r8-mapping

R8 Mapping: download and deobfuscate

Download the R8 mapping.txt for a Flipcash release build and use it to deobfuscate stack traces.

Background

Release builds are minified/obfuscated by R8. The mapping file is uploaded as part of the release-artifacts artifact in the "Flipcash2 Build and Deploy" GitHub Actions workflow (ID 229420296). The mapping lives at mapping/release/mapping.txt inside the artifact.

R8 class merging: R8 may merge multiple unrelated classes into one obfuscated class. Use line numbers from the stack trace to disambiguate which original class a frame belongs to.

Step 1 — Download the mapping

Parse $ARGUMENTS for a versionCode (integer). If not provided, ask the user.

bash .claude/skills/r8-mapping/scripts/r8-mapping.sh <versionCode>

The script emits JSON:

{
  "mapping_path": "/tmp/r8-mapping-3797/mapping/release/mapping.txt",
  "run_id": 26846060877,
  "version_code": 3797,
  "line_count": 1211075
}

Step 2 — Deobfuscate classes

To find what an obfuscated class name maps to:

grep " -> <obfuscated_class>:" <mapping_path>

This returns lines like:

com.original.ClassName -> ag3:
com.other.MergedClass -> ag3:

Multiple results means R8 merged those classes. Use stack trace line numbers to disambiguate — each class section in the mapping contains line-number ranges for its methods.

Step 3 — Deobfuscate methods

After finding the class section, look for method mappings within it:

# Find the class section and its method mappings
grep -A 200 "^com.original.ClassName -> <obfuscated>:" <mapping_path> | head -200

Method lines look like:

    1:5:void run():123:127 -> run
    6:10:void otherMethod():45:49 -> a

The format is:

    <obfuscated_line_start>:<obfuscated_line_end>:<return_type> <original_method>(<params>):<original_line_start>:<original_line_end> -> <obfuscated_method>

Match the line number from the stack trace against obfuscated_line_start:obfuscated_line_end to find the original method and its original line numbers.