1HTTP::Proxy::BodyFilterU(s3e)r Contributed Perl DocumentaHtTiToPn::Proxy::BodyFilter(3)
2
6 HTTP::Proxy::BodyFilter - A base class for HTTP messages body filters
7
9 package MyFilter;
10 use base qw( HTTP::Proxy::BodyFilter );
12 # a simple modification, that may break things
14 sub filter {
15 my ( $self, $dataref, $message, $protocol, $buffer ) = @_;
16 $$dataref =~ s/PERL/Perl/g;
17 }
18 1;
20
22 The HTTP::Proxy::BodyFilter class is used to create filters for HTTP
23 request/response body data.
24 Creating a BodyFilter
26 A BodyFilter is just a derived class that implements some methods
27 called by the proxy. Of all the methods presented below, only
28 "filter()" must be defined in the derived class.
29 filter()
31 The signature of the filter() method is the following:
32 sub filter {
34 my ( $self, $dataref, $message, $protocol, $buffer ) = @_;
35 ...
36 }
37 where $self is the filter object, $dataref is a reference to the
39 chunk of body data received, $message is a reference to either a
40 HTTP::Request or a HTTP::Response object, and $protocol is a
41 reference to the LWP::Protocol protocol object.
42 Note that this subroutine signature looks a lot like that of the
44 call- backs of LWP::UserAgent (except that $message is either a
45 HTTP::Request or a HTTP::Response object).
46 $buffer is a reference to a buffer where some of the unprocessed
48 data can be stored for the next time the filter will be called (see
49 "Using a buffer to store data for a later use" for details). Thanks
50 to the built-in HTTP::Proxy::BodyFilter::* filters, this is rarely
51 needed.
52 It is possible to access the headers of the message with
54 "$message->headers()". This HTTP::Headers object is the one that
55 was sent to the client (if the filter is on the response stack) or
56 origin server (if the filter is on the request stack). Modifying it
57 in the "filter()" method is useless, since the headers have already
58 been sent.
59 Since $dataref is a reference to the data string, the referent can
61 be modified and the changes will be transmitted through the filters
62 that follows, until the data reaches its recipient.
63 A HTTP::Proxy::BodyFilter object is a blessed hash, and the base
65 class reserves only hash keys that start with "_hpbf".
66 new()
68 The constructor is defined for all subclasses. Initialisation tasks
69 (if any) for subclasses should be done in the "init()" method (see
70 below).
71 init()
73 This method is called by the "new()" constructeur to perform all
74 initisalisation tasks. It's called once in the filter lifetime.
75 It receives all the parameters passed to "new()".
77 begin()
79 Some filters might require initialisation before they are able to
80 handle the data. If a "begin()" method is defined in your subclass,
81 the proxy will call it before sending data to the "filter()"
82 method.
83 It's called once per HTTP message handled by the filter, before
85 data processing begins.
86 The method signature is as follows:
88 sub begin {
90 my ( $self, $message ) = @_
91 ...
92 }
93 end()
95 Some filters might require finalisation after they are finished
96 handling the data. If a "end()" method is defined in your subclass,
97 the proxy will call it after it has finished sending data to the
98 "filter()" method.
99 It's called once per HTTP message handled by the filter, after all
101 data processing is done.
102 This method does not expect any parameters.
104 will_modify()
106 This method return a boolean value that indicate if the filter will
107 modify the body data on the fly.
108 The default implementation returns a true value.
110 Using a buffer to store data for a later use
112 Some filters cannot handle arbitrary data: for example a filter that
113 basically lowercases tag name will apply a simple regex such as
114 "s/<\s*(\w+)([^>]*)>/<\L$1\E$2>/g". But the filter will fail is the
115 chunk of data contains a tag that is cut before the final ">".
116 It would be extremely complicated and error-prone to let each filter
118 (and its author) do its own buffering, so the HTTP::Proxy architecture
119 handles this too. The proxy passes to each filter, each time it is
120 called, a reference to an empty string ($buffer in the above signature)
121 that the filter can use to store some data for next run.
122 When the reference is "undef", it means that the filter cannot store
124 any data, because this is the very last run, needed to gather all the
125 data left in all buffers.
126 It is recommended to store as little data as possible in the buffer, so
128 as to avoid (badly) reproducing what HTTP::Proxy::BodyFilter::complete
129 does.
130 In particular, you have to remember that all the data that remains in
132 the buffer after the last piece of data is received from the origin
133 server will be sent back to your filter in one big piece.
134 The store and forward approach
136 HTTP::Proxy implements a store and forward mechanism, for those filters
137 which need to have the whole message body to work. It's enabled simply
138 by pushing the HTTP::Proxy::BodyFilter::complete filter on the filter
139 stack.
140 The data is stored in memory by the "complete" filter, which passes it
142 on to the following filter once the full message body has been
143 received.
144 Standard BodyFilters
146 Standard HTTP::Proxy::BodyFilter classes are lowercase.
147 The following BodyFilters are included in the HTTP::Proxy distribution:
149 lines
151 This filter makes sure that the next filter in the filter chain
152 will only receive complete lines. The "chunks" of data received by
153 the following filters with either end with "\n" or will be the last
154 piece of data for the current HTTP message body.
155 htmltext
157 This class lets you create a filter that runs a given code
158 reference against text included in a HTML document (outside
159 "<script>" and "<style>" tags). HTML entities are not included in
160 the text.
161 htmlparser
163 Creates a filter from a HTML::Parser object.
164 simple
166 This class lets you create a simple body filter from a code
167 reference.
168 save
170 Store the message body to a file.
171 complete
173 This filter stores the whole message body in memory, thus allowing
174 some actions to be taken only when the full page has been received
175 by the proxy.
176 tags
178 The HTTP::Proxy::BodyFilter::tags filter makes sure that the next
179 filter in the filter chain will only receive complete tags. The
180 current implementation is not 100% perfect, though.
181 Please read each filter's documentation for more details about their
183 use.
184
186 Some methods are available to filters, so that they can eventually use
187 the little knowledge they might have of HTTP::Proxy's internals. They
188 mostly are accessors.
189 proxy()
191 Gets a reference to the HTTP::Proxy objects that owns the filter.
192 This gives access to some of the proxy methods.
193
195 Philippe "BooK" Bruhat, <book@cpan.org>.
196
198 HTTP::Proxy, HTTP::Proxy::HeaderFilter.
199
201 Copyright 2003-2015, Philippe Bruhat.
202
204 This module is free software; you can redistribute it or modify it
205 under the same terms as Perl itself.
206perl v5.32.1 2021-01-27 HTTP::Proxy::BodyFilter(3)