gistfile1.txt

# Socket.io Chat App

## 1. Connection & Identity Registration

- Client connects with a username
- Server accepts or rejects the connection
- Server assigns a socket ID
- User is removed from state on disconnect

### Topics
- `io.on("connection")`
- `socket.id`
- `socket.handshake.auth`
- `io.use(...)`
- `disconnect` / `disconnecting`
- Disconnect reason

## 2. Namespaces 

- `/chat` — normal chat behavior
- `/admin` — read server-originated monitoring events only

### Topics
- `io.of("/namespace")`
- Namespace-level `connection`
- Namespace-specific middleware
- Namespace isolation
- Server-only emits

## 3. Room Membership

- Clients can join and leave named rooms
- Server tracks room membership
- Messages to rooms are allowed only for members

### Topics
- `socket.join(room)`
- `socket.leave(room)`
- `socket.rooms`
- Default socket ID room

## 4. Direct Messaging

Client sends a direct message to another client

### Topics
- Implicit socket ID rooms
- `io.to(socketId).emit(...)`

## 5. Room Messaging (Group Chat)

Client sends a message to a room to all members of that room

### Topics
- `io.to(room).emit(...)`
- `io.in(room).emit(...)`
- Room-scoped broadcasting

## 6. Global Messaging

Client sends a message to all connected clients

### Topics
- `io.emit(...)`
- Namespace-wide broadcast

## 7. Broadcast-Except-Sender Messaging

Client sends a message to everyone except themselves
Server excludes sender from delivery

### Topics
- `socket.broadcast.emit(...)`

## 8. Acknowledged Messaging

- Client sends a message
- Server validates message payload
- Server responds with:
  - success acknowledgment
  - error acknowledgment

### Topics
- Event acknowledgements
- Callback-based responses
- `socket.timeout(ms)`

## 9. Volatile Events (Typing Indicators)

Clients emit typing indicators, delivery is not guaranteed

### Topics
- `socket.volatile.emit(...)`

## 10. Presence Tracking

Server tracks total connected users and users per room Presence updates are emitted on:
- connect
- room join
- room leave
- disconnect

### Topics
- Connection lifecycle hooks
- `disconnecting` timing
- Server-originated emits

## 11. Reconnection & State Recovery

Client reconnects automatically and restores user identity and room membership

### Topics
- `socket.recovered`
- `connectionStateRecovery`
- Reconnection handling

## 12. Error Emission

Invalid actions emit structured error events with code and context

### Topics
- Custom error events
- Error propagation patterns