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.

perl v5.36.0                                       2022-12-04                       HTTP::Proxy::BodyFilter(3pm)