Trailer header

Syntax

Trailer: header-names

Directives

header-names

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

• Content-Encoding, Content-Type, Content-Range, and Trailer
• Authentication headers (e.g., Authorization or Set-Cookie)
• 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)

Examples

Server-Timing as HTTP trailer

Some browsers support showing server timing data in developer tools when the Server-Timing header is sent as a trailer. In the following response, the Trailer header is used to indicate that a Server-Timing header will follow the response body. A metric custom-metric with a duration of 123.4 milliseconds is sent:

HTTP/1.1 200 OK
Transfer-Encoding: chunked
Trailer: Server-Timing

--- response body ---
Server-Timing: custom-metric;dur=123.4

Specifications

Browser compatibility

See also

• Server-Timing
• Transfer-Encoding
• TE
• Chunked transfer encoding