Discussion: Capitalize the header names of outgoing headers.

Although, as per RFC 2616, All the HTTP/1.1 headers should be case-insensitive. However, as a general practice, most of the major web servers have their headers capitalized. Also, some broken HTTP/1.1 implementations do not recognize some specific headers(e.g.: Server header for Apache Benchmark) if they are not properly capitalized. It would be better if the header can be capitalized.

Performance Concerns: Compared to str.lower(), str.title() is slower. However, this can be migrated by adding an LRU Cache into the header capitalization process to solve the problem.

[Lukasa]

I strongly recommend making it possible to emit headers with any capitalisation, while making the current behaviour the default.

The reality is that HTTP implementations that require title cased headers are wrong. Their inability to tolerate them, forcing other implementations to psychically tolerate their preferences, is a bad behaviour and should be punished. However, it should clearly be possible to overrule that behaviour if needed to make an application work.

Note that the “capitalise as a matter of course” servers and clients are on the way out. HTTP/2 forcibly lowercases header names, which means a lot of these bad implementations get fixed as they get support for HTTP/2. So this may be a problem that reduces in scope over time.

A final note: RFC 2616 is dead. Long live RFCs 723[0-3]!

[njsmith]

Preserving the raw headers on incoming messages is tricky. I hear you on case being nice to have in debug output, but on the other hand… preserving non-meaningful case is also the root cause of all these bugs where people accidentally write case-sensitive programs.

One thing I’ve wondered is whether we should explicitly save the raw headers separately as a dedicated debugging feature (e.g. as a raw byte string, so you can see all the whitespace, header case, etc.). There’s also some discussion in https://github.com/python-hyper/h11/issues/92 of doing more normalization of header values, which would be another case where separate debug output might be useful.