Fix USB CAT write/read NPE when port I/O races an in-progress (re)open

[patrickrb]

Root cause

CommonUsbSerialPort.open() publishes mConnection before openInt() assigns mReadEndpoint/mWriteEndpoint:

mConnection = connection;          // (1) connection is now visible
try {
    openInt(connection);           // (2) endpoints assigned here
    ...

openInt() and the catch-path close() both need the connection during setup, so the ordering is deliberate — but it leaves a window where mConnection != null while mWriteEndpoint/mReadEndpoint are still null.

read()/write() only guarded mConnection == null. A call landing in that window passed the guard and then dereferenced a null endpoint:

if (mWriteBuffer == null) {
    mWriteBuffer = new byte[mWriteEndpoint.getMaxPacketSize()]; // NPE
}

CableSerialPort.sendData() catches IOException but not the RuntimeException NPE, so it escaped to the TX worker thread and crashed the app.

Evidence

Sentry fatal (Pixel 8 / Android 16, radio.ks3ckc.ft8af@1.1.0-dev+5):

NullPointerException: 'int android.hardware.usb.UsbEndpoint.getMaxPacketSize()' on a null object reference
  at CommonUsbSerialPort.write(CommonUsbSerialPort.java:233)
  at CableSerialPort.writeIfOpen / sendData
  at CableConnector.setPttOn
  at Yaesu39Rig.setPTT
  at MainViewModel$6.beginKeying / onBeforeTransmit
  at FT8TransmitSignal$DoTransmitRunnable.run   (ThreadPoolExecutor worker)

The window is hit in practice during CAT auto-reconnect: CableSerialPort.prepare() allocates a fresh port (driver.getPorts().get(portNum), endpoints null) and connect() calls open(); a TX PTT firing from the transmit thread during that open() keys the crash. This is the endpoint-side twin of the earlier disconnect-race guards (writeIfOpen, PR #647).

Fix

Guard the endpoint as well as the connection, via a small unit-testable helper applied symmetrically to read() and write():

static boolean ioEndpointReady(Object connection, Object endpoint) {
    return connection != null && endpoint != null;
}

A missing connection or endpoint now throws the same recoverable IOException("Connection closed") that the CAT/TX layer already handles, instead of crashing. This is a strict superset of the previous mConnection == null check — no behavior change once the port is fully open.

Testing

• New CommonUsbSerialPortEndpointReadyTest (pure JVM) covers the readiness decision, including the exact crash case ioEndpointReady(connection, null) == false.
• ./gradlew :app:testDebugUnitTest — full suite green.

Risk

Very low. Localized to two guard checks in CommonUsbSerialPort; only adds an earlier, already-handled IOException on a previously-crashing path. No protocol, DSP, or performance impact.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 36.81%. Comparing base (ac169cc) to head (77c776c).
⚠️ Report is 6 commits behind head on dev.

Additional details and impacted files

@@             Coverage Diff              @@
##                dev     #651      +/-   ##
============================================
+ Coverage     36.73%   36.81%   +0.08%     
- Complexity      197      207      +10     
============================================
  Files           216      218       +2     
  Lines         26888    27012     +124     
  Branches       3287     3315      +28     
============================================
+ Hits           9877     9945      +68     
- Misses        16785    16832      +47     
- Partials        226      235       +9     

Flag	Coverage Δ
android	15.35% <ø> (+0.31%)	⬆️
native	9.93% <ø> (ø)

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see 8 files with indirect coverage changes

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[Copilot]

Pull request overview

This PR hardens the USB-serial CAT transport against a real-world race during (re)open where mConnection becomes visible before openInt() assigns mReadEndpoint/mWriteEndpoint, preventing an uncaught NullPointerException from escaping CommonUsbSerialPort.read()/write() and crashing the TX/CAT worker thread.

Changes:

• Add CommonUsbSerialPort.ioEndpointReady(connection, endpoint) to centralize the “safe to do I/O” decision and make it unit-testable.
• Update CommonUsbSerialPort.read() and write() to treat a missing endpoint the same as a missing connection (throw recoverable IOException("Connection closed")).
• Add a pure-JVM unit test covering endpoint readiness cases, including the exact crash window.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
ft8af/app/src/main/java/com/k1af/ft8af/serialport/CommonUsbSerialPort.java	Adds an endpoint-readiness helper and extends read/write guards to cover the connection-published/endpoint-null race window.
ft8af/app/src/test/java/com/k1af/ft8af/serialport/CommonUsbSerialPortEndpointReadyTest.java	Adds JVM unit coverage for the readiness decision to prevent regressions of the crash window.

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