/*  $Id: http_client.pl,v 1.9 2006/09/02 15:49:23 jan Exp $

    Part of XPCE --- The SWI-Prolog GUI toolkit

    Author:        Jan Wielemaker and Anjo Anjewierden
    E-mail:        jan@swi.psy.uva.nl
    WWW:           http://www.swi.psy.uva.nl/projects/xpce/
    Copyright (C): 1985-2002, 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 Lesser 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(pce_http_client, []).
:- use_module(library(pce)).
:- use_module(library(url)).
:- use_module(library(option)).

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
This module defines the clas http_client, a subclass of class socket for
fetching data from HTTP servers (aka `web-servers').

It can deal with two HTTP operations

	# GET
	Get data from an URL

	# HEAD
	Get only the header from an URL.

The GET operation is implemented by ->fetch_data:

http_client ->fetch_data: Into:object, Confirm:[code]*, Location:[string]
	Fetches data from the server.  Data is stored into `Into' in
	chunks using `->append: string' to this object.

	If confirm is not @nil, ->fetch_data returns after connecting
	and sending the request to the server.  On completion, the
	Confirm message is executed with

		@arg1	The http_client object
		@arg2	The `Into' object

	If `Confirm' is @nil, ->fetch_data blocks until all data has
	been received.

	In addition to returning the data, the header of the HTTP reply
	is attached to the data in a sheet using the attribute `http_header'.
	Field-names are in lowercase.  The date and last-modified fields
	appear as XPCE date objects and the content-length as an XPCE
	integer.

http_client <-data --> String
	Simple interface to get data.  Returns a string with http_header
	attribute sheet (see above).  Blocks until all data has been received.

http_client <-header --> Sheet
	Yield a sheet containing the header only the header data for the
	URL.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

:- pce_begin_class(http_client, socket,
		   "Client socket for HTTP Protocol").

:- pce_global(@nl_regex, new(regex('\n'))).
:- pce_global(@http_reply_regex,
	      new(regex('HTTP/([0-9]\\.[0-9])\\s*(\\d+)\\s*(\\w*)'))).
:- pce_global(@http_field_regex,
	      new(regex('([a-zA-Z0-9-]+):\\s*(.*)$'))).
:- pce_global(@http_empty_line_regex,
	      new(regex('\\s*\r?$'))).

:- initialization
   new(_, error(http_bad_header,
		'%O: Bad header line: %s',
		warning)),
   new(_, error(url_bad_protocol,
		'%O: Can only handle %s URLs',
		error)),
   new(_, error(url_bad_syntax,
		'%O: Not a legal URL: %s')).

variable(host,	       name,	       get,  "Host-name of URL").
variable(location,     string,	       get,  "Location on server").
variable(message,      code*,	       both, "Message send on completion").
variable(data_object,  object*,	       get,  "Object holding data").
variable(received,     int*,	       get,  "Data received").
variable(remaining,    int*,	       get,  "Remaining data").
variable(request,      {header,data}*, get,  "Last request").
variable(req_status,   name*,          get,  "Progress").
variable(http_version, name,	       both, "Used version (1.0/1.1)").
variable(user_agent,   name,	       both, "Provided User-Agent").
variable(verbose,      {silent,connect,transfer} := connect,
				       both, "Verbosity").

initialise(S, URL:prolog) :->
	"Create from URL or parsed URL"::
	(   atomic(URL)
	->  (   parse_url(URL, Parts)
	    ->  true
	    ;   send(S, error, url_bad_syntax, URL),
		fail
	    )
	;   Parts = URL
	),
	(   memberchk(protocol(http), Parts)
	->  true
	;   send(S, error, url_bad_protocol, 'HTTP'),
	    fail
	),
	option(host(Host), Parts),
	option(port(Port), Parts, 80),
	http_location(Parts, Location),
	send(S, slot, host, Host),
	send(S, slot, location, Location),
	send(S, slot, http_version, '1.0'),
	send(S, slot, user_agent, 'XPCE/SWI-Prolog'),
	send_super(S, initialise, tuple(Host, Port)).

:- pce_group(feedback).

req_status(S, Status:{connecting,connected,header,data,complete}) :->
	"Indicate status changes"::
	send(S, slot, req_status, Status),
	(   get(S, verbose, silent)
	->  true
	;   message(Status, S, Message),
	    ignore(send(S, Message))
	).

message(connecting, S, report(progress, 'Connecting %s', Host)) :-
	get(S, host, Host).
message(connected, _, report(progress, 'Connected')).
message(header,	   _, report(progress, 'Receiving header')).
message(data,	   _, report(progress, 'Receiving data')).
message(complete,  _, report(done)).

progress(S, Progress:int, What:{percent,bytes}) :->
	"Indicate progress"::
	(   get(S, verbose, transfer),
	    send(S, report, progress, 'Received %d %s', Progress, What)
	->  true
	;   true
	).

:- pce_group(connect).

connect(S) :->
	"Connect to <-host"::
	(   get(S, status, connected)
	->  true
	;   send(S, req_status, connecting),
	    send_super(S, connect),
	    send(S, req_status, connected)
	).

:- pce_group(fetch).

fetch_data(S,
	   Object:into=object,
	   Confirm:confirm=[code]*,
	   Location:location=[string]) :->
	"Fetch data from location into Object"::
	send(S, slot, data_object, Object),
	(   Confirm == @default
	->  true
	;   send(S, slot, message, Confirm)
	),
	(   Location == @default
	->  true
	;   send(S, slot, location, Location)
	),
	send(S, slot, request, data),
	send(S, send_header, 'GET'),
	(   get(S, message, Msg),
	    Msg \== @nil
	->  true
	;   send(S, wait)
	).

header(S, Location:[string], Header:sheet) :<-
	"Fetch header data from location as a sheet"::
	new(Object, object),
	send(S, slot, data_object, Object),
	(   Location == @default
	->  true
	;   send(S, slot, location, Location)
	),
	send(S, slot, request, header),
	send(S, send_header, 'HEAD'),
	send(S, wait),
	get(Object, http_header, Header),
	send(Header, lock_object, @on),
	send(Object, delete_attribute, http_header),
	get(Header, unlock, _).

data(S, Data:string) :<-
	"Fetch data from location as string"::
	new(TB, text_buffer),
	send(TB, undo_buffer_size, 0),
	send(S, fetch_data, TB),
	get(TB, contents, Data),
	get(TB, http_header, Header),
	send(Data, attribute, http_header, Header),
	free(TB).

:- pce_group(internal).

send_header(S, Action:name) :->
	"Send request header to HTTP server"::
	get(S, host, Host),
	send(S, slot, received, 0),
	send(S, prepare_header),
	send(S, slot, req_status, @nil),
	send(S, connect),
	get(S, http_version, Version),
	get(S, user_agent, Agent),
	get(S, location, Location),
	send(S, format, '%s %s HTTP/%s\r\n', Action, Location, Version),
	send(S, format, 'Host: %s\r\n', Host),
	send(S, format, 'User-Agent: %s\r\n', Agent),
	send(S, format, '\r\n').

wait(S) :->
	"Wait for completion"::
	repeat,
	(   get(S, req_status, complete)
	->  !
	;   send(@display, dispatch),
	    fail
	).

prepare_header(S) :->
	"Prepare for receiving header info"::
	send(S, record_separator, @nl_regex),
	send(S, input_message, message(S, header_line, @arg1)),
	send(S?data_object, attribute, http_header, new(sheet)).

header_line(S, Line:string) :->
	"Handle the header lines as they come in"::
	(   send(@http_field_regex, match, Line)
	->  get(@http_field_regex, register_value, Line, 1, name, FieldName0),
	    get(FieldName0, downcase, FieldName),
	    get(@http_field_regex, register_value, Line, 2, string, Value),
	    send(Value, strip),
	    field_type(FieldName, Type),
	    get(@pce, convert, Value, Type, FieldValue),
	    get(S, data_object, DataObject),
	    send(DataObject?http_header, value, FieldName, FieldValue)
	;   send(@http_reply_regex, match, Line)
	->  get(S, data_object, DataObject),
	    get(@http_reply_regex, register_value, Line, 2, int, ReplyStatus),
	    send(DataObject?http_header, value, status, ReplyStatus),
	    send(S, req_status, header)
	;   send(@http_empty_line_regex, match, Line)
	->  send(S, prepare_data)
	;   send(S, error, http_bad_header, Line)
	).

field_type('content-length', int).
field_type('date',	     date).
field_type('last-modified',  date).
field_type(_,		     name).

prepare_data(S) :->
	"Header has been received, prepare for content"::
	(   get(S, request, header)
	->  send(S, req_status, complete)
	;   (   get(S, data_object, Object),
	        get(Object?http_header, value, 'content-length', Length)
	    ->  send(S, slot, remaining, Length)
	    ;   send(S, slot, remaining, @nil)
	    ),
	    send(S, input_message, message(S, data_record, @arg1)),
	    send(S, record_separator, @nil)
	).

data_record(S, Record:string) :->
	"Receive a data record"::
	get(S, data_object, Data),
	(   get(S, remaining, Rem),
	    Rem \== @nil
	->  get(Record, size, Read),
	    NewRem is Rem - Read,
	    get(Data?http_header, value, 'content-length', Len),
	    Percent is ((Len-NewRem)*100)//Len,
	    send(S, progress, Percent, percent),
	    (	NewRem >= 0
	    ->	send(Data, append, Record),
		send(S, slot, remaining, NewRem),
		(   NewRem == 0
		->  send(S, complete)
		;   true
		)
	    ;	send(Record, truncate, Rem),
		send(Data, append, Record),
		send(S, complete)
	    )
	;   send(Data, append, Record),
	    get(Record, size, Bytes),
	    get(S, received, Rec0),
	    Rec is Rec0 + Bytes,
	    send(S, slot, received, Rec),
	    send(S, progress, Rec, bytes)
	).
	    
end_of_file(S) :->
	"Implicit completion"::
	send(S, close),
	(   get(S, req_status, complete)
	->  true
	;   send(S, complete)
	).

complete(S) :->
	"We received all data"::
	send(S, req_status, complete),
	(   get(S, message, Message),
	    Message \== @nil
	->  get(S, data_object, Data),
	    send(Message, forward, S, Data)
	;   send(S, req_status, complete)
	).

:- pce_end_class.



