Networking

WebSocket

Persistent bi-directional connection over a single TCP socket.

In plain terms

Upgrades from HTTP via 101 Switching Protocols. The default for browser-side real-time before HTTP/3 streams.

Origin

RFC 6455 (2011). Replaced the long-polling and Comet hacks of the late 2000s. Browser support became universal around 2012.

Where it shows up in production

Slack / Discord / Zoom chat A persistent WebSocket per client. Tens of millions concurrent at peak for big platforms.
Trading platforms Market-data feeds push tick-by-tick updates over WebSocket — sub-millisecond from edge to UI.

On Semicolony

Sources & further reading

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