Add missing transfer encoding header for chunked

Author: joelwurtz

spec/ContentLengthPluginSpec.php

@@ -37,6 +37,7 @@ function it_streams_chunked_if_no_size(RequestInterface $request, StreamInterfac
 
         $stream->getSize()->shouldBeCalled()->willReturn(null);
         $request->withBody(Argument::type('Http\Message\Encoding\ChunkStream'))->shouldBeCalled()->willReturn($request);
+        $request->withAddedHeader('Transfer-Encoding', 'chunked')->shouldBeCalled()->willReturn($request);
 
         $this->handleRequest($request, function () {}, function () {});
     }

src/ContentLengthPlugin.php

@@ -24,6 +24,7 @@ public function handleRequest(RequestInterface $request, callable $next, callabl
             if (null === $stream->getSize()) {
                 $stream = new ChunkStream($stream);
                 $request = $request->withBody($stream);
+                $request = $request->withAddedHeader('Transfer-Encoding', 'chunked');
             } else {
                 $request = $request->withHeader('Content-Length', $stream->getSize());
             }