Switch to next slave on -LOADING error response.

This prevents an early failure of the command execution on the client
when one slave gets back online but is still loading the dataset from
disk (when this happens, Redis returns the -LOADING error response).

This commit fixes #280.

src/Connection/Aggregate/MasterSlaveReplication.php

@@ -19,6 +19,7 @@ use Predis\Connection\FactoryInterface;
 use Predis\Connection\NodeConnectionInterface;
 use Predis\Replication\MissingMasterException;
 use Predis\Replication\ReplicationStrategy;
+use Predis\Response\ErrorInterface as ResponseErrorInterface;
 
 /**
  * Aggregate connection handling replication of Redis nodes configured in a
@@ -431,7 +432,12 @@ class MasterSlaveReplication implements ReplicationInterface
     {
         RETRY_COMMAND: {
             try {
-                $response = $this->getConnection($command)->$method($command);
+                $connection = $this->getConnection($command);
+                $response = $connection->$method($command);
+
+                if ($response instanceof ResponseErrorInterface && $response->getErrorType() === 'LOADING') {
+                    throw new ConnectionException($connection, "Redis is loading the dataset in memory [$connection]");
+                }
             } catch (ConnectionException $exception) {
                 $connection = $exception->getConnection();
                 $connection->disconnect();

tests/Predis/Connection/Aggregate/MasterSlaveReplicationTest.php

@@ -15,6 +15,7 @@ use Predis\Connection;
 use Predis\Command;
 use Predis\Profile;
 use Predis\Replication\ReplicationStrategy;
+use Predis\Response;
 use PredisTestCase;
 
 /**
@@ -682,6 +683,50 @@ class MasterSlaveReplicationTest extends PredisTestCase
         $replication->executeCommand($cmdSet);
     }
 
+    /**
+     * @group disconnected
+     */
+    public function testDiscardsSlaveWhenRespondsLOADINGAndExecutesReadOnlyCommandOnNextSlave()
+    {
+        $master = $this->getMockConnection('tcp://host1?alias=master');
+        $master->expects($this->never())
+               ->method('executeCommand');
+
+        $slave1 = $this->getMockConnection('tcp://host2?alias=slave1');
+        $slave1->expects($this->once())
+               ->method('executeCommand')
+               ->with($this->isRedisCommand(
+                   'EXISTS', array('key')
+               ))
+               ->will($this->returnValue(
+                   new Response\Error('LOADING')
+               ));
+
+        $slave2 = $this->getMockConnection('tcp://host3?alias=slave2');
+        $slave2->expects($this->once())
+               ->method('executeCommand')
+               ->with($this->isRedisCommand(
+                   'EXISTS', array('key')
+               ))
+               ->will($this->returnValue(1));
+
+        $replication = new MasterSlaveReplication();
+
+        $replication->add($master);
+        $replication->add($slave1);
+        $replication->add($slave2);
+
+        $replication->switchTo($slave1);
+
+        $response = $replication->executeCommand(
+            Command\RawCommand::create('exists', 'key')
+        );
+
+        $this->assertSame(1, $response);
+        $this->assertNull($replication->getConnectionById('slave1'));
+        $this->assertSame($slave2, $replication->getConnectionById('slave2'));
+    }
+
     /**
      * @group disconnected
      * @expectedException \Predis\Connection\ConnectionException