A concurrent TCP chat server written in Go.
go run server.goConnects on port 9000. Use telnet or nc to join:
nc localhost 9000| Command | Description |
|---|---|
/users |
List connected users |
/stats |
Show your message count |
/help |
Show available commands |
/quit |
Leave the chatroom |
/msg <user> <body> |
Send a direct message to another user |
The server keeps the most recent 50 broadcast messages in an in-memory ring buffer. After a user connects, picks a username, and enters the chat, those buffered messages are replayed to that client before the server announces their join to everyone else.
This history currently includes public chat traffic and join/leave broadcasts. It does not include private messages or sender-only command responses like /users, /stats, or /help.
Single hub goroutine for shared state. All mutations to the clients map — registration, lookup, deletion — go through a single hub() goroutine via channels (msgChan, registerChan, leaveChan, userListChan). This avoids mutexes entirely and makes the concurrency model easy to reason about: only one goroutine ever touches shared state.
Per-client write goroutine. Each client gets a dedicated writeLoop() goroutine that drains a buffered writeChan. Writing to a TCP connection blocks; isolating it per-client means a slow or stalled client doesn't block the hub or other clients' message delivery.
Channel-typed requests with reply channels. Operations that need a response (e.g. registering a username, listing users) use a request struct with an embedded reply chan field. The caller blocks on the reply channel after sending the request, and the hub responds directly. This keeps request/response semantics clean without callbacks or shared memory.
BroadcastType enum. The Message struct carries a BroadcastType (ToAll, ToSender, ToAllButSender, ToUser) rather than having separate channel types for each delivery pattern. The broadcast() function switches on this field, making it easy to add new delivery modes.
- Chat rooms —
/join <room>and/leave, with broadcasts scoped to room membership - Ping / keepalive — periodic writes to detect and evict stale connections
- Rate limiting — per-client token bucket to prevent message spam
- Admin commands — first-connected client gets operator status;
/kick <user>and/ban <user>