Ns register filter

Man page: http://aolserver.com/man/4.0/tcl/ns_filter.html

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NAME

ns_register_filter, ns_register_trace - Register a filter or trace callback

SYNOPSIS

ns_register_filter ?-first? when method URLpatttern procname ?arg arg ...?

ns_register_trace method URLpatttern procname ?arg arg ...?

ns_register_filter_shortcut when method URLpatttern (new in AOLserver 4.5.2)

ns_register_filter_error ?-first? when method URLpatttern (ampools module for AOLserver 4.5.2.)

DESCRIPTION

Registers a Tcl filter script for the specified method/URL combination on a virtual server. The script can be called at one of several times as indicated by the when argument:

• read - upcoming in AOLserver 4.6 - runs in the driver thread while in the read state in a different Tcl interpreter from the rest of the connection - procedure will not receive a conn id so should not have arguments(?) and normal ns_conn and similar commands will not work.
• prequeue - runs in the driver thread while in the ready state in a different Tcl interpreter from the rest of the connection - new in AOLserver 4.5 but there are known memory leak issues that are fixed in upcoming AOLserver 4.6. Procedure will not receive a conn id so should not have arguments(?) and normal ns_conn and similar commands will not work.
• preauth - pre-authorization
• postauth- post-authorization before page data has been returned to the user
• write - upcoming in AOLserver 4.6 - Invokes proc after each write to the client. Server normally buffers response output so this callback is called potentially just once when flushing the connection output buffers.
• trace - after the connection has been processed and closed.

The registered script will be called at the specified stage of a connection, if the method/URL combination for the filter matches the method/URL combination for the connection using glob style (i.e. as in string match) matching. For example, these are valid URLpatterns:

   /employees/*.tcl
   /accounts/*/out

Using pre-authorization, the procedure will be called (assuming that the method/URL combination matches) just before authorization. If the procedure returns with a code of:

• TCL_OK (using: return "filter_ok"): The server will continue to the next pre-authorization filter for this connection, or, if there are no more pre-authorization filters, it will continue on with authorization.
• TCL_BREAK (using: return "filter_break"): The server will not process any more pre-authorization filters for this connection, and it will continue on with authorization.
• TCL_RETURN (using: return "filter_return"): The server will close the connection and will not run any more pre-authorization filters. It will not authorize the request, and it will not run the function registered for this METHOD/URL. It WILL run any trace functions registered for this METHOD/URL, usually including logging. It is assumed that the filter has sent a proper response (e.g., using ns_return) to the client before returning TCL_RETURN.

Using post-authorization, the procedure will be called (assuming that the method/URL combination matches) just after successful authorization. If the procedure returns:

• TCL_OK (using: return "filter_ok"): The server will continue to the next post-authorization filter for this connection, or, if there are no more post-authorization filters, it will run the function registered to handle this request.
• TCL_BREAK (using: return "filter_break"): The server will not process any more post-authorization filters for this connection, and it will run the function registered to handle this request.
• TCL_RETURN (using: return "filter_return"): The server will close the connection and will not run any more post-authorization filters and it will not run the function registered for this METHOD/URL. It WILL run any trace functions registered for this METHOD/URL, usually including logging. It is assumed that the filter has returned a proper response (e.g., using ns_return) to the client before returning TCL_RETURN.

Using trace, the procedure will be called (assuming that the method/URL combination match) after the connection has been totally processed and closed. If the procedure returns:

• TCL_OK (using: return "filter_ok"): The server will continue to the next trace filter.
• TCL_BREAK (using: return "filter_break"): The rest of the trace filters are ignored.
• TCL_RETURN (using: return "filter_break"): The rest of the trace filters are ignored.

Syntax for the registered procedure:

The conn (connection id) argument is optional for procedures registered by ns_register_filter if the procedure has 1 or 2 arguments (including why but not including conn). The following examples show the variations that can be used in this case:

   ns_register_filter trace GET /noargs filter_noargs
   ns_register_filter trace GET /context filter_context fnord
   ns_register_filter trace GET /conncontext filter_conncontext

   proc filter_noargs { why } {
   ns_log Notice "filter noargs"
   return filter_ok
   } ;# filter_noargs

   proc filter_context { arg why } {
   ns_log Notice "filter context. Arg: $arg"
   return filter_ok
   } ;# filter_noargs

   proc filter_conncontext { conn arg why } {
   ns_log Notice "filter conn context"
   return filter_ok
   } ;# filter_noargs

The conn (connection) argument is required for procedures registered by ns_register_filter if the procedure has 3 or more arguments (including why but not including conn). The conn argument is automatically filled with the connection id. The first argument following conn will always take the value supplied by ns_register_filter, if there is one, or an empty value. The why argument at the end is automatically filled with the type of filter requested (the when it was registered for). All other arguments must supply a default value. The following examples show the variations that can be used in this case:

   
   ns_register_filter postauth GET /threeargs threeargs aaa
   ns_register_filter postauth GET /fourargs fourargs aaa bbb ccc
   

   proc threeargs { conn context { greeble bork } why } {
   ...
   } ;

   proc fourargs { conn context { greeble bork } {hoover quark} why } {
   ...
   } ;

When a GET of /threeargs is requested, the conn and why arguments will be filled automatically, the context argument will be assigned "aaa" and the greeble argument will be assigned the default value "bork". When a GET of /fourargs is requested, the conn and why arguments will be filled automatically, the context argument will be assigned "aaa", the greeble argument will be assigned "bbb", and the hoover argument will be assigned the default value "quark".

ns_register_trace:

This command is very similar to ns_register_filter trace. Known internally as void_traces, procedures registered by this command fire after the procedures registered by ns_register_filter trace and differ in that they only execute if a response was successfully sent to the client (i.e. not a Server Error), plus their return value is ignored.

NOTES

Note ns_register_filter (and _trace) is similar to ns_register_proc except that the pattern-matching for the URL is performed differently. With ns_register_proc, the specified URL is used to match that URL and any URL below it in the hierarchy. Wildcards such as "*" are meaningful only for the final part of the URL, such as /scripts/*.tcl. With ns_register_filter, the URLpattern is used to match URLs as a string with standard string-matching characters. ns_register_proc always results in a single match to just one procedure, whereas multiple procedures registered with ns_register_filter can be matched and will be called in the order they were registered.

In AOLserver 4.5.2, you can use the optional -first switch to specify that the procedure should go to the top of registered filters for a particular pattern and therefore to be called first.

To be more precise the allowed matching characters in URLpattern are determined by Tcl_StrMatch which in turn is determined by TCL string match.

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