LWP::Protocol - Base class for LWP protocols


 package LWP::Protocol::foo;
 require LWP::Protocol;


This class is used a the base class for all protocol implementations supported by the LWP library.

When creating an instance of this class using LWP::Protocol::create($url), and you get an initialised subclass appropriate for that access method. In other words, the LWP::Protocol::create() function calls the constructor for one of its subclasses.

All derived LWP::Protocol classes need to override the request() method which is used to service a request. The overridden method can make use of the collect() function to collect together chunks of data as it is received.

The following methods and functions are provided:

$prot = LWP::Protocol->new()

The LWP::Protocol constructor is inherited by subclasses. As this is a virtual base class this method should not be called directly.

$prot = LWP::Protocol::create($scheme)

Create an object of the class implementing the protocol to handle the given scheme. This is a function, not a method. It is more an object factory than a constructor. This is the function user agents should use to access protocols.

$class = LWP::Protocol::implementor($scheme, [$class])

Get and/or set implementor class for a scheme. Returns '' if the specified scheme is not supported.

 $response = $protocol->request($request, $proxy, undef);
 $response = $protocol->request($request, $proxy, '/tmp/sss');
 $response = $protocol->request($request, $proxy, \&callback, 1024);

Dispatches a request over the protocol, and returns a response object. This method needs to be overridden in subclasses. Refer to the LWP::UserAgent manpage for description of the arguments.

$prot->collect($arg, $response, $collector)

Called to collect the content of a request, and process it appropriately into a scalar, file, or by calling a callback. If $arg is undefined, then the content is stored within the $response. If $arg is a simple scalar, then $arg is interpreted as a file name and the content is written to this file. If $arg is a reference to a routine, then content is passed to this routine.

The $collector is a routine that will be called and which is responsible for returning pieces (as ref to scalar) of the content to process. The $collector signals EOF by returning a reference to an empty sting.

The return value from collect() is the $response object reference.

Note: We will only use the callback or file argument if $response->is_success(). This avoids sending content data for redirects and authentication responses to the callback which would be confusing.

$prot->collect_once($arg, $response, $content)

Can be called when the whole response content is available as $content. This will invoke collect() with a collector callback that returns a reference to $content the first time and an empty string the next.


Inspect the LWP/Protocol/ and LWP/Protocol/ files for examples of usage.


Copyright 1995-2001 Gisle Aas.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.