On 07/02/2017 08:11 PM, Vinnie Falco via Boost wrote:
To my understanding, chunk-extensions are a rare niche use-case with meaning only to applications using a custom interpretation at each end of the connection. In fact 5 years ago the IETF almost deprecated them: https://trac.ietf.org/trac/httpbis/ticket/343
That was scary reading, because HTTPbis seemed to be unaware that such deprecation would break some of IETF's own standards, e.g. RFC 3507.
On the other hand, I do not have significant expertise with HTTP servers; if a compelling use-case presents itself this is an aspect of the library which may be improved, in a backward-compatible way.
Chunk extensions were originally designed for per-chunk signatures. I do not know how extensively this is used. Another use-case that is used in practice is for in-band meta-data. Consider an Internet radio station that sends a constant stream of audio. When a new track is played this will be signaled by meta-data telling the track title, artist name, etc. Some audio codec formats embed this meta-data into the stream itself (e.g. MP3 ID3 tags), while others do not. In the latter case, chunk extensions are used to carry the meta-data.