Add libmagic1 to Dockerfile dependencies

[nijel]

This allows us to use language bindings such as python-magic inside pre-commit checks.

[nijel]

Discovered via fsfe/reuse-tool#1244, it falls back to less performant and worse working detection using other libraries.

[carmenbianca]

You could also consider installing file instead of libmagic1. file has a dependency on libmagic1 and is a fairly useful and standard Unix-y util.

[asottile]

could you comment on the size this adds to the image? would make it easier to understand whether this is a good idea or not

I'm surprised python-magic doesn't ship a wheel with it bundled (as is typical for manylinux and friends)

[nijel]

The library itself is 200 kB, but it pulls the detection data which is 7 MB. That might me also the reason why it's not shipped in the wheel...

[carmenbianca]

There is an unmerged PR against python-magic which does just that: ahupp/python-magic#294

[ddelange]

The library itself is 200 kB, but it pulls the detection data which is 7 MB. That might me also the reason why it's not shipped in the wheel...

check out the compressed sizes (including the mime database and the libmagic binary) here. uncompressed, magic.mgc is 10.4MB and libmagic.so.1 (manylinux_x86_64) is 896kB.

[asottile]

so should I merge this or should the other thing use python-magic-standalone instead?

[ddelange]

It looks like my PR wont get merged any time soon, which is why python-magic-standalone was created in the first place (see the end of the thread). That's ment to be a temporary solution until my PR gets merged.