当 websocket 已经可用时，是否有理由需要 HTTP2？

Question

Is there a reason why HTTP2 is required when websocket is already available?

Nathan Aw (Singapore)

Answer 1

Why do we need HTTP/2 when we have WebSockets? Well why did we need WebSockets when we have TCP? Or even IP? Protocols are basically agreed standards that can be implemented by independent parties.

WebSockets are good for two way communication but are mostly unstructured on top of that and application specific. HTTP is (mostly) a series of one-way requests to the server (ask for a resource, receive an answer) — though HTTP/2 enhances that slightly with HTTP/2 push and the binary framing layer could in theory be used more for proper two way push. So the full two way nature of WebSockets — the very thing they are good at — is not really needed for most HTTP use cases.

Looking at HTTP, it has various extras that WebSockets does not have. Including defined methods, headers and compression. This allows a well-defined understanding between various HTTP implementations to facilitate communications for its use case including features like multiplexing , caching, compression, redirects, error handling... etc. If you had to reinvent all of those on top of WebSockets (which is a very raw protocol), you'd end up with an HTTP/2 like protocol.

Could HTTP/2 have used WebSockets to act as it's underlying transport layer? Possibly, but that's an unnecessary extra level of abstraction (IP->TCP->WS->HTTP2->HTTP), not to mention that websockets are often established over HTTP initially. HTTP is big enough to have its own transport protocol so in fact they've gone the other way and specified WebSockets over HTTP/2 .

Finally, it should also be noted that HTTP/2 does not make Web Sockets obselete either. They are different and with different advantages and disadvantages.