MIME type selection and priorities

Fabian Aichele fabian.aichele at t-online.de
Wed Apr 6 20:13:11 BST 2011


I've developed a kdelibs addon that is capable of converting information
on file extensions and the contents of the native start menu on the
Windows platform, and am now at a stage where I need answers to a few
questions related to the priority and handling of MIME type information
by KMimeTypeTrader and related classes in kdelibs.

Suppose I have two different MIME type definitions (as an example for
Word documents (.doc)): 
* One defined as "application/msword" (as shipped with KDE, defined in
* The other defined as "application/vnd.kde.windows.doc", defined in the
user's home directory (under

Here the abbreviated definition as shipped with KDE:
  <mime-type type="application/msword">
    <comment>Word document</comment>    
    <sub-class-of type="application/x-ole-storage"/>
    <generic-icon name="x-office-document"/>
    <magic priority="60">
      <match value="\x31\xbe\x00\x00" type="string" offset="0"/>
      <match value="PO^Q`" type="string" offset="0"/>
      <match value="\376\067\0\043" type="string" offset="0"/>
      <match value="\333\245-\0\0\0" type="string" offset="0"/>
      <match value="MSWordDoc" type="string" offset="2112"/>
      <match value="MSWordDoc" type="string" offset="2108"/>
      <match value="Microsoft Word document data" type="string"
      <match value="bjbj" type="string" offset="546"/>
      <match value="jbjb" type="string" offset="546"/>
    <glob pattern="*.doc"/>
    <alias type="application/vnd.ms-word"/>
    <alias type="application/x-msword"/>
And here my custom definition:
   <mime-type type="application/vnd.kde.windows.doc">
        <comment>Microsoft Word-Dokument</comment>
        <glob pattern="*.doc"/>

The latter only contains the glob pattern, since this actually is all
that is relevant on the Windows platform to determine a file's type.

Here, KDE's method of determining a file's true type using the "magic
pattern" given in the first of the two MIME type definitions is way
smarter than Windows' own one, which is a good thing.

On the other hand, I also extract the corresponding icons used by
Windows Explorer for file extensions, which are tied to the MIME type
definition I give in my custom-generated MIME type.
Here, it seems the "closer match" is winning, i. e. a .doc file is
determined to be "application/msword" instead of
"application/vnd.kde.windows.doc". Now the trouble starts: If I don't
put "application/msword" as MIME type into the .desktop file that
defines the program to handle .doc files:

[Desktop Entry]
Name=Microsoft Office Word
GenericName=Microsoft Office Word
Comment=Microsoft Word-Dokument
Exec=classexec "%f" --action Open --class Word.Document.8

Konqueror/Dolphin don't "detect" the fact that MS Word is available to
handle .doc files, and instead still present me with the native Windows
"Select program to open" dialog. Additionally, the icon displayed for
.doc is that shipped with KDE, not the one I've converted from the
native platform.

Hence my question: Is it possible to override the MIME type priorities
so that my custom-generated MIME types are used instead of those
KMimeTypeTrader would select by default (even if that selection is a
better match than solely by the file extension given)?

If yes, how do I accomplish that?

If no, what would be alternative suggestions instead?

With best regards,
Fabian Aichele

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