The magic-launch launcher: Fix file type detection based on libmagic in the snap runtime

doc
1

This launcher that fixes libmagic file type autodetection compatibility in snaps.

How to use

  1. Merge the following part definition to your Snapcraft recipe:

    parts:
  # Launcher for fixing libmagic applications
  # https://forum.snapcraft.io/t/the-magic-launch-launcher-fix-file-type-detection-based-on-libmagic-in-the-snap-runtime/10442
  magic-launch:
    source: https://github.com/Lin-Buo-Ren/magic-launch.git
    source-tag: v2.0.0
    plugin: dump
    stage:
      - bin/*

  2. In the apps stanza, insert bin/magic-launch into the command chain:

    apps:
  _app_name_:
    # The command to run the application, the value should be a
    # *relative path* to an executable file rooted from the `prime` directory
    command: bin/magic-launch "${SNAP}"/bin/_app_command_

    if you’re using the full adapter:

    apps:
  _app_name_:
    # The environment adapter style to use, `command-chain` is only supported
    # by the `full` adapter
    adapter: full

    # The command to run the application, the value should be a
    # *relative path* to an executable file rooted from the `prime` directory
    command: bin/_app_command_
    command-chain:
      - bin/magic-launch

The implementation

Snaps that use this stage snap

References

file(1) manual page

Happy snapcrafting!

1 Like
2

Interesting. In a python3 snap (the review-tools) I use:

apps:
  foo:
    environment:
      MAGIC: $SNAP/usr/share/misc/magic
...
parts:
  bar:
    plugin: nil
    ...
    install: ./snap-fixup.sh
    ...
    stage-packages:
    - file
    - libmagic1
...

Where snap-fixup.sh has:

#!/bin/sh
...
SNAPDIR="$(pwd)/../install"
echo "Symlinking libmagic.so"
libmagic=$(find "$SNAPDIR"/usr/lib -name libmagic.so.1.0.0)
cd $(dirname "$libmagic")
ln -s libmagic.so.1.0.0 libmagic.so
cd -
...

This ‘works’ but isn’t exactly beautiful :slight_smile: Curious if you tried your part with python3 (import magic)? Either way, I’ll be taking a look at this. Thanks!

1 Like
3

It works:

$ test-magic 
Python 3.6.7 (default, Oct 22 2018, 11:32:17) 
[GCC 8.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import magic
>>> 

name: test-magic
base: core18
summary: ' '
description: ' ' 
version: '0.1'

grade: stable
confinement: strict

parts:
  magic-launch:
    plugin: nil
    stage-snaps:
    - magic-launch

  main:
    source: .
    plugin: dump
    stage-packages:
    - python3-magic
    - libmagic1
    organize:
      'test-magic.bash': bin/

apps:
  test-magic:
    adapter: full
    command: bin/test-magic.bash
    command-chain:
    - bin/magic-launch


#!/usr/bin/env bash
python3