mimetype.pl

/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  2002-2018, University of Amsterdam
                              VU University Amsterdam
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*/

:- module(mimetype,
          [ file_mime_type/2,           % +Path, -Type
            file_content_type/2,        % +Path, -Type
            file_content_type/3         % +Path, ?MediaType, -Type
          ]).

/** <module> Determine mime-type for a file

Simple library to guess the mime-type from   the extension of a file. As
various applications need  to  do  this   type  ofinferencing  it  seems
worthwhile to place this functionality in an extensible library.

@tbd    Consider content handling (using the Unix file command)
@tbd    Allow parameters? (e.g. text/html; charset=UTF-8)
*/

:- multifile
    mime:mime_extension/2,
    mime:text_mimetype/1,
    mime:charset/3.

%!  file_mime_type(+FileName, -MimeType) is semidet.
%
%   True when MimeType is  the  mime-type   to  be  used for sending
%   FileName. The default rules can be overridden and extended using
%   the hook mime:mime_extension/2.
%
%   @param MimeType is a compound term of the form Type/SubType.

file_mime_type(File, MimeType) :-
    file_name_extension(_, Ext, File),
    (   current_prolog_flag(windows, true)
    ->  downcase_atom(Ext, Lower),
        mime_extension(Lower, MimeType)
    ;   mime_extension(Ext, M0)
    ->  MimeType = M0
    ;   downcase_atom(Ext, Lower),
        mime_extension(Lower, MimeType)
    ),
    !.
file_mime_type(File, MimeType) :-
    file_base_name(File, Base),
    downcase_atom(Base, Lower),
    name_mimetype(Lower, Mime),
    !,
    MimeType = Mime.
file_mime_type(_, MimeType) :-
    default_mimetype(MimeType).

%!  mime:mime_extension(+Ext, -MimeType) is semidet.
%
%   Hook that is called by file_mime_type/2 before the default table
%   is examined.

mime_extension(Ext, MimeType) :-
    (   mime:mime_extension(Ext, Mime)
    ->  MimeType = Mime
    ;   ext_mimetype(Ext, Mime)
    ->  MimeType = Mime
    ).

%!  default_mimetype(-MimeType) is semidet.
%
%   If the mime-type cannot be determined   from the file extension,
%   this predicate is used as fallback.  It takes the value from the
%   Prolog flag =default_mimetype=. To change the default, use e.g.,
%
%     ==
%     :- set_prolog_flag(default_mimetype, text/plain).
%     ==
%
%   The initial default mime-type   is  =|application/unknown|=. Use
%   the value =|-|= to denote there is no default.

:- create_prolog_flag(default_mimetype, application/unknown, [keep(true)]).

default_mimetype(MimeType) :-
    current_prolog_flag(default_mimetype, MimeType),
    MimeType = _/_.


%!  ext_mimetype(+Extension, -MimeType) is semidet.
%
%   Built-in table of file-name extension to mime-type mappings.
%
%   @tbd    Update this list, e.g., from
%           http://www.webmaster-toolkit.com/mime-types.shtml

                                        % plain text
ext_mimetype(txt,  text/plain).
                                        % markup
ext_mimetype(htm,  text/html).
ext_mimetype(html, text/html).
ext_mimetype(xhtml, application/'xhtml+xml').
ext_mimetype(sgml, text/'x-sgml').
ext_mimetype(sgm,  text/'x-sgml').
ext_mimetype(xml,  text/xml).
ext_mimetype(css,  text/css).
ext_mimetype(xsl,  text/xml).           % Unclear what this should be.
ext_mimetype(md,   text/markdown).
                                        % Other data markup
ext_mimetype(json, application/json).
ext_mimetype(yaml, application/yaml).   % Not official
                                        % semantic web stuff
ext_mimetype(rdf,  application/'rdf+xml').
ext_mimetype(rdfs, application/'rdf+xml').
ext_mimetype(owl,  application/'rdf+xml').
ext_mimetype(ttl,  application/turtle).
ext_mimetype(nt,   application/'n-triples').
ext_mimetype(nq,   application/'n-quads').
                                        % Prolog source
ext_mimetype(pl,   text/plain).
                                        % Other languages
ext_mimetype(c,    text/'x-c').
ext_mimetype(h,    text/'x-c').
ext_mimetype(cc,   text/'x-c').
ext_mimetype(py,   text/'x-python').
ext_mimetype(java, text/'x-java').
ext_mimetype(sh,   text/plain).
                                        % Packaged formats
ext_mimetype(gz,   application/'x-gzip').
ext_mimetype(zip,  application/zip).
ext_mimetype(tgz,  application/'x-gtar').
                                        % Some document formats
ext_mimetype(pdf,  application/pdf).
ext_mimetype(doc,  application/msword).
                                        % Java classes
ext_mimetype(class, application/'octet-stream').
ext_mimetype(jar,  application/'x-java-archive').
                                        % JavaScript
ext_mimetype(js,   text/javascript).
                                        % Visual Basic Script :-(
ext_mimetype(vbs,  text/vbscript).
                                        % Some image formats
ext_mimetype(jpg,  image/jpeg).
ext_mimetype(jpeg, image/jpeg).
ext_mimetype(gif,  image/gif).
ext_mimetype(png,  image/png).
ext_mimetype(tif,  image/tiff).
ext_mimetype(tiff, image/tiff).
ext_mimetype(xpm,  image/'x-xpixmap').
ext_mimetype(ico,  image/'x-ico').
ext_mimetype(svg,  image/'svg+xml').
                                        % Google earth
ext_mimetype(kml,  application/'vnd.google-earth.kml+xml').
ext_mimetype(kmz,  application/'vnd.google-earth.kmz').

                                        % Flash
ext_mimetype(swf,  application/'x-shockwave-flash').
ext_mimetype(flv,  video/'x-flv').
                                        % MP3
ext_mimetype(mp3,  audio/mpeg).
                                        % Downloads
ext_mimetype(rpm,  application/'x-rpm').
ext_mimetype(exe,  application/'x-executable').

%!  name_mimetype(+DownCaseFileName, -MimeType) is semidet.
%
%   Determine the mime-type of files based on the entire filename.

name_mimetype(makefile,       text/plain).
name_mimetype(configure,      text/plain).
name_mimetype('configure.in', text/plain).
name_mimetype('configure.ac', text/plain).
name_mimetype('makefile.in',  text/plain).
name_mimetype('makefile.am',  text/plain).
name_mimetype('readme.in',    text/plain).

%!  text_mimetype(+MimeType) is semidet.
%
%   True when documents of MimeType are text documents and thus may need
%   a charset specification.

text_mimetype(MimeType) :-
    mime:text_mimetype(MimeType),
    !.
text_mimetype(text/_).

%!  file_content_type(+File:atom, -ContentType:atom) is det.
%!  file_content_type(+File:atom, ?MediaType, -ContentType:atom) is det.
%
%   True if File should be served using =|ContentType:|= ContentType. It
%   takes the following steps:
%
%     1. Determine the media type using file_mime_type/2, unless
%        already specified using file_content_type/3.
%     2. Determine it is a text file using text_mimetype/1
%     3. Use the charset from the Prolog flag `default_charset`
%
%   The behavior is controlled by several hooks and a flag.
%
%     - mime:mime_extension/2 defines the media type
%     - mime:text_mimetype/1 defines the media type is text
%     - mime:charset/3 derives the charset for a file with a given
%       media type, if the media type is text according to
%	mime:text_mimetype/1.
%     - If mime:text_mimetype/1 succeeds and mime:charset/3 fails, the
%       flag `default_charset` defines the charset unless it is set
%       to `-`.  The flag set by default to =UTF-8= if the Prolog
%       flag `encoding` is set to `utf8`.

file_content_type(File, ContentType) :-
    file_content_type(File, _, ContentType).
file_content_type(File, MediaType, ContentType) :-
    (   ground(MediaType)
    ->  true
    ;   file_mime_type(File, MediaType)
    ),
    (   text_mimetype(MediaType),
        (   mime:charset(File, MediaType, Charset0)
        ->  Charset = Charset0
        ;   default_charset(Charset)
        )
    ->  format(atom(ContentType), '~w; charset=~w', [MediaType, Charset])
    ;   format(atom(ContentType), '~w', [MediaType])
    ).

%!  mime:charset(+File, +MediaType, -Charset) is semidet.
%
%   Hook that determines the  Charset  for   File  that  has  media type
%   MediaType. This hook allows overruling file_content_type/2.
%
%   @see mime:text_mimetype/1.

default_charset(Charset) :-
    current_prolog_flag(default_charset, Charset),
    Charset \== (-).

set_default_charset :-
    current_prolog_flag(default_charset, _),
    !.
set_default_charset :-
    current_prolog_flag(encoding, utf8),
    !,
    set_prolog_flag(default_charset, 'UTF-8').
set_default_charset.

:- initialization(set_default_charset).