This was going to be a statement in support, read the classics / rfc793. Priors being you should definitely implement http from the RFC a la 199x, and:

I assumed rfc793 was shorter than 9293; false. 9293 is significantly shorter.

9293 also has a lot of implementation notes from the past.. many years of folks that have done this.

So yeah, 9293. Seems like a solid rec.