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This document is not a general tutorial on authoring scripts, CGI or any other. A large number of references in the popular computing press covers all aspects of this technology, usually quite comprehensively. The information here is about the specifics of scripting in the WASD environment, which is generally very much like any other implementation, VMS or otherwise (although there are always annoying idiosyncracies, see 2.4 CGI Function Library for a partial solution to smoothing out some of these wrinkles for VMS environments).
Scripts are mechanisms for creating Web applications and services, sending data to (and often receiving data from) a client, extending the capabilities of the basic HTTPd. Scripts execute in processes and accounts separate from the actual HTTP server but under its control and interacting with it.
WASD manages a script's execution environment as an independent detached process created and managed by the HTTP server. By configuration a script also can be executed in a process created using DECnet. Originally, WASD scripted in subprocesses but this is obsolete. There is no analogue of the Apache loadable module executed within the server process itself.
WASD scripting can be deployed in a number of environments. Other sections cover the specifics of these. Don't become bewildered or be put off by all these apparent options, they are basically variations on a CGI theme.
It is strongly recommended to execute scripts in an account distinct from that executing the server. This minimises the risk of both unintentional and malicious interference with server operation through either Inter-Process Communication (IPC) or scripts manipulating files used by the server.
The default WASD installation creates two such accounts, with distinct UICs, usernames and default directory space. The UICs and home areas can be specified differently to the displayed defaults. Nothing should be assumed or read into the scripting account username – it's just a username.
| Username | UIC | Default | Description |
|---|---|---|---|
| HTTP$SERVER | [077,001] | WASD_ROOT:[HTTP$SERVER] | Server Account |
| HTTP$NOBODY | [076,001] | WASD_ROOT:[HTTP$NOBODY] | Scripting Account |
During startup the server checks for the existence of the default scripting account and automatically configures itself to use this for scripting. If it is not present it falls-back to using the server account. Other account names can be used if the startup procedures are modified accordingly. The default scripting username may be overridden using the /SCRIPT=AS=<username> qualifier (see Server Startup in WASD Installation). The default scripting account cannot be a member of the SYSTEM group and cannot have any privilege other than NETMBX and TMPMBX (‘Privileged User Scripting’ in 1.2.2.1 Persona Scripting describes how to configure to allow this).
Scripting under a separate account is not available with subprocess scripting and is distinct from PERSONA scripting (even though it uses the same mechanism, see below).
Process creation under the VMS operating system is notoriously slow and expensive. This is an inescapable overhead when scripting via child processes. An obvious strategy is to avoid, at least as much as possible, the creation of these processes. The only way to do this is to share processes between multiple scripts/requests, addressing the attendant complications of isolating potential interactions between requests. These could occur through changes made by any script to the process' enviroment. For VMS this involves symbol and logical name creation, and files opened at the DCL level. In reality few scripts need to make logical name changes and symbols are easily removed between uses. DCL-opened files are a little more problematic, but again, in reality most scripts doing file manipulation will be images.
A reasonable assumption is that for almost all environments scripts can quite safely share processes with great benefit to response latency and system impact (see Server Performance of WASD Features) for a table with some comparative performances). If the local environment requires absolute script isolation for some reason then this process-persistance may easily be disabled with a consequent trade-off on performance.
The term zombie is used to describe processes when persisting between uses (the reason should be obvious, they are neither "alive" (processing a request) nor are they "dead" (deleted :^) Zombie processes have a finite time to exist (non-life-time?) before they are automatically run-down (see below). This keeps process clutter on the system to a minimum.
Scripting processes are created on-demand, within configuration limits and timeout periods. There are no arbitrary limits, only system resource limits, on the number of scripting processes. WASD_CONFIG_GLOBAL directives control the configuration limits of these (see Global Configuration of WASD Configuration).
Scripting processes of all kinds (CGI, CGIplus and RTE) are created on-demand up until [DclHardLimit] is reached. If all scripting processes are busy with requests at that limit then the server provides a 503 (too busy) response.
If there are more than [DclSoftLimit] scripting processes then the least-recently-used of any idle processes (those not currently processing a request) are proactively run-down until the soft-limit is reached. This provides head-room for the immediate creation of additional scripting processes for new requests that cannot be satisfied from currently instantiated processes. Soft-limit should of course be configured less than hard-limit (and if not WASD makes it that way).
Idle scripting processes (those not having been given a request to process) are proactively run-down (see 1.2.5 Script Process Run-Down) after configured periods.
[DclZombieLifeTime] specifies the period in minutes a CGI scripting process can remain idle.
[DclCgiPlusLifeTime] specifies the period a CGIplus script (inside a CGIplus scripting process) or a RTE process can remain idle.
If requests being serviced by scripts drop to zero for a period (governed by the above lifetimes) then eventually all scripting processes should be run-down leaving only the server process.
The default is for WASD to execute scripts in detached processes created and managed completely independently of the server process itself. This offers a significant number of advantages
Creation of a process is expensive in terms of system resources and initial invocation response latency (particularly if extensive login procedures are required), but this quickly becomes negligable as most script processes are used multiple times for successive scripts and/or requests.
There is no WASD analogue of the Apache loadable module executed within the server process itself.
With detached processes the server must explicitly ensure that each scripting process is removed from the system during server shutdown (cf. subprocesses where the VMS executive provides that automatically). This is performed by the server exit handler. With VMS it is possible to bypass the exit handler (using a $DELPRC or the equivalent $STOP/ID= for instance), making it possible for "orphaned" scripting processes to remain – and potentially accumulate on the system!
To address this possibility the server scans the system for candidate processes during each startup. These are identified by a terminal mailbox (SYS$COMMAND device), and then further that the mailbox has an ACL with two entries; the first identifying itself as a WASD HTTPd mailbox and the second allowing access to the account the script is being executed under. Such a device ACL looks like the following example.
This rights identifier is generated from the server process name and is therefore system-unique (so multiple autonomous servers will not accidentally cleanup the script processes of others), and is created during server startup if it does not already exist. For example, if the process name was "HTTPd:80" (the default for a standard service) the rights identifier name would be "WASD_HTTPD_80" (as shown in the example above).
Scripting processes are created through the full "LOGINOUT" life-cycle and execute all system and account LOGIN procedures. Although immune to the effects of most actions within these procedures, and absorbing any output generated during this phase of the process life-cycle, some consideration should be given to minimising the LOGIN procedure paths. This can noticably reduce initial script latency on less powerful platforms.
The usual recommendations for non-interactive LOGIN procedures apply for script environments as well. Avoid interactive-only commands and reduce unnecessary interactive process environment setup. This is usually accomplished though code structures such as the following
WASD scripting processes can be specifically detected using DCL tests similar to the following. This checks the mode, that standard output is a mailbox, and the process name. These are fairly reliable (but not absolutely infallible) indicators.
There are advantages in running a script under a non-server account. The most obvious of these is the security isolation it offers with respect to the rest of the Web and server environment. It also means that the server account does not need to be resourced especially for any particularly demanding application.
The $PERSONA functionality must be explicitly enabled at server startup using the /PERSONA qualifier (Server Account and Environment of WASD Installtion). The ability for the server to be able to execute scripts under any user account is a very powerful (and potentially dangerous) capability, and so is designed that the site administrator must explicitly and deliberately enable the functionality. Configuration files need to be rigorously protected against unauthorized modification.
A specific script or directory of scripts can be designated for execution under a specified account using the WASD_CONFIG_MAP configuration file set script=as= mapping rule. The following example illustrates the essentials.
Access to package scripting directories (e.g. WASD_ROOT:[CGI-BIN]) is controlled by ACLs and possession of the rights identifier WASD_HTTP_NOBODY. If a non-server account requires access to these areas it too will need to be granted this identifier.
In some situations it may be desirable to allow the average Web user to experiment with or implement scripts. If the set script=as= mapping rule specifies a tilde character then for a user request the mapped SYSUAF username is substituted. Note that this requires the script to be colocated with the user account Web location and that the script is run under that account.
The following example shows the essentials of setting up a user environment where access to a subdirectory in the user's home directory, [.WWW] with script's located in a subdirectory of that, [.WWW.CGI-BIN].
Where the site administrator has less than full control of the scripting environment it may be prudent to put some constraints on the quantity of resource that potentially can be consumed by non-core or errant scripting. The following WASD_CONFIG_MAP rule allows the "maximum" CPU time consumed by a single script to be constrained.
Note that this is on a per-script basis, contrasted to the sort of limit a CPULM-type constraint would place on a scripting process.
The following WASD_CONFIG_GLOBAL rule specifies at which priority the scripting process executes. This can be used to provide the server and its infrastructure an advantage over user scripts.
If the set script=as= mapping rule specifies a dollar then a request that has been SYSUAF authenticated has the SYSUAF username substituted. Note that the script itself can be located anywhere provided the user account has read and/or execute access to the area and file.
If the script has not been subject to SYSUAF authorization then this causes the script activation to fail. To allow authenticated requests to be executed under the corresponding VMS account and non-authenticated requests to script as the usual server/scripting account use the following variant.
If the server startup included /PERSONA=AUTHORIZED then only requests that have been subject to HTTP authorization and authentication are allowed to script under non-server accounts.
By default a privileged account cannot be used for scripting. This is done to reduce the chance of unintended capabilities when executing scripts. With additional configuration it is possible to use such accounts. Great care should be exercised when undertaking this.
To allow the server to activate a script using a privileged account the keyword /PERSONA=RELAXED must be used with the persona startup qualifier. If the keywords /PERSONA=RELAXED=AUTHORIZED are used then privileged accounts are allowed for scripting but only if the request has been subject to HTTP authorization and authentication.
By default, activating the /PERSONA server startup qualifier allows all the modes described above to be deployed using appropriate mapping rules. Of course there may be circumstances where such broad capabilities are inappropriate or otherwise undesirable. It is possible to control which user accounts are able to be used in this fashion with a rights identifier. Only those accounts granted the identifier can have scripts activated under them. This means all accounts … including the server account!
This is enabled by specifying the name of a rights identifier as a parameter to the /PERSONA qualifier. This may be any identifier but the one shown in the following example is probably as good as any.
This identifier could be created using the following commands
Meaningful combinations of startup parameters are possible:
When detached processes are created they can be assigned differing priorities depending on the origin and purpose. The objective is to give the server process a slight advantage when competing with scripts for system resources. This allows the server to respond to new requests more quickly (reducing latency) even if a script may then take some time to complete the request.
The allocation of base process priorities is determined from the WASD_CONFIG_GLOBAL [DclDetachProcessPriority] configuration directive, which takes one or two (comma-separated) integers that determine how many priorities lower than the server scripting processes are created. The first integer determines server processes. A second, if supplied, determines user scripts. User scripts may never be a higher priority that server scripts. The following provides example directives.
Scripts executed under the server account, or those created using a mapped username (i.e. "script=as=username"), have a process priority set by the first/only integer.
Scripts activated from user mappings (i.e. "script=as=~" or "script=as=$") have a process priority set by any second integer, or fall back to the priority of the first/only integer.
For standard CGI and CGIplus script the script process' default device and directory is established using a SET DEFAULT command immediately before activating the script. This default is derived from the script file specification.
An alternative default location may be specified using the mapping rule shown in the following example.
The default may be specified in VMS or Unix file system syntax as appropriate. If in Unix syntax (beginning with a forward-slash) no SET DEFAULT is performed using DCL. The script itself must access this value using the SCRIPT_DEFAULT CGI variable and perform a chdir().
On platforms where the Extended File Specification (EFS) is supported a SET PROCESS /PARSE=EXTENDED or SET PROCESS /PARSE=TRADITIONAL is executed by the scripting process before script activation depending on whether the script path is located on an ODS-2 or ODS-5 volume.
The server can stop a script process at any point, although this is generally done at a time and in such a way as to eliminate any disruption to request processing. Reasons for the server running-down a script process.
In running down a script process the server must both update its own internal data structures as well as manage the run-down of the script process environment and script process itself. These are the steps.
Generally CGIplus processes delete themselves immediately. With standard CGI scripts executing an image it may take from zero to a few seconds for the image run-down to be detected by the server. A script is allowed approximately one minute to complete the image run-down.
If a client disconnects from a running script (by hitting the browser Stop button, or selecting another hyperlink) the loss of network connectivity is detected by the server at the next output write.
Generally it is necessary for there to be some mechanism for a client to stop long-running (and presumably resource consuming) scripts. Network disconnection is the only viable one. Experience would indicate however that most scripts are short running and most disconnections are due to clients changing their minds about waiting for a page to build or having seen the page superstructure moving on to something else.
With these considerations in mind there is significiant benefit in not running-down a script immediately the client disconnection is detected. A short wait will result in most scripts completing their output elegantly (the script itself unaware the output is not being transmitted on to the client), and in the case of persistent scripts remaining available for the next request, or for standard CGI the process remaining for use in the next CGI script.
The period allowing the script to complete its processing may be set using the WASD_CONFIG_GLOBAL configuration directive [DclBitBucketTimeout]. It should be set to say fifteen seconds, or whatever is appropriate to the local site.
NB. "Bit-bucket" is a common term for the place discarded data is stored. :^)
Script proctoring proactively creates and maintains the specified minimum number of scripting processes, configured persistent scripts, and scripting environments (RTEs). It is primarily intended for those environments that have significant startup latency but can also be used to maintain idle scripting processes ready for immediate use.
The script proctor initially instantiates configured items during server startup and before enabling request acceptance and processing.
Then during subsequent request processing, at each scripting process run-down it scans current DCL task list counting the number of instances of each configured item. The proctor facility can differentiate between idle and active instances of the script/RTE and will optionally maintain a specified number of idle processes in addition to any currently active. If fewer than the configured requirement(s) one or more new processes are instantiated.
It is possible (and probably likely) that a proctored script specification will at some stage fail to activate the script (activation specification error, script unavailable for some reason, etc.) which would lead to a runaway series of attempts to proctor with each process exit. To help avoid this situation proctored processes that exit before successfully completing initial startup are quickly suppressed from further proctoring action. This suppression then more slowly times out, again allowing proctoring for that item.
Proctored scripts and RTEs contain nothing of the usual request-related environment. No CGI variables to speak of, no service, no request method, nothing! This means that rules used for proctor activations must be outside all virtual service conditionals (i.e. outside of any specific [[service:port]] in the rules, can be inside [[*:*]]) and anything else that may be dependent on a request characteristic.
The easiest way for a script to detect if its been proctored into existence is to look for the absence of this or these. No REQUEST_METHOD is a fair indicator as it should exist with all "real" requests. Of course a proctored script is really just there to instantiate itself, not to do anything directly productive, and so a script/RTE can just recognise this and conclude with perhaps a 204 HTTP status (no content) and then remain quiescent (awaiting its first actual request). Any and all output from a proctored script goes to the bit-bucket.
Once proctored into existance the script process is then subject to the normal scripting process management and (for example) if idle for a period exceeding a lifetime value will be procactively removed. Of course, during that process rundown the proctor facility will effectively replace it with a new instance, maintaining the overall requirement.
The Server Admin, DCL Report includes a Proctor List with the currently configured proctor items and associated statistics.
Proctored script activation can be WATCHed just like any other script activation using the [x]CGI and [x]DCL items. To explicitly trigger such an event merely $STOP/ID=pid a proctored scripting process.
Proctor global configuration is introduced with the WASD_CONFIG_GLOBAL [DclScriptProctor] item with each following line representing one script/RTE to be proctored. Each line contains three mandatory and one optional, space-separated components.
The zombie form is
The minimum plus any idle requirement cannot exceed the [DclSoftLimit] configuration value (in order to minimise potential process thrashing).
The proctor facility works by matching the identification string to the script paths as present in the DCL task list (and as presented in the Server Admin, DCL Report). So it needs to contain something unique to that script or environment and often contains a wildcard specification.
The activation path used to activate the script/RTE is the same as if it was activated via a scripting request.
For an RTE the activation script specification does not actually need to exist. It must contain a minimum path to activate the desired environment but the script itself is not checked to exist by WASD and does not need to exist. If it does then it should do whatever is required to instantiate its required environment and return a 204 (no content) response. If it does not exist then the RTE itself should detect it's a proctored activation and return a default 204 response itself, instantiating only the RTE environment.
Proctored scripts can be detected during mapping using
Specific information can also be passed to the proctored script during mapping using such conditional processing in concert with the SET
The combination of these allows some control of proctored scripting.
A proctor item with a minimum (and optionally idle) value of zero can be specified as a place-marker; the facility ignores zero valued items.
This example illustrates a number of non-trivial proctoring scenarios. Only configuration items directly involved in the proctoring are shown; others would be involved in the general web-server infrastructure.
The [DclScriptProctor] contains five items. The first two specify that two scripts each be maintained, the third specifies four, the final two maintain zombie processes. The mapping rules (below) contain a conditional detecting the absence of a REQUEST_METHOD and processing the proctored scripts inside that decision structure. Proctor-specific mapping rules tend to be used only to supplement otherwise fundamental (but in this case proctored) scripting.
The WASD cache was originally provided to reduce file-system access (a somewhat expensive activity under VMS). With the expansion in the use of dynamically generated page content (e.g. PHP, Perl, Python) there is an obvious need to reduce the system impact of some of these activities. While many such responses have content specific to the individual request a large number are also generated as general site pages, perhaps with simple time or date components, or other periodic information. Non-file caching is intended for this type of dynamic content.
Revalidation of non-file content is difficult to implement for a number of reasons, both by the server and by the scripts, and so is not provided. Instead the cache entry is flushed on expiry of the [CacheValidateSeconds], or as otherwise specified by path mapping, and the request is serviced by the content source (script, PHP, Perl, etc.) with the generated response being freshly cached. Browser requests specifying no-caching are honoured (within server configuration parameters) and will flush the entry, resulting in the content being reloaded.
Determining which script content is to be cached and which not, and how long before flushing, is done using mapping rules (described in detail in Request Processing Configuration of WASD Configuration). The source of script cache content is specified using one or a combination of the following SET rules against general or specific paths in WASD_CONFIG_MAP. All mapping rules (script and non-script) are described here to put the script oriented ones into context. Those specific to script output caching are noted.
A good understanding of site requirements and dynamic content sources, along with considerable care in specifying cache path SETings, is required to cache dynamic content effectively. It is especially important to get the content revalidation period appropriate to the content of the pages. This is specified using the following path SETings.
To cache the content of PHP-generated home pages that contain a time-of-day clock, resolving down to the minute, would require a mapping rule similar to the following.
To prevent requests from flushing a particular scripts output (say the main page of a site) using no-cache fields until the server determines that it needs reloading use the cache guard period.
By default the server accesses scripts using the search list logical name CGI-BIN, although this can be significantly changed using mapping rules. CGI-BIN is defined to first search WASD_ROOT:[CGI-BIN] and then WASD_ROOT:[AXP-BIN], WASD_ROOT:[IA64-BIN], or WASD_ROOT:[VAX-BIN] depending on the platform. [CGI-BIN] is intended for architecture-neutral script files (.CLASS., COM, .PL, .PY, etc.) and the architecture specific directories for executables (.EXE, .DLL, etc.)
These directories are delivered empty and it is up to the site to populate them with the desired scripts. A script is made available by copying its file(s) into the appropriate directory. By default ACLs will be propagated to allow access by the default scripting account. Scripts can be made unavailable by deleting them from these directories.
WASD script executables are built into the WASD_ROOT:[AXP], WASD_ROOT:[IA64] or WASD_ROOT:[VAX] directories depending on the architecture. Other script files, such as DCL procedures, Perl examples, Java class examples, etc. are located in other directories in the WASD_ROOT:[SRC] tree. The procedure WASD_ROOT:[INSTALL]SCRIPTS.COM assists in the installation or deinstallation of groups of WASD scripts.
Scripts are enabled using the exec/uxec or script rules in the mapping file (also see Request Processing Configuration of WASD Configuration). The script portion of the result must be a URL equivalent of the physical VMS procedure or executable specification.
All files in a directory may be mapped as scripts using the exec rule. For instance, in the WASD_CONFIG_MAP configuration file can be found a rule
Multiple such paths may be designated as executable, with their contents expected to be scripts, either directly executable by VMS (e.g. .EXEs and .COMs) or processable by a designated interpreter, etc., (e.g. .PLs, .CLASSes) (4. Run-Time Environments).
In addition individual files may be specified as scripts. This is done using the script rule. In the following example the request path "/help" activates the "Conan The Librarian" script.
Of course, multiple such rules may be used to map such abbreviated or self-explanatory script paths to the actual script providing the application.
It is not necessary to move/copy scripts into the server directory structure to make them accessible. In fact there are probably good reasons for not doing so! For instance, it keeps a package together so that at the next upgrade there is no possibility of the "server-instance" of that application being overlooked.
To make scripts provided by third party packages available for server activation three requirements must be met.
Most packages having such an interface for Web server access would provide details on mapping into the package directory. For illustration the following mapping rules provide access to a package's scripts (assuming it provides more than one) and also into a documentation area.
The hypothetical "Application X" directory locations are
The required mapping rules would be
Access to X's scripts would be using a path such as
Sometimes it may be necessary to provide a particular non-WASD, local, or third-party script with a particular environment in which to execute. This can be provided by wrapping the script executable or interpreted script in a DCL procedure (of course, if the local or third-party script is already activated by a DCL procedure, then that may need to be directly modified). Simply create a DCL procedure, in the same directory as the script executable, containing the required environmental commands.
For example, the following DCL procedure defines a scratch directory and provides the location of the configuration file. It is assumed the script executable is APPLICATIONX_ROOT:[CGI-BIN]APPX.EXE and the script wrapper APPLICATIONX_ROOT:[CGI-BIN]APPX.COM.
A script is merely an executed or interpreted file. Although by default VMS executables and DCL procedures can be used as scripts, other environments may also be configured. For example, scripts written for the Perl language may be transparently given to the Perl interpreter in a script process. This type of script activation is based on a unique file type (extension following the file name), for the Perl example this is most commonly ".PL", or sometimes ".CGI". Both of these may be configured to automatically invoke the site's Perl interpreter, or any other for that matter.
This configuration is performed using the WASD_CONFIG_GLOBAL [DclScriptRunTime] directive, where a file type is associated with a run-time interpreter. This parameter takes two components, the file extension and the run-time verb. The verb may be specified as a simple, globally-accessible verb (e.g. one embedded in the CLI tables), or in the format to construct a foreign-verb, providing reasonable versatility. Run-time parameters may also be appended to the verb if desired. The server ensures the verb is foreign-assigned if necessary, then used on a command line with the script file name as the final parameter to it.
The following is an example showing a Perl interpreter being specified. The first line assumes the "Perl" verb is globally accessible on the system (e.g. perhaps provided by the DCL$PATH logical) while the second (for the sake of illustration) shows the same Perl interpreter being configured for a different file type using the foreign verb syntax.
A file contain a Perl script then may be activated merely by specifying a path such as the following
To add any required parameters just append them to the verb specified.
If a more complex run-time interpreter is required it may be necessary to wrap the script's execution in a DCL procedure.
The WASD server does not require a file type (extension) to be explicitly provided when activating a script. This can help hide the implementation detail of any script. If the script path does not contain a file type the server searches the script location for a file with one of the known file types, first ".COM" for a DCL procedure, then ".EXE" for an executable, then any file types specified using script run-time configuration directive, in the order specified.
For instance, the script activated in the Perl example above could have been specified as below and (provided there was no "EXAMPLE.COM" or "EXAMPLE.EXE" in the search) the same script would have been executed.
CGI environment variables SCRIPT_FILENAME and PATH_TRANSLATED can be provided to any script (CGI, CGIplus, RTE) in Unix file-system syntax should that script require or prefer it using this format.
The path mapping rule "SET script=syntax=unix" changes the default syntax from VMS to Unix file-system. For example; by default using the URL
If the script path had been specifically mapped using
Note that the CGI or CGIplus script file is still activated using VMS file-system syntax, it is just the CGI representation that is changed. This can be particularly useful for environments ported from Unix expecting to manipulate paths using Unix syntax. This would most commonly occur with RTE engines such as PHP, Perl, etc.
Two logicals provide some control of and input to the DCL process scripting environment (which includes standard CGI, CGIplus and ISAPI, DECnet-based CGI, but excludes DECnet-based OSU).
Note that each layer of execution added to the scripting environment increases both system overhead and response latency.
If the logical name value is a dotted-decimal specified IP address the verify is only applied to scripts associated with requests originating from that address. This is useful when trying to trouble-shoot scripts on a live server.
Note that most WASD scripts also contain logical names that can be set for debugging purposes. These are generally in the format script_name$DBUG and if exist activate debugging statements throughout the script.
Scripts often require temporary file space during execution. Of course this can be located anywhere the scripting account (most often HTTP$SERVER) has appropriate access. The WASD package does provide a default area for such purposes with permissions set during startup to allow the server account full access. The default area is located in
The server provides for the routine clean-up of old files in WASD_SCRATCH: left behind by aborted or misbehaving scripts (although as a matter of design all scripts should attempt to clean up after themselves). The WASD_CONFIG_GLOBAL directives
Of course there is always the potential for interaction between scripts using a common area for such purposes. At the most elemetary, care must be taken to ensure unique file name are generated. At worst there is the potential for malicious interaction and information leakage. Use such common areas with discretion.
The "UNIQUE_ID" CGI variable provides a unique 19 character alpha-numeric string (‘UNIQUE_ID Note’ in 2.1 CGI Environment Variables) suitable for many uses including the type extension of temporary files. The following DCL illustrates the essentials of generating a script-unqiue file name. For mutliple file names add further text to the type, as shown below.
A similar approach can be used for script coded using the C language, with the useful capacity to mark the file for delete-on-close (of course this is only really useful if it is, say, only to be written, rewound and then re-read without closing first – but I'm sure you get the idea).
DCL is the native scripting environment for VMS and provides a rich set of constructs and capabilities for ad hoc and low usage scripting, and as a glue when several processing steps need to be undertaken for a particular script. In common with many interpreted environments care must be taken with effective exception handling and data validation. To assist with the processing of request content and response generation from within DCL procedures the CGIUTL utility is available in WASD_ROOT:[SRC.MISC]
Functionality includes
Most usefully it can read the request body, decoding form-URL-encoded contents into DCL symbols and/or a scratch file, allowing a DCL procedure to easily and effectively process this form of request.
A source code collection of C language functions useful for processing the more vexing aspects of CGI and general script programming is available in CGILIB. This and an example implementation is available in WASD_ROOT:[SRC.MISC]
Functionality includes
The WASD scripts use this library extensively and may serve as example applications.
Of course a script can generate any output it requires including non-success (non-200) pages (e.g. 400, 401, 302, etc.) For error pages a certain consistency results from making these substantially the same layout and content as those generated by the server itself. To this end, script response header output can contain one or more of several extension fields to indicate to the server that instead of sending the script response to the client it should internally generate an error response using the script-supplied information. These fields are listed in ‘Script-Control:’ in 2.2.1 CGI Compliant Output section of 2.2.1 CGI Compliant Output and are available in any scripting environment.
If a "Script-Control: X-error-text="text of error message"" field occurs in the script response header the server stops processing further output and generates an error message. Other error fields can be used to provide additional or message-modifying information. A significant example is the "Script-Control: X-error-vms-status=integer" field which supplies a VMS status value for a more detailed, status-related error message explanation.
Essentially the script just generates a standard CGI "Status: nnn" response and includes at least the "X-error-text=" field before the header-terminating empty record (blank line). Some variations are shown in the following DCL examples.
Interestingly, because CGI environments should ignore response fields unknown to them, for scripts deployed across multiple server platforms it should be possible to have these WASD-specific elements in every header for WASD uses followed by other explicitly error page content for use in those other environments.
An example implemented using DCL is available
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