NAME

RPC::XML - A set of classes for core data, message and XML handling

SYNOPSIS

    use RPC::XML;

    $req = RPC::XML::request->new('fetch_prime_factors',
                                  RPC::XML::int->new(985120528));
    ...
    $resp = RPC::XML::Parser->new()->parse(STREAM);
    if (ref($resp))
    {
        return $resp->value->value;
    }
    else
    {
        die $resp;
    }

DESCRIPTION

The RPC::XML package is a reference implementation of the XML-RPC standard. As a reference implementation, it is geared more towards clarity and readability than efficiency.

The package provides a set of classes for creating values to pass to the constructors for requests and responses. These are lightweight objects, most of which are implemented as tied scalars so as to associate specific type information with the value. Classes are also provided for requests, responses, faults (errors) and a parser based on the the XML::Parser manpage package from CPAN.

This module does not actually provide any transport implementation or server basis. For these, see the RPC::XML::Client manpage and the RPC::XML::Server manpage, respectively.

EXPORTABLE FUNCTIONS

At present, only two functions are available for import. They must be explicitly imported as part of the use statement, or with a direct call to import:

time2iso8601([$time]): Convert the integer time value in $time (which defaults to calling the built-in time if not present) to a ISO 8601 string in the UTC time zone. This is a convenience function for occassions when the return value needs to be of the dateTime.iso8601 type, but the value on hand is the return from the time built-in.
smart_encode(@args): Converts the passed-in arguments to datatype objects. Any that are already encoded as such are passed through unchanged. The routine is called recursively on hash and array references. Note that this routine can only deduce a certain degree of detail about the values passed. Boolean values will be wrongly encoded as integers. Pretty much anything not specifically recognizable will get encoded as a string object. Thus, for types such as fault, the ISO time value, base-64 data, etc., the program must still explicitly encode it. However, this routine will hopefully simplify things a little bit for a majority of the usage cases.

CLASSES

The classes provided by this module are broken into two groups: datatype classes and message classes.

Data Classes

The following data classes are provided by this library. Each of these provide at least the set of methods below. Note that these classes are designed to create throw-away objects. There is currently no mechanism for changing the value stored within one of these object after the constructor returns. It is assumed that a new object would be created, instead.

The common methods to all data classes are:

new($value): Constructor. The value passed in is the value to be encapsulated in the new object.
value: Returns the value kept in the object. Processes recursively for array and struct objects.
as_string: Returns the value as a XML-RPC fragment, with the proper tags, etc.
type: Returns the type of data being stored in an object. The type matches the XML-RPC specification, so the normalized form datetime_iso8601 comes back as dateTime.iso8601.
is_fault: All types except the fault class return false for this. This is to allow consistent testing of return values for fault status, without checking for a hash reference with specific keys defined.

The classes themselves are:

RPC::XML::int

Creates an integer value. Constructor expects the integer value as an argument.

RPC::XML::i4

This is like the int class. Note that services written in strictly-typed languages such as C, C++ or Java may consider the i4 and int types as distinct and different.

RPC::XML::double

Creates a floating-point value.

RPC::XML::string

Creates an arbitrary string. No special encoding is done to the string (aside from XML document encoding, covered later) with the exception of the <, > and & characters, which are XML-escaped during object creation, and then reverted when the value method is called.

RPC::XML::boolean

Creates a boolean value. The value returned will always be either of 1 or 0, for true or false, respectively. When calling the constructor, the program may specify any of: 0, no, false, 1, yes, true.

RPC::XML::datetime_iso8601

Creates an instance of the XML-RPC dateTime.iso8601 type. The specification for ISO 8601 may be found elsewhere. No processing is done to the data.

RPC::XML::base64

Creates an object that encapsulates a chunk of data that will be treated as base-64 for transport purposes. The value may be passed in as either a string or as a scalar reference. Additionally, a second (optional) parameter may be passed, that if true identifies the data as already base-64 encoded. If so, the data is decoded before storage. The value method returns decoded data, and the as_string method encodes it before stringification.

RPC::XML::array

Creates an array object. The constructor takes zero or more data-type instances as arguments, which are inserted into the array in the order specified. value returns an array reference of native Perl types. If a non-null value is passed as an argument to value(), then the array reference will contain datatype objects (a shallow rather than deep copy).

RPC::XML::struct

Creates a struct object, the analogy of a hash table in Perl. The keys are ordinary strings, and the values must all be data-type objects. The value method returns a hash table reference, with native Perl types in the values. Key order is not preserved. Key strings are not encoded for special XML characters, so the use of such (<, >, etc.) is discouraged. If a non-null value is passed as an argument to value(), then the hash reference will contain the datatype objects rather than native Perl data (a shallow vs. deep copy, as with the array type above).

RPC::XML::fault

A fault object is a special case of the struct object that checks to ensure that there are two keys, faultCode and faultString.

As a matter of convenience, since the contents of a RPC::XML::fault structure are specifically defined, the constructor may be called with exactly two arguments, the first of which will be taken as the code, and the second as the string. They will be converted to RPC::XML types automatically and stored by the pre-defined key names.

Also as a matter of convenience, the fault class provides the following accessor methods for directly retrieving the integer code and error string from a fault object:

code
string

Both names should be self-explanatory. The values returned are Perl values, not RPC::XML class instances.

Message Classes

The message classes are used both for constructing messages for outgoing communication as well as representing the parsed contents of a received message. Both implement the following methods:

new: This is the constructor method for the two message classes. The response class may have only a single value (as a response is currently limited to a single return value), and requests may have as many arguments as appropriate. In both cases, the arguments are passed to the exported smart_encode routine described earlier.
as_string: Returns the message object expressed as an XML document. The document will be lacking in linebreaks and indention, as it is not targeted for human reading.

The two message-object classes are:

RPC::XML::request

This creates a request object. A request object expects the first argument to be the name of the remote routine being called, and all remaining arguments are the arguments to that routine. Request objects have the following methods (besides new and as_string):

name: The name of the remote routine that the request will call.
args: Returns a list reference with the arguments that will be passed. No arguments will result in a reference to an empty list.

RPC::XML::response

The response object is much like the request object in most ways. They may take only one argument, as that is all the specification allows for in a response. Responses have the following methods (in addition to new and as_string):

value: The value the response is returning. It will be a RPC::XML data-type.
is_fault: A boolean test whether or not the response is signalling a fault. This is the same as taking the value method return value and testing it, but is provided for clarity and simplicity.

DIAGNOSTICS

All constructors return undef upon failure, with the error message available in the package-global variable $RPC::XML::ERROR.

CAVEATS

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.

CREDITS

LICENSE

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 itself.

AUTHOR

Randy J. Ray <rjray@blackperl.com>