Implement async chat server and CLI client

[SonicDev111]

Summary

Full implementation of the simple-chat assignment: an async TCP chat server and interactive CLI client, built with Tokio.

Author

Shivendra

Architecture

The project is a Cargo workspace with three crates:

• protocol — shared message types (ClientMessage, ServerMessage) serialized as newline-delimited JSON via serde_json
• server — async TCP server binary backed by a server_lib library crate
• client — async CLI client binary

Server

• Built on Tokio — fully non-blocking, each connection is handled in its own spawned task
• Room manages connected users in a HashMap<String, broadcast::Sender> protected by a std::sync::Mutex (held only for bookkeeping, never across await points)
• Each user gets their own tokio::sync::broadcast channel — messages are fanned out to all other users with zero copying of the sender's own messages
• Usernames are enforced to be unique — duplicate join attempts receive an Error message and are dropped
• Clean disconnect handling: both explicit Leave messages and TCP disconnects trigger leave() cleanup and notify remaining users

Client

• Accepts --host, --port, --username as CLI flags or CHAT_HOST, CHAT_PORT, CHAT_USERNAME environment variables (via clap)
• Automatically connects and sends a Join on startup
• Two concurrent async tasks: one reads from the server and prints messages, one reads stdin and sends commands
• Supported commands:
  • send <MSG> — broadcasts a message to the room
  • leave — sends a Leave message and exits cleanly

Tests

19 tests total, all passing:

Suite	Count
protocol unit tests	7
server_lib::room unit tests	5
Integration tests (real TCP)	7

Integration tests cover: single user join, duplicate username rejection, message broadcast, leave notification, join notification, sender does not receive own message, and multi-user chat.

Bonus

• Pre-commit hook at hooks/pre-commit — runs cargo fmt --check, cargo clippy -- -D warnings, and cargo build
• GitHub Actions CI (.github/workflows/ci.yml) — runs on every push and PR:
  • check job: fmt, clippy, build, and full test suite
  • integration job: starts the server, connects via nc, sends a message, and verifies clean exit

Checklist

• Async server with Tokio
• Unique usernames enforced
• Broadcast to all users except sender
• Clean leave / disconnect handling
• Async CLI client with env var + CLI arg support
• send <MSG> and leave commands
• Unit tests
• Integration tests
• cargo fmt — no issues
• cargo clippy -- -D warnings — zero warnings
• Pre-commit hook
• GitHub Actions CI