Codecs

Codec Negotiation (JSON and MessagePack)

The WebSocket wire format is negotiated at handshake time via the Sec-WebSocket-Protocol header.

Protocol header value	Frame type	Notes
(none) or restnio.json	Text	Default. Envelopes are UTF-8 JSON.
restnio.msgpack	Binary	MessagePack envelopes. Requires optional dep @msgpack/msgpack.

The server negotiates automatically — no extra server-side code required.

JSON (default)

Clients connect without a subprotocol (or explicitly request restnio.json). All message envelopes are plain JSON text frames:

{ "path": "/chat", "params": { "text": "hello" }, "token": "<jwt>" }

MessagePack

Install the optional dependency:

npm install @msgpack/msgpack

Clients connect with the restnio.msgpack subprotocol. Envelopes are binary MessagePack frames. The server uses a first-byte sniff to distinguish codec envelopes from raw binary data.

setBinRoute() always takes priority over the codec sniff. See Binary Routing.

Codec registry

The codec registry is available for inspection or extension:

RestNio.codecs   // inspect registered codecs or add custom ones

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