WebSocket

WebSocket is a computer communications protocol that provides full-duplex, bidirectional communication channels over a single, long-lived TCP connection. It is standardized as RFC 6455 by the Internet Engineering Task Force and is designed to enable real-time interaction on the web. A WebSocket connection begins with an HTTP/1.1 based handshake in which the client requests an upgrade to the WebSocket protocol and the server agrees to switch protocols.

After the handshake, the connection remains open and data are exchanged as frames. Each frame carries a small piece of data, and frames can encode text or binary data. Client-to-server frames are masked for security, while server-to-client frames are not. The protocol supports control frames such as ping and pong to keep the connection alive and to check liveness. A close frame terminates the connection gracefully.

WebSocket can run over TLS as wss://, providing encryption and server authentication. Subprotocols may be negotiated during the handshake to specify higher-level message formats (for example, json or chat). Extensions such as permessage-deflate may be negotiated to reduce payload sizes. Security considerations include same-origin policy considerations, origin checks, and the potential impact of long-lived connections on servers and proxies. Some network intermediaries require explicit support for WebSocket, otherwise the connection may be downgraded or blocked.

In web browsers, the WebSocket API provides an interface (for example, new WebSocket(url) with onopen, onmessage, onerror, and onclose) for real-time applications. On the server side, many languages provide libraries to implement the protocol. WebSocket is commonly used for chat, collaborative editing, live feeds, online gaming, and other real-time applications, offering lower latency and reduced overhead compared to HTTP polling or server-sent events. It is not intended for one-way streaming of media from server to client; for media, WebRTC or other protocols may be more appropriate.