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    1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2006-2015, University of Amsterdam
    7                              VU University Amsterdam
    8    All rights reserved.
    9
   10    Redistribution and use in source and binary forms, with or without
   11    modification, are permitted provided that the following conditions
   12    are met:
   13
   14    1. Redistributions of source code must retain the above copyright
   15       notice, this list of conditions and the following disclaimer.
   16
   17    2. Redistributions in binary form must reproduce the above copyright
   18       notice, this list of conditions and the following disclaimer in
   19       the documentation and/or other materials provided with the
   20       distribution.
   21
   22    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   24    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   25    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   26    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   27    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   28    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   29    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   30    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   31    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   32    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   33    POSSIBILITY OF SUCH DAMAGE.
   34*/
   35
   36:- module(www_browser,
   37          [ www_open_url/1,             % +UrlOrSpec
   38            expand_url_path/2           % +Spec, -URL
   39          ]).   40:- autoload(library(lists),[member/2]).   41
   42:- if(exists_source(library(process))).   43:- autoload(library(process), [process_create/3]).   44:- endif.   45
   46:- multifile
   47    known_browser/2.

Open a URL in the users browser

This library deals with the highly platform specific task of opening a web page. In addition, is provides a mechanism similar to absolute_file_name/3 that expands compound terms to concrete URLs. For example, the SWI-Prolog home page can be opened using:

?- www_open_url(swipl(.)).

*/

 www_open_url(+Url)
Open URL in running version of the users' browser or start a new browser. This predicate tries the following steps:
  1. If a prolog flag (see set_prolog_flag/2) browser is set and this is the name of a known executable, use this. The flag may be set to Command-Mode, where mode is one of fg or bg, requesting Command to run in foreground or background mode. Default is bg.
  2. On Windows, use win_shell(open, URL)
  3. Find a generic `open' comment. Candidates are xdg-open, open or gnome-open.
  4. If a environment variable BROWSER is set and this is the name of a known executable, use this.
  5. Try to find a known browser.
    @tbd Figure out the right tool in step 3 as it is not uncommon that multiple are installed.
   85www_open_url(Spec) :-                   % user configured
   86    expand_url_path(Spec, URL),
   87    open_url(URL).
   88
   89open_url(URL) :-
   90    current_prolog_flag(browser, Browser),
   91    expand_browser_flag(Browser, Command, Mode),
   92    has_command(Command),
   93    !,
   94    run_command(Command, [URL], Mode).
   95:- if(current_predicate(win_shell/2)).   96open_url(URL) :-                        % Windows shell
   97    win_shell(open, URL).
   98:- endif.   99open_url(URL) :-                        % Unix `open document'
  100    open_command(Open),
  101    has_command(Open),
  102    !,
  103    run_command(Open, [URL], fg).
  104open_url(URL) :-                        % user configured
  105    getenv('BROWSER', Browser),
  106    has_command(Browser),
  107    !,
  108    run_browser(Browser, URL).
  109open_url(URL) :-                        % something we know
  110    known_browser(Browser, _),
  111    has_command(Browser),
  112    !,
  113    run_browser(Browser, URL).
  114
  115expand_browser_flag(Command-Mode, Command, Mode) :- !.
  116expand_browser_flag(Command, Command, bg) :- atomic(Command).
  117
  118open_command(open) :-                   % Apples open command
  119    current_prolog_flag(apple, true).
  120open_command('xdg-open').               % Free desktop
  121open_command('gnome-open').             % Gnome (deprecated in favour of xdg-open
  122open_command(open).                     % Who knows
 run_browser(+Browser, +URL) is det
Open a page using a browser.
  128run_browser(Browser, URL) :-
  129    run_command(Browser, [URL], bg).
 run_command(+Command, +Args, +Background)
Run OS command Command using Args, silencing the error output because many browsers are rather verbose.
  136:- if(current_predicate(process_create/3)).  137run_command(Command, Args, fg) :-
  138    !,
  139    process_create(path(Command), Args, [stderr(null)]).
  140:- endif.  141:- if(current_prolog_flag(unix, true)).  142run_command(Command, [Arg], fg) :-
  143    format(string(Cmd), "\"~w\" \"~w\" &> /dev/null", [Command, Arg]),
  144    shell(Cmd).
  145run_command(Command, [Arg], bg) :-
  146    format(string(Cmd), "\"~w\" \"~w\" &> /dev/null &", [Command, Arg]),
  147    shell(Cmd).
  148:- else.  149run_command(Command, [Arg], fg) :-
  150    format(string(Cmd), "\"~w\" \"~w\"", [Command, Arg]),
  151    shell(Cmd).
  152run_command(Command, [Arg], bg) :-
  153    format(string(Cmd), "\"~w\" \"~w\" &", [Command, Arg]),
  154    shell(Cmd).
  155:- endif.
 known_browser(+FileBaseName, -Compatible)
True if browser FileBaseName has a remote protocol compatible to Compatible.
  162known_browser(firefox,   netscape).
  163known_browser(mozilla,   netscape).
  164known_browser(netscape,  netscape).
  165known_browser(konqueror, -).
  166known_browser(opera,     -).
 has_command(+Command)
Succeeds if Command is in $PATH. Works for Unix systems. For Windows we have to test for executable extensions.
  174:- dynamic
  175    command_cache/2.  176:- volatile
  177    command_cache/2.  178
  179has_command(Command) :-
  180    command_cache(Command, Path),
  181    !,
  182    Path \== (-).
  183has_command(Command) :-
  184    (   getenv('PATH', Path),
  185        (   current_prolog_flag(windows, true)
  186        ->  Sep = (;)
  187        ;   Sep = (:)
  188        ),
  189        atomic_list_concat(Parts, Sep, Path),
  190        member(Part, Parts),
  191        prolog_to_os_filename(PlPart, Part),
  192        atomic_list_concat([PlPart, Command], /, Exe),
  193        access_file(Exe, execute)
  194    ->  assert(command_cache(Command, Exe))
  195    ;   assert(command_cache(Command, -)),
  196        fail
  197    ).
  198
  199
  200                 /*******************************
  201                 *            NET PATHS         *
  202                 *******************************/
 url_path(+Alias, -Expansion) is nondet
Define URL path aliases. This multifile predicate is defined in module user. Expansion is either a URL, or a term Alias(Sub).
  209:- multifile
  210    user:url_path/2.  211
  212user:url_path(swipl,          'http://www.swi-prolog.org').
  213user:url_path(swipl_book,     'http://books.google.nl/books/about/\c
  214                               SWI_Prolog_Reference_Manual_6_2_2.html?\c
  215                               id=q6R3Q3B-VC4C&redir_esc=y').
  216
  217user:url_path(swipl_faq,      swipl('FAQ')).
  218user:url_path(swipl_man,      swipl('pldoc/doc_for?object=manual')).
  219user:url_path(swipl_mail,     swipl('Mailinglist.html')).
  220user:url_path(swipl_download, swipl('Download.html')).
  221user:url_path(swipl_pack,     swipl('pack/list')).
  222user:url_path(swipl_bugs,     swipl('bug.html')).
  223user:url_path(swipl_quick,    swipl('man/quickstart.html')).
 expand_url_path(+Spec, -URL)
Expand URL specifications similar to absolute_file_name/3. The predicate url_path/2 plays the role of file_search_path/2.
Errors
- existence_error(url_path, Spec) if the location is not defined.
  233expand_url_path(URL, URL) :-
  234    atomic(URL),
  235    !.                 % Allow atom and string
  236expand_url_path(Spec, URL) :-
  237    Spec =.. [Path, Local],
  238    (   user:url_path(Path, Spec2)
  239    ->  expand_url_path(Spec2, URL0),
  240        (   Local == '.'
  241        ->  URL = URL0
  242        ;   sub_atom(Local, 0, _, _, #)
  243        ->  atom_concat(URL0, Local, URL)
  244        ;   atomic_list_concat([URL0, Local], /, URL)
  245        )
  246    ;   throw(error(existence_error(url_path, Path), expand_url_path/2))
  247    )