[joe_guy]

I had never heard of HTTP trailers. So FYI

> 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.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Tr...

[lloeki]

I suppose even fewer people have heard that Transfer-Encoding: chunked supports chunk extensions, which allows one to supply arbitrary metadata without trailers.

https://datatracker.ietf.org/doc/html/rfc2616#section-3.6.1

Ever went to some site that generates compressed downloads or database exports on the fly, got no progress bar as a result, and were severely annoyed by that lack of feedback? I was, so I used chunk extensions to submit a draft to emit progress information dynamically:

https://datatracker.ietf.org/doc/html/draft-lnageleisen-http...

As noted at the end of the draft, this could be generalized and extended to have additional capabilities such as in flight integrity checks, or whatever you can think of.

[k__]

Haven't headers and trailers been renamed in the recent past?

[akshayshah]

Yes, slightly - RFC 9110 ("HTTP Semantics") calls them "header fields" and "trailer fields," and it calls "headers" and "trailers" colloquialisms. In a nod to gRPC-style usage, the section on trailer fields even says, "Trailer fields can be useful for supplying...post-processing status information."

https://www.rfc-editor.org/rfc/rfc9110.html#header.fields

https://www.rfc-editor.org/rfc/rfc9110.html#trailer.fields