Updated SapiEmitterTest to changes for #90

Since a stream's `getSize()` **CAN** return `null`, we need to **SKIP**
injection of the `Content-Length` header when it does. The
`CallbackStream` introduced in #90 leverages this feature, so we
**MUST** support it.

Author: weierophinney

src/Response/SapiEmitter.php

@@ -30,7 +30,11 @@ public function emit(ResponseInterface $response, $maxBufferLevel = null)
         }
 
         if (! $response->hasHeader('Content-Length')) {
-            $response = $response->withHeader('Content-Length', (string) $response->getBody()->getSize());
+            // PSR-7 indicates int OR null for the stream size; for null values,
+            // we will not auto-inject the Content-Length.
+            if (null !== $response->getBody()->getSize()) {
+                $response = $response->withHeader('Content-Length', (string) $response->getBody()->getSize());
+            }
         }
 
         $this->emitStatusLine($response);

test/Response/SapiEmitterTest.php

@@ -10,6 +10,8 @@
 namespace ZendTest\Diactoros\Response;
 
 use PHPUnit_Framework_TestCase as TestCase;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\StreamInterface;
 use Zend\Diactoros\Response;
 use Zend\Diactoros\Response\SapiEmitter;
 use ZendTest\Diactoros\TestAsset\HeaderStack;
@@ -57,4 +59,21 @@ public function testEmitsMessageBody()
         $this->expectOutputString('Content!');
         $this->emitter->emit($response);
     }
+
+    public function testDoesNotInjectContentLengthHeaderIfStreamSizeIsUnknown()
+    {
+        $stream = $this->prophesize('Psr\Http\Message\StreamInterface');
+        $stream->__toString()->willReturn('Content!');
+        $stream->getSize()->willReturn(null);
+        $response = (new Response())
+            ->withStatus(200)
+            ->withBody($stream->reveal());
+
+        ob_start();
+        $this->emitter->emit($response);
+        ob_end_clean();
+        foreach (HeaderStack::stack() as $header) {
+            $this->assertNotContains('Content-Length:', $header);
+        }
+    }
 }