Symbolize Android stacktrace (Flutter + Codemagic)

Turn an obfuscated Google Play Console crash/ANR stacktrace into a symbolized one (file + line for every native and Flutter frame), so you can reason about the bug.

When to use this

All three must hold — if any is false, this skill is the wrong tool:

1. The app is a Flutter app targeting Android.
2. The trace was exported from the Google Play Console (Crash dashboard or ANR dashboard) — typically a .txt/.log with pc 0x… frames, optionally a # Application: / # Version: header.
3. The release build was produced by Codemagic CI/CD, with the workflow uploading both android_native_debug_symbols.zip and <AppName>_<N>_artifacts.zip (Flutter's split-debug-info .symbols files) as build artefacts. Without those, there is nothing to match the obfuscated PCs against. mapping.txt (R8/ProGuard) is also pulled when present — it lets the symbolizer turn Ka.n.l+8 style Java frames back into io.flutter.embedding.engine.FlutterJNI.onSurfaceDestroyed, which is the difference between a readable Java side and a wall of obfuscated names.

If you're unsure whether the build was from Codemagic, check codemagic.yaml at the repo root or ask the user.

Setup (caller's machine)

Requirement	How to satisfy
Codemagic API key	Generate at Codemagic → User settings → Integrations → Personal API token. Provide it via either: (a) CODEMAGIC_API_KEY env var, or (b) a .codemagic-api-key file at the repo root containing the key as plaintext — the script walks up from CWD and stops at the .git boundary. The file is convenient for teams who want a shared key checked into a private repo; accept that risk before doing it.
Android NDK with llvm-addr2line	Default lookup: ~/Library/Android/sdk/ndk/27.3.13750724. Override with ANDROID_NDK_HOME=/path/to/ndk. Any recent NDK ships llvm-addr2line and llvm-readelf.
unzip, python3 (3.10+), bash	Standard. The Python script uses stdlib only.

If neither the env var nor the file is present, stop and ask the user rather than guessing — every Codemagic call will 401.

There is no other setup. In particular, gh is not required — see step 3.

Bundled scripts

• scripts/codemagic_fetch_artifacts.py — three-mode discovery + download tool. JSON to stdout, progress to stderr. Also pulls mapping.txt when the build produced one.
• scripts/symbolize_flutter_anr.sh — order-insensitive trace + symbol bundler. Detects which input is which (trace, native zip, Flutter zip, mapping.txt).
• scripts/deobfuscate_r8.py — bulk R8/ProGuard mapping resolver. Invoked once per trace by the bash symbolizer; not normally called directly.

All three ship with --help (or a header docstring). Read it before improvising flags.

Workflow

1. Save the trace to a file

If the user pasted text rather than attaching a file, write it to /tmp/play-stacktrace.log. The bash script needs a real path (it greps the file twice — for ABI detection and frame extraction).

2. Identify app + version from the trace

The trace usually contains the package name embedded in /data/app/.../<applicationId>-…/split_config.<abi>.apk:

/data/app/~~xxxx==/com.example.foo-yyyy==/split_config.arm64_v8a.apk
                   ^^^^^^^^^^^^^^^

For the version, prefer (in order):

1. A # Version: header line in the trace (Crashlytics-style export).
2. The version the user stated when sharing the trace.
3. If still unknown, stop and ask. The user is downloading the trace from the Google Play Console and can read the versionName straight off the crash detail page next to the trace they sent you. Do not guess from the most recent Codemagic build — Symbol Build IDs only resolve when the version matches the crashing build exactly, and a mismatch silently produces [UNRESOLVED: no symbol file for BuildId …] for every app frame.

3. Fetch symbols from Codemagic

Three-step discovery (skip steps you don't need):

# (a) List visible apps. Read the JSON to pick the right `appName`,
#     then use that exact string for --app in step (b).
python3 scripts/codemagic_fetch_artifacts.py

# (b) List finished Android builds for the app, to confirm the version exists.
python3 scripts/codemagic_fetch_artifacts.py --app "Pixel Buddy"

# (c) Download both symbol zips for that version. Most-recent build wins on ties.
python3 scripts/codemagic_fetch_artifacts.py --app "Pixel Buddy" --build 1.2.3

--app accepts the Codemagic display name (case-insensitive exact match against appName) — that's the canonical selector and works on any machine. If you'd rather pass the Android applicationId (e.g. com.chunkytofustudios.pixel_buddy), install and authenticate the gh CLI (gh auth login); the script then resolves applicationId from the repo's android/app/build.gradle{,.kts}. Don't install gh for this skill alone — start by listing apps and matching by name.

The download is cached under ~/.cache/codemagic-fetch-artifacts/codemagic/<appId>/<buildId>/ — repeat invocations on the same build are instant.

Step (c)'s stdout is JSON — parse .cacheDir and .files[].path to feed the next step. Example:

{
  "cacheDir": "/Users/you/.cache/codemagic-fetch-artifacts/codemagic/<appId>/<buildId>",
  "files": [
    { "name": "android_native_debug_symbols.zip", "path": "…/android_native_debug_symbols.zip", "size": 123456789, "cached": true },
    { "name": "PixelBuddy_42_artifacts.zip",       "path": "…/PixelBuddy_42_artifacts.zip",       "size": 12345678,  "cached": false },
    { "name": "mapping.txt",                       "path": "…/mapping.txt",                       "size": 6543210,   "cached": false }
  ]
}

mapping.txt is optional and only present when the build enabled R8/ProGuard. Apps without minification simply won't have an entry — that's fine, just skip the mapping.txt argument in step 4.

If the app or version isn't found, the script exits non-zero with the available list — surface that to the user instead of looping.

4. Symbolize

bash scripts/symbolize_flutter_anr.sh \
  /tmp/play-stacktrace.log \
  ~/.cache/codemagic-fetch-artifacts/codemagic/<appId>/<buildId>/android_native_debug_symbols.zip \
  ~/.cache/codemagic-fetch-artifacts/codemagic/<appId>/<buildId>/<AppName>_<N>_artifacts.zip \
  ~/.cache/codemagic-fetch-artifacts/codemagic/<appId>/<buildId>/mapping.txt   # optional

Argument order doesn't matter — the script sniffs each input and classifies it as the trace, the native zip, the Flutter symbols zip, or the R8 mapping.txt. Defaults the output to <trace>.symbolized.txt next to the input. Override with -o. Use --json for a machine-readable summary on stdout.

When mapping.txt is provided, user-app Java frames (paths like <userPackage>/base.apk, <userPackage>/oat/.../base.odex, or /memfd:jit-cache) get a [JAVA: …] annotation with the deobfuscated <class>.<method>. Frames whose class isn't in the mapping (typical for Flutter SDK code that R8 left alone, or for stale mappings) are tagged [JAVA: not in mapping.txt]. If you skip mapping.txt, those same frames get [JAVA: pass mapping.txt to deobfuscate] so it's clear what to do next.

5. Read the symbolized output and debug

The output interleaves the original lines with resolved frames:

  #07  pc 0x00000000004bfb78  /data/app/.../split_config.arm64_v8a.apk (flutter::SurfaceDestroyed(_JNIEnv*, _jobject*, long)+…) (BuildId: d73e2148…)
    -> /Users/.../libflutter.so
flutter::SurfaceDestroyed(_JNIEnv*, _jobject*, long)
shell/platform/android/platform_view_android_jni_impl.cc:1234

Frames the script couldn't resolve get [UNRESOLVED]. The summary at the end reports Frames and Unresolved counts.

Gotchas

• Build IDs are the contract. A symbol file matches a frame only if its BuildId: (from llvm-readelf --notes) equals the BuildId: in the trace line. Wrong version → no matches → every frame [UNRESOLVED]. The script's first warning when most frames fail is "wrong build artifacts (common)".
• The version string must match the Codemagic build's version field exactly. Codemagic stores e.g. "2.3.1"; a v prefix is tolerated, but appending the build number (2.3.1+42) is not. If unsure, run codemagic_fetch_artifacts.py --app … (no --build) to see the available versions.
• ABI is detected from the trace by greps for arm64, armeabi, x86_64, x86. The 99% case is arm64-v8a. If the trace genuinely lacks an ABI hint, the script defaults to arm64-v8a.
• The Flutter symbols zip is named <AppName>_<N>_artifacts.zip where <N> is the Codemagic build sequence (not the version). The fetch script picks it up via the regex .+_\d+_artifacts\.zip. If the Codemagic workflow renamed the artifact, update FLUTTER_ARTIFACTS_RE in scripts/codemagic_fetch_artifacts.py.
• System library frames stay unresolved on purpose. Frames in libc.so, libart.so, com.google.android.gms, com.google.android.webview, /data/misc/apexdata/com.android.art/.../boot.oat (Android Runtime's pre-compiled boot image), system_server, etc. aren't from your build — those PCs match Android system binaries no Codemagic artifact ships. The script tags them [SYSTEM: …]. Don't chase them; focus on frames pointing into split_config.<abi>.apk for your package.
• R8-obfuscated Java frames need mapping.txt. Names like Ka.n.l+8 in a <userPackage>/base.apk frame are your own code, just minified. Codemagic uploads mapping.txt alongside the symbol zips, and the symbolizer applies it automatically when you pass it as the fourth argument. Without it, Java frames get a [JAVA: pass mapping.txt to deobfuscate] hint instead of being silently lumped into [SYSTEM]. Frames in <userPackage>/oat/.../base.odex and /memfd:jit-cache (AOT- and JIT-compiled user Java) get the same treatment; boot.oat and framework.jar are correctly classified as system instead.
• Flutter engine frames (libflutter.so) ship stripped. The libflutter.so bundled in android_native_debug_symbols.zip carries the Build ID but no DWARF debug info, so even a correct Build-ID match resolves to no source coordinates — the script tags those [UNRESOLVED: BuildId … matched but PC has no debug info (Flutter engine binaries ship stripped)]. The trace's own (flutter::Foo()+offset) text from Play Console is already the best we get for engine frames; the skill's value-add lives in the libapp.so (Dart AOT) frames that resolve cleanly via the app.android-<abi>.symbols file.
• Non-Codemagic builds will fail at step 3. If the Codemagic workflow didn't run for the version that crashed (e.g. it was a local flutter build appbundle upload), the API simply has nothing — bail and tell the user.
• The --json flag on symbolize_flutter_anr.sh prints {"frames", "resolved", "unresolved", "unresolved_nomatch", "unresolved_stripped", "java_deobfuscated", "java_not_deobfuscated", "system", "abi", "output"} to stdout with all status logs on stderr — use this when chaining the symbolizer into another script. unresolved is the sum of unresolved_nomatch (BuildId not in archives → wrong build) and unresolved_stripped (BuildId matched but binary lacks debug info → typically libflutter.so). java_deobfuscated + java_not_deobfuscated covers user-app Java frames; the latter splits semantically into "no mapping.txt provided" vs "class wasn't in mapping.txt" depending on whether the file was passed in.

Quick reference

# End-to-end, when you already know the display name + version:
export CODEMAGIC_API_KEY=...   # or drop a `.codemagic-api-key` file at the repo root
python3 scripts/codemagic_fetch_artifacts.py --app "Pixel Buddy" --build 1.2.3 \
  | tee /tmp/cm.json
CACHE=$(jq -r .cacheDir /tmp/cm.json)
bash scripts/symbolize_flutter_anr.sh \
  /tmp/play-stacktrace.log \
  "$CACHE/android_native_debug_symbols.zip" \
  "$CACHE"/*_artifacts.zip \
  "$CACHE/mapping.txt"        # omit if the build didn't run R8/ProGuard
# → /tmp/play-stacktrace.symbolized.txt