fix: stop polling if the poller has an error (#1936)

This will stop polling for FS events if there’s an error polling for fs events. Added tests for the JS. Tests for the c++ are harder.

This supersedes #1804 and ensures no more events are fired if one reports an error. Fixes #1803 based upon @nfrasser's work.

packages/bindings/lib/poller.js

@@ -1,12 +1,12 @@
 const debug = require('debug')
 const logger = debug('serialport/bindings/poller')
 const EventEmitter = require('events')
-const FDPoller = require('bindings')('bindings.node').Poller
+const PollerBindings = require('bindings')('bindings.node').Poller
 
 const EVENTS = {
-  UV_READABLE: 1,
-  UV_WRITABLE: 2,
-  UV_DISCONNECT: 4,
+  UV_READABLE: 0b0001,
+  UV_WRITABLE: 0b0010,
+  UV_DISCONNECT: 0b0100,
 }
 
 function handleEvent(error, eventFlag) {
@@ -35,7 +35,7 @@ function handleEvent(error, eventFlag) {
  * Polls unix systems for readable or writable states of a file or serialport
  */
 class Poller extends EventEmitter {
-  constructor(fd) {
+  constructor(fd, FDPoller = PollerBindings) {
     logger('Creating poller')
     super()
     this.poller = new FDPoller(fd, handleEvent.bind(this))

packages/bindings/lib/poller.test.js

@@ -0,0 +1,60 @@
+const Poller = require('./poller')
+
+class MockPollerBidnings {
+  constructor(fd, callback) {
+    this.fd = fd
+    this.callback = callback
+  }
+  poll(flag) {
+    this.lastPollFlag = flag
+    setImmediate(() => this.callback(null, flag))
+  }
+}
+
+class ErrorPollerBindings {
+  constructor(fd, callback) {
+    this.fd = fd
+    this.callback = callback
+  }
+  poll(flag) {
+    this.lastPollFlag = flag
+    setImmediate(() => this.callback(new Error('oh no!'), flag))
+  }
+}
+
+describe('Poller', () => {
+  it('constructs', () => {
+    new Poller(1, MockPollerBidnings)
+  })
+  it('can listen to the readable event', done => {
+    const poller = new Poller(1, MockPollerBidnings)
+    poller.once('readable', err => {
+      assert.equal(err, null)
+      assert.equal(poller.poller.lastPollFlag, 1)
+      done(err)
+    })
+  })
+  it('can listen to the writable event', done => {
+    const poller = new Poller(1, MockPollerBidnings)
+    poller.once('writable', err => {
+      assert.equal(err, null)
+      assert.equal(poller.poller.lastPollFlag, 2)
+      done(err)
+    })
+  })
+  it('can listen to the disconnect event', done => {
+    const poller = new Poller(1, MockPollerBidnings)
+    poller.once('disconnect', err => {
+      assert.equal(err, null)
+      assert.equal(poller.poller.lastPollFlag, 4)
+      done(err)
+    })
+  })
+  it('reports errors on callback', done => {
+    const poller = new Poller(1, ErrorPollerBindings)
+    poller.once('readable', err => {
+      assert.notEqual(err, null)
+      done()
+    })
+  })
+})

packages/bindings/src/poller.cpp

@@ -49,22 +49,29 @@ void Poller::stop() {
   }
 }
 
+int Poller::_stop() {
+  return uv_poll_stop(poll_handle);
+}
+
 void Poller::onData(uv_poll_t* handle, int status, int events) {
   Nan::HandleScope scope;
   Poller* obj = static_cast<Poller*>(handle->data);
   v8::Local<v8::Value> argv[2];
+
+  // if Error
   if (0 != status) {
     // fprintf(stdout, "OnData Error status=%s events=%d\n", uv_strerror(status), events);
     argv[0] = v8::Exception::Error(Nan::New<v8::String>(uv_strerror(status)).ToLocalChecked());
     argv[1] = Nan::Undefined();
+    obj->_stop(); // doesn't matter if this errors
   } else {
-    // fprintf(stdout, "OnData status=%d events=%d\n", status, events);
+    // fprintf(stdout, "OnData status=%d events=%d subscribed=%d\n", status, events, obj->events);
     argv[0] = Nan::Null();
     argv[1] = Nan::New<v8::Integer>(events);
+    // remove triggered events from the poll
+    int newEvents = obj->events & ~events;
+    obj->poll(newEvents);
   }
-  // remove triggered events from the poll
-  int newEvents = obj->events & ~events;
-  obj->poll(newEvents);
 
   obj->callback.Call(2, argv, obj);
 }

packages/bindings/src/poller.h

@@ -22,6 +22,7 @@ class Poller : public Nan::ObjectWrap, public Nan::AsyncResource {
   ~Poller();
   void poll(int events);
   void stop();
+  int _stop();
 
   static NAN_METHOD(New);
   static NAN_METHOD(poll);