/* Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: J.Wielemaker@vu.nl
WWW: http://www.swi-prolog.org
Copyright (c) 2015-2020, VU University Amsterdam
CWI, Amsterdam
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
*/
:- module(iostream,
[ open_any/5, % +Spec, +Mode, -Stream, -Close, +Options
close_any/1 % +Close
]).
:- autoload(library(apply),[partition/4]).
:- autoload(library(error),
[instantiation_error/1,uninstantiation_error/1,must_be/2]).
:- autoload(library(option),[option/2]).
:- if(exists_source(library(uri))).
:- use_module(library(uri), [uri_file_name/2]).
:- 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/1. 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.