Add accessor for reading individual files.

This method is not part of the PSR7 interfaces, but I think it is
a useful addition as it makes reading files out of the request much
simpler.

src/Network/Request.php

@@ -1691,6 +1691,22 @@ public function getAttributes()
         return $this->attributes + $emulated;
     }
 
+    /**
+     * Get the uploaded file from a dotted path.
+     *
+     * @param string $path The dot separated path to the file you want.
+     * @return null|Psr\Http\Message\UploadedFileInterface
+     */
+    public function getUploadedFile($path)
+    {
+        $file = Hash::get($this->uploadedFiles, $path);
+        if (!$file instanceof UploadedFile) {
+            return null;
+        }
+
+        return $file;
+    }
+
     /**
      * Get the array of uploaded files from the request.
      *

tests/TestCase/Network/RequestTest.php

@@ -550,6 +550,38 @@ public function testWithUploadedFiles()
         $this->assertSame(['picture' => $file], $new->getUploadedFiles());
     }
 
+    /**
+     * Test getting a single file
+     *
+     * @return void
+     */
+    public function testGetUploadedFile()
+    {
+        $file = new UploadedFile(
+            __FILE__,
+            123,
+            UPLOAD_ERR_OK,
+            'test.php',
+            'text/plain'
+        );
+        $request = new Request();
+        $new = $request->withUploadedFiles(['picture' => $file]);
+        $this->assertNull($new->getUploadedFile(''));
+        $this->assertSame($file, $new->getUploadedFile('picture'));
+
+        $new = $request->withUploadedFiles([
+            'pictures' => [
+                [
+                    'image' => $file
+                ]
+            ]
+        ]);
+        $this->assertNull($new->getUploadedFile('pictures'));
+        $this->assertNull($new->getUploadedFile('pictures.0'));
+        $this->assertNull($new->getUploadedFile('pictures.1'));
+        $this->assertSame($file, $new->getUploadedFile('pictures.0.image'));
+    }
+
     /**
      * Test replacing files with an invalid file
      *