blog/data/2016-06-05-open-your-files.txt

   1 Title: A program should be able to open its own files on Linux
   2 Tags: english, debian
   3 Date: 2016-06-05 08:30
   4
   5 <p>Many years ago, when koffice was fresh and with few users, I
   6 decided to test its presentation tool when making the slides for a
   7 talk I was giving for NUUG on Japhar, a free Java virtual machine.  I
   8 wrote the first draft of the slides, saved the result and went to bed
   9 the day before I would give the talk.  The next day I took a plane to
  10 the location where the meeting should take place, and on the plane I
  11 started up koffice again to polish the talk a bit, only to discover
  12 that kpresenter refused to load its own data file.  I cursed a bit and
  13 started making the slides again from memory, to have something to
  14 present when I arrived.  I tested that the saved files could be
  15 loaded, and the day seemed to be rescued.  I continued to polish the
  16 slides until I suddenly discovered that the saved file could no longer
  17 be loaded into kpresenter.  In the end I had to rewrite the slides
  18 three times, condensing the content until the talk became shorter and
  19 shorter.  After the talk I was able to pinpoint the problem &ndash;
  20 kpresenter wrote inline images in a way itself could not understand.
  21 Eventually that bug was fixed and kpresenter ended up being a great
  22 program to make slides.  The point I'm trying to make is that we
  23 expect a program to be able to load its own data files, and it is
  24 embarrassing to its developers if it can't.</p>
  25
  26 <p>Did you ever experience a program failing to load its own data
  27 files from the desktop file browser?  It is not a uncommon problem.  A
  28 while back I discovered that the screencast recorder
  29 gtk-recordmydesktop would save an Ogg Theora video file the KDE file
  30 browser would refuse to open.  No video player claimed to understand
  31 such file.  I tracked down the cause being <tt>file --mime-type</tt>
  32 returning the application/ogg MIME type, which no video player I had
  33 installed listed as a MIME type they would understand.  I asked for
  34 <a href="http://bugs.gw.com/view.php?id=382">file to change its
  35 behavour</a> and use the MIME type video/ogg instead.  I also asked
  36 several video players to add video/ogg to their desktop files, to give
  37 the file browser an idea what to do about Ogg Theora files.  After a
  38 while, the desktop file browsers in Debian started to handle the
  39 output from gtk-recordmydesktop properly.</p>
  40
  41 <p>But history repeats itself.  A few days ago I tested the music
  42 system Rosegarden again, and I discovered that the KDE and xfce file
  43 browsers did not know what to do with the Rosegarden project files
  44 (*.rg).  I've reported <a href="http://bugs.debian.org/825993">the
  45 rosegarden problem to BTS</a> and a fix is commited to git and will be
  46 included in the next upload.  To increase the chance of me remembering
  47 how to fix the problem next time some program fail to load its files
  48 from the file browser, here are some notes on how to fix it.</p>
  49
  50 <p>The file browsers in Debian in general operates on MIME types.
  51 There are two sources for the MIME type of a given file.  The output from
  52 <tt>file --mime-type</tt> mentioned above, and the content of the
  53 shared MIME type registry (under /usr/share/mime/).  The file MIME
  54 type is mapped to programs supporting the MIME type, and this
  55 information is collected from
  56 <a href="https://www.freedesktop.org/wiki/Specifications/desktop-entry-spec/">the
  57 desktop files</a> available in /usr/share/applications/.  If there is
  58 one desktop file claiming support for the MIME type of the file, it is
  59 activated when asking to open a given file.  If there are more, one
  60 can normally select which one to use by right-clicking on the file and
  61 selecting the wanted one using 'Open with' or similar.  In general
  62 this work well.  But it depend on each program picking a good MIME
  63 type (preferably
  64 <a href="http://www.iana.org/assignments/media-types/media-types.xhtml">a
  65 MIME type registered with IANA</a>), file and/or the shared MIME
  66 registry recognizing the file and the desktop file to list the MIME
  67 type in its list of supported MIME types.</p>
  68
  69 <p>The <tt>/usr/share/mime/packages/rosegarden.xml</tt> entry for
  70 <a href="http://www.freedesktop.org/wiki/Specifications/shared-mime-info-spec">the
  71 Shared MIME database</a> look like this:</p>
  72
  73 <p><blockquote><pre>
  74 &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  75 &lt;mime-info xmlns="http://www.freedesktop.org/standards/shared-mime-info"&gt;
  76   &lt;mime-type type="audio/x-rosegarden"&gt;
  77     &lt;sub-class-of type="application/x-gzip"/&gt;
  78     &lt;comment&gt;Rosegarden project file&lt;/comment&gt;
  79     &lt;glob pattern="*.rg"/&gt;
  80   &lt;/mime-type&gt;
  81 &lt;/mime-info&gt;
  82 </pre></blockquote></p>
  83
  84 <p>This states that audio/x-rosegarden is a kind of application/x-gzip
  85 (it is a gzipped XML file).  Note, it is much better to use an
  86 official MIME type registered with IANA than it is to make up ones own
  87 unofficial ones like the x-rosegarden type used by rosegarden.</p>
  88
  89 <p>The desktop file of the rosegarden program failed to list
  90 audio/x-rosegarden in its list of supported MIME types, causing the
  91 file browsers to have no idea what to do with *.rg files:</p>
  92
  93 <p><blockquote><pre>
  94 % grep Mime /usr/share/applications/rosegarden.desktop
  95 MimeType=audio/x-rosegarden-composition;audio/x-rosegarden-device;audio/x-rosegarden-project;audio/x-rosegarden-template;audio/midi;
  96 X-KDE-NativeMimeType=audio/x-rosegarden-composition
  97 %
  98 </pre></blockquote></p>
  99
 100 <p>The fix was to add "audio/x-rosegarden;" at the end of the
 101 MimeType= line.</p>
 102
 103 <p>If you run into a file which fail to open the correct program when
 104 selected from the file browser, please check out the output from
 105 <tt>file --mime-type</tt> for the file, ensure the file ending and
 106 MIME type is registered somewhere under /usr/share/mime/ and check
 107 that some desktop file under /usr/share/applications/ is claiming
 108 support for this MIME type.  If not, please report a bug to have it
 109 fixed. :)</p>