How to do an HTTP duplex handler in Go?

Question

I heard here that

once you write anything in the response, the request body will be closed which prevents you from reading anything from it

If that is true, how can I write a proper duplex handler that is able to read from the request body, make some kind of transformation, and then write to the response body, in a streaming fashion just like people do in node.js ?

Answer 1

I ended up managing to do this with http.Hijacker.

After the request is made and the request headers are parsed, I can read from *http.Request.Body, then hijack the connection and write to it, at the same time, like this:

hj, ok := w.(http.Hijacker)
if !ok {
    http.Error(w, "hijacking not supported", 500)
    return
}

conn, bufrw, err := hj.Hijack()
if err != nil {
    http.Error(w, err.Error(), 500)
    return
}
defer conn.Close()

And then conn is a net.Conn which is the underlying TCP connection to the client, bufrw is a *bufio.ReadWriter, and to write the response without closing the body all I have to do is

_, err = bufrw.WriteString("HTTP/1.1 200 OK\n\n")
_, err = bufrw.WriteString("this")
_, err = bufrw.WriteString("is")
_, err = bufrw.WriteString("the")
_, err = bufrw.WriteString("response")
_, err = bufrw.WriteString("body")

And then I'm not sure about this but maybe someone can complete the answer, it's a good idea to flush the buffers down the connection once in a while with

err := bufrw.Flush()