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

    use RPC::XML;

    $req = RPC::XML::request->new('fetch_prime_factors',
                                  RPC::XML::int->new(9));
    ...
    $resp = RPC::XML::Parser->new()->parse(STREAM);
    if (ref($resp))
    {
        return $resp->value->value;
    }
    else
    {
        die $resp;
    }

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 XML::Parser package from CPAN.

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

At present, three simple functions are available for import. They must be explicitly imported as part of the CWuse statement, or with a direct call to CWimport:

time2iso8601([$time])

Convert the integer time value in CW$time (which defaults to calling the built-in CWtime 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 CWtime 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 CWfault, 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.

bytelength([$string])

Returns the length of the string passed in, in bytes rather than characters. In Perl prior to 5.6.0 when there was little or no Unicode support, this has no difference from the CWlength function. if the bytes pragme is available, then the length measured is raw bytes, even when faced with multi-byte characters. If no argument is passed in, operates on CW$_.

In addition to these three, the following helper functions are also available. They may be imported explicitly, or via a tag of CW:types:

    RPC_BOOLEAN RPC_INT RPC_I4 RPC_DOUBLE RPC_DATETIME_ISO8601
    RPC_BASE64 RPC_STRING

Each creates a data object of the appropriate type from a single value. They are merely short-hand for calling the constructors of the data classes directly.

All of the above (helpers and the first three functions) may be imported via the tag CW:all.

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

as_string

Returns the value as a XML-RPC fragment, with the proper tags, etc.

serialize($filehandle)

Send the stringified rendition of the data to the given file handle. This allows messages with arbitrarily-large Base-64 data within them to be sent without having to hold the entire message within process memory.

length

Returns the length, in bytes, of the object when serialized into XML. This is used by the client and server classes to calculate message length.

type

Returns the type of data being stored in an object. The type matches the XML-RPC specification, so the normalized form CWdatetime_iso8601 comes back as CWdateTime.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 CWint class. Note that services written in strictly-typed languages such as C, or Java may consider the CWi4 and CWint 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 CW<, CW> and CW& characters, which are XML-escaped during object creation, and then reverted when the CWvalue 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: CW0, CWno, CWfalse, CW1, CWyes, CWtrue.

RPC::XML::datetime_iso8601

Creates an instance of the XML-RPC CWdateTime.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 CWvalue method returns decoded data, and the CWas_string method encodes it before stringification. Alternately, the constructor may be given an open filehandle argument instead of direct data. When this is the case, the data is never read into memory in its entirety, unless the CWvalue or CWas_string methods are called. This allows the manipulation of arbitrarily-large Base-64-encoded data chunks. In these cases, the flag (optional second argument) is still relevant, but the data is not pre-decoded if it currently exists in an encoded form. It is only decoded as needed. Note that the filehandle passed must be open for reading, at least. It will not be written to, but it will be read from. The position within the file will be preserved between operations. Because of this, this class supports a special method called CWto_file, that takes one argument. The argument may be either an open, writable filehandle or a string. If it is a string, CWto_file will attempt to open it as a file and write the decoded data to it. If the argument is a an open filehandle, the data will be written to it without any pre- or post-adjustment of the handle position (nor will it be closed upon completion). This differs from the CWserialize method in that it always writes the decoded data (where the other always writes encoded data), and in that the XML opening and closing tags are not written. The return value of CWto_file is the size of the data written in bytes.

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. CWvalue returns an array reference of native Perl types. If a non-null value is passed as an argument to CWvalue(), 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 CWvalue method returns a hash table reference, with native Perl types in the values. Key order is not preserved. Key strings are now encoded for special XML characters, so the use of such (CW<, CW>, etc.) should be transparent to the user. If a non-null value is passed as an argument to CWvalue(), 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). When creating RPC::XML::struct objects, there are two ways to pass the content in for the new object: Either an existing hash reference may be passed, or a series of key/value pairs may be passed. If a reference is passed, the existing data is copied (the reference is not re-blessed), with the values encoded into new objects as needed.

RPC::XML::fault

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

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 CWsmart_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.

serialize($filehandle)

Serialize the message to the given file-handle. This avoids creating the entire XML message within memory, which may be relevant if there is especially-large Base-64 data within the message.

length

Returns the total size of the message in bytes, used by the client and server classes to set the Content-Length header.

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 CWnew and CWas_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. It may take only one argument, as that is all the specification allows for in a response. Responses have the following methods (in addition to CWnew and CWas_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 CWvalue method return value and testing it, but is provided for clarity and simplicity.

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

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://www.opensource.org/licenses/artistic-license.php> for the license itself.

RPC::XML::Client, RPC::XML::Server, RPC::XML::Parser, XML::Parser

Randy J. Ray <rjray@blackperl.com>