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type Response struct {
	// As of Go 1.12, the Body will also implement io.Writer
	// on a successful "101 Switching Protocols" response,
	// as used by WebSockets and HTTP/2's "h2c" mode.
	Body io.ReadCloser
}

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// readResponse reads an HTTP response (or two, in the case of "Expect:
// 100-continue") from the server. It returns the final non-100 one.
// trace is optional.
func (pc *persistConn) readResponse(rc requestAndChan, trace *httptrace.ClientTrace) (resp *Response, err error) {
	if resp.isProtocolSwitch() {
		resp.Body = newReadWriteCloserBody(pc.br, pc.conn)
	}

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// isProtocolSwitchResponse reports whether the response code and
// response header indicate a successful protocol upgrade response.
func isProtocolSwitchResponse(code int, h Header) bool {
	return code == StatusSwitchingProtocols && isProtocolSwitchHeader(h)
}


// isProtocolSwitchHeader reports whether the request or response header
// is for a protocol switch.
func isProtocolSwitchHeader(h Header) bool {
	return h.Get("Upgrade") != "" &&
		httpguts.HeaderValuesContainsToken(h["Connection"], "Upgrade")
}