Fetch updated slots map from node indicated by -MOVED response.

This optimization makes it possible to fetch the slots map directly
from the server indicated by the -MOVED response eliminating the need
to use a random node in the pool, which in turn could require Predis
to open a new and useless connection.

src/Connection/Aggregate/RedisCluster.php

@@ -175,14 +175,16 @@ class RedisCluster implements ClusterInterface, IteratorAggregate, Countable
     }
 
     /**
-     * Generates the current slots map by fetching the cluster configuration to
-     * one of the nodes by leveraging the CLUSTER NODES command.
+     * Generates an updated slots map fetching the cluster configuration using
+     * the CLUSTER NODES command against the specified node or a random one from
+     * the pool.
      *
+     * @param  NodeConnectionInterface $connection Optional connection instance.
      * @return array
      */
-    public function askSlotsMap()
+    public function askSlotsMap(NodeConnectionInterface $connection = null)
     {
-        if (!$connection = $this->getRandomConnection()) {
+        if (!$connection && !$connection = $this->getRandomConnection()) {
             return array();
         }
 
@@ -408,7 +410,7 @@ class RedisCluster implements ClusterInterface, IteratorAggregate, Countable
         }
 
         if ($this->askSlotsMap) {
-            $this->askSlotsMap();
+            $this->askSlotsMap($connection);
         }
 
         $this->move($connection, $slot);

tests/Predis/Connection/Aggregate/RedisClusterTest.php

@@ -680,25 +680,23 @@ class RedisClusterTest extends PredisTestCase
     {
         $cmdGET = Command\RawCommand::create('GET', 'node:1001');
         $rspMOVED = new Response\Error('MOVED 1970 127.0.0.1:6380');
-
-        $cmdCLUSTER = Command\RawCommand::create('CLUSTER', 'SLOTS');
         $rspSlotsArray = array(
             array(0   ,  8191, array('127.0.0.1', 6379)),
             array(8192, 16383, array('127.0.0.1', 6380)),
         );
 
         $connection1 = $this->getMockConnection('tcp://127.0.0.1:6379');
-        $connection1->expects($this->at(2))
+        $connection1->expects($this->once())
                     ->method('executeCommand')
                     ->with($cmdGET)
                     ->will($this->returnValue($rspMOVED));
-        $connection1->expects($this->at(3))
-                    ->method('executeCommand')
-                    ->with($cmdCLUSTER)
-                    ->will($this->returnValue($rspSlotsArray));
 
         $connection2 = $this->getMockConnection('tcp://127.0.0.1:6380');
-        $connection2->expects($this->once())
+        $connection2->expects($this->at(0))
+                    ->method('executeCommand')
+                    ->with($this->isRedisCommand('CLUSTER', array('SLOTS')))
+                    ->will($this->returnValue($rspSlotsArray));
+        $connection2->expects($this->at(2))
                     ->method('executeCommand')
                     ->with($cmdGET)
                     ->will($this->returnValue('foobar'));