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wzbillings
Asked: 2024-09-12 09:48:09 +0800 CST

Why are my empty files not being assigned the correct mimetype?

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For a course, I am using the Racket language, which bundles its own IDE (Dr Racket) with the install. I successfully installed it on my Ubuntu 22.04 machine.

However, the installer does not create a mimetype for .rkt files (the default extension for Racket code files used by the IDE). I wanted my .rkt files to open in the Racket IDE when I click on them, so I created a custom mimetype, called text/rkt, which worked fine. The custom icon works and when I double click the files they open in the Racket IDE. On code files I've already created with code inside them, the custom mimetype seems to work correctly.

However, if I do touch test.rkt for example to create a new file, this file gets assigned the text/plain mimetype and when I double click it, it opens the text editor instead of the Racket IDE. This is not ideal, because I would like to be able to create empty files from the terminal and open them in the IDE (it's more convenient than doing Save As -> whatever every time in the IDE).

Is it possible to have my empty files with the *.rkt extension be recognized as my custom mimetype, instead of as plain text?

Here's the code for my custom mime type in case I did something wrong:

<?xml version="1.0" encoding="UTF-8"?>
<mime-info xmlns='http://www.freedesktop.org/standards/shared-mime-info'>
        <mime-type type="text/rkt">
                <comment>Racket code file</comment>
                <glob pattern="*.rkt"/>
        </mime-type>
</mime-info>

I followed the Ubuntu documentation here which I can see was last edited in 2014, as well as a post here which is more recent but maybe something changed since then. I'm new to linux so maybe I don't know where to look to find the correct instructions.

mime-type

1 Answers

  1. Best Answer

    this file gets assigned the text/plain mimetype

    Actually, it gets assigned the application/x-zerosize MIME-type, whose default handler is usually the default text editor.

    Quoting Emmanuele Bassi, from the GNOME team:

    • if you pass the file name, and either the file does not exist or you explicit asked for a guess because you’re not really accessing a file on a local storage, the XDG shared-mime database will use its glob rules (which include the extension, because we are like Windows, regardless of what you may think) to determine the closest MIME type applicable
    • if you pass the file name and the file exist, or you pass a bunch of bytes from the file, the XDG shared-mime database will use its “magic” content matching rules, and return the MIME type of the file

    Which means that if the file exists and is on a local storage, we won't do it like Windows (guessing based on the extension), but we'll look at magic numbers. For a 0-length file, looking at magic numbers will result in application/x-zerosize:

    % touch foo.txt
% xdg-mime query filetype foo.txt
application/x-zerosize
% xdg-mime query default application/x-zerosize
org.gnome.TextEditor.desktop

    This however isn't the case for other distributions / desktop environments. On my OpenSuse Leap / KDE box:

    % touch foo.txt
% xdg-mime query filetype foo.txt
text/plain
% xdg-mime query default text/plain
org.kde.kate.desktop

    So there could be a way to make Ubuntu / GNOME work like OpenSuse Leap / KDE. I tried researching this, but so far I haven't understood neither how this could be done nor whether this would require changing source code somewhere.

    However, for the purpose of having "empty" .rkt files opening with Dr Racket after touching them, since non-0-length .rkt files are opened by Dr Racket already, you could override touch's behavior by having it create a .rkt file containing just a comment in case the command follows the synopsys touch <filename_ending_in_.rkt> and <filename_ending_in_.rkt> doesn't exist, by defining a Bash function such as this one (which will defer to the actual touch if fed more than one argument / the argument doesn't end in .rkt / a directory, file etc with the same name as the argument exists already):

    touch() {
    [ $# -eq 1 ] && [ "${1##*.}" == rkt ] && [ ! -e "${1}" ] || {
        "$(which touch)" "$@"

        return
    }

    printf ';' >"${1}"
}
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