Attempt to overwrite response headers when gorilla/websocket upgrade fails

[maxeth]

In transport/websocket.go, when Upgrader.Upgrade() returns an error, we try to send a http.StatusBadRequest

func (t Websocket) Do(w http.ResponseWriter, r *http.Request, exec graphql.GraphExecutor) {
	t.injectGraphQLWSSubprotocols()
	ws, err := t.Upgrader.Upgrade(w, r, http.Header{}) // <-- already writes errors
	if err != nil {
                // error to request already written
		log.Printf("unable to upgrade %T to websocket %s: ", w, err.Error())
		SendErrorf(w, http.StatusBadRequest, "unable to upgrade") // <-- overwriting headers. Seems unnecessary?
		return
	}

but the gorilla Upgrade func itself already writes HTTP errors if Upgrader.Upgrade() returns an error, quoting the source of v1.5.0:

// If the upgrade fails, then Upgrade replies to the client with an HTTP error
// response.
func (u *Upgrader) Upgrade(w http.ResponseWriter, r *http.Request, responseHeader http.Header) (*Conn, error)

so we end up attempting to overwrite response headers every time an upgrade fails (e.g. when CheckOrigin returns false, a HTTP 403 Forbidden is written in Upgrader.Upgrade(), but we attempt to overwrite it with 400 Bad Request).

It's nothing dramatic, but my console is full of:

[GIN-debug] [WARNING] Headers were already written. Wanted to override status code 403 with 400