NAME

       HTTP::Proxy::HeaderFilter - A base class for HTTP message header filters

SYNOPSIS

           package MyFilter;

           use base qw( HTTP::Proxy::HeaderFilter );

           # changes the User-Agent header in all requests
           # this filter must be pushed on the request stack
           sub filter {
               my ( $self, $headers, $message ) = @_;

               $message->headers->header( User_Agent => 'MyFilter/1.0' );
           }

           1;

DESCRIPTION

       The HTTP::Proxy::HeaderFilter class is used to create filters for HTTP request/response
       headers.

   Creating a HeaderFilter
       A HeaderFilter is just a derived class that implements some methods called by the proxy.
       Of all the methods presented below, only "filter()" must be defined in the derived class.

       filter()
           The signature of the "filter()" method is the following:

               sub filter { my ( $self, $headers, $message) = @_; ... }

           where $self is the filter object, $headers is a HTTP::Headers object, and $message is
           either a HTTP::Request or a HTTP::Response object.

           The $headers HTTP::Headers object is the one that will be sent to the client (if the
           filter is on the response stack) or origin server (if the filter is on the request
           stack). If $headers is modified by the filter, the modified headers will be sent to
           the client or server.

           The "init()" method (if it exists) is called by the "new()" constructeur to perform
           all initisalisation tasks. It's called once in the filter lifetime.

           A HTTP::Proxy::HeaderFilter object is a blessed hash, and the base class reserves only
           hash keys that start with "_hphf".

       new()
           The constructor is defined for all subclasses. Initialisation tasks (if any) for
           subclasses should be done in the "init()" method (see below).

       init()
           This method is called by the "new()" constructeur to perform all initisalisation
           tasks. It's called once in the filter lifetime.

           It receives all the parameters passed to "new()".

   Standard HeaderFilters
       Standard HTTP::Proxy::HeaderFilter classes are lowercase.

       The following HeaderFilters are included in the HTTP::Proxy distribution:

       simple
           This class lets you create a simple header filter from a code reference.

       standard
           This is the filter that provides standard headers handling for HTTP::Proxy.  It is
           loaded automatically by HTTP::Proxy.

       Please read each filter's documentation for more details about their use.

USEFUL METHODS FOR SUBCLASSES

       Some methods are available to filters, so that they can eventually use the little
       knowledge they might have of HTTP::Proxy's internals. They mostly are accessors.

       proxy()
           Gets a reference to the HTTP::Proxy objects that owns the filter.  This gives access
           to some of the proxy methods.

AUTHOR

       Philippe "BooK" Bruhat, <book@cpan.org>.

SEE ALSO

       HTTP::Proxy, HTTP::Proxy::BodyFilter.

COPYRIGHT

       Copyright 2003-2015, Philippe Bruhat.

LICENSE

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