"libh2o is written in C"... Somewhat sad to see that in this day and age.
What is sad about using C? I'm using plenty of C programs/applicactions/tools each day which work great!
It works, there's no question about that.
But it is also a language that's obviously very hard to write correct code in, considering the myriads of CVEs out there.
Since we've got languages like Rust now, you don't really need to sacrifice performance for security anymore, which is why it's sad to see a project that could have "gone with the times" instead going with the old-but-tried approach.