Add WritableStream which is useful for sinks

Author: igorw

ThroughStream.php

@@ -2,8 +2,6 @@
 
 namespace React\Stream;
 
-use Evenement\EventEmitter;
-
 class ThroughStream extends ReadableStream implements WritableStreamInterface
 {
     private $pipeSource;

WritableStream.php

@@ -0,0 +1,51 @@
+<?php
+
+namespace React\Stream;
+
+use Evenement\EventEmitter;
+
+class WritableStream extends EventEmitter implements WritableStreamInterface
+{
+    public $closed = false;
+    private $pipeSource;
+
+    public function __construct()
+    {
+        $this->on('pipe', array($this, 'handlePipeEvent'));
+    }
+
+    public function handlePipeEvent($source)
+    {
+        $this->pipeSource = $source;
+    }
+
+    public function write($data)
+    {
+    }
+
+    public function end($data = null)
+    {
+        if (null !== $data) {
+            $this->write($data);
+        }
+
+        $this->close();
+    }
+
+    public function isWritable()
+    {
+        return !$this->closed;
+    }
+
+    public function close()
+    {
+        if ($this->closed) {
+            return;
+        }
+
+        $this->closed = true;
+        $this->emit('end', array($this));
+        $this->emit('close', array($this));
+        $this->removeAllListeners();
+    }
+}