Use master for connect() on empty slaves pool.

Internally the replication class uses this order to pick which server
it should connect to: current connection, one of the slaves, master.

If there is at least 1 slave, connect() will not fail even if master
is undefined. If there are no slaves, connect() will pick master. If
there are no connections registered for replication, connect() will
fail immediatly.

src/Connection/Aggregate/MasterSlaveReplication.php

@@ -53,16 +53,6 @@ class MasterSlaveReplication implements ReplicationInterface
         $this->strategy = $strategy ?: new ReplicationStrategy();
     }
 
-    /**
-     * Checks if one master and at least one slave have been defined.
-     */
-    protected function check()
-    {
-        if (!isset($this->master) || !$this->slaves) {
-            throw new \RuntimeException('Replication needs one master and at least one slave.');
-        }
-    }
-
     /**
      * Resets the connection state.
      */
@@ -156,8 +146,6 @@ class MasterSlaveReplication implements ReplicationInterface
      */
     public function switchTo($connection)
     {
-        $this->check();
-
         if (!$connection instanceof NodeConnectionInterface) {
             $connection = $this->getConnectionById($connection);
         }
@@ -242,9 +230,12 @@ class MasterSlaveReplication implements ReplicationInterface
      */
     public function connect()
     {
-        if ($this->current === null) {
-            $this->check();
-            $this->current = $this->pickSlave();
+        if (!$this->current) {
+            if (!$this->current = $this->pickSlave()) {
+                if (!$this->current = $this->getMaster()) {
+                    throw new ClientException("No available connection for replication");
+                }
+            }
         }
 
         $this->current->connect();

tests/Predis/Connection/Aggregate/MasterSlaveReplicationTest.php

@@ -65,8 +65,8 @@ class MasterSlaveReplicationTest extends PredisTestCase
 
     /**
      * @group disconnected
-     * @expectedException \RuntimeException
-     * @expectedExceptionMessage Replication needs one master and at least one slave.
+     * @expectedException \Predis\ClientException
+     * @expectedExceptionMessage No available connection for replication
      */
     public function testThrowsExceptionOnEmptyReplication()
     {
@@ -76,26 +76,18 @@ class MasterSlaveReplicationTest extends PredisTestCase
 
     /**
      * @group disconnected
-     * @expectedException \RuntimeException
-     * @expectedExceptionMessage Replication needs one master and at least one slave.
      */
-    public function testThrowsExceptionOnMissingMaster()
+    public function testConnectsToOneOfSlaves()
     {
-        $replication = new MasterSlaveReplication();
-        $replication->add($this->getMockConnection('tcp://host2?alias=slave1'));
+        $master = $this->getMockConnection('tcp://host1?alias=master');
+        $master->expects($this->never())->method('connect');
 
-        $replication->connect();
-    }
+        $slave = $this->getMockConnection('tcp://host2?alias=slave1');
+        $slave->expects($this->once())->method('connect');
 
-    /**
-     * @group disconnected
-     * @expectedException \RuntimeException
-     * @expectedExceptionMessage Replication needs one master and at least one slave.
-     */
-    public function testThrowsExceptionOnMissingSlave()
-    {
         $replication = new MasterSlaveReplication();
-        $replication->add($this->getMockConnection('tcp://host1?alias=master'));
+        $replication->add($master);
+        $replication->add($slave);
 
         $replication->connect();
     }
@@ -103,19 +95,15 @@ class MasterSlaveReplicationTest extends PredisTestCase
     /**
      * @group disconnected
      */
-    public function testConnectForcesConnectionToOneOfSlaves()
+    public function testConnectsToMasterOnMissingSlaves()
     {
         $master = $this->getMockConnection('tcp://host1?alias=master');
-        $master->expects($this->never())->method('connect');
-
-        $slave = $this->getMockConnection('tcp://host2?alias=slave1');
-        $slave->expects($this->once())->method('connect');
 
         $replication = new MasterSlaveReplication();
         $replication->add($master);
-        $replication->add($slave);
 
         $replication->connect();
+        $this->assertSame($master, $replication->getCurrent());
     }
 
     /**