Client in C

The first of the two clients that give this atlas its name: a real terminal client for the chat, in C, talking the exact WebSocket protocol built in websocket-protocol-from-scratch. The interesting problem here isn't the network code — it's the UI loop. A chat client has two independent sources of activity, keyboard input and incoming network messages, and neither can be allowed to block the other; this branch builds that loop with poll/select, parses WebSocket frames from the client side (which has its own asymmetry from the server side — a client masks its outgoing frames, a server doesn't), and adds reconnection with exponential backoff so a dropped connection doesn't mean a dead client.

Planned notes

• The client-side WebSocket handshake: sending the Upgrade request, generating Sec-WebSocket-Key, and verifying the server's Sec-WebSocket-Accept
• Parsing frames from the client side: what's symmetric with the server implementation and what isn't (masking direction, primarily)
• A non-blocking terminal UI: raw mode input, and why line-buffered stdin breaks a chat client
• The poll/select loop serving keyboard input and socket data at the same time, without a dedicated thread for either
• Rendering incoming messages without corrupting whatever the user is currently typing
• Handling ping/pong and unsolicited close frames from the server correctly while the user is mid-input
• Detecting a dropped connection and reconnecting with exponential backoff instead of a tight retry loop
• Resuming into a room's state (presence, recent history) after a reconnect, not just re-opening the socket
• A minimal .chatrc for server address, room, and display name
• Comparing this client's code size and complexity directly against the TypeScript client in the next branch

Core sources

• Atlas I and II's terminal I/O material — continuation of the non-blocking stdin handling patterns used there.
• man poll, man select — the loop primitives for this client.
• RFC 6455 — the client-side sections specifically (masking direction, close-handshake initiation from a client).

Connects to: WebSocket Protocol from Scratch · Client in TypeScript