Add code POOL_ENQUEUELIMIT to error reaching queueLimit

Author: dougwilson

Changes.md

@@ -6,6 +6,7 @@ you spot any mistakes.
 
 ## HEAD
 
+* Add code `POOL_ENQUEUELIMIT` to error reaching `queueLimit`
 * Add `enqueue` event to protocol and connection #381
 * Blacklist unsupported connection flags #881
 * Make only column names enumerable in `RowDataPacket` #549 #895

lib/Pool.js

@@ -58,13 +58,7 @@ Pool.prototype.getConnection = function (cb) {
     });
   }
 
-  if (this.config.queueLimit && this._connectionQueue.length >= this.config.queueLimit) {
-    return cb(new Error('Queue limit reached.'));
-  }
-
-  if (cb && process.domain)
-    cb = process.domain.bind(cb);
-  this._connectionQueue.push(cb);
+  this._enqueueCallback(cb);
 };
 
 Pool.prototype.acquireConnection = function acquireConnection(connection, cb) {
@@ -190,6 +184,25 @@ Pool.prototype.query = function (sql, values, cb) {
   return query;
 };
 
+Pool.prototype._enqueueCallback = function _enqueueCallback(callback) {
+
+  if (this.config.queueLimit && this._connectionQueue.length >= this.config.queueLimit) {
+    process.nextTick(function () {
+      var err = new Error('Queue limit reached.');
+      err.code = 'POOL_ENQUEUELIMIT';
+      callback(err);
+    });
+    return;
+  }
+
+  // Bind to domain, as dequeue will likely occur in a different domain
+  var cb = process.domain
+    ? process.domain.bind(callback)
+    : callback;
+
+  this._connectionQueue.push(cb);
+};
+
 Pool.prototype._purgeConnection = function _purgeConnection(connection) {
   var pool = this;
 

test/unit/pool/test-queue-limit.js

@@ -30,6 +30,7 @@ server.listen(common.fakeServerPort, function (err) {
       assert.ifError(err);
       assert.ok(error);
       assert.equal(error.message, 'Queue limit reached.');
+      assert.equal(error.code, 'POOL_ENQUEUELIMIT');
       server.destroy();
     });
   });