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yap-6.3/packages/http/http_stream.pl
2010-07-19 14:47:39 +01:00

254 lines
9.2 KiB
Prolog

/* $Id$
Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: wielemak@science.uva.nl
WWW: http://www.swi-prolog.org
Copyright (C): 1985-2007, University of Amsterdam
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
As a special exception, if you link this library with other files,
compiled with a Free Software compiler, to produce an executable, this
library does not by itself cause the resulting executable to be covered
by the GNU General Public License. This exception does not however
invalidate any other reasons why the executable file might be covered by
the GNU General Public License.
*/
:- module(http_stream,
[ http_chunked_open/3, % +Stream, -DataStream, +Options
stream_range_open/3, % +Stream, -DataStream, +Options
% CGI Stream interaction
cgi_open/4, % +Stream, -DataStream, :Hook, +Options
cgi_property/2, % +Stream, -Property
cgi_set/2, % +Stream, -Property
cgi_discard/1, % +Stream
is_cgi_stream/1 % +Stream
]).
:- expects_dialect(swi).
:- assert(system:swi_io).
:- use_module(library(shlib)).
:- use_foreign_library(foreign(http_stream)).
/** <module> HTTP Streams
This module realises encoding and decoding filters, implemented as
Prolog streams that read/write to an underlying stream. This allows for
sequences of streams acting as an in-process pipeline.
The predicate http_chunked_open/3 realises encoding and decoding of the
HTTP _Chunked_ encoding. This encoding is an obligatory part of the HTTP
1.1 specification. Messages are split into chunks, each preceeded by the
length of the chunk. Chunked encoding allows sending messages over a
serial link (typically a TCP/IP stream) for which the reader knows when
the message is ended. Unlike standard HTTP though, the sender does not
need to know the message length in advance. The protocol allows for
sending short chunks. This is supported totally transparent using a
flush on the output stream.
The predicate stream_range_open/3 handles the Content-length on an input
stream for handlers that are designed to process an entire file. The
filtering stream claims end-of-file after reading a specified number of
bytes, dispite the fact that the underlying stream may be longer.
@see The HTTP 1.1 protocol http://www.w3.org/Protocols/rfc2616/rfc2616.html
@author Jan Wielemaker
*/
%% http_chunked_open(+RawStream, -DataStream, +Options) is det.
%
% Create a stream to realise HTTP chunked encoding or decoding.
% The technique is similar to library(zlib), using a Prolog stream
% as a filter on another stream. Options:
%
% * close_parent(+Bool)
% If =true= (default =false=), the parent stream is closed
% if DataStream is closed.
%
% * max_chunk_size(+PosInt)
% Define the maximum size of a chunk. Default is the
% default buffer size of fully buffered streams (4096).
% Larger values may improve throughput. It is also
% allowed to use =|set_stream(DataStream, buffer(line))|=
% on the data stream to get line-buffered output. See
% set_stream/2 for details. Switching buffering to =false=
% is supported.
%
% Here is example code to write a chunked data to a stream
%
% ==
% http_chunked_open(Out, S, []),
% format(S, 'Hello world~n', []),
% close(S).
% ==
%
% If a stream is known to contain chunked data, we can extract
% this data using
%
% ==
% http_chunked_open(In, S, []),
% read_stream_to_codes(S, Codes),
% close(S).
% ==
%
% The current implementation does not generate chunked extensions
% or an HTTP trailer. If such extensions appear on the input they
% are silently ignored. This is compatible with the HTTP 1.1
% specifications. Although a filtering stream is an excellent
% mechanism for encoding and decoding the core chunked protocol,
% it does not well support out-of-band data.
%
% After http_chunked_open/3, the encoding of DataStream is the
% same as the encoding of RawStream, while the encoding of
% RawStream is =octet=, the only value allowed for HTTP chunked
% streams. Closing the DataStream restores the old encoding on
% RawStream.
%
% @error io_error(read, Stream) where the message context provides
% an indication of the problem. This error is raised if
% the input is not valid HTTP chunked data.
%% stream_range_open(+RawStream, -DataStream, +Options) is det.
%
% DataStream is a stream whose size is defined by the option
% size(ContentLength). Closing DataStream does not close
% RawStream.
:- meta_predicate cgi_open(+, -, :, +).
%% cgi_open(+OutStream, -CGIStream, :Hook, +Options) is det.
%
% Process CGI output. OutStream is normally the socket returning
% data to the HTTP client. CGIStream is the stream the (Prolog)
% code writes to. The CGIStream provides the following functions:
%
% * At the end of the header, it calls Hook using
% call(Hook, header, Stream), where Stream is a stream holding
% the buffered header.
%
% * If the stream is closed, it calls Hook using
% call(Hook, data, Stream), where Stream holds the buffered
% data.
%
% The stream calls Hook, adding the event and CGIStream to the
% closure. Defined events are:
%
% * header
% Called if the header is complete. Typically it uses
% cgi_property/2 to extract the collected header and combines
% these with the request and policies to decide on encoding,
% transfer-encoding, connection parameters and the complete
% header (as a Prolog term). Typically it uses cgi_set/2 to
% associate these with the stream.
%
% * send_header
% Called if the HTTP header must be sent. This is immediately
% after setting the transfer encoding to =chunked= or when the
% CGI stream is closed. Typically it requests the current
% header, optionally the content-length and sends the header
% to the original (client) stream.
%
% * close
% Called from close/1 on the CGI stream after everything is
% complete.
%
% The predicates cgi_property/2 and cgi_set/2 can be used to
% control the stream and store status info. Terms are stored as
% Prolog records and can thus be transferred between threads.
%% cgi_property(+CGIStream, ?Property) is det.
%
% Inquire the status of the CGI stream. Defined properties are:
%
% * request(-Term)
% The original request
% * header(-Term)
% Term is the header term as registered using cgi_set/2
% * client(-Stream)
% Stream is the original output stream used to create
% this stream.
% * thread(-ThreadID)
% ThreadID is the identifier of the `owning thread'
% * transfer_encoding(-Tranfer)
% One of =chunked= or =none=.
% * connection(-Connection)
% One of =Keep-Alife= or =close=
% * content_length(-ContentLength)
% Total byte-size of the content. Available in the close
% handler if the transfer_encoding is =none=.
% * header_codes(-Codes)
% Codes represents the header collected. Available in the
% header handler.
% * state(-State)
% One of =header=, =data= or =discarded=
%% cgi_set(+CGIStream, ?Property) is det.
%
% Change one of the properies. Supported properties are:
%
% * request(+Term)
% Associate a request to the stream.
% * header(+Term)
% Register a reply header. This header is normally retrieved
% from the =send_header= hook to send the reply header to the
% client.
% * connection(-Connection)
% One of =Keep-Alife= or =close=.
% * transfer_encoding(-Tranfer)
% One of =chunked= or =none=. Initially set to =none=. When
% switching to =chunked= from the =header= hook, it calls the
% =send_header= hook and if there is data queed this is send
% as first chunk. Each subsequent write to the CGI stream
% emits a chunk.
%% cgi_discard(+CGIStream) is det.
%
% Discard content produced sofar. It sets the state property to
% =discarded=, causing close to omit the writing the data. This
% must be to use an alternate output (e.g. an error page) if the
% page generator fails.
%% is_cgi_stream(+Stream) is semidet.
%
% True if Stream is a CGI stream created using cgi_open/4.
:- multifile
http:encoding_filter/3. % +Encoding, +In0, -In
:- multifile
http:current_transfer_encoding/1. % ?Encoding
% http:encoding_filter(+Encoding, +In0, -In) is semidet.
%
% Install a filter to deal with =chunked= encoded messages.
http:encoding_filter(chunked, In0, In) :-
http_chunked_open(In0, In,
[ close_parent(true)
]).
% http:current_transfer_encoding(?Encoding) is semidet.
%
% True if Encoding is supported
http:current_transfer_encoding(chunked).
:- retract(system:swi_io).