dns: handle implicit bind DNS errors

cjihrig · cjihrig · commit 5587ff1ccd9b · 2017-01-30T11:48:59.000-05:00
When send() triggers an implicit bind, the send operation is added to an internal queue. If a DNS error occurs during the bind, there is currently no mechanism for clearing the queue other than sending more data. If DNS errors keep occurring, the queue will continue to grow with no upper bound. This commit reports errors with implicit binds, and clears the queue. This should be fine, given the nature of UDP. Refs: nodejs/node-v0.x-archive#8705 Refs: #10902 PR-URL: #11036 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>
diff --git a/lib/dgram.js b/lib/dgram.js
@@ -282,13 +282,27 @@ function enqueue(self, toEnqueue) {
   // event handler that flushes the send queue after binding is done.
   if (!self._queue) {
     self._queue = [];
-    self.once('listening', clearQueue);
+    self.once('error', onListenError);
+    self.once('listening', onListenSuccess);
   }
   self._queue.push(toEnqueue);
   return;
 }
 
 
+function onListenSuccess() {
+  this.removeListener('error', onListenError);
+  clearQueue.call(this);
+}
+
+
+function onListenError(err) {
+  this.removeListener('listening', onListenSuccess);
+  this._queue = undefined;
+  this.emit('error', new Error('Unable to send data'));
+}
+
+
 function clearQueue() {
   const queue = this._queue;
   this._queue = undefined;
diff --git a/test/parallel/test-dgram-implicit-bind-failure.js b/test/parallel/test-dgram-implicit-bind-failure.js
@@ -0,0 +1,55 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const dgram = require('dgram');
+const dns = require('dns');
+
+// Monkey patch dns.lookup() so that it always fails.
+dns.lookup = function(address, family, callback) {
+  process.nextTick(() => { callback(new Error('fake DNS')); });
+};
+
+const socket = dgram.createSocket('udp4');
+let dnsFailures = 0;
+let sendFailures = 0;
+
+process.on('exit', () => {
+  assert.strictEqual(dnsFailures, 3);
+  assert.strictEqual(sendFailures, 3);
+});
+
+socket.on('error', (err) => {
+  if (/^Error: fake DNS$/.test(err)) {
+    // The DNS lookup should fail since it is monkey patched. At that point in
+    // time, the send queue should be populated with the send() operation. There
+    // should also be two listeners - this function and the dgram internal one
+    // time error handler.
+    dnsFailures++;
+    assert(Array.isArray(socket._queue));
+    assert.strictEqual(socket._queue.length, 1);
+    assert.strictEqual(socket.listenerCount('error'), 2);
+    return;
+  }
+
+  if (/^Error: Unable to send data$/.test(err)) {
+    // On error, the queue should be destroyed and this function should be
+    // the only listener.
+    sendFailures++;
+    assert.strictEqual(socket._queue, undefined);
+    assert.strictEqual(socket.listenerCount('error'), 1);
+    return;
+  }
+
+  common.fail(`Unexpected error: ${err}`);
+});
+
+// Initiate a few send() operations, which will fail.
+socket.send('foobar', common.PORT, 'localhost');
+
+process.nextTick(() => {
+  socket.send('foobar', common.PORT, 'localhost');
+});
+
+setImmediate(() => {
+  socket.send('foobar', common.PORT, 'localhost');
+});
