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)  2013, VU University Amsterdam
    7    All rights reserved.
    8
    9    Redistribution and use in source and binary forms, with or without
   10    modification, are permitted provided that the following conditions
   11    are met:
   12
   13    1. Redistributions of source code must retain the above copyright
   14       notice, this list of conditions and the following disclaimer.
   15
   16    2. Redistributions in binary form must reproduce the above copyright
   17       notice, this list of conditions and the following disclaimer in
   18       the documentation and/or other materials provided with the
   19       distribution.
   20
   21    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   22    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   23    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   24    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   25    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   26    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   27    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   28    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   29    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   31    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   32    POSSIBILITY OF SUCH DAMAGE.
   33*/
   34
   35:- module(prolog_http_load, []).   36:- use_module(library(http/http_open)).   37:- use_module(library(uri)).   38
   39:- multifile
   40    user:prolog_load_file/2.   41
   42/** <module> Load Prolog code from a web server
   43
   44This module provides a hook into load_files/2 that allows loading Prolog
   45code from HTTP and HTTPS servers.  Below is an example session:
   46
   47  ==
   48  ?- [library(http/http_load)].
   49  ...
   50  true.
   51  ?- ['http://www.swi-prolog.org/download/demo/likes'].
   52  % http://www.swi-prolog.org/download/demo/likes.pl compiled 0.00 sec, 17 clauses
   53  true.
   54  ==
   55
   56*Warning* Loading code from untrusted HTTP resources may compromise your
   57security.
   58*/
   59
   60%!  user:prolog_load_file(+URL, +Options)
   61%
   62%   Hook into load_files/2  that  loads   =|http://|=  and  =|https://|=
   63%   resources directly from the web. Options  are passed to load_files/2
   64%   and http_open/2.
   65
   66user:prolog_load_file(Spec, Options) :-
   67    strip_module(Spec, Module, URL),
   68    atom(URL),
   69    (   is_http_url(URL)
   70    ->  GlobalURL = URL
   71    ;   prolog_load_context(file, Parent),
   72        is_http_url(Parent),
   73        uri_resolve(URL, Parent, GlobalURL)
   74    ),
   75    ensure_extension(GlobalURL, pl, FinalURL),
   76    setup_call_cleanup(
   77        http_open(FinalURL, In, Options),
   78        load_files(Module:FinalURL, [stream(In)|Options]),
   79        close(In)).
   80
   81is_http_url(URL) :-
   82    uri_is_global(URL),
   83    uri_components(URL, Components),
   84    uri_data(scheme, Components, Scheme),
   85    nonvar(Scheme),
   86    http_scheme(Scheme).
   87
   88http_scheme(http).
   89http_scheme(https) :-
   90    exists_source(library(http/http_ssl_plugin)).
   91
   92%!  ensure_extension(+URL, +Ext, -PlParts)
   93%
   94%   If the HTTP location is a plain path without extension, add the
   95%   .pl extension. This ensures extension-less files appearing in
   96%   file-loading directives are processed correctly.
   97
   98ensure_extension(URL0, Ext, URL) :-
   99    uri_components(URL0, Components0),
  100    uri_data(path, Components0, Path0),
  101    ensure_path_extension(Path0, Ext, Path),
  102    (   Path0 == Path
  103    ->  URL = URL0
  104    ;   uri_data(path, Components0, Path, Components),
  105        uri_components(URL, Components)
  106    ).
  107
  108ensure_path_extension(Path0, Ext, Path) :-
  109    file_name_extension(Base, '', Path0),
  110    !,
  111    file_name_extension(Base, Ext, Path).
  112ensure_path_extension(Path, _, Path)