Apache::RPC::Status - A status monitor similar to Apache::Status for RPC

    # In httpd.conf:
    </Location /rpc-status>
        SetHandler perl-script
        PerlHandler Apache::RPC::Status
    </Location>

    # In the start-up Perl file:
    use Apache::RPC::Status;

The Apache::RPC::Status package is provided as a simple status monitor for XML-RPC servers running in a mod_perl environment, using the Apache::RPC::Server class (or derivative of). Patterned after the status system provided with mod_perl itself, information is broken down into a series of screens providing information ranging from the RPC servers currently configured down to the individual methods provided by the servers.

There are three basic screens provided by the stock Apache::RPC::Status package:

Main: Listing of Servers

This screen is the first screen that comes up when the location for which this class was assigned as a handler is invoked. It lists the server objects that this running Apache process knows of. Note that if the servers are defined in such a way as to mean on-demand creation, then a given child process may not have all the configured servers in memory. This is by design, it is not a bug. See "Usage Within <Perl> Sections" in Apache::RPC::Server for details on configuring the RPC servers such that they are pre-loaded into all child processes.

Server: Details of a Server

Each of the known servers in the main screen links to this screen, which provides details on the specific server. Information such as when the server was started (which usually matches the time that Apache was started), when the specific child was started (which may not be the same), number of requests servered, and so forth is provided. Additionally, each of the methods that the server provides is listed in alphanumeric order, with a link to the next screen.

Method: Details of a Specific Method

For each of the known methods published by a server, this screen summarizes all that is known about the method itself. The signatures, help text and hidden status (whether the method is visible to the introspection API that is shipped with RPC::XML::Server) are all shown. Some optional information is shown if available: if the method has a version number associated with it, that is displayed. If the method was loaded from an external XPL file, the file path and modification-time are also displayed.

The primary purpose of this status system is to allow for checking the availability and sanity of the RPC servers themselves. For example, if a server is configured to auto-load methods, and automatically check for updates, the status system could confirm that a method is available or is at the correct version.

(Note that auto-loading and auto-updating are done on demand, when a call is made to the method in question. Thus, the status might not reflect changes until at least one call has been made. Further, if there are very many child processes handling the RPC servers, several calls may be necessary to ensure that the child process answering the status request also has the most up-to-date impression of the server.)

This package is implemented as a method handler for Apache/mod_perl. This means that is should be relatively easy to subclass this package to implement an extended version of status reporting, or to provide handlers for phases of the request lifecycle not otherwise addressed.

There are three class methods defined in this package. One is the constructor, the other two are handlers for specific phases in the Apache request lifecycle.

new(CLASS, ARGS)

This creates a new object of this class and returns a reference to it. The first argument is the class being created into, the remaining arguments are treated as key/value pairs (note: not a hash reference). At present, the only additional argument recognized is:

serverclass

This is used when the status monitor is being used with a server class other than Apache::RPC::Server directly. Because several methods from that class are invoked, it is presumed that the class named here is a subclass of Apache::RPC::Server. If not, the status monitor may not work correctly, or at all. In the absence of this value, CWApache::RPC::Server is assumed. This value may also be set with the mod_perl PerlSetVar directive. See the documentation for CWinit_handler, below.

handler(CLASS, REQUEST)

This is the primary entry-point for the package. This is the handler defined for assignment to CWPerlHandler in a location configuration block. It is invoked by mod_perl as a method handler, thus the first argument is either the name of the class (in the case of class-method, or static, invocation) or the object configured as the handler. The second argument is the Apache request object itself. This method derives the query parameters for the request from the Apache object, and treats them according to the type of information screen requested:

screen

This specifies which screen of the status monitor is to be displayed. In absence, the value defaults to main, which is the internal identifier for the primary screen of the status monitor system. If the value of this parameter does not match a known interface hook, then the handler will signify to mod_perl that it cannot handler the request, by replying with the CWCBDECLINEDCW response code.

server

When the screen parameter is set to CWserver, the monitor displays the server detail screen. In that case, this parameter specifies which server should be displayed. Servers are given unique identifiers when they are created, usually derived from the URL path that they are attached to. If the value here does not match any known servers, a warning is sent to the browser.

method

When the screen parameter is set to CWmethod, this calls for the method detail screen. The provided interface hook to deal with these requests looks for both the server parameter above and this one, which specifies by name the method to be laid out in detail. As with the server parameter, if the value in this parameter does not match any known data, an error is reported to the browser. Any additional parameters will be preserved by make_url call detailed below. These are merely the specific ones recognized by the status monitor as written.

init_handler(CLASS, REQUEST)

This is a very simple handler designed for the PerlChildInitHandler phase. At present, it only does one simple task (and thus makes no direct use of either parameter passed to it by mod_perl). However, it is included mainly as a placeholder for possible future expansion. The current behavior is to check for the existence of directory-configuration item called CWServerClass, and record the value if it is set. This is used to specifiy the class from which the RPC server objects are created, if something other than Apache::RPC::Server. If this information is passed via the CWserverclass parameter to the new method above, that value overrides any value here. However, that requires actually creating an object to use as the handler, whereas this handler may be used directly, as a static handler. It would be configured outside of any <Location> blocks, a requirement for the PerlChildInitHandler phase. It is designed to stack cleanly with any other handlers for that phase, provided your mod_perl installation supports stacked handlers.

In addition to the class methods above, the following are provided. In most cases, these do not rely on any data contained within the actual object itself. Many may also be called as static methods (these are so noted). They are provided as a utility, implemented as methods so as to avoid namespace issues:

make_url(QUERY|REQUEST, FLAG)

(May be called as a static method.) This creates a URL string for use as a hyperlink. It makes certain to preserve all parameters in a CGI-like fashion. Additionally, it can make the URL in such a fashion as to allow better integration with the Apache::Status package. If the CWFLAG parameter is passed and is any true value, then the resulting URL will be tailored for use with Apache::Status. The first argument must be either the original request object as passed by mod_perl, or a reference to a CGI object created from the request (see CGI for more on the CGI class).

Some extension may be done without necessarily subclassing this package. The class object are implemented simply as hash references. When a request is received, the screen parameter (see above) is extracted, and used to look up in the hash table. If there is a value for that key, the value is assumed to be a hash reference with at least two keys (described below). If it does not exist, the handler routine declines to handle the request. Thus, some degree of extension may be done without the need for developing a new class, if the configuration and manipulation are done within <Perl> configuration blocks.

Adding a new screen means writing a routine to handle the requests, and then adding a hook into that routine to the object that is the handler for the Apache location that serves RPC status requests. The routines that are written to handle a request should expect four arguments (in order):

The object reference for the location handler

The Apache request object reference

A query object reference (see below)

A flag that is only passed when called from Apache::Status

The routines are given both the original request object and a query object reference for sake of ease. The query object is already available prior to the dispatch, so there is no reason to have each hook routine write the same few lines to derive a query object from an Apache request. At the same time, the hooks themselves may need the Apache object to call methods on. The query object is an instance of CGI. The flag parameter is passed by the linkage from this status package to Apache::Status. The primary use for it is to pass to routines such as make_url that are sensitive to the Apache::Status context.

The return value from these routines must be a reference to a list of lines of text. It is passed to the print method of the Apache class. This is necessary for compatibility with the Apache::Status environment.

To add a new hook, merely assign it to the object directly. The key is the value of the CWscreen parameter defined above, and the value is a hash reference with two keys:

title

A string that is incorporated into the HTML title for the page.

call

A reference to a subroutine or closure that implements the hook, and conforms to the conventions described above.

A sample addition:

    $stat_obj->{dbi} = {
                           title => 'RPC-side DBI Pool',
                           call  => \&show_dbi_pool
                       };

This package is designed to integrate with the Apache::Status package that is a part of mod_perl. However, this is not currently functional. When this has been debugged, the details will be presented here.

This is the newest part of the RPC-XML package. While the package as a whole is now considered beta, this piece may yet undergo some alpha-like enhancements to the interface and such. However, the design and planning of this were carefully considered, so any such changes should be minimal.

This module is licensed under the terms of the Artistic License that covers Perl. See <http://www.opensource.org/licenses/artistic-license.php> for the license itself.

Apache::Status, Apache::RPC::Server, RPC::XML::Method

Randy J. Ray <rjray@blackperl.com>