Revision 1111817 of Trailer

<div>{{HTTPSidebar}}</div>

<p>The <strong>Trailer</strong> request header allows the sender to include additional fields at the end of chunked messages in order to supply metadata that might be dynamically generated while the message body is sent, such as a message integrity check, digital signature, or post-processing status.</p>

<div class="note">
<p>The {{HTTPHeader("TE")}} request header needs to be set to "trailers" to allow trailer fields.</p>
</div>

<table class="properties">
 <tbody>
  <tr>
   <th scope="row">Header type</th>
   <td>{{Glossary("Response header")}}</td>
  </tr>
  <tr>
   <th scope="row">{{Glossary("Forbidden header name")}}</th>
   <td>yes</td>
  </tr>
 </tbody>
</table>

<h2 id="Syntax">Syntax</h2>

<pre class="syntaxbox">
Trailer: header-names</pre>

<h2 id="Directives">Directives</h2>

<dl>
 <dt><code>header-names</code></dt>
 <dd>HTTP header fields which will be present in the trailer part of chunked messages. These header fields are <strong>disallowed</strong>:
 <ul>
  <li>message framing headers (e.g., {{HTTPHeader("Transfer-Encoding")}} and {{HTTPHeader("Content-Length")}}),</li>
  <li>routing headers (e.g., {{HTTPHeader("Host")}}),</li>
  <li>request modifiers (e.g., controls and conditionals, like {{HTTPHeader("Cache-Control")}}, {{HTTPHeader("Max-Forwards")}}, or {{HTTPHeader("TE")}}),&nbsp;</li>
  <li>authentication headers (e.g., {{HTTPHeader("Authorization")}} or {{HTTPHeader("Set-Cookie")}}),</li>
  <li>or {{HTTPHeader("Content-Encoding")}}, {{HTTPHeader("Content-Type")}}, {{HTTPHeader("Content-Range")}}, and <code>Trailer</code> itself.</li>
 </ul>
 </dd>
</dl>

<h2 id="Examples">Examples</h2>

<h3 id="Chunked_transfer_encoding_using_a_trailing_header">Chunked transfer encoding using a trailing header</h3>

<p>In this example, the {{HTTPHeader("Expires")}} header is used at the end of the chunked message and serves as a trailing header.</p>

<pre>
HTTP/1.1 200 OK 
Content-Type: text/plain 
Transfer-Encoding: chunked
Trailer: Expires

7\r\n 
Mozilla\r\n 
9\r\n 
Developer\r\n 
7\r\n 
Network\r\n 
0\r\n 
\r\n
Expires: Wed, 21 Oct 2015 07:28:00 GMT</pre>

<h2 id="Specifications">Specifications</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Title</th>
  </tr>
  <tr>
   <td>{{RFC("7230", "Trailer", "4.4")}}</td>
   <td>Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</td>
  </tr>
  <tr>
   <td>{{RFC("7230", "Chunked trailer part", "4.1.2")}}</td>
   <td>Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility">Browser compatibility</h2>

<p class="hidden">The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</p>

<p>{{Compat}}</p>

<h2 id="See_also">See also</h2>

<ul>
 <li>{{HTTPHeader("Transfer-Encoding")}}</li>
 <li>{{HTTPHeader("TE")}}</li>
 <li>
  <p><a href="https://en.wikipedia.org/wiki/Chunked_transfer_encoding">Chunked transfer encoding</a></p>
 </li>
</ul>