vapor-docs/3.0/docs/websocket/binary-stream.md

Binary Streams

WebSockets have separate text and binary data flows.

Sending binary input to a WebSocket sends it to the remote. Listening for binary on a WebSocket receives binary (and binary continuation) data from clients.

Sending binary data

Sending a Data or ByteBuffer using a WebSocket sends it to the remote.

webSocket.send(byteBuffer)
webSocket.send(data)

Receiving binary data

Binary data can be read as a ByteBuffer using the following function. Only one closure can read at a time.

webSocket.onBinary { byteBuffer in
  // use the `ByteBuffer`
}

Binary data can also, instead, be used as Foundation's Data. This is less efficient than ByteBuffer but often easier to use.

webSocket.onData { data in
  // use the `Data`
}

You can only use one of the two listeners at a time.