Exports drain event when queue finishes processing (fixes #272 #271 #306)

Thank you @grncdr and @littlebee

Author: dresende

lib/Connection.js

@@ -31,6 +31,7 @@ Connection.prototype.connect = function(cb) {
 
     this._socket.on('error', this._handleNetworkError.bind(this));
     this._protocol.on('unhandledError', this._handleProtocolError.bind(this));
+    this._protocol.on('drain', this._handleProtocolDrain.bind(this));
     this._protocol.on('end', this._handleProtocolEnd.bind(this));
   }
 
@@ -128,6 +129,10 @@ Connection.prototype._handleProtocolError = function(err) {
   this.emit('error', err);
 };
 
+Connection.prototype._handleProtocolDrain = function(err) {
+  this.emit('drain', err);
+};
+
 Connection.prototype._handleProtocolEnd = function(err) {
   this.emit('end', err);
 };

lib/protocol/Protocol.js

@@ -195,6 +195,7 @@ Protocol.prototype._dequeue = function() {
 
   var sequence = this._queue[0];
   if (!sequence) {
+    this.emit('drain');
     return;
   }
 

test/integration/connection/test-drain-event.js

@@ -0,0 +1,20 @@
+var common     = require('../../common');
+var connection = common.createConnection();
+var assert     = require('assert');
+
+connection.connect();
+
+var got_drain = false;
+
+connection.on('drain', function() {
+  got_drain = true;
+});
+
+connection.query("SELECT 1", function(err) {
+  assert.equal(got_drain, false);
+  assert.ok(!err);
+  process.nextTick(function() {
+    assert.equal(got_drain, true);
+    connection.end();
+  });
+});