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Comment by lifthrasiir | Hacker News Reader

I'm extremely confused about the claim that other tools have a worse precision or recall for APK or JAR files which are very much regular. Like, they should be a valid ZIP file with `META-INF/MANIFEST.MF` present (at least), and APK would need `classes.dex` as well, but at this point there is no other format that can be confused with APK or JAR I believe. I'd like to see which file was causing unexpected drop on precision or recall.

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People do create JAR files without a META-INF/MANIFEST.MF entry.

The tooling even supports it. https://docs.oracle.com/en/java/javase/21/docs/specs/man/jar...:

  -M or --no-manifest
     Doesn't create a manifest file for the entries

Minecraft mods 14 years ago used to tell you to open the JAR and delete the META-INF when installing them so can’t rely on that one…

The `file` command checks only the first few bytes, and doesn’t parse the structure of the file. APK files are indeed reported as Zip archives by the latest version of `file`.

This is false in every sense for https://www.darwinsys.com/file/ (probably the most used file version). It depends on the magic for a specific file, but it can check any part of your file. Many Linux distros are years out of date, you might be using a very old version.

FILE_45:

    ./src/file -m magic/magic.mgc ../../OpenCalc.v2.3.1.apk
    ../../OpenCalc.v2.3.1.apk: Android package (APK), with zipflinger virtual entry, with APK Signing Block

Interesting! I checked with file 5.44 from Ubuntu 23.10 and 5.45 on macOS using homebrew, and in both cases, I got “Zip archive data, at least v2.0 to extract” for the file here[1]. I don’t have an Android phone to check and I’m also not familiar with Android tooling, so is this a corrupt APK?

[1] https://download.apkpure.net/custom/com.apkpure.aegon-319781...

That doesn't appear to be a valid link. Try building `file` from source and using the provided default magic database.

I also tried this with the sources of file from the homepage you linked above, and I still get the same results.

You could try this for yourself using the same APKPure file which I uploaded at the following alternative link[1]. Further, while this could be a corrupt APK, I can’t see any signs of that from a cursory inspection as both the `classes.dex` and `META-INF` directory are present, and this is APKPure’s own APK, instead of an APK contributed for an app contributed by a third-party.

[1] https://wormhole.app/Mebmy#CDv86juV9H4aRCL2DSJeDw

apks are also zipaligned so it's not like random users are going to be making them either

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