Twitter Chat
Design and implement a program that allows people to chat with each
other, using short messages.
A participant uses a chat space, which is a window divided into two spaces:
the top half for listing the messages received and the bottom half for
listing the messages sent plus the one message the participant is currently
entering.
The two halves display the messages in historical order, with the most
recent message received/sent at the bottom. When the either half is full of
messages, drop the least recent lines.
Each message is at most one line of text, i.e., the width of the
window, which is 400 pixels. A line consists of two pieces:
-- an address
-- a message
where the address is separated from the message with a ":". The user sends
a message by typing the name of a participant, followed by ":" and the text
of the message. The message is sent when the user hits "\r" (return) or
when the line is too wide for the screen.
A message whose recipient is "*" is broadcast to every current participant.
Otherwise a message is sent to the designated recipient, if the string is
the valid name of a current participant.
Each received message is displayed like those that are sent, with an sender
followed by ":" and the text of the message. If the message went to all
participants, the sender's name is followed by an asterisk "*".
;; -----------------------------------------------------------------------------
protocol:
Sending and receiving message occur without any synchronization.
Clients send messages of the form (list String String) to the server. The
first string designates the recipient of the message, the second string
represents the message text.
The Chat Server swaps the name of the recipient of a message with that of
the sender; if the message is to be broadcast, it adds an asterisk "*".
The server sends sends the resulting messages to the designated recipient.
If the recipient name of a message is "*", then the server sends it all
current participants.
SERVER CLIENT (name1) CLIENT (name2)
| | |
| name1 | % name by which client is known |
| <-------------------- | |
| | |
| (list name2 txt) | |
| <-------------------- | |
| | |
| | (list name1 txt) |
| --------------------------------------------------------> |
| | |
| | |
;; Client2ServerMsg = (list String String)
;; interp. recipient followed by message text
;; Server2ClientMsg = (list String String)
;; interp. sender followed by message text.
;; -----------------------------------------------------------------------------
chat server: receive message, swap recipient for sender & send message(s)
;; -----------------------------------------------------------------------------
chat world:
+------------------------------------------------------------------+
| from: text text text text text text |
| from*: text text text text text text |
| ... |
+------------------------------------------------------------------+
| to: text text text text text text |
| *: text text text text text text |
| ... |
+------------------------------------------------------------------+
