Certain status codes never contain a body length

See https://tools.ietf.org/html/rfc7230#section-3.3.1 and
https://tools.ietf.org/html/rfc7230#section-3.3.2

README.md

@@ -356,12 +356,14 @@ This is just a example you could use of the streaming,
 you could also send a big amount of data via little chunks 
 or use it for body data that needs to calculated.
 
-If the response body is a `string` a `Content-Length` header will be added automatically.
-Unless you specify a `Content-Length` header for a ReactPHP `ReadableStreamInterface`
-response body yourself, HTTP/1.1 responses will automatically use chunked transfer encoding 
-and send the respective header
-(`Transfer-Encoding: chunked`) automatically. The server is responsible for handling
-`Transfer-Encoding` so you SHOULD NOT pass it yourself.
+If the response body is a `string`, a `Content-Length` header will be added
+automatically.
+If the response body is a ReactPHP `ReadableStreamInterface` and you do not
+specify a `Content-Length` header, HTTP/1.1 responses will automatically use
+chunked transfer encoding and send the respective header
+(`Transfer-Encoding: chunked`) automatically.
+The server is responsible for handling `Transfer-Encoding` so you SHOULD NOT
+pass this header yourself.
 If you know the length of your stream body, you MAY specify it like this instead:
 
 ```php
@@ -387,10 +389,18 @@ The `Server` will add the protocol version of the request, so you don't have to.
 
 Any response to a `HEAD` request and any response with a `1xx` (Informational),
 `204` (No Content) or `304` (Not Modified) status code will *not* include a
-message body as per the HTTP spec.
+message body as per the HTTP specs.
 This means that your callback does not have to take special care of this and any
 response body will simply be ignored.
 
+Similarly, any response with a `1xx` (Informational), `204` (No Content) status
+code will *not* include `Content-Length` or `Transfer-Encoding` header as
+these do not apply to these messages.
+Note that a response to a `HEAD` request and any response with a `304` (Not
+Modified) status code MAY include these headers even though
+the message does not contain a response body, because these header would apply
+to the message if the same request would have used an (unconditional) `GET`.
+
 A `Date` header will be automatically added with the system date and time if none is given.
 You can add a custom `Date` header yourself like this:
 

src/Server.php

@@ -336,8 +336,13 @@ public function handleResponse(ConnectionInterface $connection, RequestInterface
             $response = $response->withHeader('Connection', 'close');
         }
 
-        // response to HEAD and 1xx, 204 and 304 responses MUST NOT include a body
+        // response code 1xx and 204 MUST NOT include Content-Length or Transfer-Encoding header
         $code = $response->getStatusCode();
+        if (($code >= 100 && $code < 200) || $code === 204) {
+            $response = $response->withoutHeader('Content-Length')->withoutHeader('Transfer-Encoding');
+        }
+
+        // response to HEAD and 1xx, 204 and 304 responses MUST NOT include a body
         if ($request->getMethod() === 'HEAD' || ($code >= 100 && $code < 200) || $code === 204 || $code === 304) {
             $response = $response->withBody(Psr7Implementation\stream_for(''));
         }

tests/ServerTest.php

@@ -358,7 +358,7 @@ function ($data) use (&$buffer) {
         $this->assertNotContains("bye", $buffer);
     }
 
-    public function testResponseContainsNoResponseBodyForNoContentStatus()
+    public function testResponseContainsNoResponseBodyAndNoContentLengthForNoContentStatus()
     {
         $server = new Server($this->socket, function (RequestInterface $request) {
             return new Response(204, array(), 'bye');
@@ -382,6 +382,7 @@ function ($data) use (&$buffer) {
         $this->connection->emit('data', array($data));
 
         $this->assertContains("HTTP/1.1 204 No Content\r\n", $buffer);
+        $this->assertNotContains("\r\n\Content-Length: 3\r\n", $buffer);
         $this->assertNotContains("bye", $buffer);
     }
 
@@ -409,6 +410,7 @@ function ($data) use (&$buffer) {
         $this->connection->emit('data', array($data));
 
         $this->assertContains("HTTP/1.1 304 Not Modified\r\n", $buffer);
+        $this->assertContains("\r\nContent-Length: 3\r\n", $buffer);
         $this->assertNotContains("bye", $buffer);
     }