protocol_spec.txt

Chat server protocol spec

Each client connects separately to the chat server's IP address and port

Server accepts the socket from the client and then adds an entry to its internal
list of clients so it can retrieve that socket again for later use
Client issues HELO command followed by a CRLF to say hello (LF on Linux)
Server replies 200 OK CRLF indicating that it has successfully accepted the
new client connection and registered the client in its list of clients
Client issues NICK <nickname> command to register the nickname with the server
of the current chatter.  Nicknames cannot be greater than 15 chars in length, and
may not contain spaces or '@' characters.

Replies:
    201 OK your nickname is <nickname>.   (i.e., success)
    401 Nickname in use.  Choose another.
    402 Nickname is invalid format or length.
    501 No nickname value specified after NICK command.  

NOTE: A client will not receive broadcasted messages until it's issued the HELO command to the server.
A client will not be introduced to the rest of the chat room until the NICK command has been sent
and a 200 OK response was received by that client.

Our chat server has at-mentions and hashtags.  At-mentions begin with '@' followed
by the nickname of another chatter; hashtags can be any phrase with no spaces and no
'@' char preceded by a pound sign '#'.

To send a chat message the client simply sends the content.  The client ends the chat
message by sending a dot (.) by itself on one line.  Each individual line of a chat message
may be no more than 80 characters long.  If the client has not sent the NICK command yet, 
the server will send a "501 No nickname value specified after NICK command" reply in response.
Client SHALL send the NICK command prior to sending ANY chat messages.

All chat messages are sent to all connected clients, including the client that sent it.

To DM another chatter directly, you must send the command
DM <nickname-of-recipient>\r\n

To which the server replies the same as the NICK command.  If '200 OK' is received, then
it's time to send the direct message you want.  Clients simply send the message itself,
followed by a CRLF, and then a dot by itself on a line with another CRLF (this ends the message
and tells the server it's time to send it to the recipient.)  For a DM, only the chatter
with the nickname specified will receive the message.

Final command for a client to end its chat session is:
QUIT\r\n
The server replies:
    200 Goodbye.\r\n
and then disconnects from that chatter and also throws away the internal entry for that
client in its database.

NOTE: Messages from the server beginning with a bang character (i.e., '!') indicate system admin
messages indicating channel status etc.

A typical session is as follows:

C:<connects to server on IP and port number 9000>
C: HELO
S: 200 OK
S: <to all> !Hey everyone, @ENS_Schwartz joined the chat room.
C: NICK astrohart
S: 200 OK your nickname is astrohart.
S: <to all> !Hey everyone, @astrohart joined the chat room.
S: <to all> !Hey everyone, @birdguy343 joined the chat room.
S: <to all> !Hey everyone, @effeater6 left the chat room.
C: The quick #brownfox jumped over the lazy dog.
C: .
S: <to all> @astrohart: The quick #brownfox jumped over the lazy dog.
S: <to all> @ENS_Schwartz: Hahaha @astrohart that is #toofunny. :-)
C: DM ENS_Schwartz
S: <to @astrohart only> 200 OK, what do you want to tell @ENS_Schwartz?
C: You're a psycho.
C: .
S: <to @ENS_Schwartz only> @astrohart: You're a psycho.
C: QUIT
S: <to all EXCEPT @astrohart> !Hey everyone, @astrohart left the chat room.
S: <to @astrohart only> 200 Goodbye.
S: <disconnects>
C: <disconnects>