swi-prolog-nox 7.2.3+dfsg-6 / usr / lib / swi-prolog / library / iostream.pl

/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@cs.vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (C): 2015, VU University 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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  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(iostream,
	  [ open_any/5,		% +Spec, +Mode, -Stream, -Close, +Options
	    close_any/1		% +Close
	  ]).
:- use_module(library(option)).
:- use_module(library(error)).
:- if(exists_source(library(uri))).
:- use_module(library(uri)).
:- endif.

/** <module> Utilities to deal with streams

This  library  contains  utilities  that   deal  with  streams,  notably
originating from non-built-in sources such   as URLs, archives, windows,
processes, etc.

The predicate open_any/5 acts as a   _broker_  between applications that
can process data from a stream  and   libraries  that can create streams
from diverse sources. Without this predicate, processing data inevitally
follows  the  pattern  below.  As    _call_some_open_variation_  can  be
anything, this blocks us from writing  predicates such as load_xml(From,
DOM) that can operate on arbitrary input sources.

  ==
  setup_call_cleanup(
      call_some_open_variation(Spec, In),
      process(In),
      close(In)).
  ==

Libraries   that   can   open    streams     can    install   the   hook
iostream:open_hook/6  to  make  their  functionality  available  through
open_any/5.

@see	library(archive), library(process), library(zlib),
	library(http/http_stream)
*/

:- multifile
	open_hook/6.	% +Spec, +Mode, -Stream, -Close, +Options0, -Options

%%	open_any(+Specification, +Mode, -Stream, -Close, +Options)
%
%	Establish a stream from  Specification   that  should  be closed
%	using  Close,  which  can  either  be    called   or  passed  to
%	close_any/5. Options processed:
%
%	  - encoding(Enc)
%	  Set stream to encoding Enc.
%
%	Without loaded plugins, the open_any/5   processes the following
%	values  for  Specification.  If  no   rule  matches,  open_any/5
%	processes Specification as file(Specification).
%
%	  - Stream
%	  A plain stream handle. Possisible post-processing options such
%	  as encoding are applied. Close does _not_ close the stream,
%	  but resets other side-effects such as the encoding.
%	  - stream(Stream)
%	  Same as a plain Stream.
%	  - FileURL
%	  If Specification is of the form =file://...=, the pointed
%	  to file is opened using open/4.  Requires library(uri) to
%	  be installed.
%	  - file(Path)
%	  Explicitly open the file Path.  Path can be an Path(File)
%	  term as accepted by absolute_file_name/3.
%	  - string(String)
%	  Open a Prolog string, atom, list of characters or codes
%	  as an _input_ stream.
%
%	The typical usage scenario is  given   in  the code below, where
%	<process> processes the input.
%
%	  ==
%	  setup_call_cleanup(
%	      open_any(Spec, read, In, Close, Options),
%	      <process>(In),
%	      Close).
%	  ==
%
%	Currently, the following libraries extend this predicate:
%
%	   - library(http/http_open)
%	   Adds support for URLs using the `http` and `https` schemes.

open_any(Spec, Mode, Stream, Close, Options) :-
	\+ ( ground(Spec),			% argument sanity check
	     var(Stream),
	     var(Close),
	     is_list(Options) ), !,
	open_error(Spec, Mode, Stream, Close, Options).
open_any(Spec, _Mode, Stream, Close, Options) :-
	is_stream(Spec), !,
	Stream = Spec,
	input_options(Spec, Stream, true, Close, Options).
:- if(current_predicate(uri_file_name/2)).
open_any(Spec, Mode, Stream, Close, Options0) :-
	atomic(Spec),
	uri_file_name(Spec, File), !,
	open_any_builtin(file(File), Mode, Stream0, Close0, Options0, Options),
	input_options(Stream0, Stream, Close0, Close, Options).
:- endif.
open_any(Spec, Mode, Stream, Close, Options0) :-
	open_any_builtin(Spec, Mode, Stream0, Close0, Options0, Options), !,
	input_options(Stream0, Stream, Close0, Close, Options).
open_any(Spec, Mode, Stream, Close, Options0) :-
	open_hook(Spec, Mode, Stream0, Close0, Options0, Options), !,
	input_options(Stream0, Stream, Close0, Close, Options).
open_any(Spec, Mode, Stream, Close, Options0) :-
	open_any_builtin(file(Spec), Mode, Stream0, Close0, Options0, Options),
	input_options(Stream0, Stream, Close0, Close, Options).

open_error(Spec, _Mode, _Stream, _Close, _Options) :-
	var(Spec), !, instantiation_error(Spec).
open_error(_Spec, _Mode, Stream, _Close, _Options) :-
	nonvar(Stream), !,
	uninstantiation_error(Stream).
open_error(_Spec, _Mode, _Stream, Close, _Options) :-
	nonvar(Close), !,
	uninstantiation_error(Close).
open_error(_Spec, _Mode, _Stream, _Close, Options) :-
	\+ is_list(Options), !,
	must_be(list, Options).

%%	input_options(+Stream0, -Stream, +Close0, -Close, +Options) is det.
%
%	Establish the final stream.

input_options(Spec, Stream, Close0, Close, Options) :-
	option(encoding(Enc), Options), !,
	Stream = Spec,
	stream_property(Stream, encoding(Enc0)),
	set_stream(Stream, encoding(Enc)),
	mkconj(set_stream(Stream, encoding(Enc0)), Close0, Close).
input_options(Stream, Stream, Close, Close, _).

mkconj(set_stream(In,encoding(_)), close(In), close(In)) :- !.
mkconj(true,			   X,	      X) :- !.
mkconj(X,			   true,      X) :- !.
mkconj(X,			   Y,	      (X,Y)) :- !.

%%	open_any_builtin(+Spec, +Mode, -Stream, -Close,
%%			 +Options0, -Options) is semidet.
%
%	Built-in open-any operations

open_any_builtin(stream(Stream), _Mode, Stream, true, Options, Options) :-
	must_be(stream, Stream).
open_any_builtin(file(Spec), Mode, Stream, close(Stream), Options0, Options) :-
	(   compound(Spec)
	->  absolute_file_name(Spec, Path, [access(Mode)|Options0])
	;   Path = Spec
	),
	partition(open_option, Options0, OpenOptions, Options),
	open(Path, Mode, Stream, OpenOptions).
open_any_builtin(string(S), read, Stream, close(Stream), Options, Options) :-
	open_string(S, Stream).

open_option(encoding(_)).
open_option(type(_)).

%%	close_any(+Goal)
%
%	Execute the `Close` closure returned  by open_any/5. The closure
%	can also be called directly. Using close_any/1 can be considered
%	better style and enhances tractability of the source code.

close_any(Var) :-
	var(Var), !, instantiation_error(Var).
close_any((A,B)) :- close_any(A), close_any(B).
close_any(true).
close_any(close(Stream)) :- close(Stream).
close_any(set_stream(S, encoding(Enc))) :- set_stream(S, encoding(Enc)).


		 /*******************************
		 *	       HOOKS		*
		 *******************************/

%%	open_hook(+Spec, +Mode, -Stream, -Close, +Options0, -Options) is semidet.
%
%	Open Spec in Mode, producing Stream.
%
%	@arg Close is unified to a goal that must be called to undo the
%	side-effects of the action, e.g., typically the term close(Stream)
%	@arg Options0 are the options passed to open_any/5
%	@arg Options are passed to the post processing filters that
%	may be installed by open_any/5.