, in which case the GoServe drive is usually assumed). Relative names are assumed to be in subdirectories of some assumed default. For example, when a client asks for a file name, it is assumed to be relative to the data directory (or to a matching virtual directory).
  FORMS
    The HTML FORM element is used to create a fill-in form. A FORM element typically contains an ACTION attribute, as well as a number of elements that provide editable fields (for the client to fill in or to otherwise select). Typically a form is designed in tandem with a server-side program.

    > Although not the only way to generate a Server Side Processing Request (one can use sets of detailed URLS), FORMS are probably the easiest for the average client to deal with.

  Hosts
    It is possible for one server machine to handle requests to multiple IP addresses. This "multiple hosting" (also refered to as multi-homing) can occur either by having the server handle several numeric IP addresses, or by the existence of multiple aliases for a single numeric IP address.
  Host nickname
    SRE-http uses host nicknames when identifying which host a parameter applies to. Besides being a convenience, it allows several hosts to point to identical resources (given that each host has the same host nickname).
  HTTP : Hyper Text Transfer Protocol
    The rules by which web-aware clients and servers communicate.
  HTTP method (also known as the VERB)
    SRE-http recognizes five HTTP methods: GET, POST, HEAD, DELETE, and PUT.
- GET requests contain all information (action name and optional parameter list) in the request string (with the parameter list placed after a ? character)
- POST requests contain only the action name in the request string (the "body" of the request contains the parameter list). Currently, SRE-http assumes that all POST requests are requests for Server Side Processing.
- HEAD method requests are sent "meta information" on the requested file, the file itself is not sent.
- PUT method requests are used to upload information to the file pointed to by a request selector . SRE-http will only honor PUT method requests if specific permissions are granted for that selector (as set in the ACCESS_FILE).
- DELETE method requests are used to delete (the file pointed) a requested selector . SRE-http will only honor DELETE method requests if specific permissions are granted for that selector (as set in the ACCESS_FILE).
  HTML
    Hyper Text Markup Language (HTML) is the protocol used to create documents designed for display by WWW browsers (such as Netscape, Mosaic, MS Internet Explorer,and IBM Web Explorer). Basically, HTML consists of a set of formatting commands, which are included in a file containing the text to be displayed.

    SRE-http uses file extensions to identify HTML documents. By default, the following extensions are used: `.HTML, .HTM, .SHT, and .SHTML`. You can add to this list by modifying MEDIATYP.RXX.

    > Although there is a formal HTML standard (currently 3.2, with 4.0 under discussion), it is not rigidly adhered to. In particular, NetScape and Microsoft have their own extensions.

  Imagemap
    An image map (sometimes called a mappable image) is an inline image which, when clicked with the mouse, returns a pixel location to the server. Typically, the server then translates the pixel location into a URL, and redirects the client to that URL (which might be on an all together different server). SRE-http supports image maps using the MAPIMAGE/ "indicator string", along with NCSA and CERN style "MAP" files to use in translating pixel locations to URL's.

    > Note that some browsers (such as NETSCAPE 2.0) support "client side mappable images", which require no action by the server (but which require an HTML element not understood by many other browsers).

  IN-HOUSE
    IN-HOUSE refers to clients that are "in-house"; specifically, they have had INHOUSE privileges assigned to them. The idea is that one often wants to differentiate members of your "organization" from the rest of the world, and place fewer limits on what they can obtain from the server.
  Macrospace
    Marospace is best thought of as a global procedure cache used by OS/2. When REXX programs are asked to load external procedures, they first look in macrospace. For efficiency reasons, SRE-http makes extensive use of macrospace.
  Privileges
    SRE-http uses "privileges" to control access to selected resources. There are two classes of privileges:
    1. "resource" privileges which are assigned to server resources (such as files, or directories), using entries in the ACCESS_FILE.
    2. client privileges which are granted to clients (based on their IP address, or their explicit username/password).
    Resource privileges can be ONE_OF privileges ("or" privileges") or MUST_HAVE privileges ("and" privileges). Client privileges may be static (assigned using INITFILT.80 or the USER_FILE), or may be dynamic (set on the fly as a function of the client's earlier requests).
  Request selector
    When a client sends a request to a server, it contains three components: the http method, the selector, and the http protocol.
    For example: GET /FOO1/BAR.HTM HTTP/1.0
    In this documentation, the term request selector refers to this middle component, with leading / stripped, and character decoding performed.
    In the above example, the request selector would be `FOO1/BAR.HTM`.
    Note that if a GET HTTP method was used, the request selector may contain information following a ? (for example, `SHOWINFO?database=Prices&item=apples`).
  Response Header
    The response header contains "meta-information" about the requested document. GoServe automatically sends a few response headers (such as content length and file creation date). In addition, using the `LINK` and `HTTP-EQUIV` tags in the <HEAD> portion of your document, you can instruct SRE-http to automatically add other response headers.
  Searchable Index
    A searchable index is a document that points to a file that is to be searched. One can think of a searchable index as:

    > .. the front end to a gateway program, and the file you search as the database represented by the document.

    Typically, a searchable index contains the <ISINDEX> element.
  SEL-specific
    SEL-specific means "a piece of information specific to a request selector . Clarifying, this means that SRE-http will use the value of the request selector to find information (such as resource privilege information). Thus, SEL-specific resource privileges really means "privileges associated with a particular request selector (coming up with terminology isn't easy ....)

    Note: the SRE-http documentation sometimes uses the term URL-specific to mean SEL-specific (it's a holdover from an earlier revision of the documentation).

  Server Side Includes
    Server side includes refer to on-the-fly modifications of requested HTML documents. Inclusions can be static, in which case the use of server side includes is mostly to benefit the creation and maintenance of these documents. Dynamic includes refer to information that changes, such as the current time and date -- obviously, these can not be specified in the document a priori, but must be determined at the time of request.
  Server Side Processing
    Often, the server provides computational services to clients. An example of this is a client specified search of a database, with the results displayed using an 'attractive" HTML document (generated just for this search). Or, the client might request a map of some portion of the U.S, displaying a choice of geographic features. Such actions require the server to execute some kind of program (perhaps a REXX program, or perhaps some other executable).

    > SRE-http addons, and CGI-BIN scripts, are typical means by which Server Side Processing is provided to clients.

  Server Side Processing Request
    A Server Side Processing request is, generically speaking, "a set of parameters, sent by a client, and an action name, that dictate Server Side Processing". Often these are generated by a client responding to a FORM element in an HTML document (alternatively, they may be "hand coded" into a URL included in a HTML document). Server Side Processing requests are recognized by:
- If the GET method was used: the presence of a ?options string after a "non-HTML" action name; where options contains the "set of parameters".
  Notes:
  - SRE-http assumes that, regardless of the presence of a ? in the request selector , all action names that end with a .HTM, .HTML, .SHT, or .SHTML are requests for HTML documents (that is, are not requests for server side processing),
  - Actions which require no parameters must have a ? trailing the action name.
  - Server side programs are sometimes referred to as gateway programs.
- If the request selector starts with `CGI-BIN/` , then it's assumed to be a request for a CGI-BIN script.
- If the POST method was used, SRE-http assumes a Server Side Processing Request, with the request selector treated as the action (which identifies the program to run), and the "set of parameters" contained in the "body" of the request.
  STEM. variables
    STEM variables are REXX's way of implementing arrays. A STEM variable consists of a NAME.INDEX1.INDEX2 syntax (that is, with a . used to indicate "array indices"). SRE-http uses STEM variables for several of it's configuration parameters.
  SUPERUSER status
    Clients with SUPERUSER status are granted full privileges. Currently, this includes:
- Never having to logon (SUPERUSERs are INHOUSE users)
- Automatically granted CONTROL privileges (can perform remote server resets)
- File uploads are never blocked.
  URL: Uniform Resource Locator.
    URL's are a scheme for specifying Internet resources using a single line of printable ASCII characters. A URL should contain a protocol, domain name, port number (optional), the location of the resource, and an (optional) option list (following a ?).
    In this documentation, the URL term connotes "a link coded into an HTML document".
    Upon selecting such a link, the client sends back a request string that contains the verb (the HTTP method), the request selector , and the http protocol (typically, HTTP/1.0)
    Example:given a URL of http://www.econ.ag.gov/calc/calc.htm
    the resulting request selector would be `calc/calc.htm`
  URL character encoding
    Since several characters have very specific meanings in the HTTP protocol (such as the & and the > characters), and since spaces are not allowed in request strings, a set of character encoding rules are needed to transmit such characters.

    > Caution: When handcoding URL's with an option list following a ? and seperated by & characters, you must encode the & character.

    For example:
    - INCORRECT: <A HREF="/GETAFILE?dir=PUBLIC/&showdate=YES">
    - CORRECT: <A HREF="/GETAFILE?dir=PUBLIC/&amp;showdate=YES">
  Web Browser
    A Web Browser is a program that can communicate over the Internet, and that is capable of displaying HTML documents. NetScape, Mosaic. and IBM Web Explorer are examples of Web Browsers.
  Wildcard matching
    Wildcard matching use the * as a wildcard character in a natural fashion.
    Examples:

          /JOE/*  will match /JOE/FOO.HTM
          /JOAN/SRCH.HTM?*  will match /JOAN/SRCH.HTM?search+me
          /JOAN/SRCH.HTM?*  will NOT match /JOAN/SRCH.HTM
                 (/JOAN/SRCH.HTM* will match BOTH these examples)
          /PETS/*INDEX.HTM will match
             /PETS/INDEX.HTM, /PETS/CAT/INDEX.HTM and /PETS/PUPPY/LAB/INDEX.HTM
                     but will NOT match
             /PETS/CAT/PUREBRED.HTM

    SRE-http files that support wildcard matching are: ALIAS_FILE, RECORD_ALL_FILE, SENDFILE_FILE, ACCESS_FILE, and the PUBLIC_URL stem variables.
    The COUNTER_FILE does not support wildcard matching.

  Wildcard matching with substitution
    Wildcard matching with substitution is similar to wildcard matching. However, rather then being a "many to one" match, it is a "many to many" match.
    The basic rule is that both a "target" and a "replacement" should contain * characters. When a wildcard match between the target and a candidate occurs, the "covered portion of the candidate" is inserted into the "replacement". In other words, the * character in the replacement is deleted, and the "covered portion" is inserted.

    Example:

    - If the request selector is: `project/jillwork.htm`
    - and there is an alias of: `project/* /research/ongoing/*`
    - SRE-http will convert the request selector to `/research/ongoing/jillwork.htm`
  GoServe Working Directory
    The GoServe Working Directory in the directory containing GOSERVE.EXE (typically, \GOSERV). You should copy the various SRE-http files to it (see the installation section for details).
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