and server roles</a>: clients send requests and servers send back responses.
        When a client and server have established a connection, the client sends
        a series of requests while the server sends back at least one response for
        each received request in the order those requests were received.
      </p>
<p>
        A request or response is an <a href="https://tools.ietf.org/html/rfc7230#section-3" target="_top">HTTP
        message</a> (referred to hereafter as "message") having two
    