HTTP Chunked Encoding. Need an example of 'Trailer' mentioned in SPEC

Question

I am writing an HTTP parser for a transparent proxy. What is stumping me is the Trailer: mentioned in the specs for Transfer-Encoding: chunked. What does it look like?

Normally, a HTTP chunked ends like this.

0\r\n
\r\n

What I am confused about is how to detect the end of the chunk if there is some sort of trailing headers...

UPDATE: I believe that a simple \r\n\r\n i.e. an empty line is enough to detect the end of trailing headers... Is that correct?

Answer 1

Below is a copy of an example trailer I copied from The TCP/IP Guide site.

As we can see, if we want to use trailer header, we need add a "Trailer:header_name" header field with a header name and then add the trailer header entity after chunked body area.

We can add 0 or more trailer headers in a HTTP body per the RFC. Section 4.1.2 of RFC7230 bans the use of following headers in trailer header area:

A sender MUST NOT generate a trailer that contains a field necessary for message framing (e.g., Transfer-Encoding and Content-Length), routing (e.g., Host), request modifiers (e.g., controls and conditionals in Section 5 of RFC7231), authentication (e.g., see RFC7235 and RFC6265), response control data (e.g., see Section 7.1 of RFC7231), or determining how to process the payload (e.g., Content-Encoding, Content-Type, Content-Range, and Trailer).

This means we can use other standard headers and custom headers in trailer header area.