Structured Field Values for HTTP is an upcoming RFC from the HTTP Wording Group defining a set of well-defined data types to use in HTTP headers and trailers.

This new format will improve the interoperability and the safety of HTTP by allowing to create generic parsers and serializers suitable for all HTTP headers. It is already used in the wild, for instance for the new security headers supported by Google Chrome (Sec-Fetch-Dest etc), the Signature proposal in Prefer-Push or in Vulcain.

After the RFC publication, it would be nice to be able to parse and generate such headers directly using the standard library.

I proposed a patch adding support for this spec in #41045. The code is also available as a standalone library: https://github.com/dunglas/httpsfv