Add clear method to pipeline (#749)

* Add clear method to pipeline

Ability to clean pipeline and responses when reusing pipelines.
Allows pipeline to be executed using chunks without out-of-control
increase in memory usage.

* spacing

Co-authored-by: Till Krüss <tillkruss@users.noreply.github.com>

src/Pipeline/Pipeline.php

@@ -225,6 +225,19 @@ class Pipeline implements ClientContextInterface
         return $this->responses;
     }
 
+    /**
+     * Clear the buffer holding all of the commands and responses.
+     *
+     * @return $this
+     */
+    public function clear()
+    {
+        $this->responses = array();
+        $this->pipeline = new \SplQueue();
+
+        return $this;
+    }
+
     /**
      * Returns if the pipeline should throw exceptions on server errors.
      *

tests/Predis/Pipeline/PipelineTest.php

@@ -234,6 +234,59 @@ class PipelineTest extends PredisTestCase
         $this->assertSame(array('one', 'two', 'three', 'four'), $pipeline->execute());
     }
 
+    /**
+     * @group disconnected
+     */
+    public function testClearBuffer()
+    {
+        $connection = $this->getMock('Predis\Connection\NodeConnectionInterface');
+        $connection->expects($this->never())
+            ->method('writeRequest');
+        $connection->expects($this->never())
+            ->method('readResponse')
+            ->will($this->returnCallback($this->getReadCallback()));
+
+        $pipeline = new Pipeline(new Client($connection));
+
+        $pipeline->echo('one');
+        $pipeline->echo('two');
+
+        $pipeline->clear();
+
+        $this->assertSame(array(), $pipeline->execute());
+    }
+
+    /**
+     * @group disconnected
+     */
+    public function testClearResponses()
+    {
+        $connection = $this->getMock('Predis\Connection\NodeConnectionInterface');
+        $connection->expects($this->exactly(4))
+            ->method('writeRequest');
+        $connection->expects($this->exactly(4))
+            ->method('readResponse')
+            ->will($this->returnCallback($this->getReadCallback()));
+
+        $pipeline = new Pipeline(new Client($connection));
+
+        $pipeline->echo('one');
+        $pipeline->echo('two');
+
+        $this->assertSame(array('one', 'two'), $pipeline->execute());
+
+        $pipeline->clear();
+
+        $pipeline->echo('three');
+        $pipeline->echo('four');
+
+        $this->assertSame(array('three', 'four'), $pipeline->execute());
+
+        $pipeline->clear();
+
+        $this->assertSame(array(), $pipeline->execute());
+    }
+
     /**
      * @group disconnected
      */