# WASD Hypertext Services - Scripting Environment

## 2 - CGI

> 2.1 - CGI Environment Variables
> 2.2 - Script Output
> 2.2.1 - CGI Compliant Output
> 2.2.2 - Non-Parsed-Header Output
> 2.3 - Raw HTTP Input (POST Processing)

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The information in this chapter merely outlines the WASD implementation details, which are in general very much vanilla CGI and NCSA CGI (Common Gateway Interface) compliant, originally based the INTERNET-DRAFT authored by D.Robinson (drtr@ast.cam.ac.uk), 8 January 1996, and confirmed against the latest INTERNET-DRAFT authored by Ken A.L.Coar (drtr@etrade.co.uk), 12 June 1999.

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2.1 - CGI Environment Variables

With the standard CGI environment variables are provided to the script via DCL global symbols. Each CGI variable symbol name is prefixed with "WWW_" (by default, although this can be changed using the "/CGI_PREFIX" qualifier and the SET CGIPREFIX mapping rule, see "Technical Overview", this is not recommended if the WASD VMS scripts are to be used, as they expect CGI variable symbols to be prefixed in this manner).

There are a number of non-"standard" CGI variables to assist in tailoring scripts for the WASD environment. Do not make your scripts dependent on any of these if portability is a goal.

> Never, ever substitute

> the contents of CGI variables directly into the code stream using interpreters that will allows this (e.g. DCL, Perl). You run a very real risk of having unintended content maliciously change the intended function of the code. For example, never use comma substitution of a CGI variable at the DCL command line as in

>       $ COPY 'WWW_FORM_SRC' 'WWW_FORM_DST'

> Always pre-process the content of the variable first, ensuring there has been nothing inserted that could subvert the intended purpose (repeated here to emphasize the significance of this rule).

CGI variable capacity now varies significantly with VMS version.

The total size of all CGI variable names and values is determined by the value of [BufferSizeDclCommand] configuration directive, which determines the total buffer space of a mailbox providing the script's SYS$COMMAND. The default value of 4096 bytes will be ample for the typical CGI script request, however if it contains very large individual variables or a large number of form fields, etc., it may be possible to exhaust this quantity.

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VMS V7.3-2 and later ...

CGI variables may contain up to approximately 8150 characters (the full 8192 symbol capacity cannot be realized due to the way the symbols are created via the CLI). This is a significant increase on earlier capacities. Mailbox buffer [BufferSizeDclCommand] may need to be increased if this capacity is to be fully utilized.

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VMS V7.3-1 and earlier ...

Values are limited to approximately 980 characters. This should still be sufficient for most circumstances (if not consider using CGIplus or ISAPI, extensions to CGI programming which remove this limitation). Why such an odd number and why a little rubbery? A DCL command line with these versions is limited to 255 characters so the symbols for larger variables are built up over successive DCL commands with the limit of 980 characters determined by CLI constraints.

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CGI Variables

Remember, by default all variables are prefixed by "WWW_" (though this may be modified using the set CGIprefix= mapping rule), and not all variables will be present for all requests.

CGI Environment Variables

Name | Description | Origin
| AUTH_ACCESS | "READ" or "READ+WRITE" | WASD
| AUTH_AGENT | used by an authorization agent (specialized use) | WASD | AUTH_GROUP | authentication group | WASD | AUTH_PASSWORD | plain-text password, only if EXTERNAL realm | WASD | AUTH_REALM | authentication realm | WASD | AUTH_REALM_DESCRIPTION | browser displayed string | WASD | AUTH_TYPE | authentication type (BASIC or DIGEST) | CGI | AUTH_USER | details of authenticated user | WASD | CONTENT_LENGTH | "Content-Length:" from request header | CGI | CONTENT_TYPE | "Content-Type:" from request header | CGI | DOCUMENT_ROOT | generally empty, configurable path setting | Apache | FORM_field-name | query string "&" separated form elements | WASD | GATEWAY_BG | device name of raw client socket (specialized use) | WASD | GATEWAY_EOF | End of request sentinal (specialized use) | WASD | GATEWAY_EOT | End of callout sentinal (specialized use) | WASD | GATEWAY_ESC | Callout escape sentinal (specialized use) | WASD | GATEWAY_INTERFACE | "CGI/1.1" | CGI | GATEWAY_MRS | maximum record size of script SYS$OUTPUT | WASD | HTTP_ACCEPT | any list of browser-accepted content types | CGI | HTTP_ACCEPT_CHARSET | any list of browser-accepted character sets | CGI | HTTP_ACCEPT_LANGUAGE | any list of browser-accepted languages | CGI | HTTP_AUTHORIZATION | any from request header (specialized use) | CGI | HTTP_CACHE_CONTROL | HTTP/1.1 cache control directive | CGI | HTTP_COOKIE | any cookie sent by the client | CGI | HTTP_FORWARDED | any proxy/gateway hosts that forwarded the request | CGI | HTTP_HOST | host and port request was sent to | CGI | HTTP_IF_MODIFIED_SINCE | any last modified GMT time string | CGI | HTTP_PRAGMA | any pragma directive of request header | CGI | HTTP_REFERER | any source document URL for this request | CGI | HTTP_USER_AGENT | client/browser identification string | CGI | HTTP_X_FORWARDED_FOR | proxied client host name or address | Squid | HTTP_field-name | any other unknown request header field | WASD | KEY_n | query string "+" separated elements | WASD | KEY_COUNT | number of "+" separated elements | WASD | PATH_INFO | virtual path of data requested in URL | CGI | PATH_TRANSLATED | VMS file path of data requested in URL | CGI | QUERY_STRING | un-URL-decoded string following "?" in URL | CGI | REMOTE_ADDR | IP host address of HTTP client | CGI | REMOTE_HOST | IP host name of HTTP client | CGI | REMOTE_USER | authenticated remote user name (or empty) | CGI | REQUEST_CHARSET | any server-determined request character set | WASD | REQUEST_METHOD | "GET", "PUT", etc. | CGI | REQUEST_SCHEME | "http:" or "https:" | WASD | REQUEST_TIME_GMT | GMT time request received | WASD | REQUEST_TIME_LOCAL | Local time request received | WASD | REQUEST_URI | full, unescaped request string | Apache | SCRIPT_DEFAULT | mapped default directory for script | WASD | SCRIPT_FILENAME | script file name (e.g. CGI-BIN:[000000]QUERY.COM) | Apache | SCRIPT_NAME | script being executed (e.g. "/query") | CGI | SERVER_ADDR | IP host name of server system | WASD | SERVER_ADMIN | email address for server administration | Apache | SERVER_CHARSET | server default character set | WASD | SERVER_GMT | offset from GMT (e.g. "+09:30") | WASD | SERVER_NAME | IP host name of server | CGI | SERVER_PROTOCOL | HTTP protocol version (always "HTTP/1.0") | CGI | SERVER_PORT | IP port request was received on | CGI | SERVER_SIGNATURE | server ID, host name and port | Apache | SERVER_SOFTWARE | software ID of HTTP server | CGI | UNIQUE_ID | unique 19 character string | Apache

If the request path is set to provide them, there are also be variables providing information about a Secure Sockets Layer transported request's SSL environment.

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Query String Variables

In line with other CGI implementations, additional, non-compliant variables are provided to ease CGI interfacing. These provide the various components of any query string. A keyword query string and a form query string are parsed into

      WWW_KEY_number
      WWW_KEY_COUNT
      WWW_FORM_form-element-name

Variables named WWW_KEY_number will be generated if the query string contains one or more plus ("+") and no equate symbols ("=").

Variables named WWW_FORM_form-element-name will be generated if the query string contains one or more equate symbols. Generally such a query string is used to encode form-URL-encoded (MIME type x-www-form-urlencoded) requests. By default the server will report an incorrect encoding with a 400 error response. However some scripts use malformed encodings and so this behaviour may be suppressed using the set script=query=relaxed mapping rule.

       set /cgi-bin/script-name* script=query=relaxed

To suppress this decoding completely (and save a few CPU cycles) use the following rule.

       set /cgi-bin/script-name* script=query=none

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UNIQUE_ID Note

The UNIQUE_ID variable is a mostly Apache-compliant implementation (the "_" has been substituted for the "@" to allow it's use in file names), for each request generating a globally and temporally unique 19 character string that can be used where such a identifier might be needed. This string contains only "A"-"Z", "a"-"z", "0"-"9", "_" and "-" characters and is generated using a combination of time-stamp, host IP address, server system process identifier and counter, and is "guaranteed" to be unique in (Internet) space and time.

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VMS Apache (CSWS) Compliance

WASD v7.0 had it's CGI environment tailored slightly to ease portability between VMS Apache (Compaq Secure Web Server) and WASD. This included the provision of an APACHE$INPUT: stream and several Apache-specific CGI variables (see the table below). The CGILIB C function library (1.10 - Scripting Function Library) has also been made CSWS V1.0-1 and later (Apache 1.3.12 and higher) compliant.

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CGI Variable Demonstration

The basic CGI symbol names are demonstrated here with a call to a script that simply executes the following DCL code:

      $ SHOW SYMBOL WWW_*
      $ SHOW SYMBOL *

Note how the request components are represented for "ISINDEX"-style searching (third item) and a forms-based query (fourth item).

- /cgi-bin/cgi_symbols
- /cgi-bin/cgi_symbols/ht_root/doc/htd
- /cgi-bin/cgi_symbols/ht_root/doc/htd/*.*?string1+string2
- /cgi-bin/cgi_symbols/ht_root/doc/htd?FirstField=for&SecondField=this

Script source:

> HT_ROOT:[SRC.OTHER]CGI_SYMBOLS.COM

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2.2 - Script Output

This information applies to all non-DECnet based scripting, CGI, CGIplus, RTE, ISAPI. WASD uses mailboxes for script inter-process communication (IPC). These are efficient, versatile and allow direct output from all VMS environments and utilities. Like many VMS record-oriented devices however there are some things to consider when using them.

- Record-Oriented

  The mailboxes are created record, not stream oriented. This means records output by standard VMS means (e.g. DCL, utilities, programming languages) are discretely identified and may be processed appropriately by the server as text or binary depending on the content-type.

- Maximum Record Size

  Being record oriented there is a maximum record size (MRS) that can be output. Records larger than this result in SYSTEM-F-MBTOOSML errors. The WASD default is 4096 bytes. This may be changed using the [BufferSizeDclOutput] configuration directive. This allocation consumes process BYTLM with each mailbox created so the account must be dimensioned sufficiently to supply demands for this quota. The maximum possible size for this is a VMS-limit of 60,000 bytes.

- Buffer Space

  When created the mailbox has it's buffer space set. With WASD IPC mailboxes this is the same as the MRS. The total data buffered may not exceed this without the script entering a wait state (for the mailbox contents to be cleared by the server). As mailboxes use a little of the buffer space to delimit records stored in it the amount of data is actually less than the total buffer space.

To determine the maximum record size and total capacity of the mailbox buffer between server and script WASD provides a CGI environment variable, GATEWAY_MRS, containing an integer with this value.

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2.2.1 - CGI Compliant Output

Script response may be CGI or NPH compliant (2.2.2 - Non-Parsed-Header Output). CGI compliance means the script's response must begin with a line containing one of the following fields.

- Status: an HTTP status code and associated explanation string

- Content-Type: the script body's MIME content-type

- Location: a redirection URL (either full or internal)

Other HTTP-compliant response fields may follow, with the response header terminated and the response body begun by a single empty line. The following is an example of a CGI-compliant response.

      Content-Type: text/html
      Content-Length: 35

      <HTML>
      <B>Hello world!</B>
      </HTML>

Strict CGI output compliance can be enabled and disabled using the [CgiStrictOutput] configuration directive. With it disabled the server will accept any output from the script, if not CGI or NPH compliant then it automatically generates plain-text header. When enabled, if not a CGI or NPH header the server returns a "502 Bad Gateway" error. For debugging scripts generating this error introduce a plain-text debug mode and header, or use the WATCH facility's CGI item (see the Technical Overview).

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WASD Specifics

This section describes how WASD deals with some particular output issues.

- Content-Type: text/...

  If the script response content-type is "text/..." (text document) WASD assumes that output will be line-oriented and requiring HTTP carriage-control (each record/line terminated by a line-feed), and will ensure each record it receives is correctly terminated before passing it to the client. In this way DCL procedure output (and the VMS environment in general) is supported transparently. Any other content-type is assumed to be binary and no carriage-control is enforced. This default behaviour may be modified as described below.

- Carriage-Control

  Carriage-control behaviour for any content-type may be explicitly set using either of two additional response header fields. The term stream is used to describe the server just transfering records, without additional processing, as they were received from the script. This is obviously necessary for binary/raw content such as images, octet-streams, etc. The term record describes the server ensuring each record it receives has correct carriage-control - a trailing newline. If not present one is added. This mode is useful for VMS textual streams (e.g. output from DCL and VMS utilities).

  Using the Apache Group's proposed CGI/1.2 "Script-Control:" field. The WASD extension-directives X-record-mode and X-stream-mode sets the script output into each of the respective modes (Script-Control:).

  Examples of usage this field:

        Script-Control: X-stream-mode
        Script-Control: X-record-mode

- Script Output Buffering

  By default WASD writes each record received from the script to the client as it is received. This can range from a single byte to a complete mailbox buffer full. WASD leaves it up to the script to determine the rate at which output flows back to the client.

  While this allows a certain flexibility it can be inefficient. There will be many instances where a script will be providing just a body of data to the client, and wish to do it as quickly and efficiently as possible. Using the proposed CGI/1.2 "Script-Control:" field with the WASD extension directive X-buffer-records a script can direct the server to buffer as many script output records as possible before transfering it to the client. The following should be added to the CGI response header.

        Script-Control: X-buffer-records

  While the above offers some significant improvements to efficiency and perceived throughput the best approach is for the script to provide records the same size as the mailbox (2.2 - Script Output for detail on determining this size if required). The can be done explicitly by the script programming or if using the C language simply by changing stdout to a binary stream. With this environment the C-RTL will control output, automatically buffering as much as possible before writing it to the server.

        if ((stdout = freopen ("SYS$OUTPUT", "w", stdout, "ctx=bin")) == NULL)
           exit (vaxc$errno);

  Also see the section describing NPH C Script.

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Script-Control:

The Apache Group has proposed a CGI/1.2 that includes a Script-Control: CGI response header field. WASD implements the one proposed directive, along with a number of WASD extensions (those beginning with the "X-"). Note that by convention extensions unknown by an agent should be ignored, meaning that they can be freely included, only being meaningful to WASD and not significant to other implementations.

- no-abort - The server must not terminate the script during processing for either no output or no-progress timeouts. The script is to be left completely alone to control it's own termination. Caution, such scripts if problematic could easily accumulate and "clog up" a server or system.

- X-buffer-records - Buffer records written by the script until there is [BufferSizeDclOutput] bytes available then write it as a single block to the client.

- X-content-handler=keyword - The output of the script is stripped of the CGI reponse header and the body is given to the specified content handler. Currently only the SSI engine is supported using "X-content-handler=SSI".

- X-crlf-mode - The server should always ensure each record has trailing carriage-return then newline characters (0x0d, 0x0a). This is generally what VMS requires for carriage control on terminals, printers, etc.

- X-error-line=integer - Source code module line number META in server generated error message (optional).

- X-error-module=string - Source code module name META in server generated error message (optional).

- X-error-text="string" - Text of error message (mandatory, to trigger server message generation). If without a VMS status value this is the entire error explanation. If with a VMS status it becomes the context of the status.

- X-error-vms-status=integer - VMS status value in decimal or VMS hexadecimal (e.g. %X0000002C, optional). Changes format of error message to detailed explanation of status.

- X-error-vms-text="string" - Context of a VMS status value (optional). Usually a VMS file specification of other text related to the status value (in commented content of error message).

- X-lifetime=value - The number of minutes before the idle scripting process is deleted by the server. Zero sets it back to the default, "none" disables this functionality.

- X-record-mode - The server should always ensure each record has a trailing newline character (0x0a), regardless of whether the response is a text/... content-type or not. This is what is usually required by browsers for carriage-control in text documents.

- X-stream-mode - The server is not to adjust the carriage-control of records regardless of whether the response is a text/... content-type or not. What the script writes is exactly what the client is sent.

- X-timeout-noprogress=value - The number of minutes allowed where the script does not transfer any data to the server before the server deletes the process. Zero sets it back to the default, "none" disables this functionality.

- X-timeout-output=value - The number of minutes allowed before an active script is deleted by the server, regardless of it still processing the request. Zero sets it back to the default, "none" disables this functionality.

The following is a simple example response where the server is instructed not to delete the script process under any circumstances, and that the body does not require any carriage-control changes.

      Content-Type: text/plain
      Script-Control: no-abort; X-stream-mode

      long, slowww script-output ...

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Example DCL Scripts

A simple script to provide the system time might be:

      $ say = "write sys$output"
      $! the next two lines make it CGI-compliant
      $ say "Content-Type: text/plain"
      $ say ""
      $! start of plain-text body
      $ show time

A script to provide the system time more elaborately (using HTML):

      $ say = "write sys$output"
      $! the next two lines make it CGI-compliant
      $ say "Content-Type: text/html"
      $ say ""
      $! start of HTML script output
      $ say "<HTML>"
      $ say "Hello ''WWW_REMOTE_HOST'"  !(CGI variable)
      $ say "<P>"
      $ say "System time on node ''f$getsyi("nodename")' is:"
      $ say "<H1>''f$cvtime()'</H1>"
      $ say "</HTML>"

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2.2.2 - Non-Parsed-Header Output

A script does not have to output a CGI-compliant data stream. If it begins with a HTTP header status line WASD assumes it will supply a raw HTTP data stream, containing all the HTTP requirements. This is the same as or equivalent to the non-parsed-header, or "nph..." scripts of many environments. This is an example of such a script response.

      HTTP/1.0 200 Success
      Content-Type: text/html
      Content-Length: 35

      <HTML>
      <B>Hello world!</B>
      </HTML>

Any such script must observe the HyperText Transfer Protocol, supplying a full response header and body, including correct carriage-control. Once the server detects the HTTP status header line it pays no more attention to any response header fields or body records, just transfering everything directly to the client. This can be very efficient, the server just a conduit between script and client, but does transfer the responsibility for a correct HTTP response onto the script.

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NPH DCL Script

The following example shows a DCL script. Note the full HTTP header and each line explicitly terminated with a carriage-return and line-feed pair.

      $ lf[0,8] = %x0a
      $ crlf[0,16] = %x0d0a
      $ say = "write sys$output"
      $! the next line determines that it is raw HTTP stream
      $ say "HTTP/1.0 200 Success" + crlf
      $ say "Content-Type: text/html" + crlf
      $! response header separating blank line
      $ say crlf
      $! start of HTML script output
      $ say "<HTML>" + lf
      $ say "Hello ''WWW_REMOTE_HOST'" + lf
      $ say "<P>" + lf
      $ say "Local time is ''WWW_REQUEST_TIME_LOCAL'" + lf
      $ say "</HTML>" + lf

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CGIUTL Utility

This assists with the generation of HTTP responses, including the transfer of binary content from files (copying a file back to the client as part of the request), and the processing of the contents of POSTed requests from DCL (1.9 - DCL Processing of Requests).

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NPH C Script

When scripting using the C programming language there can be considerable efficiencies to be gained by providing a binary output stream from the script. This results in the C Run-Time Library (C-RTL) buffering output up to the maximum supported by the IPC mailbox. This may be enabled using a code construct similar to following to reopen stdout in binary mode.

      if ((stdout = freopen ("SYS$OUTPUT", "w", stdout, "ctx=bin")) == NULL)
         exit (vaxc$errno);

This is used consistently in WASD scripts. Carriage-control must be supplied as part of the C standard output (no differently to any other C program). Output can be be explicitly sent to the client at any stage using the fflush() standard library function. Note that if the fwrite() function is used the current contents of the C-RTL buffer are automatically flushed along the the content of the fwrite().

         fprintf (stdout,
      "HTTP/1.0 200 Success\r\n\
      Content-Type: text/html\r\n\
      \r\n\
      <HTML>\n\
      Hello %s\n\
      <P>\n\
      System time is %s\n\
      </HTML>\n",
         getenv("WWW_REMOTE_HOST"),
         getenv("WWW_REQUEST_TIME_LOCAL"));

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CGI Function Library

A source code collection of C language functions useful for processing the more vexing aspects of CGI/CGIplus programming (1.10 - Scripting Function Library).

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2.3 - Raw HTTP Input (POST Processing)

For POST and PUT HTTP methods (e.g. a POSTed HTML form) the body of the request may be read from the HTTP$INPUT stream. For executable image scripts requiring the body to be present on SYS$INPUT (the C language stdin stream) a user-mode logical may be defined immediately before invoking the image, as in the example.

      $ EGSCRIPT = "$HT_EXE:EGSCRIPT.EXE"
      $ DEFINE /USER SYS$INPUT HTTP$INPUT
      $ EGSCRIPT

The HTTP$INPUT stream may be explicitly opened and read. Note that this is a raw stream, and HTTP lines (carriage-return/line-feed terminated sequences of characters) may have been blocked together for network transport. These would need to be explicity parsed by the program.

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