node: allow websocket and HTTP on the same port (#20810)

This change makes it possible to run geth with JSON-RPC over HTTP and
WebSocket on the same TCP port. The default port for WebSocket
is still 8546. 

    geth --rpc --rpcport 8545 --ws --wsport 8545

This also removes a lot of deprecated API surface from package rpc.
The rpc package is now purely about serving JSON-RPC and no longer
provides a way to start an HTTP server.

node/rpcstack_test.go

@@ -0,0 +1,38 @@
+package node
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/rpc"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewWebsocketUpgradeHandler_websocket(t *testing.T) {
+	srv := rpc.NewServer()
+
+	handler := NewWebsocketUpgradeHandler(nil, srv.WebsocketHandler([]string{}))
+	ts := httptest.NewServer(handler)
+	defer ts.Close()
+
+	responses := make(chan *http.Response)
+	go func(responses chan *http.Response) {
+		client := &http.Client{}
+
+		req, _ := http.NewRequest(http.MethodGet, ts.URL, nil)
+		req.Header.Set("Connection", "upgrade")
+		req.Header.Set("Upgrade", "websocket")
+		req.Header.Set("Sec-WebSocket-Version", "13")
+		req.Header.Set("Sec-Websocket-Key", "SGVsbG8sIHdvcmxkIQ==")
+
+		resp, err := client.Do(req)
+		if err != nil {
+			t.Error("could not issue a GET request to the test http server", err)
+		}
+		responses <- resp
+	}(responses)
+
+	response := <-responses
+	assert.Equal(t, "websocket", response.Header.Get("Upgrade"))
+}