WASD Features and Facilities

10.WATCH Facility

The WATCH facility is a powerful adjunct in server administration. From the Server Administration facility (9. Server Administration) it provides an online, real-time, in-browser-window view of request processing in the running server. The ability to observe live request processing on an ad hoc basis, without changing server configuration or shutting-down/restarting the server process, makes this facility a great configuration and problem resolution tool. It allows (amongst other uses)

• assessment of mapping rules
• assessment of authorization rules
• investigation of request processing problems
• observation of script interaction
• general observation of server behaviour

A single client per server process can access the WATCH facility at any one time. It can be used in one of two modes.

• As a one-shot, one-off WATCH of a particular request. This is available from the Request Report page of the Server Administration facility. In this case the single indicated request is tagged to be WATCHed in all categories (see below) for the duration of the request (or until the client stops WATCHing).
• As described in the following chapter the server and all new requests being processed are candidates for being WATCHed. Categories are selected before initiating the WATCH and the report can be generated for a user-specified number of seconds or aborted at any time using the browser's stop button.

Options immediately below the duration selector allows the WATCH output to concurrently be included in the server process log. This allows a permanent record (at least as permanent as server logs) to be simply produced.

10.1Server Instances

With a single instance (see 8.1 Server Instances) access to WATCH is always through the one server process. If multiple instances are configured WATCH requests, in common with all others, will be serviced by any one of the associated processes depending on the momentary state of the round-robin distribution.

This is often an issue for request WATCHing. The simplest scenario involves two instances. When the WATCH report is activated it will be serviced by the first process, when the request wishing to be WATCHed is accessed it (in the absence of any other server activity) will be serviced by the other process and will not be reported by WATCH on the first.

The solution is to suspend the round-robin request processing for the period of the WATCH activity. This does not shut any instance down but instead makes all but the supervisor instance quiescent. (Technically, it dequeues all the listening I/Os from non-supervisor instance server sockets, making the TCP/IP network driver send all connection requests to the one instance left with listening I/Os.) It is just a matter of making the non-supervisor instances active again when the WATCH activity is concluded.

This may be done from the command-line using

10.2Event Categories

An event is considered any significant point for which the server code has a reporting call provided. These have been selected to provide maximum information with minimum clutter and impact on server performance. Obvious examples are connection acceptance and closure, request path resolution, error report generation, network reads and writes, etc. Events are collected together into groupings to allow clearly defined areas of interest to be selected for reporting.

The report menu provides for the inclusion of any combination of the following categories.

Request

• Processing – Each major step in a request's progress. For example, path resolution and final response status.
• Header – Provides the HTTP request header as a section of blank-line terminated text.
• Body – The content (if a POST or PUT method) of the request. This is provided as a hexadecimal dump on the left and with printable characters rendered on the right, 32 bytes per line.

Response

• Processing – Each major step in generating a response to the request. These generally reflect calls to a major server module such as file CACHE, FILE access, INDEX-OF, SSI processing, etc. One or more of these events may occur for each request. For instance a directory listing will show an INDEX-OF call and then usually a FILE call as any read-me file is accessed.
• Header – The blank-line terminated HTTP header to the response. Only server-generated headers are included. Scripts that provide a full HTTP stream do not have the header explicitly reported. The response body category must be enabled to observe these (indicated by a STREAM notation).
• Body – The content of the response. This is provided as a hexadecimal dump on the left and with printable characters rendered on the right, 32 bytes per line. Some requests also generate very large responses which will clutter output. Generally this category would be used when investigating specific request response body problems.

General

• Connection – Each TCP/IP connection acceptance and closure. The connect shows which service the request is using (scheme, host name and port).
• Path Mapping – This, along with the authorization report, provides one of the most useful aspects of the WATCH facility. It comprises an event line indicating the path to be mapped (it can also show a VMS file specification if a reverse-mapping has been requested). Then as each rule is processed a summary showing current path, match "Y"/"N" for each path template and any conditional, then the result and conditional. Finally an event entry shows the resulting path, VMS file specification, any script name and specification resolved. The path mapping category allows the administrator to directly assess mapping rule processing with live or generated traffic.
• Authorization – When authorization is deployed this category shows the rules examined to determine if a path is controlled, any authentication events in assessing username and password, and the consequent group, user and request capabilities (read and/or write) for that path. No password information is displayed.
• Error – The essential elements of a request error report are displayed. This may include a VMS status value and associated system message.
• CGI – This category displays the generated CGI variable names and values as used by various forms of scripting and by SSI documents, as well as the processing of the response header returned by scripts.
• DCL – Debugging scripts can sometimes present particular difficulties. This category may help. It reports on all input/output streams with the process (SYS$INPUT, SYS$OUTPUT, SYS$COMMAND, CGIPLUSIN).
• DECnet – For the same reason as above this category reports all DECnet scripting input/output of the DECnet link. In particular, it allows the observation of the OSU scripting protocol.
• WebDAV – Provides WebDAV specific processing points including request and meta-data XML associated with resources.

Network

• Activity – For each raw network read and write the VMS status code and size of the I/O is recorded.
• Data – For each raw network read or write the contents are provided as a hexadecimal dump on the left and with printable characters rendered on the right, 32 bytes per line.
• HTTP/2 – Provides a detailed overview of the underlying HTTP/2 framing and connection management exchanges between client and server. See ‘HTTP/2 and WATCH’ in 5.1 WASD HTTP/2 for further detail.

Other

• Logging – Access logging events include log open, close and flush, as well as request entries.
• Match – Shows a significant level of detail during string matching activities. May be useful during mapping, authorization and conditional processing.
• Script – Sets CGI variable WATCH_SCRIPT allowing a script to explicitly detect this so as to output specific debugging or other information when being WATCHed.
• SSL – If the Secure Sockets Layer image is in use this category provides a indication of high-level activity.
• Internal – Includes information on other significant internal server processing. Examples are dictionary entries at various stages of request processing, and the high-level timing and timeout events occuring within that processing and the server in general.

Proxy

• Processing – Each major step during the serving of a proxied request.
• Request Header – The proxy server rebuilds the request originally received from the client. This category shows that rebuilt request, the one that is sent to the remote server.
• Request Body – In the case of HTTP POST or PUT methods any request body is displayed. This is provided as a hexadecimal dump on the left and with printable characters rendered on the right, 32 bytes per line.
• Response Header – The blank-line terminated HTTP header to the response from the remote, proxied server.
• Response Body – The content of the response sent from the remote server. This is provided as a hexadecimal dump on the left and with printable characters rendered on the right, 32 bytes per line.
• Rework – When reworking (see 7.6.2 Proxy Rework) the string matching and substitution is displayed.

Code Modules

If the server has been compiled using the WATCH_MOD=1 macro a set of module WATCHing statements is included. These provide far more detailed processing information than available with the generic WATCH, are intended primarily for debugging the server during development and testing. This is considered a specialized tool, with the quantity and level of detail produced most likely proving counter-productive in addressing general site configuration issues. The module items are shown below the usual WATCH items.

10.3Request Filtering

By default all requests to all services are WATCHed. Fine control may be exercised over exactly which requests are reported, allowing only a selected portion of all requests being processed to be concentrated on, even on a live and busy server. This is done by filtering requests according the following criteria.

• Protocol – The HTTP protocol being used to transport the request. Multiple protocols may be selected and concurrently filtered against.
• Client – The originating host name or address. Unless server DNS host name resolution is enabled this must be expressed in dotted-decimal notation. The " moi " checkbox filters on the WATCHing party's host address.
• Service – The service connected to. This includes the scheme of the service (i.e. "http:", "https:"), the host name (real or virtual), and the port. The host name is the official name of the service as reported during server startup. As the port number is a essential part of the service specification it must always be explicitly supplied or wildcarded.
• Request – This filter operates on the entire HTTP request header. All fields supplied with the request are available to be filtered against. As this is a large, multi-line dataset filters can become quite complex and regular expression (see String Matching of WASD Configuration) matching may be useful (see examples below).
• URI – This is the string provided by the client and specifying the requested resource. It includes the resource path along with any query string. It can contain URL-encoded (sometimes referred to as percent-encoded) characters. Some characters have alternate encodings, such as the space, as + or %20.
• Realm & User – This filters against request authentication information. As authorization occurs relatively late in request processing some data reported earlier by WATCH will not be available.
• HTTP Status – This allows a class of response status (1 (informational), 2 (success), 3 (redirection), 4 (client error) and 5 (server error)) or a specific response status (e.g. 200 (success), 404 (not found), 503 (service unavailable), etc.) to be filtered into the WATCH report. As this happens very late in request processing the number of reported events are limited but may provide some insight into particular processing problems.

In addition there are in and out selectors against each of the filters which include or exclude the particular request based on it matching the filter.

These filters are controlled using fully-specified, wildcarded strings or using regular expression patterns (see Request processing Configuration of WASD Configuration). In common with all WASD processing, filter matching is case-insensitive. Of course, due to the point of application of a particular filter during request processing, some information may or may not be displayed. When a request is into or out of the report because of a matching filter a FILTER informational item is reported.

Examples

1. This first example shows various strings and patterns that could be applied to the client filter.
   alpha.example.com *.example.com 131.185.250.202 131.185.250.* ^10.68.250.*|10.68.251.*
2. This example various filters applied to the service (virtual server).
   beta.example.com:8000 beta.example.com:* http://* https:* *:80
3. The request filter contains the entire HTTP request header. This includes multiple, newline-delimited fields. Filtering can be simple or quite complex. These examples filter all POST requests (either in or out of the report depending on the respective selector), and all POSTs to the specified script respectively.
   POST * POST /cgi-bin/example*

   These are the equivalent regular expressions but also will stop comparing at the end of the initial request line. The second, in this case, will also only filter against HTTP/1.1 version requests (note the final period matching the <CR> of the <CR><LF> carriage control).

   ^^POST .*$ ^^POST */cgi-bin/example *HTTP/1\.1.$

   This example uses a regular expression to constrain the match to a single header field (line, or newline-delimited string), matching all requests where the user agent reports using the "Gecko" browser component (Mozilla, Firefox, etc.)

   ^^User-agent:.*Gecko.*$
4. The path and track filter. The path contains a proxied origin server request and so can be used to filter proxy requests to specific sites.
   /wasd_root/src/* /cgi-bin/* /web/*/cyrillic/* $ORoKJAOef8sAAAkuACc http://proxied.host.name/*
5. The authentication filters, realm and user, can be used to select requests for a particular authenticated user, all authenticated requests or all non-authenticated requests, amongst other application. The realm field allows the authenticated user to be further narrowed as necessary. All of the following examples show only the user field with the default in selector set.

   Authenticated requests for user DANIEL.

   DANIEL

   All authenticated requests.

   %*

10.4Report Format

The following example illustrates the format of the WATCH report. It begins with multi-line heading. The first two record the date, time and official server name, with underline. The third provides the WASD server version. The fourth provides some TCP/IP agent information. Lines following can show OpenSSL version (if deployed), system information, server startup command-line, and then current server process quotas. The last three lines of the header provide a list of the categories being recorded, the filters in use, and the last, column headings described as follows:

• time the event was recorded
• the module name of the originating source code
• the line in the code module
• a unique item number for each thread being WATCHed
• event category name
• free-form, but generally interpretable event data

Note that some items also include a block of data. The request header category does this, providing the blank-line terminated text comprising the HTTP header. Rule mapping also provides a block of information representing each rule as it is interpreted. Generally WATCH-generated information can be distinguished from other data by the uniform format and delimiting vertical bars. Initiative and imagination is sometimes required to interpret the free-form data but a basic understanding of HTTP serving and a little consideration is generally all that is required to deduce the essentials of any report.

10.5Usage Suggestions

The following provides a brief explanation on the way WATCH operates and any usage implications.

A single client may be connected to the WATCH facility at any given time. When connecting the client is sent an HTTP response header and the WATCH report heading lines. The request then remains connected until the WATCH duration expires or the client overtly aborts the connection. During this period the browser behaves as if receiving a sometimes very slow, sometimes stalled, plain-text document. As the server processes WATCHable events the text generated is sent to the WATCH-connected client.

If the connection is aborted by the user some browsers will consider document retrieval to be incomplete and attempt to reconnect to the service if an attempt is made to print or save the resulting document. As the printing of WATCH information is often quite valuable during problem resolution this behaviour can result in loss of information and generally be quite annoying. Appropriate use of the duration selector when requesting a report can work around this, as at expiry the server disconnects, browsers generally interpreting this as legitimate end-of-document (when no content-length has been specified).

During report processing some browsers may not immediately update the on-screen information to reflect received data without some application activity. If scroll-bars are present on the document window manipulating either the horizonal or vertical slider will often accomplish this. Failing that minimizing then restoring the application will usually result in the most recent information being visible.

Browser reload/refresh may be used to restart the report. A browser will quite commonly attempt to remain at the current position in the document, which with a WATCH report's sustained but largely indeterminate data stream may take some time to reach. It is suggested the user ensure that any vertical scroll-bar is at the beginning of the current report, then refresh the report.

Selecting a large number of categories, those that generate copious output for a single event (e.g. response body) or collecting for extended periods can all result in the receipt of massive reports. Some browsers do not cope well with documents megabytes in size.

When supplying WATCH output as part of a problem report please ZIP the file and include it an an e-mail attachment. Mailers often mangle the report format making it difficult to interpret.

10.6Command-Line Use

Although intended primarily as a tool for online use WATCH can be deployed at server startup with a command-line qualifier and provide report output to the server process log. This is slightly more cumbersome than the Web interface but may still be useful in some circumstances. Full control over event categories and filters is possible.

• /NOWATCH Disables the use of the online WATCH facility.
• /WATCH= Enables the server WATCH facility, dumping to standard output (and the server process log if detached). When in effect the online facility is unavailable. The string supplied to the qualifier may comprise four comma-separated components. Only the first is manadatory. Stated order is essential. It will probably be necessary to enclose the complete string in quotation marks.
  • LIST – The LIST keyword provides a list of all the categories (items) available for WATCHing.
  • NOSTARTUP – This keyword suppresses WATCH output until the server is ready to process requests. It must be the leading keyword.
  • items – A parenthesized, comma-separated list of category keywords. Available keywords can be displayed using the LIST facility.
  • filters – A client, service and path filters can be provided following the specification of required items. They must be provided in the order listed above. Leading filters that are not required must be provided as single, asterisk wildcards. WATCH parameter with filters containing forward-slashes will require quoting.

The following examples illustrate the command-line WATCH specification.