krossbow-websocket-core/org.hildan.krossbow.websocket/WebSocketCloseCodes/REQUIRED_EXTENSION

REQUIRED_EXTENSION

const val REQUIRED_EXTENSION: Int = 1010(source)

"1010 indicates that an endpoint (client) is terminating the connection because it has expected the server to negotiate one or more extension, but the server didn't return them in the response message of the WebSocket handshake. The list of extensions that are needed SHOULD appear in the /reason/ part of the Close frame. Note that this status code is not used by the server, because it can fail the WebSocket handshake instead."