HTTP Over UDP Control API

• Client_udp()
  Client_udp maintains a UDP connection to the server. When called by the proxy, this function sends either HTTP request or HTTP done. Particularly after sending HTTP request, it waits for HTTP ack from the server, so that the proxy can join the multicast group and start to listen.
• Server_udp()
  It receives HTTP request and HTTP done from the proxy. If receiving HTTP request, it determines whether to create a new multicast group or not and keeps track of the number of members. If the multicast group for the request URL is created or exists, it sends HTTP ack to the proxy. It continues to call the multicast function until the number of members in the multicast group becomes zero. On receiving http DONE, it removes the member from the group.