ECEN 602 MP2 — TCP Simple Broadcast Chat (SBCP)

A chat server and client implementing the Simple Broadcast Chat Protocol (SBCP).

Team Roles

Member	Role
Chiahsiang Shyu	Client implementation, client test cases
Lian Chu	Server implementation, server test cases

Build

make          # builds ./server and ./client
make clean    # removes binaries and object files

Requires g++ on a standard Linux system.

Usage

Server

./server <server_ip> <server_port> <max_clients>

Argument	Description
server_ip	Kept for the required command-line format; the server listens on all local IPv4 and IPv6 addresses regardless of this value
server_port	Port to listen on (1024–65535 recommended)
max_clients	Maximum number of clients in the chat room, should be an integer between 1-30

Client

./client <username> <server_ip> <server_port>

Argument	Description
username	Chat name, 1–16 characters, must be unique in the room, case sensitive
server_ip	Server address: IPv4, IPv6, or hostname (e.g. 127.0.0.1, ::1, localhost)
server_port	Server port

Type a line and press Enter to send a message. Press Ctrl+D to leave the chat.

Example

./server 127.0.0.1 9000 3
./client alice 127.0.0.1 9000
./client bob   127.0.0.1 9000

Architecture

Message format. Every SBCP message is a 4-byte header (Version:9 | Type:7 | Length:16) followed by zero or more TLV attributes (Type:16 | Length:16 | Payload). All multi-byte fields are sent in network byte order. Version and Type are packed into one uint16_t (Version(9b) | Type(7b)).

Server. Uses getaddrinfo(NULL, port) with AI_PASSIVE to create two listening sockets, one IPv4 and one IPv6, both on the given port. It watches both listening sockets and every connected client socket with select(). New connections are accepted; JOIN registers a username (duplicates are rejected); SEND is converted to FWD and broadcast to all other clients; a read() returning 0 means the client left, and its resources and username are released.

Client. Watches stdin and the server socket with select(). Sends each line from stdin to the server, and decodes and displays messages from the server.

Bonus Functions

• OFFLINE/ONLINE: Whenever a user joins or disconnects, the server also send an ONLINE/OFFLINE message to all the users
• ACK: When a user joins, the server sends an ACK message telling current server user count(including the new user), as well as a list of id of all online user(excluding the new user).
• NAK: When a request for join is declined by the server, the server sends a NAK message to the declined user, including the reason why the user is declined.
• IDLE: A user is considered active for both joining and sending a message. If the last active time of an user exceeds 10 sec, an IDLE message is sent from the idle user to the server, and the server would then forward this information to all the other users (idle or not) in server
• IPV6/IPV4: As mentioned before, this work supports both ipv6 and ipv4.

Errata

• One message per read(). If the header Length does not match the number of bytes read, the message is discarded (as required by the spec). If TCP delivers two server messages in a single read, both are discarded.
• Long input. Input longer than 512 characters is split by fgets(); the remainder is treated as a separate message.
• Pasting multiple lines. Because fgets() buffers stdin, pasting several lines at once may delay the later lines until the next keypress. Normal typing is not affected.
• IDLE timing. The idle timer has 1-second resolution, so IDLE is sent 9–10 seconds after the last message. IDLE is sent once per idle period, and is only reset by sending a chat message (receiving messages does not reset it).
• IDLE is not replayed. A client that joins after another client became idle will not be told about it.