Mongoose is only selecting for the listening socket, so the comparison there isn't particularly valid. Mongoose scales as well as threads on its platform scale.

Mongoose also does a fair bit more than your software does, including SSL, CGI, HTTP Authorization, and file uploads.

Neither of them, frankly, are particularly trustworthy in their present state (Mongoose has apparently actually been audited by someone, but it too stores lengths in signed u64s). But Mongoose, for all its extra functionality, is actually somewhat smaller than yours.

I'm glad you're playing with this and wish you the best of luck, and would only urge caution about advocating that people adopt this code (or Mongoose). Most developers would almost always be better off with a better tested server, or one implemented entirely in a high-level language.