Added discovery strategy (#13)

src/Httplug/DiscoveryStrategy.php

@@ -0,0 +1,43 @@
+<?php
+
+namespace Nyholm\Psr7\Httplug;
+
+use Http\Discovery\Strategy\DiscoveryStrategy as HttplugDiscoveryStrategy;
+use Nyholm\Psr7\Factory\MessageFactory;
+use Nyholm\Psr7\Factory\StreamFactory;
+use Nyholm\Psr7\Factory\UriFactory;
+
+/**
+ * A discovery strategy to use our factories with HTTPlug auto discovery.
+ *
+ * @author Tobias Nyholm <tobias.nyholm@gmail.com>
+ */
+class DiscoveryStrategy implements HttplugDiscoveryStrategy
+{
+    /**
+     * @var array
+     */
+    private static $classes = [
+        'Http\Message\MessageFactory' => [
+            ['class' => MessageFactory::class],
+        ],
+        'Http\Message\StreamFactory' => [
+            ['class' => StreamFactory::class],
+        ],
+        'Http\Message\UriFactory' => [
+            ['class' => UriFactory::class],
+        ],
+    ];
+
+    /**
+     * {@inheritdoc}
+     */
+    public static function getCandidates($type)
+    {
+        if (isset(self::$classes[$type])) {
+            return self::$classes[$type];
+        }
+
+        return [];
+    }
+}