Remember the context here. This is for the browser, not some universal solution. There's going to be the main page, which is probably HTML, and that's going to trigger CSS, JavaScript, and images.

HTTP responses can be comfortabley modelled as status line, headers, and body. Status line ends with \r\n. Headers end with \r\n\r\n, and don't need to be parsed until they've been received. They do need to be parsed before the body, to get either the length of the body, or that the body is chunked.

The spec says don't expect headers to take up too much space, and the status line should be tiny (relatively).

I've been thinking too much like a server - that I'm going to get random hits that I've got to handle right now. But I'm a client. I'm asking servers to send me data, I look at that data at my leasure, and then maybe I ask for more.