Add formatter interface

Author: sagikazarmark

src/Formatter.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace Http\Message;
+
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
+
+/**
+ * Formats a request and/or a response as a string.
+ *
+ * @author Márk Sági-Kazár <[email protected]>
+ */
+interface Formatter
+{
+    /**
+     * Formats a request.
+     *
+     * @param RequestInterface $request
+     *
+     * @return string
+     */
+    public function formatRequest(RequestInterface $request);
+
+    /**
+     * Formats a response.
+     *
+     * @param ResponseInterface $response
+     *
+     * @return string
+     */
+    public function formatResponse(ResponseInterface $response);
+}