Trailer

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The Trailer response 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.

Note: The TE request header needs to be set to "trailers" to allow trailer fields.

Header type	Request header, Response header, Content header
Forbidden header name	yes

Syntax

http

Trailer: header-names

Directives

header-names

HTTP header fields which will be present in the trailer part of chunked messages. These header fields are disallowed:

message framing headers (e.g., Transfer-Encoding and Content-Length),
routing headers (e.g., Host),
request modifiers (e.g., controls and conditionals, like Cache-Control, Max-Forwards, or TE),
authentication headers (e.g., Authorization or Set-Cookie),
or Content-Encoding, Content-Type, Content-Range, and Trailer itself.

Examples

Chunked transfer encoding using a trailing header

In this example, the Expires header is used at the end of the chunked message and serves as a trailing header.

http

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
Expires: Wed, 21 Oct 2015 07:28:00 GMT\r\n
\r\n

Specifications

Specification
HTTP Semantics # field.trailer
HTTP/1.1 # chunked.trailer.section

Browser compatibility

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