blog/archive/2016/06/06.rss

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   4                 <title>Petter Reinholdtsen - Entries from June 2016</title>
   5                 <description>Entries from June 2016</description>
   6                 <link>http://people.skolelinux.org/pere/blog/</link>
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   8
   9         <item>
  10                 <title>A program should be able to open its own files on Linux</title>
  11                 <link>http://people.skolelinux.org/pere/blog/A_program_should_be_able_to_open_its_own_files_on_Linux.html</link>
  12                 <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/A_program_should_be_able_to_open_its_own_files_on_Linux.html</guid>
  13                 <pubDate>Sun, 5 Jun 2016 08:30:00 +0200</pubDate>
  14                 <description>&lt;p&gt;Many years ago, when koffice was fresh and with few users, I
  15 decided to test its presentation tool when making the slides for a
  16 talk I was giving for NUUG on Japhar, a free Java virtual machine.  I
  17 wrote the first draft of the slides, saved the result and went to bed
  18 the day before I would give the talk.  The next day I took a plane to
  19 the location where the meeting should take place, and on the plane I
  20 started up koffice again to polish the talk a bit, only to discover
  21 that kpresenter refused to load its own data file.  I cursed a bit and
  22 started making the slides again from memory, to have something to
  23 present when I arrived.  I tested that the saved files could be
  24 loaded, and the day seemed to be rescued.  I continued to polish the
  25 slides until I suddenly discovered that the saved file could no longer
  26 be loaded into kpresenter.  In the end I had to rewrite the slides
  27 three times, condensing the content until the talk became shorter and
  28 shorter.  After the talk I was able to pinpoint the problem &amp;ndash;
  29 kpresenter wrote inline images in a way itself could not understand.
  30 Eventually that bug was fixed and kpresenter ended up being a great
  31 program to make slides.  The point I&#39;m trying to make is that we
  32 expect a program to be able to load its own data files, and it is
  33 embarrassing to its developers if it can&#39;t.&lt;/p&gt;
  34
  35 &lt;p&gt;Did you ever experience a program failing to load its own data
  36 files from the desktop file browser?  It is not a uncommon problem.  A
  37 while back I discovered that the screencast recorder
  38 gtk-recordmydesktop would save an Ogg Theora video file the KDE file
  39 browser would refuse to open.  No video player claimed to understand
  40 such file.  I tracked down the cause being &lt;tt&gt;file --mime-type&lt;/tt&gt;
  41 returning the application/ogg mime type, which no video player I had
  42 installed listed as a MIME type they would understand.  I asked for
  43 &lt;a href=&quot;http://bugs.gw.com/view.php?id=382&quot;&gt;file to change its
  44 behavour&lt;/a&gt; and use the MIME type video/ogg instead.  I also asked
  45 several video players to add video/ogg to their desktop files, to give
  46 the file browser an idea what to do about Ogg Theora files.  After a
  47 while, the desktop file browsers in Debian started to handle the
  48 output from gtk-recordmydesktop properly.&lt;/p&gt;
  49
  50 &lt;p&gt;But history repeats itself.  A few days ago I tested the music
  51 system Rosegarden again, and I discovered that the KDE and xfce file
  52 browsers did not know what to do with the Rosegarden project files
  53 (*.rg).  I&#39;ve reported &lt;a href=&quot;http://bugs.debian.org/825993&quot;&gt;the
  54 rosegarden problem to BTS&lt;/a&gt; and a fix is commited to git and will be
  55 included in the next upload.  To increase the chance of me remembering
  56 how to fix the problem next time some program fail to load its files
  57 from the file browser, here are some notes on how to fix it.&lt;/p&gt;
  58
  59 &lt;p&gt;The file browsers in Debian in general operates on MIME types.
  60 There are two sources for the MIME type of a given file.  The output from
  61 &lt;tt&gt;file --mime-type&lt;/tt&gt; mentioned above, and the content of the
  62 shared MIME type registry (under /usr/share/mime/).  The file mime
  63 type is mapped to programs supporting the mime type, and this
  64 information is collected from
  65 &lt;a href=&quot;https://www.freedesktop.org/wiki/Specifications/desktop-entry-spec/&quot;&gt;the
  66 desktop files&lt;/a&gt; available in /usr/share/applications/.  If there is
  67 one desktop file claiming support for the MIME type of the file, it is
  68 activated when asking to open a given file.  If there are more, one
  69 can normally select which one to use by right-clicking on the file and
  70 selecting the wanted one using &#39;Open with&#39; or similar.  In general
  71 this work well.  But it depend on each program picking a good mime
  72 type (preferably
  73 &lt;a href=&quot;http://www.iana.org/assignments/media-types/media-types.xhtml&quot;&gt;a
  74 MIME type registered with IANA&lt;/a&gt;), file and/or the shared mime
  75 registry recognizing the file and the desktop file to list the MIME
  76 type in its list of supported MIME types.&lt;/p&gt;
  77
  78 &lt;p&gt;The &lt;tt&gt;/usr/share/mime/packages/rosegarden.xml&lt;/tt&gt; entry for
  79 &lt;a href=&quot;http://www.freedesktop.org/wiki/Specifications/shared-mime-info-spec&quot;&gt;the
  80 Shared MIME database&lt;/a&gt; look like this:&lt;/p&gt;
  81
  82 &lt;p&gt;&lt;blockquote&gt;&lt;pre&gt;
  83 &amp;lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot;?&amp;gt;
  84 &amp;lt;mime-info xmlns=&quot;http://www.freedesktop.org/standards/shared-mime-info&quot;&amp;gt;
  85   &amp;lt;mime-type type=&quot;audio/x-rosegarden&quot;&amp;gt;
  86     &amp;lt;sub-class-of type=&quot;application/x-gzip&quot;/&amp;gt;
  87     &amp;lt;comment&amp;gt;Rosegarden project file&amp;lt;/comment&amp;gt;
  88     &amp;lt;glob pattern=&quot;*.rg&quot;/&amp;gt;
  89   &amp;lt;/mime-type&amp;gt;
  90 &amp;lt;/mime-info&amp;gt;
  91 &lt;/pre&gt;&lt;/blockquote&gt;&lt;/p&gt;
  92
  93 &lt;p&gt;This states that audio/x-rosegarden is a kind of application/x-gzip
  94 (it is a gzipped XML file).  Note, it is much better to use an
  95 official MIME type registered with IANA than it is to make up ones own
  96 unofficial ones like the x-rosegarden type used by rosegarden.&lt;/p&gt;
  97
  98 &lt;p&gt;The desktop file of the rosegarden program failed to list
  99 audio/x-rosegarden in its list of supported MIME types, causing the
 100 file browsers to have no idea what to do with *.rg files:&lt;/p&gt;
 101
 102 &lt;p&gt;&lt;blockquote&gt;&lt;pre&gt;
 103 % grep Mime /usr/share/applications/rosegarden.desktop
 104 MimeType=audio/x-rosegarden-composition;audio/x-rosegarden-device;audio/x-rosegarden-project;audio/x-rosegarden-template;audio/midi;
 105 X-KDE-NativeMimeType=audio/x-rosegarden-composition
 106 %
 107 &lt;/pre&gt;&lt;/blockquote&gt;&lt;/p&gt;
 108
 109 &lt;p&gt;The fix was to add &quot;audio/x-rosegarden;&quot; at the end of the
 110 MimeType= line.&lt;/p&gt;
 111
 112 &lt;p&gt;If you run into a file which fail to open the correct program when
 113 selected from the file browser, please check out the output from
 114 &lt;tt&gt;file --mime-type&lt;/tt&gt; for the file, ensure the file ending and
 115 MIME type is registered somewhere under /usr/share/mime/ and check
 116 that some desktop file under /usr/share/applications/ is claiming
 117 support for this MIME type.  If not, please report a bug to have it
 118 fixed. :)&lt;/p&gt;
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