serial: Fix getSignals() error handling

resources/chromium/fake-serial.js

@@ -93,11 +93,13 @@ class FakeSerialPort {
       ringIndicator: false,
       dataSetReady: false
     };
+    this.inputSignalFailure_ = false;
     this.outputSignals_ = {
       dataTerminalReady: false,
       requestToSend: false,
       break: false
     };
+    this.outputSignalFailure_ = false;
   }
 
   open(options, client) {
@@ -170,10 +172,18 @@ class FakeSerialPort {
     this.inputSignals_ = signals;
   }
 
+  simulateInputSignalFailure(fail) {
+    this.inputSignalFailure_ = fail;
+  }
+
   get outputSignals() {
     return this.outputSignals_;
   }
 
+  simulateOutputSignalFailure(fail) {
+    this.outputSignalFailure_ = fail;
+  }
+
   writable() {
     if (this.writable_)
       return Promise.resolve();
@@ -241,6 +251,10 @@ class FakeSerialPort {
   }
 
   async getControlSignals() {
+    if (this.inputSignalFailure_) {
+      return {signals: null};
+    }
+
     const signals = {
       dcd: this.inputSignals_.dataCarrierDetect,
       cts: this.inputSignals_.clearToSend,
@@ -251,6 +265,10 @@ class FakeSerialPort {
   }
 
   async setControlSignals(signals) {
+    if (this.outputSignalFailure_) {
+      return {success: false};
+    }
+
     if (signals.hasDtr) {
       this.outputSignals_.dataTerminalReady = signals.dtr;
     }

serial/serialPort_getSignals.https.any.js

@@ -41,3 +41,23 @@ serial_test(async (t, fake) => {
   signals = await port.getSignals();
   assert_object_equals(signals, expectedSignals, 'DSR set');
 }, 'getSignals() returns the current state of input control signals');
+
+serial_test(async (t, fake) => {
+  const {port, fakePort} = await getFakeSerialPort(fake);
+  await port.open({baudRate: 9600});
+
+  fakePort.simulateInputSignalFailure(true);
+  await promise_rejects_dom(t, 'NetworkError', port.getSignals());
+
+  fakePort.simulateInputSignalFailure(false);
+  const expectedSignals = {
+    dataCarrierDetect: false,
+    clearToSend: false,
+    ringIndicator: false,
+    dataSetReady: false
+  };
+  const signals = await port.getSignals();
+  assert_object_equals(signals, expectedSignals);
+
+  await port.close();
+}, 'getSignals() rejects on failure');

serial/serialPort_setSignals.https.any.js

@@ -43,3 +43,17 @@ serial_test(async (t, fake) => {
   expectedSignals.break = false;
   assert_object_equals(fakePort.outputSignals, expectedSignals, 'invert');
 }, 'setSignals() modifies the state of the port');
+
+serial_test(async (t, fake) => {
+  const {port, fakePort} = await getFakeSerialPort(fake);
+  await port.open({baudRate: 9600});
+
+  fakePort.simulateOutputSignalFailure(true);
+  await promise_rejects_dom(t, 'NetworkError', port.setSignals({break: true}));
+
+  fakePort.simulateOutputSignalFailure(false);
+  await port.setSignals({break: true});
+  assert_true(fakePort.outputSignals.break);
+
+  await port.close();
+}, 'setSignals() rejects on failure');