🔗 HTTP is not simple

I often hear or see people claim that HTTP is a simple protocol. Primarily of course from people without much experience or familiarity with actual implementations. I think I personally also had thoughts in that style back when I started working with the protocol.

After personally having devoted soon three decades on writing client-side code doing HTTP and having been involved in the IETF on all the HTTP specs produced since 2008 or so, I think I am in a decent position to give a more expanded view on it. HTTP is not a simple protocol. Far from it. Even if we presume that people actually mean HTTP/1 when they say that.

HTTP/1 may appear simple because of several reasons: it is readable text, the most simple use case is not overly complicated and existing tools like curl and browsers help making HTTP easy to play with.

The HTTP idea and concept can perhaps still be considered simple and even somewhat ingenious, but the actual machinery is not.

But yes, you can telnet to a HTTP/1 server and enter a GET / command manually and see a response. However I don’t think that is enough to qualify the entire thing as simple.

I don’t believe anyone has tried to claim that HTTP/2 or HTTP/3 are simple. In order to properly implement version two or three, you pretty much have to also implement version one so in that regard they are accumulating complexity and bring quite a lot of extra challenges in their own respective specifications.

Let me elaborate on some aspects of the HTTP/1 protocol that make me say it is not simple.