Upgrade upgrades the HTTP server connection to the WebSocket protocol.

This function is deprecated, use websocket.Upgrader instead.

The application is responsible for checking the request origin before calling Upgrade. An example implementation of the same origin policy is:

if req.Header.Get("Origin") != "http://"+req.Host {
	http.Error(w, "Origin not allowed", 403)

If the endpoint supports subprotocols, then the application is responsible for negotiating the protocol used on the connection. Use the Subprotocols() function to get the subprotocols requested by the client. Use the Sec-Websocket-Protocol response header to specify the subprotocol selected by the application.

The responseHeader is included in the response to the client's upgrade request. Use the responseHeader to specify cookies (Set-Cookie) and the negotiated subprotocol (Sec-Websocket-Protocol).

The connection buffers IO to the underlying network connection. The readBufSize and writeBufSize parameters specify the size of the buffers to use. Messages can be larger than the buffers.

If the request is not a valid WebSocket handshake, then Upgrade returns an error of type HandshakeError. Applications should handle this error by replying to the client with an HTTP error response.