rea/docs/android-analysis.md

Static Android APK analysis

REA wraps an existing headless JADX engine through src/android/. Its source is kept as an unmodified, commit-pinned Git submodule; see upstream provenance. CLI and MCP use the same application workflow and return artifact-bound Evidence inline.

This family is present on repository main and in npm 4.1.0. Check the released package boundary and the connected server's tool list before selecting it.

Supply tools

Use a full JDK 17 or newer (including its compiler module) and jadx-headless-mcp 0.7.1. REA runs its packaged Java metadata bridge in source-file mode against the unmodified engine JAR. REA does not install Java, an Android SDK, JADX, a device service or an emulator. Set the path in the shell or MCP server environment:

export REA_JADX_MCP_JAR=/absolute/path/jadx-headless-mcp-0.7.1-all.jar
# Optional: select an existing JDK rather than java on PATH.
export JAVA_HOME=/absolute/path/existing-jdk

The current metadata bridge is verified on macOS arm64 with OpenJDK 21 and the public Appium ApiDemos fixture. The POSIX adapter also supports Linux; the new bridge has not yet undergone real verification on Linux/JDK 25. Windows is unsupported for this provider's owned stdio process boundary.

Answer an analyst question

rea inspect-android-package /path/Example.apk
rea search-android-classes /path/Example.apk MainActivity
rea inspect-android-class /path/Example.apk example.MainActivity
rea inspect-android-method /path/Example.apk example.MainActivity onCreate
rea inspect-android-method /path/Example.apk example.MainActivity select --overload-index 1
rea trace-android-references /path/Example.apk example.MainActivity
rea trace-android-references /path/Example.apk example.MainActivity --method-name onCreate

Equivalent MCP methods are inspect_android_package, search_android_classes, inspect_android_class, inspect_android_method and trace_android_references. Every request includes path. Class/method operations use class_name, method_name and optional overload_index as applicable. For example:

{
  "name": "inspect_android_method",
  "arguments": {
    "path": "/path/Example.apk",
    "class_name": "example.MainActivity",
    "method_name": "select",
    "overload_index": 1
  }
}

Use inspect_android_class to choose an overload. REA rejects an ambiguous method request rather than silently selecting the first match. The engine's method reference operation cannot select overloads, so REA reports that boundary as unsupported when multiple same-name methods exist.

The engine's smali fallback also joins same-name overloads; REA rejects that fallback for an overloaded method instead of attributing all bodies to one selected overload. Native/abstract methods with no decompiled body report body_status: "not_available" without inferring which implementation flag caused it.

Interpret the result

• Package inspection retains decoded manifest XML, summary declarations, permissions and class/resource counts. Summary fields are extracted by the upstream engine and should be checked against the retained XML when needed. Signature verification is explicitly not_performed.
• Class search consumes all pages and checks their counts. An empty query inventories all class names; class names are decompiler representations.
• Class inventories read parsed metadata without generating source and return full reported display types, fields and inner class names. Synthetic members that code generation hides can appear in the inventory; it stays consistent after method decompilation within the retained session. Exact DEX descriptors are unknown. Overload indices are tied to this artifact and engine, not stable identities across different builds.
• Method inspection reports Java or smali, fallback markers and complete/partial returned text. Decompiled source is a derived representation. A complete text result does not establish complete semantics or a byte-identical reconstruction.
• Reference results are incoming static relationships between provider nodes. Source lines and DEX instruction offsets remain unknown. They are not observed runtime calls.
• Original requests, APK SHA-256, actual engine JAR SHA-256 and raw producer responses remain in Evidence. Source revision is populated only for bytes matching the audited release JAR.

These operations do not execute the APK or provide split APK/AAB handling, signature validation, full resource-table semantics, native-library analysis or Android runtime capture. Existing artifact inventory/extraction tools can supply archive evidence. Project that Evidence with the execution-free inventory tool:

rea project-android-application-graph '{"inventory_evidence":[<inventory_artifact Evidence>]}'

{
  "name": "project_android_application_graph",
  "arguments": {
    "inventory_evidence": ["<inventory_artifact Evidence>"]
  }
}

The projection reports exact component paths and hashes, runtime-family hints, and path-based bridge hypotheses. It does not decode DEX or claim observed runtime calls. Bridge hypotheses form a DEX/JVM-class by native-library Cartesian product. The projection computes the product and exact serialized candidate-array size before creating candidate objects, then retains a deterministic prefix within a 2 MiB UTF-8 JSON budget. If candidates are omitted, bridge_candidate_coverage reports total, emitted, and omitted counts; overall coverage is partial while component arrays still include every component from the supplied inventory pages. A path pair does not establish that a managed declaration names, loads, or calls the native library.

Resource and lifecycle limits

REA retains one serialized session with private, immutable APK, engine JAR and metadata-bridge copies. Matching requests reuse the loaded engine. APK/engine digests and JVM configuration are checked before reuse; changed inputs retire the previous session. Sessions are cleaned after 60 seconds of inactivity, on target/configuration changes, failure, timeout, cancellation, MCP disconnect or server shutdown. One-shot CLI commands always join cleanup before returning. REA never writes to the original APK or launches target code.

If process cleanup cannot be confirmed, REA retains the workspace and reports its location. That provider instance blocks subsequent engine launches until the caller resolves the reported resources and starts a fresh instance.

The provider uses one JADX analysis worker independently of JVM processor and garbage-collector settings. REA supplies no default heap or visible-CPU override; Java uses its normal ergonomics and inherits caller JVM settings. Optional provider settings add explicit JVM arguments:

export REA_JADX_HEAP_MIB=8192
# Optional, independent of the single JADX worker:
export REA_JADX_ACTIVE_PROCESSOR_COUNT=4
# Or select settings through Java's standard environment options:
export JAVA_TOOL_OPTIONS=-Xmx8g

Both REA settings must be positive safe integers; processor counts must also fit the JVM's signed 32-bit range. REA preserves JAVA_TOOL_OPTIONS, JDK_JAVA_OPTIONS and _JAVA_OPTIONS rather than replacing them. Java's standard precedence applies: explicit command-line heap settings override JAVA_TOOL_OPTIONS, while _JAVA_OPTIONS can override command-line settings. Evidence reports the worker's observed Runtime.maxMemory() rounded down to MiB and retains exact bytes, Java version and visible processors in its raw runtime response. The observed allocatable heap can differ from configured -Xmx, especially with Serial GC. Heap is not a total RSS cap: the JVM also uses native memory. Independent REA instances have independent queues. Whole operations have a 120-second execution deadline after reaching the queue's front; upstream decompilation is limited to 90 seconds.

Decoded manifest and method text have a 1 MiB upstream byte budget and report truncation. Class-name pages use indexed slices of up to 4,096 names without changing the complete, case-sensitive search contract. A protocol frame above 8 MiB, or combined stdout/stderr above 32 MiB per operation, fails with a diagnostic instead of returning an incomplete inventory as complete. These are memory-safety boundaries, not undocumented result caps.

Real verification

Download the explicit public fixtures once; this installs no tools:

npm run fixtures:android
export REA_JADX_MCP_JAR="$PWD/_reference/apk-integration/jadx-headless-mcp-0.7.1-all.jar"
export REA_ANDROID_TEST_APK="$PWD/_reference/apk-integration/ApiDemos-debug.apk"
npm run verify:android

The download script verifies fixed SHA-256 values, reuses matching files and refuses to overwrite a different existing file. APK/JAR files live under ignored _reference/ and are excluded from package contents. The lane exercises actual REA CLI and MCP results with the real engine, separately from synthetic protocol regressions. It needs no Gradle build, emulator, Android SDK or Ghidra.