Apache::RPC::Status - A status monitor similar to Apache::Status for RPC
SYNOPSIS
# In httpd.conf:
</Location /rpc-status>
SetHandler perl-script
PerlHandler Apache::RPC::Status
</Location>
# In the start-up Perl file:
use Apache::RPC::Status;
DESCRIPTION
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.
Information Screens
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.)
SUBCLASSING AND EXTENDING
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.
Class Methods
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, "Apache::RPC::Server" is assumed. This
value may also be set with the mod_perl PerlSetVar directive. See the
documentation for "init_handler", below.
handler(CLASS, REQUEST)
This is the primary entry-point for the package. This is the handler defined
for assignment to "PerlHandler" 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
"DECLINED" response code.
server
When the screen parameter is set to "server", 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 "method", 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 "ServerClass",
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 "serverclass"
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.
Additional Methods
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:
version
(May be called as a static method.) Returns the current version of this
module.
apache_status_attach
Attach the Apache::RPC::Status module to the main screen of the
Apache::Status display.
default_object
(May be called as a static method.) Returns a default Apache::RPC::Status
instance when called as a static method. Returns the calling reference itself,
otherwise.
header(REQUEST, TITLE)
Produces the HTML header for a page. Uses the passed-in title parameter to
give the page a title, and extracts any request-specific information from the
Apache request object passed as the first parameter.
footer(REQUEST)
Produces the HTML footer.
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 "FLAG"
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).
main_screen(REQUEST, QUERY, INTERNAL)
Renders the HTML (minus the header and footer) for the main screen. The
arguments are the Apache request object, a CGI query object created
from the request, and a boolean flag indicating whether the call into this
method was made from within this module or made from the Apache::Status
page.
server_summary(SERVER)
Creates an HTML snippet to provide a summary for the server passed in as an
argument. The passed-in value should be the server object, not the name.
server_detail(REQUEST, QUERY, INTERNAL)
Renders the HTML (minus header and footer) for a screen describing a server
instance in detail. The server is specified by name in the query parameters.
The arguments are the same as for "main_screen".
method_summary(SERVER, METHOD, BASEURL)
Creates and HTML snippet to provide a summary for the specified method of the
specified server. The third argument is a base-URL to use for making links to
the detailed method page.
method_detail(REQUEST, QUERY, INTERNAL)
Renders the HTML (minus header and footer) for a screen describing a method on
a specific server instance, in detail. The method and server are specified by
name in the query parameters. The arguments are the same as for
"main_screen".
Use and Extension Within Perl Sections
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 "screen" 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.
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.
CAVEATS
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.
