WebSocket & Real-Time

Full-duplex communication protocol over a single persistent TCP connection; established via an HTTP upgrade handshake.

"We switched the live dashboard from polling every 5 seconds to a WebSocket connection — latency dropped from 5s to under 50ms."

The initial HTTP GET request with an Upgrade: websocket header that transitions the connection from HTTP to the WebSocket protocol.

"The handshake response returns 101 Switching Protocols — after this the connection is a full-duplex WebSocket channel."

Communication mode where both client and server can send messages independently and simultaneously over the same connection.

"Full-duplex means the server can push a notification to the client at any moment, while the client simultaneously sends user actions — no turn-taking required."

One-way server-to-client streaming over a persistent HTTP connection; simpler than WebSocket for push notifications that flow only from server to client.

"The news feed uses SSE — the server pushes new articles as text/event-stream and the browser's EventSource API handles reconnection automatically."

Client sends a request and the server holds it open until new data is available, then responds and the client immediately sends another request.

"Before WebSocket support was widespread we used long polling — the server held each request for up to 30 seconds before responding with an empty body."

Periodic ping/pong frames exchanged between client and server to keep the connection alive and detect silently dead connections.

"Our server sends a ping frame every 30 seconds — if it receives no pong within 10 seconds it closes and the client reconnects."

The WebSocket binary format where each message has an opcode (text/binary/ping/pong/close), a masking key for client frames, and a variable-length payload header.

"Understanding message framing helps when implementing a custom WebSocket server — the first two bytes encode the opcode, masking flag, and payload length."

Condition where a fast sender produces messages faster than a slow receiver can process them; must be handled to avoid unbounded memory growth.

"The writable stream's write() returned false, signalling backpressure — we paused reading from the WebSocket until the drain event fired."

Named group within a Socket.IO server; a socket can join multiple rooms and events broadcast to a room are received only by its members.

"Each collaborative document gets a room named by its ID — joins, edits, and cursor positions are emitted only to users in that room."

Virtual partition within a Socket.IO server identified by a path like /chat or /admin; sockets in different namespaces cannot communicate directly.

"We use /notifications and /chat as separate namespaces so the notification service can be scaled independently of the chat service."

Simple Text Orientated Messaging Protocol; a text-based messaging protocol that runs over WebSocket for publish/subscribe and point-to-point messaging.

"The Spring Boot backend exposes a STOMP broker endpoint — the JavaScript client subscribes to /topic/prices and receives live market data."

Real-time channel that tracks which users are currently connected; used for online status indicators, typing indicators, and collaborative cursors.

"The presence channel broadcasts join and leave events so every participant's avatar lights up or greys out as teammates connect."

Logic to automatically re-establish a dropped WebSocket connection using exponential backoff with jitter to avoid thundering-herd reconnect storms.

"Our reconnection strategy starts with a 1s delay and doubles it on each failure up to 30s, with ±30% jitter to spread reconnect attempts across clients."

Peer-to-peer channel for transmitting arbitrary binary or text data directly between browsers; no server relay required after the initial signalling.

"File transfer in our collaboration tool uses a WebRTC data channel — large files flow directly peer-to-peer without passing through our server."

The WebSocket connection lifecycle: CONNECTING (0), OPEN (1), CLOSING (2), CLOSED (3). Always check readyState before sending.

"We guard every send call with if (ws.readyState === WebSocket.OPEN) to avoid throwing when the connection is closing."