NAME

       HTTP::Proxy::BodyFilter - A base class for HTTP messages body filters

SYNOPSIS

           package MyFilter;

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

           # a simple modification, that may break things
           sub filter {
               my ( $self, $dataref, $message, $protocol, $buffer ) = @_;
               $$dataref =~ s/PERL/Perl/g;
           }

           1;

DESCRIPTION

       The HTTP::Proxy::BodyFilter class is used to create filters for HTTP request/response body
       data.

   Creating a BodyFilter
       A BodyFilter 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, $dataref, $message, $protocol, $buffer ) = @_;
                   ...
               }

           where $self is the filter object, $dataref is a reference to the chunk of body data
           received, $message is a reference to either a HTTP::Request or a HTTP::Response
           object, and $protocol is a reference to the LWP::Protocol protocol object.

           Note that this subroutine signature looks a lot like that of the call- backs of
           LWP::UserAgent (except that $message is either a HTTP::Request or a HTTP::Response
           object).

           $buffer is a reference to a buffer where some of the unprocessed data can be stored
           for the next time the filter will be called (see "Using a buffer to store data for a
           later use" for details). Thanks to the built-in HTTP::Proxy::BodyFilter::* filters,
           this is rarely needed.

           It is possible to access the headers of the message with "$message->headers()". This
           HTTP::Headers object is the one that was sent to the client (if the filter is on the
           response stack) or origin server (if the filter is on the request stack). Modifying it
           in the "filter()" method is useless, since the headers have already been sent.

           Since $dataref is a reference to the data string, the referent can be modified and the
           changes will be transmitted through the filters that follows, until the data reaches
           its recipient.

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

       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()".

       begin()
           Some filters might require initialisation before they are able to handle the data. If
           a "begin()" method is defined in your subclass, the proxy will call it before sending
           data to the "filter()" method.

           It's called once per HTTP message handled by the filter, before data processing
           begins.

           The method signature is as follows:

               sub begin {
                   my ( $self, $message ) = @_
                   ...
               }

       end()
           Some filters might require finalisation after they are finished handling the data. If
           a "end()" method is defined in your subclass, the proxy will call it after it has
           finished sending data to the "filter()" method.

           It's called once per HTTP message handled by the filter, after all data processing is
           done.

           This method does not expect any parameters.

       will_modify()
           This method return a boolean value that indicate if the filter will modify the body
           data on the fly.

           The default implementation returns a true value.

   Using a buffer to store data for a later use
       Some filters cannot handle arbitrary data: for example a filter that basically lowercases
       tag name will apply a simple regex such as "s/<\s*(\w+)([^>]*)>/<\L$1\E$2>/g".  But the
       filter will fail is the chunk of data contains a tag that is cut before the final ">".

       It would be extremely complicated and error-prone to let each filter (and its author) do
       its own buffering, so the HTTP::Proxy architecture handles this too. The proxy passes to
       each filter, each time it is called, a reference to an empty string ($buffer in the above
       signature) that the filter can use to store some data for next run.

       When the reference is "undef", it means that the filter cannot store any data, because
       this is the very last run, needed to gather all the data left in all buffers.

       It is recommended to store as little data as possible in the buffer, so as to avoid
       (badly) reproducing what HTTP::Proxy::BodyFilter::complete does.

       In particular, you have to remember that all the data that remains in the buffer after the
       last piece of data is received from the origin server will be sent back to your filter in
       one big piece.

   The store and forward approach
       HTTP::Proxy implements a store and forward mechanism, for those filters which need to have
       the whole message body to work. It's enabled simply by pushing the
       HTTP::Proxy::BodyFilter::complete filter on the filter stack.

       The data is stored in memory by the "complete" filter, which passes it on to the following
       filter once the full message body has been received.

   Standard BodyFilters
       Standard HTTP::Proxy::BodyFilter classes are lowercase.

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

       lines
           This filter makes sure that the next filter in the filter chain will only receive
           complete lines. The "chunks" of data received by the following filters with either end
           with "\n" or will be the last piece of data for the current HTTP message body.

       htmltext
           This class lets you create a filter that runs a given code reference against text
           included in a HTML document (outside "<script>" and "<style>" tags). HTML entities are
           not included in the text.

       htmlparser
           Creates a filter from a HTML::Parser object.

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

       save
           Store the message body to a file.

       complete
           This filter stores the whole message body in memory, thus allowing some actions to be
           taken only when the full page has been received by the proxy.

       tags
           The HTTP::Proxy::BodyFilter::tags filter makes sure that the next filter in the filter
           chain will only receive complete tags. The current implementation is not 100% perfect,
           though.

       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::HeaderFilter.

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.