Chat Application Protocol

The table below shows the protocol of the chat application used in the Lab.

Message	Sent by	Description
HELLO-FROM <name>\n	Client	First hand-shake message. The client sends this in an attempt to log in.
HELLO <name>\n	Server	Second hand-shake message. The server sends this if the handshake (i.e., log-in) is successful.
IN-USE\n	Server	Sent during handshake if the user cannot log in because the chosen username is already in use.
BUSY\n	Server	Sent during handshake if the user cannot log in because the maximum number of clients has been reached.
LIST\n	Client	Request for all currently logged-in users.
LIST-OK <name1>,...,<namen>\n	Server	A list containing all currently logged-in users.
SEND <name> <msg>\n	Client	A chat message for a user with username name. Note that the message cannot contain the newline character, because it is used as the message delimiter.
SEND-OK\n	Server	Response to a client if their ‘SEND’ message is processed successfully.
BAD-DEST-USER\n	Server	Sent in response to a SEND message to indicate that the destination user is not currently logged in.
DELIVERY <name> <msg>\n	Server	A chat message from a user with username name.
BAD-RQST-HDR\n	Server	Sent if the last message received from the client contains an error in the header.
BAD-RQST-BODY\n	Server	Sent if the last message received from the client contains an error in the body.