WebSockets

In short: WebSockets are a persistent, bidirectional connection between browser and server over which both sides can send messages at any time.

In more detail: Normal HTTP works as question and answer: the browser asks, the server answers, then it is over. For chats, live games, stock prices or shared editing that is too sluggish. A WebSocket stays open, and the server can send on its own (“push”).

In Depth

• Set-up: the browser starts with a normal HTTP request and asks for an “upgrade”. Afterwards the connection continues as a WebSocket (address ws:// or encrypted wss://, see TLS).
• Advantages: very low latency, little overhead per message, real time in both directions.
• Disadvantages: the open connection occupies server resources (scaling is harder). If it drops, the client must reconnect.
• Alternatives: polling (asking again and again), server-sent events (server → client only) and services that wrap WebSockets.
• Security: check the origin (Origin), authenticate users, validate messages like any input, use wss://.

See also: port, API, sockets