Static Methods¶

These methods are static to the package, and are used to provide external access to internal settings:

INSTALL_DIR

Returns the directory that this module is installed into. This is used by methods such as add_default_methods to locate the XPL files that are shipped with the distribution.

version

Returns the version string associated with this package.

product_tokens

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.

Methods¶

The following are object (non-static) methods. Unless otherwise explicitly noted, all methods return the invoking object reference upon success, and a non-reference error string upon failure.

See "Content Compression" below for details of how the server class manages gzip-based compression and expansion of messages.

new(OPTIONS)

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::ParserFactory-generated object, and a dispatch table with the set of default procedures pre-loaded. The options that new accepts are passed as a hash of key/value pairs (not a hash reference). The accepted options are:

url

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 "undef".

requests

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.

response

Each instance of this class (and any subclasses that do not completely override the "new" method) 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.

started([BOOL])

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 "time2iso8601" routine exported by the RPC::XML package.

timeout(INT)

You can call this method to set the timeout of new connections after they are received. This function returns the old timeout value. If you pass in no value then it will return the old value without modifying the current value. The default value is 10 seconds.

server_fault(STRING, STRING)

Create a RPC::XML::fault object of the specified type, optionally including the second (string) parameter. See "Server Faults" for the list of faults defined by RPC::XML::Server (as well as documentation on creating your own).

add_method(FILE | HASHREF | OBJECT)

add_procedure(FILE | HASHREF | OBJECT)

add_function(FILE | HASHREF | OBJECT)

This adds a new published method/procedure/function to the server object that invokes it. The new method may be specified in one of three ways: as a filename, a hash reference or an existing object (generally of either RPC::XML::Procedure, RPC::XML::Method or RPC::XML::Function classes).

If passed as a hash reference, the following keys are expected:

delete_method(NAME)

delete_procedure(NAME)

delete_function(NAME)

Delete the named method/procedure/function from the calling object. Removes the entry from the internal table that the object maintains. If the method is shared across more than one server object (see "share_methods"), then the underlying object for it will only be destroyed when the last server object releases it. On error (such as no method by that name known), an error string is returned.

The delete_procedure and delete_function calls are identical, supplied for the sake of symmetry. All calls return the matched object regardless of its underlying type.

list_methods

list_procedures

list_functions

This returns a list of the names of methods and procedures the server current has published. Note that the returned values are not the method objects, but rather the names by which they are externally known. The "hidden" status of a method is not consulted when this list is created; all methods and procedures known are listed. The list is not sorted in any specific order.

The list_procedures and list_functions calls are provided for symmetry. All calls list all published routines on the calling server object, regardless of underlying type.

xpl_path([LISTREF])

Get and/or set the object-specific search path for "*.xpl" files (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.

get_method(NAME)

get_procedure(NAME)

get_function(NAME)

Returns a reference to an object of the class RPC::XML::Method, RPC::XML::Function or RPC::XML::Procedure, which is the current binding for the published method NAME. If there is no such method known to the server, then "undef" is returned. 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.

The get_procedure and get_function calls are provided for symmetry. All will return the same object for NAME, regardless of the underlying type.

server_loop(HASH)

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 "dispatch" method 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 "HUP" or "KILL" signal 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 "INT" signal. 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:

dispatch(REQUEST)

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.

The dispatched method may communicate error in several ways. First, any non-reference return value is presumed to be an error string, and is encoded and returned as an RPC::XML::fault response. The method is run under an "eval()", so errors conveyed by $@ are similarly encoded and returned. As a special case, a method may explicitly "die()" with a fault response, which is passed on unmodified.

add_default_methods([DETAILS])

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 "*.xpl" extension, 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 "*.xpl" extension 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.status" method while still loading all the rest of the defaults. (It then provides a more Apache-centric status method.)

Note that there are no symmetric calls in this case. The provided API is implemented as methods, and thus only this interface is provided.

add_methods_in_dir(DIR [, DETAILS])

add_procedures_in_dir(DIR [, DETAILS])

add_functions_in_dir(DIR [, DETAILS])

This is exactly like add_default_methods above, save that the caller specifies which directory to scan for "*.xpl" files. In fact, the add_default_methods routine simply calls this routine with the installation directory as the first argument. The definition of the additional arguments is the same as above.

add_procedures_in_dir and add_functions_in_dir are provided for symmetry.

share_methods(SERVER, NAMES)

share_procedures(SERVER, NAMES)

share_functions(SERVER, NAMES)

The calling server object shares the methods/procedures/functions listed in NAMES with the source-server passed as the first object. The source must derive from this package in order for this operation to be permitted. At least one method must be specified, and all are specified by name (not by object reference). Both objects will reference the same exact RPC::XML::Procedure (or derivative thereof) object in this case, meaning that call-statistics and the like will reflect the combined data. If one or more of the passed names are not present on the source server, an error message is returned and none are copied to the calling object.

Alternately, one or more of the name parameters passed to this call may be regular-expression objects (the result of the qr operator). Any of these detected are applied against the list of all available methods known to the source server. All matching ones are inserted into the list (the list is pared for redundancies in any case). This allows for easier addition of whole classes such as those in the "system.*" name space (via "qr/^system[.]/"), for example. There is no substring matching provided. Names listed in the parameters to this routine must be either complete strings or regular expressions.

The share_procedures and share_functions calls are provided for symmetry.

copy_methods(SERVER, NAMES)

copy_procedures(SERVER, NAMES)

copy_functions(SERVER, NAMES)

These behave like the methods share_* above, with the exception that the calling object is given a clone of each method, rather than referencing the same exact method as the source server. The code reference part of the method is shared between the two, but all other data are copied (including a fresh copy of any list references used) into a completely new RPC::XML::Procedure (or derivative) object, using the "clone()" method from that class. Thus, while the calling object has the same methods available, and is re-using existing code in the Perl runtime, the method objects (and hence the statistics and such) are kept separate. As with the above, an error is flagged if one or more are not found.

This routine also accepts regular-expression objects with the same behavior and limitations. Again, copy_procedures and copy_functions are provided for symmetry.

Specifying Server-Side Remote Procedures¶

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 remote procedures be explicitly published in one of the several ways provided. Procedures may be added directly within code by using add_procedure/add_method/add_function as described above, with full data provided for the code reference, signature list, etc. The add_* 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::Procedure class, see RPC::XML::Procedure). 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.

The Three Types of Procedures¶

There are three types of procedures that RPC::XML::Server marshalls calls to. All are provided by the RPC::XML::Procedure module. You should not need to load or reference this module directly, as loading RPC::XML::Server (or a derivative) makes it available. The three types are:

Methods (RPC::XML::Method)

Code that is considered a "method" by the server is called as though it were, in fact, a method in that class. The first argument in the list is the server object itself, with the arguments to the call making up the rest of the list. The server checks the signature of the method against the arguments list before the call is made. See below ("How Procedures Are Called") for more on the invocation of code as methods.

Procedures (RPC::XML::Procedure)

Code that is considered a "procedure" by the server is called like a normal (non-method) subroutine call. The server object is not injected into the arguments list. The signature of the procedure is checked again the list of arguments before the call is made, as with methods.

Functions (RPC::XML::Function)

Lastly, code that is considered a "function" is the simplest of the three: it does not have the server object injected into the arguments list, and no check of signatures is done before the call is made. It is the responsibility of the function to properly understand the arguments list, and to return a value that the caller will understand.

There is (currently) no version that is called like a method but ignores signatures like a function.

How Procedures Are Called¶

When a routine is called via the server dispatcher, it is called with the arguments that the client request passed. Depending on whether the routine is considered a "function", a "procedure" or a "method", there may be an extra argument at the head of the list. The extra argument is present when the routine being dispatched is part of a RPC::XML::Method object. The extra argument is a reference to a RPC::XML::Server object (or a subclass thereof). This is derived from a hash reference, and will include these special keys:

method_name

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.

signature

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.

peerfamily

This is the address family, "AF_INET" or "AF_INET6", of a network address of the client that has connected and made the current request. It is required for unpacking "peeraddr" properly.

peeraddr

This is the address part of a packed SOCKADDR_IN or SOCKADDR_IN6 structure, as returned by "pack_sockaddr_in" in Socket or "pack_sockaddr_in6" in Socket, which contains the address of the client that has connected and made the current request. This is provided "raw" in case you need it. While you could re-create it from "peerhost", it is readily available in both this server environment and the Apache::RPC::Server environment and thus included for convenience. Apply "inet_ntop" in Socket to "peerfamily" and this value to obtain textual representation of the address.

peerhost

This is the address of the remote (client) end of the socket, in "x.x.x.x" (dotted-quad) format. If you wish to look up the clients host-name, you can use this to do so or utilize the encoded structure above directly.

peerport

This is the port of the remote (client) end of the socket, taken from the SOCKADDR_IN structure.

request

The HTTP::Request object for this request. Can be used to read HTTP headers sent by the client ("X-Forwarded-For" for your access checks, for example).

Those keys should only be referenced within method code itself, as they are not set on the server object outside of that context.

Note that by passing the server object reference first, method-classed routines 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 routines should not make (excessive) use of global variables, for obvious reasons. When the routines are loaded from XPL files, the code is created as a closure that forces execution in the RPC::XML::Procedure package (unless the XPL specifies a namespace, see RPC::XML::Procedure). If the code element of a procedure/method is passed in as a direct code reference by one of the other syntaxes allowed by the constructor, the package may well be different. Thus, routines should strive to be as localized as possible, independent of specific namespaces. If a group of routines are expected to work in close concert, each should explicitly set the namespace with a "package" declaration as the first statement within the routines themselves.

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:

system.identity

Returns a string value identifying the server name, version, and possibly a capability level. Takes no arguments.

system.introspection

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.

system.listMethods

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).

system.methodHelp

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.

system.methodSignature

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.

system.multicall

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 "methodName" member, which provides the name of the method to call. If there is also a "params" member, it refers to an array of the parameters that should be passed to the call.

system.status

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.

Content Compression¶

The RPC::XML::Server class now supports compressed messages, both incoming and outgoing. If a client indicates that it can understand compressed content, the server will use the Compress::Zlib (available from CPAN) module, if available, to compress any outgoing messages above a certain threshold in size (the default threshold is set to 4096 bytes). The following methods are all related to the compression support within the server class:

compress

Returns a false value if compression is not available to the server object. This is based on the availability of the Compress::Zlib module at start-up time, and cannot be changed.

compress_thresh([MIN_LIMIT])

Return or set the compression threshold value. Messages smaller than this size in bytes will not be compressed, even when compression is available, to save on CPU resources. If a value is passed, it becomes the new limit and the old value is returned.

Spooling Large Messages¶

If the server anticipates handling large out-bound messages (for example, if the hosted code returns large Base64 values pre-encoded from file handles), the "message_file_thresh" and "message_temp_dir" settings may be used in a manner similar to RPC::XML::Client. Specifically, the threshold is used to determine when a message should be spooled to a filehandle rather than made into an in-memory string (the RPC::XML::base64 type can use a filehandle, thus eliminating the need for the data to ever be completely in memory). An anonymous temporary file is used for these operations.

Note that the message size is checked before compression is applied, since the size of the compressed output cannot be known until the full message is examined. It is possible that a message will be spooled even if its compressed size is below the threshold, if the uncompressed size exceeds the threshold.

message_file_thresh

message_temp_dir

These methods may be used to retrieve or alter the values of the given keys as defined earlier for the "new" method.

Server Faults¶

Previous versions of this library had a very loosely-organized set of fault codes that a server might return in certain (non-fatal) error circumstances. This has been replaced by a more configurable, adjustable system to allow users to better integrate the server-defined faults with any that their application may produce. It also allows for the definition of additional fault types so that the same mechanism for formatting the pre-defined faults can be used within sub-classes and user applications.

The server method server_fault is used to generate RPC::XML::fault objects for these situations. It takes one or two arguments, the first being the name of the type of fault to create and the second being the specific message. If a fault is defined with a static message, the second argument may be skipped (and will be ignored if passed).

In addition to defining their own faults, a user may override the definition of any of the server's pre-defined faults.

Defining faults

The user may define their own faults using the "fault_table" argument to the constructor of the server class being instantiated. They may also override any of the pre-defined faults (detailed in the next section) by providing a new definition for the name.

The value of the "fault_table" argument is a hash reference whose keys are the names of the faults and whose values are one of two types:

An integer

If the value for the key is a scalar, it is assumed to be an integer and will be used as the fault code. When the fault is created, the message argument (the second parameter) will be used verbatim as the fault message.

A 2-element list reference

If the value is a list reference, it is assumed to have two elements: the first is the integer fault code to use, and the second is a message "template" string to use as the fault message. If the string contains the sequence %s, this will be replaced with the message argument (the second parameter) passed to server_fault. If that sequence is not in the string, then the fault message is considered static and the message argument is ignored.

An example of defining faults:

    my $server = RPC::XML::Server->new(
        ...
        fault_table => {
            limitexceeded => [ 500 => 'Call limit exceeded' ],
            accessdenied  => [ 600 => 'Access denied: %s' ],
            serviceclosed => 700
        },
        ...
    );

In this example, the fault-type "limitexceeded" is defined as having a fault code of 500 and a static message of "Call limit exceeded". The next fault defined is "accessdenied", which has a code of 600 and message that starts with "Access denied:" and incorporates whatever message was passed in to the fault creation. The last example defines a fault called "serviceclosed" that has a code of 700 and uses any passed-in message unaltered.

Server-defined faults

The RPC::XML::Server class defines the following faults and uses them internally. You can override the codes and messages for these by including them in the table passed as a "fault_table" argument. The faults fall into three groups:

Request Initialization

Faults in this group stem from the initialization of the request and the parsing of the XML. The codes for this group fall in the range 100-199.

Method Resolution

This group covers problems with mapping the request to a known method or function on the server. These codes will be in the range 200-299.

Execution

Lastly, these faults are for problems in actually executing the requested code. Their codes are in the range 300-399.

The faults, and the phases they apply to, are:

badxml (Request Initialization)

This fault is sent back to the client when the XML of the request did not parse as a valid XML-RPC request.

The code is 100, and the message is of the form, "XML parse error: %s". The specific error from the XML parser is included in the message.

badmethod (Method Resolution)

This fault is sent when the requested method is unknown to the server. No method has been configured on the server by that name.

The code is 200, and the message is of the form, "Method lookup error: %s". The name of the method and other information is included in the message.

badsignature (Method Resolution)

If a method is known on the server, but there is no signature that matches the sequence of arguments passed, this fault is returned. This fault cannot be triggered by server-side code configured via RPC::XML::Function, as no signature-checking is done for those.

The code is 201, and the message is of the form, "Method signature error: %s". The name of the method and the signature of the arguments is included in the message.

execerror (Execution)

This fault relates back to the client any exception thrown by the remote code during execution. If the invoked code returned their error in the form of a RPC::XML::fault object, that fault is returned instead. Otherwise, the value of $@ is used in the message of the fault that gets generated.

The code is 300, and the message is of the form, "Code execution error: %s". The actual text of the exception thrown is included in the message.

There is one special server-fault whose code and message cannot be overridden. If a call is made to server_fault for an unknown type of fault, the returned object will have a code of "-1" and a message stating that the fault-type is unknown. The message will include both the requested type-name and any message (if any) that was passed in.

Adjusting the server-defined codes

If you just want to "move" the range of codes that the server uses out of the way of your application's own faults, this can be done with the "fault_code_base" parameter when constructing the server object. The value of the parameter must be an integer, and it is added to the value of all existing fault codes. For example, a value of 10000 would make the code for the "badxml" fault be 10100, the code for "badmethod" be 10200, etc.

This is applied before any user-defined faults are merged in, so their code values will not be affected by this value.