- SEE ALSO
RPC::XML::Server - A sample server implementation based on RPC::XML
use RPC::XML::Server; ... $srv = RPC::XML::Server->new(port => 9000); # Several of these, most likely: $srv->add_method(...); ... $srv->server_loop; # Never returns
This is a sample XML-RPC server built upon the RPC::XML data classes, and using HTTP::Daemon and HTTP::Response for the communication layer.
Use of the RPC::XML::Server is based on an object model. A server is instantiated from the class, methods (subroutines) are made public by adding them through the object interface, and then the server object is responsible for dispatching requests (and possibly for the HTTP listening, as well).
The following methods are provided by the RPC::XML::Server class. Unless otherwise explicitly noted, all methods return the invoking object reference upon success, and a non-reference error string upon failure.
Creates a new object of the class and returns the blessed reference. Depending on the options, the object will contain some combination of an HTTP listener, a pre-populated HTTP::Response object, a RPC::XML::Parser object, and a dispatch table with the set of default methods pre-loaded. The options that new accepts are passed as a hash of key/value pairs (not a hash reference). The accepted options are:
If passed with a
truevalue, prevents the creation and storage of the HTTP::Daemon and the pre-configured HTTP::Response objects. This allows for deployment of a server object in other environments. Note that if this is set, the accept_loop method described below will silently return immediately.
If passed with a
truevalue, prevents the loading of the default methods provided with the RPC::XML distribution. These may be later loaded using the add_default_methods interface described later. The methods themselves are described below (see "The Default Methods Provided").
These four are mainly relevant only to HTTP-based implementations. The last three are not used at all if
no_httpis set. The path argument sets the additional URI path information that clients would use to contact the server. Internally, it is not used except in outgoing status and introspection reports. The host, port and queue arguments are passed to the HTTP::Daemon constructor if they are passed. They set the hostname, TCP/IP port, and socket listening queue, respectively. Again, they are not used if the
no_httpargument was set.
If you plan to add methods to the server object by passing filenames to the
add_methodcall, this argument may be used to specify one or more additional directories to be searched when the passed-in filename is a relative path. The value for this must be an array reference. See also add_method and xpl_path, below.
If specified and set to a true value, enables the automatic searching for a requested remote method that is unknown to the server object handling the request. If set to "no" (or not set at all), then a request for an unknown function causes the object instance to report an error. If the routine is still not found, the error is reported. Enabling this is a security risk, and should only be permitted by a server administrator with fully informed acknowledgement and consent.
If specified and set to a "true" value, enables the checking of the modification time of the file from which a method was originally loaded. If the file has changed, the method is re-loaded before execution is handed off. As with the auto-loading of methods, this represents a security risk, and should only be permitted by a server administrator with fully informed acknowledgement and consent.
By default, the server class uses the RPC::XML::Method class to manage the manipulation and tracking of the methods the server objects make available. If the developer chooses to sub-class this method implementation (or even provide a completely new one), the name of the class must be passed in via this parameter. It will be used in all the internal creation/manipulation routines within the server class.
Any other keys in the options hash not explicitly used by the constructor are copied over verbatim onto the object, for the benefit of sub-classing this class. All internal keys are prefixed with "
__" to avoid confusion. Feel free to use this prefix only if you wish to re-introduce confusion.
Returns the version string associated with this package.
This returns the identifying string for the server, in the format "
NAME/VERSION" consistent with other applications such as Apache and LWP. It is provided here as part of the compatibility with HTTP::Daemon that is required for effective integration with Net::Server.
This returns the HTTP URL that the server will be responding to, when it is in the connection-accept loop. If the server object was created without a built-in HTTP listener, then this method returns
Returns the number of requests this server object has marshalled. Note that in multi-process environments (such as Apache or Net::Server::PreFork) the value returned will only reflect the messages dispatched by the specific process itself.
Each instance of this class (and any subclasses that do not completely override the
newmethod) creates and stores an instance of HTTP::Response, which is then used by the HTTP::Daemon or Net::Server processing loops in constructing the response to clients. The response object has all common headers pre-set for efficiency. This method returns a reference to that object.
Gets and possibly sets the clock-time when the server starts accepting connections. If a value is passed that evaluates to true, then the current clock time is marked as the starting time. In either case, the current value is returned. The clock-time is based on the internal time command of Perl, and thus is represented as an integer number of seconds since the system epoch. Generally, it is suitable for passing to either localtime or to the
time2iso8601routine exported by the RPC::XML package.
- add_method(FILE | HASHREF)
This adds a new published method to the server object that invokes it. The new method may be specified in one of two ways: as a filename or as a hash reference.
If passed as a hash reference, the following keys are expected:
The published (externally-visible) name for the method.
An optional version stamp. Not used internally, kept mainly for informative purposes.
If passed and evaluates to a
truevalue, then the method should be hidden from any introspection API implementations. This parameter is optional, the default behavior being to make the method publically-visible.
A code reference to the actual Perl subroutine that handles this method. A symbolic reference is not accepted. The value can be passed either as a reference to an existing routine, or possibly as a closure. See "How Methods are Called" for the semantics the referenced subroutine must follow.
A list reference of the signatures by which this routine may be invoked. Every method has at least one signature. Though less efficient for cases of exactly one signature, a list reference is always used for sake of consistency.
Optional documentation text for the method. This is the text that would be returned, for example, by a system.methodHelp call (providing the server has such an externally-visible method).
If a file is passed, then it is expected to be in the XML-based format, described in the RPC::XML::Method manual (see RPC::XML::Method). If the name passed is not an absolute pathname, then the file will be searched for in any directories specified when the object was instantiated, then in the directory into which this module was installed, and finally in the current working directory. If the operation fails, the return value will be a non-reference, an error message. Otherwise, the return value is the object reference.
For more on the creation and manipulation of methods as objects, see RPC::XML::Method.
Get and/or set the object-specific search path for
*.xplfiles (files that specify methods) that are specified in calls to add_method, above. If a list reference is passed, it is installed as the new path (each element of the list being one directory name to search). Regardless of argument, the current path is returned as a list reference. When a file is passed to add_method, the elements of this path are searched first, in order, before the installation directory or the current working directory are searched.
Returns a reference to an object of the class RPC::XML::Method, which is the current binding for the published method NAME. If there is no such method known to the server, then
undefis returned. The object is implemented as a hash, and has the same key and value pairs as for
add_method, above. Thus, the reference returned is suitable for passing back to
add_method. This facilitates temporary changes in what a published name maps to. Note that this is a referent to the object as stored on the server object itself, and thus changes to it could affect the behavior of the server.
Enters the connection-accept loop, which generally does not return. This is the
accept()-based loop of HTTP::Daemon if the object was created with an instance of that class as a part. Otherwise, this enters the run-loop of the Net::Server class. It listens for requests, and marshalls them out via the
dispatchmethod described below. It answers HTTP-HEAD requests immediately (without counting them on the server statistics) and efficiently by using a cached HTTP::Response object.
Because infinite loops requiring a
KILLsignal to terminate are generally in poor taste, the HTTP::Daemon side of this sets up a localized signal handler which causes an exit when triggered. By default, this is attached to the
INTsignal. If the Net::Server module is being used instead, it provides its own signal management.
The arguments, if passed, are interpreted as a hash of key/value options (not a hash reference, please note). For HTTP::Daemon, only one is recognized:
If passed, should be the traditional name for the signal that should be bound to the exit function. The user is responsible for not passing the name of a non-existent signal, or one that cannot be caught. If the value of this argument is 0 (a
falsevalue) or the string
NONE, then the signal handler will not be installed, and the loop may only be broken out of by killing the running process (unless other arrangements are made within the application).
The options that Net::Server responds to are detailed in the manual pages for that package. All options passed to
server_loopin this situation are passed unaltered to the
run()method in Net::Server.
This is the server method that actually manages the marshalling of an incoming request into an invocation of a Perl subroutine. The parameter passed in may be one of: a scalar containing the full XML text of the request, a scalar reference to such a string, or a pre-constructed RPC::XML::request object. Unless an object is passed, the text is parsed with any errors triggering an early exit. Once the object representation of the request is on hand, the parameter data is extracted, as is the method name itself. The call is sent along to the appropriate subroutine, and the results are collated into an object of the RPC::XML::response class, which is returned. Any non-reference return value should be presumed to be an error string. If the dispatched method encountered some sort of error, it will not be propagated upward here, but rather encoded as an object of the RPC::XML::fault class, and returned as the result of the dispatch. This distinguishes between server-centric errors, and general run-time errors.
This method adds all the default methods (those that are shipped with this extension) to the calling server object. The files are denoted by their
*.xplextension, and are installed into the same directory as this Server.pm file. The set of default methods are described below (see "The Default Methods Provided").
If any names are passed as a list of arguments to this call, then only those methods specified are actually loaded. If the
*.xplextension is absent on any of these names, then it is silently added for testing purposes. Note that the methods shipped with this package have file names without the leading "
status." part of the method name. If the very first element of the list of arguments is "
except" (or "
-except"), then the rest of the list is treated as a set of names to not load, while all others do get read. The Apache::RPC::Server module uses this to prevent the loading of the default
system.statusmethod while still loading all the rest of the defaults. (It then provides a more Apache-centric status method.)
- add_methods_in_dir(DIR, [DETAILS])
This is exactly like add_default_methods above, save that the caller specifies which directory to scan for
*.xplfiles. In fact, the defaults routine simply calls this routine with the installation directory as the first argument. The definition of the additional arguments is the same as above.
Specifying Server-Side Remote Methods
Specifying the methods themselves can be a tricky undertaking. Some packages (in other languages) delegate a specific class to handling incoming requests. This works well, but it can lead to routines not intended for public availability to in fact be available. There are also issues around the access that the methods would then have to other resources within the same running system.
The approach taken by RPC::XML::Server (and the Apache::RPC::Server subclass of it) require that methods be explicitly published in one of the several ways provided. Methods may be added directly within code by using
add_method as described above, with full data provided for the code reference, signature list, etc. The
add_method technique can also be used with a file that conforms to a specific XML-based format (detailed in the manual page for the RPC::XML::Method class, see RPC::XML::Method). Entire directories of files may be added using
add_methods_in_dir, which merely reads the given directory for files that appear to be method definitions.
How Methods Are Called
When a routine is called via the server dispatcher, it is called with the arguments that the client request passed, plus one. The extra argument is the first one passed, a reference to a RPC::XML::Server object (or a subclass thereof). This is derived from a hash reference, and will include two special keys:
This is the name by which the method was called in the client. Most of the time, this will probably be consistent for all calls to the server-side method. But it does not have to be, hence the passing of the value.
This is the signature that was used, when dispatching. Perl has a liberal view of lists and scalars, so it is not always clear what arguments the client specifically has in mind when calling the method. The signature is an array reference containing one or more datatypes, each a simple string. The first of the datatypes specifies the expected return type. The remainder (if any) refer to the arguments themselves.
Note that by passing the server object reference first, the methods themselves are essentially expected to behave as actual methods of the server class, as opposed to ordinary functions. Of course, they can also discard the initial argument completely.
The methods should not make (excessive) use of global variables. Likewise, methods should not change their package space within the definition. Bad Things Could Happen.
The Default Methods Provided
The following methods are provided with this package, and are the ones installed on newly-created server objects unless told not to. These are identified by their published names, as they are compiled internally as anonymous subroutines and thus cannot be called directly:
Returns a string value identifying the server name, version, and possibly a capability level. Takes no arguments.
Returns a series of struct objects that give overview documentation of one or more of the published methods. It may be called with a string identifying a single routine, in which case the return value is a struct. It may be called with an array of string values, in which case an array of struct values, one per element in, is returned. Lastly, it may be called with no input parameters, in which case all published routines are documented. Note that routines may be configured to be hidden from such introspection queries.
Returns a list of the published methods or a subset of them as an array of string values. If called with no parameters, returns all (non-hidden) method names. If called with a single string pattern, returns only those names that contain the string as a substring of their name (case-sensitive, and this is not a regular expression evaluation).
Takes either a single method name as a string, or a series of them as an array of string. The return value is the help text for the method, as either a string or array of string value. If the method(s) have no help text, the string will be null.
As above, but returns the signatures that the method accepts, as array of string representations. If only one method is requests via a string parameter, then the return value is the corresponding array. If the parameter in is an array, then the returned value will be an array of array of string.
This is a simple implementation of composite function calls in a single request. It takes an array of struct values. Each struct has at least a
methodNamemember, which provides the name of the method to call. If there is also a
paramsmember, it refers to an array of the parameters that should be passed to the call.
Takes no arguments and returns a struct containing a number of system status values including (but not limited to) the current time on the server, the time the server was started (both of these are returned in both ISO 8601 and UNIX-style integer formats), number of requests dispatched, and some identifying information (hostname, port, etc.).
In addition, each of these has an accompanying help file in the
methods sub-directory of the distribution.
These methods are installed as
*.xpl files, which are generated from files in the
methods directory of the distribution using the make_method tool (see make_method). The files there provide the Perl code that implements these, their help files and other information.
Unless explicitly stated otherwise, all methods return some type of reference on success, or an error string on failure. Non-reference return values should always be interpreted as errors unless otherwise noted.
This began as a reference implementation in which clarity of process and readability of the code took precedence over general efficiency. It is now being maintained as production code, but may still have parts that could be written more efficiently.
The XML-RPC standard is Copyright (c) 1998-2001, UserLand Software, Inc. See <http://www.xmlrpc.com> for more information about the XML-RPC specification.
This module is licensed under the terms of the Artistic License that covers Perl. See <http://language.perl.com/misc/Artistic.html> for the license.
Randy J. Ray <email@example.com>