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Android serial plugin

Architecture (fd + Rust drivers)

SerialPlugin → UsbFdBridge (Kotlin) → openDeviceFd / enumerateJson
UsbNative (JNI) ↔ fd_bridge.rs ↔ driver_host.rs ↔ android-usb-serial (nusb)
RX: Rust reader thread → PortRxHub poll-loop (same as desktop)

Kotlin keeps UsbDeviceConnection and the raw fd. Rust duplicates the fd (dup), opens nusb::Device::from_fd, claims interfaces, and runs vendor drivers from the android-usb-serial crate. There is no vendored usb-serial-for-android Java tree in this repo.

Consumer app requirements

  1. Declare USB host in the app manifest (uses-feature android.hardware.usb.host optional).
  2. Ship a device_filter.xml aligned with device_filter.xml / ProbeTable::default_table().
  3. Request runtime USB permission before open (the plugin uses PendingIntent.FLAG_MUTABLE + setPackage()).

JVM unit tests (Robolectric)

Requires JDK 17:

export JAVA_HOME=$(/usr/libexec/java_home -v 17)  # macOS
cd android && ./gradlew test

Kotlin ↔ Rust JNI integration tests (instrumented)

Stable sources: examples/serialport-test/android-integration/.

Uses FakeTransport via android-test-harness (no Kotlin USB fakes).

cd examples/serialport-test
pnpm android:integration-test

Debug harness JNI (test_harness.rs): testHarnessReset, testOpenFakePort, testFakeInjectRx, testFakeTakeTx, testFakeInjectError, testHubBufferedLen, testInvokeWrite, testRegistryHasPort.

Layout

File Role
SerialPlugin Tauri plugin load → UsbFdBridge
UsbFdBridge enumerate, permission, fd open/close, attach/detach
UsbNative JNI for enumerate + fd lifecycle
MobileBridge JNI callbacks (onUsbError, onDeviceDetached, port list change, …)

Golden fixture regen

Rust drivers are verified against frozen JSON fixtures (crates/android-usb-serial/tests/fixtures/).

cargo run -p android-usb-serial --features fake-transport --bin golden_record
cargo test -p android-usb-serial --features fake-transport --test golden_parity

See docs/golden-recorder-archive/README.md for the retired JVM recorder workflow.

Logcat: adb logcat -s UsbFdBridge SerialPlugin RustStdoutStderr

CMUX virtual paths

  • exchange / at on physical#dlci=N: Routed through the Rust CMUX session (same as desktop).
  • cancel_exchange: Sets the virtual cancel flag, fails the active DLCI waiter, and clears the virtual TX queue.
  • rx_prepare: drain: Uses the shared RX hub drain before write (idle bytes may still be replayed via take_idle_bytes).