budgetchat

3: Budget Chat

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Thu, 22 Sep 2022 13:00:00

Modern messaging software uses too many computing resources, so we're going back to basics. Budget Chat is a simple** TCP-based chat room protocol**.

Each message is a single line of ASCII text terminated by a newline character ('\n', or ASCII 10). Clients can send multiple messages per connection. Servers may optionally strip trailing whitespace, such as carriage return characters ('\r', or ASCII 13). All messages are raw ASCII text, not wrapped up in JSON or any other format.

Upon connection

Setting the user's name

When a client connects to the server, it does not yet have a name and is not considered to have joined. The server must prompt the user by sending a single message asking for a name. The exact text of this message is implementation-defined.

Example:

Welcome to budgetchat! What shall I call you?

The first message from a client sets the user's name, which must contain at least 1 character, and must consist entirely of alphanumeric characters (uppercase, lowercase, and digits).

Implementations may limit the maximum length of a name, but must allow at least 16 characters. Implementations may choose to either allow or reject duplicate names.

If the user requests an illegal name, the server may send an informative error message to the client, and the server must disconnect the client, without sending anything about the illegal user to any other clients.

Presence notification

Once the user has a name, they have joined the chat room and the server must announce their presence to other users (see "A user joins" below).

In addition, the server must send the new user a message that lists all present users' names, not including the new user, and not including any users who have already left. The exact text of this message is implementation-defined, but must start with an asterisk ('*'), and must contain the users' names. The server must send this message even if the room was empty.

Example:

- The room contains: bob, charlie, dave
  All subsequent messages from the client are chat messages.

Chat messages

When a client sends a chat message to the server, the server must relay it to all other clients as the concatenation of:

• open square bracket character
• the sender's name
• close square bracket character
• space character
• the sender's message

If "bob" sends "hello", other users would receive "[bob] hello".

Implementations may limit the maximum length of a chat message, but must allow at least 1000 characters.

The server must no_t send the chat message back to the originating client, or to connected clients that have not yet _joined.

For example, if a user called "alice" sends a message saying "Hello, world!", all users except alice would receive:

[alice] Hello, world!

A user joins

When a user joins the chat room by setting an acceptable name, the server must send all other users a message to inform them that the user has joined. The exact text of this message is implementation-defined, but must start with an asterisk ('*'), and must contain the user's name.

Example:

- bob has entered the room

The server must send this message to other users that have already joined, but not to connected clients that have not yet joined.

A user leaves

When a joined user is disconnected from the server for any reason, the server must send all other users a message to inform them that the user has left. The exact text of this message is implementation-defined, but must start with an asterisk ('*'), and must contain the user's name.

Example:

- bob has left the room

The server must send this message to other users that have already joined, but not to connected clients that have not yet joined.

If a client that has not yet joined disconnects from the server, the server must not send any messages about that client to other clients.

Example session

In this example, "-->" denotes messages from the server to Alice's client, and "<--" denotes messages from Alice's client to the server.

--> Welcome to budgetchat! What shall I call you?
<-- alice
--> _ The room contains: bob, charlie, dave
<-- Hello everyone
--> [bob] hi alice
--> [charlie] hello alice
--> _ dave has left the room

Alice connects and sets her name. She is given a list of users already in the room. She sends a message saying "Hello everyone". Bob and Charlie reply. Dave disconnects.

Other requirements

Accept TCP connections.

Make sure you support at least 10 simultaneous clients.