My recollection from circa 2013 is that Node.js at least used to use the nginx HTTP parser, which was a horror of manually-implemented state machine written so

My recollection from circa 2013 is that Node.js at least used to use the nginx HTTP parser, which was a horror of manually-implemented state machine written so in the name of performance, but consequently basically unmaintainable and fairly bug-riddled. And not as fast as it should have been, anyway. (The state machine approach is fine, but it should have used a lot more code generation.) It read the method byte by byte into the state machine, and baulked at unknown methods. Evidently they’ve kept that limitation, whatever they may have changed since in the parser they use (and I think nginx did eventually abandon and replace that parser entirely). (These are my recollections from investigation I did back in 2013 when I was writing the first serious Rust HTTP library.)