Fix Apktool resource decoding bugs

[Sleeeee]

On obfuscated APKs, Apktool will struggle with resource decoding and throw different kinds of errors, which propagate to patch-apk when trying to rebuild an APK. We can catch the error logs and fix them programmatically, and re-run the build command.

Since Apktool's error printing is capped to 20 errors, we can do trial and error to fix them 20 at a time. The time to fully fix can be increased a lot depending on the amount of times it has to rebuild.

Error 1 : namespacing error

W: /tmp/tmp6ug84c13/apk_decoded/res/animator/APKTOOL_RENAMED_0x7f020002.xml:4: error: attribute android:APKTOOL_RENAMED_0x7f0409ce not found.

See this issue for details about this error. Basically, it assigns the android: namespace to properties that should be assigned app:.

From patch-apk, we can retrieve the filename and attribute that caused the error, then remove the android: prefix.

Error 2 : duplicate attributes

W: /tmp/tmpppawd3a1/apk_decoded/res/font/alternative.xml:4: error: duplicate attribute.
W: /tmp/tmpppawd3a1/apk_decoded/res/font/alternative.xml: error: file failed to compile.

We can match duplicates inside their files with a regex and keep only one occurence.

Error 3 : incompatible flags

W: /tmp/tmpofrmlkwo/apk_decoded/res/layout/telco_buy_image_header.xml:9: error: '0x0' is incompatible with attribute foregroundGravity (attr) flags [bottom=80, center=17, center_horizontal=1, center_vertical=16, clip_horizontal=8, clip_vertical=128, fill=119, fill_horizontal=7, fill_vertical=112, left=3, right=5, top=48].

Enumerations with no actual value will be decoded as an invalid 0x0 value. We can remove this attribute completely.

Example output on a test app:

$ patch-apk --extract-only com.example.myapp
[*] Using package: com.example.myapp
[*] Pulled 2 APK(s)
[*]  - base.apk
[*]  - split_config.arm64_v8a.apk
[*] Split APK set detected (2)
[*] Disassembling base.apk with apktool
[*] Disassembling split_config.arm64_v8a.apk with apktool
[*] Merging split APKs into base
[*] Detected duplicate attribute error, trying to resolve automatically
[*] Removed 5 duplicates, restarting build
[*] Detected resource namespace mismatch, trying to resolve automatically
[*] Fixed 20 broken namespaces, restarting build
[*] Detected resource namespace mismatch, trying to resolve automatically
[*] Fixed 20 broken namespaces, restarting build
[*] Detected resource namespace mismatch, trying to resolve automatically
[*] Fixed 20 broken namespaces, restarting build
[*] Detected resource namespace mismatch, trying to resolve automatically
[*] Fixed 19 broken namespaces, restarting build
[*] Detected resource namespace mismatch, trying to resolve automatically
[*] Fixed 5 broken namespaces, restarting build
[*] Detected incompatible flags error, trying to resolve automatically
[*] Removed 1 incompatible flags, restarting build
[*] Saved APK: com.example.myapp.apk

[Sleeeee]

Error 1 fix was merged in Apktool, so catching this error might not be needed anymore. Maybe it's still relevant to match error patterns even though they're not supposed to appear ?

[TheDauntless]

@Sleeeee Can you maybe update the PR to just detect the errors in case they pop up again and link to your issue on apktool?

[Sleeeee]

The fixes for error 1 and error 3 have been merged but there was no new Apktool release since then (waiting for 3.0.3 or 3.1.0). Error 2 is still unfixed and there's no public issue that I know of. I may look into it when I have the right setup.

For patch-apk, what I could do is tweak the code so that :

• By default, it looks at the error messages and suggests the right fixes (build Apktool from source or update when it's available).
• Add a flag that aggressively matches the errors to the identified fixes (the current code).

Sounds good ? If not, I can definitely just do step 1 and remove the aggressive fixes.

[Sleeeee]

Let me know what you think, it's ready on my end 😉 Refactored a tiny bit to make separate error handling and make the changes more readable.