/* 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. /** 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 % processes the input. % % == % setup_call_cleanup( % open_any(Spec, read, In, Close, Options), % (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(newline(_)). 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.