http_server_files.pl

/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  2009-2014, VU University, Amsterdam
    All rights reserved.

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*/

:- module(http_server_files,
          [ serve_files_in_directory/2  % +Alias, +HTTPRequest
          ]).
:- use_module(library(http/http_path)).
:- use_module(library(http/http_dispatch)).

/** <module> Serve files needed by modules from the server

This module provides an infrastructure   for serving resource-files such
as icons, JavaScript, CSS files, etc.   The default configuration serves
the    HTTP    locations    =icons=,     =css=      and     =js=    (see
http_absolute_location/3)

The location for these services  can  be   changed  by  adding rules for
http:location/3.  Directories  providing  additional    or   alternative
resources can be achieved by adding rules for user:file_search_path/2.
*/

:- multifile
    http:location/3.                % Alias, Expansion, Options
:- dynamic
    http:location/3.                % Alias, Expansion, Options

http:location(icons, root(icons), [ priority(-100) ]).
http:location(css,   root(css),   [ priority(-100) ]).
http:location(js,    root(js),    [ priority(-100) ]).

:- multifile
    user:file_search_path/2.
:- dynamic
    user:file_search_path/2.

user:file_search_path(icons, library('http/web/icons')).
user:file_search_path(css,   library('http/web/css')).
user:file_search_path(js,    library('http/web/js')).

:- http_handler(icons(.), serve_files_in_directory(icons),
                [prefix, priority(-100)]).
:- http_handler(css(.),   serve_files_in_directory(css),
                [prefix, priority(-100)]).
:- http_handler(js(.),    serve_files_in_directory(js),
                [prefix, priority(-100)]).

%!  serve_files_in_directory(+Alias, +Request)
%
%   Serve files from the directory  Alias   from  the path-info from
%   Request.    This    predicate    is     used    together    with
%   file_search_path/2. Note that multiple  clauses   for  the  same
%   file_search_path alias can be used to merge files from different
%   physical locations onto the same HTTP   directory. Note that the
%   handler must be declared  as  =prefix=.   Below  is  an  example
%   serving images from  http://<host>/img/...   from  the directory
%   =http/web/icons=.
%
%       ==
%       http:location(img, root(img), []).
%       user:file_search_path(icons, library('http/web/icons')).
%
%       :- http_handler(img(.), serve_files_in_directory(icons), [prefix]).
%       ==
%
%   This predicate calls http_404/2 if the   physical file cannot be
%   located. If the requested  path-name   is  unsafe  (i.e., points
%   outside  the  hierarchy  defines    by   the  file_search_path/2
%   declaration), this handlers returns a _403 Forbidden_ page.
%
%   @see http_reply_file/3

serve_files_in_directory(Alias, Request) :-
    memberchk(path_info(PathInfo), Request),
    !,
    Term =.. [Alias,PathInfo],
    (   catch(http_safe_file(Term, []),
              error(permission_error(read, file, _), _),
              fail)
    ->  (   absolute_file_name(Term, Path,
                               [ access(read),
                                 file_errors(fail)
                               ])
        ->  http_reply_file(Path,
                            [ unsafe(true),
                              static_gzip(true)
                            ], Request)
        ;   http_404([], Request)
        )
    ;   memberchk(path(Path), Request),
        throw(http_reply(forbidden(Path)))
    ).
serve_files_in_directory(_Alias, Request) :-
    memberchk(path(Path), Request),
    throw(http_reply(forbidden(Path))).