fix(sentinel): improve the error message when connection to sentinel is rejected

Closes #280

Author: luin

lib/connectors/sentinel_connector.js

@@ -37,6 +37,7 @@ SentinelConnector.prototype.connect = function (callback) {
   }
 
   var _this = this;
+  var lastError;
   connectToNext();
 
   function connectToNext() {
@@ -50,7 +51,11 @@ SentinelConnector.prototype.connect = function (callback) {
       }
       if (typeof retryDelay !== 'number') {
         debug('All sentinels are unreachable and retry is disabled, emitting error...');
-        return callback(new Error('All sentinels are unreachable.'));
+        var error = 'All sentinels are unreachable.';
+        if (lastError) {
+          error += ' Last error: ' + lastError.message;
+        }
+        return callback(new Error(error));
       }
       debug('All sentinels are unreachable. Retrying from scratch after %d', retryDelay);
       setTimeout(connectToNext, retryDelay);
@@ -68,9 +73,11 @@ SentinelConnector.prototype.connect = function (callback) {
         callback(null, _this.stream);
       } else if (err) {
         debug('failed to connect to sentinel %s:%s because %s', endpoint.host, endpoint.port, err);
+        lastError = err;
         connectToNext();
       } else {
-        debug('connected to sentinel %s:%s successfully, but got a invalid reply: %s', endpoint.host, endpoint.port, resolved);
+        debug('connected to sentinel %s:%s successfully, but got a invalid reply: %s',
+          endpoint.host, endpoint.port, resolved);
         connectToNext();
       }
     });

lib/redis/parser.js

@@ -148,7 +148,7 @@ exports.returnReply = function (reply) {
     item = this.commandQueue.shift();
     if (!item) {
       return this.emit('error',
-        new Error('Command queue state error. If you can reproduce this, please report it.' + reply.toString()));
+        new Error('Command queue state error. If you can reproduce this, please report it. Last reply: ' + reply.toString()));
     }
     if (_.includes(Command.FLAGS.ENTER_SUBSCRIBER_MODE, item.command.name)) {
       this.condition.subscriber = new SubscriptionSet();

test/functional/sentinel.js

@@ -129,6 +129,31 @@ describe('sentinel', function () {
       });
     });
 
+    it('should reject when sentinel is rejected', function (done) {
+      var sentinel = new MockServer(27379, function (argv) {
+        if (argv[0] === 'sentinel' && argv[1] === 'get-master-addr-by-name') {
+          return new Error('just rejected');
+        }
+      });
+
+      var redis = new Redis({
+        sentinels: [
+          { host: '127.0.0.1', port: '27379' }
+        ],
+        name: 'master',
+        sentinelRetryStrategy: null,
+        lazyConnect: true
+      });
+
+      redis.connect().then(function () {
+        throw new Error('Expect `connect` to be thrown');
+      }).catch(function (err) {
+        expect(err.message).to.eql('All sentinels are unreachable. Last error: just rejected');
+        redis.disconnect();
+        sentinel.disconnect(done);
+      });
+    });
+
     it('should connect to the next sentinel if getting master failed', function (done) {
       var sentinel = new MockServer(27379, function (argv) {
         if (argv[0] === 'sentinel' && argv[1] === 'get-master-addr-by-name') {