Can an persistent HTTP client send more than one request at a time?

Question

I am writing a HTTP proxy server and I noticed that many clients use the "Connection: Keep-Alive" header to keep a persistent connection. Is it possible that the client sends another HTTP request before the server processes the first?

For example, the client sends "GET / HTTP/1.1" but before the server has a chance to respond, the client sends "GET /favicon.ico HTTP/1.1". Is that possible? Or will the client pause for the response before sending the second request?

Also, when using a persistent connection, is it safe to assume all requests through that connection will have the same "Host: " header?

Answer 1

"Also, when using a persistent connection, is it safe to assume all requests through that connection will have the same "Host: " header?"

I don't think so, see HTTPbis P1, Section 2.2:

Recipients MUST consider every message in a connection in isolation; because HTTP is a stateless protocol, it cannot be assumed that two requests on the same connection are from the same client or share any other common attributes. In particular, intermediaries might mix requests from different clients into a single server connection. Note that some existing HTTP extensions (e.g., [RFC4559]) violate this requirement, thereby potentially causing interoperability and security problems.