rpc: add PeerInfo (#24255)

This replaces the sketchy and undocumented string context keys for HTTP requests
with a defined interface. Using string keys with context is discouraged because
they may clash with keys created by other packages.

We added these keys to make connection metadata available in the signer, so this
change also updates signer/core to use the new PeerInfo API.

rpc/websocket.go

@@ -60,7 +60,7 @@ func (s *Server) WebsocketHandler(allowedOrigins []string) http.Handler {
 			log.Debug("WebSocket upgrade failed", "err", err)
 			return
 		}
-		codec := newWebsocketCodec(conn)
+		codec := newWebsocketCodec(conn, r.Host, r.Header)
 		s.ServeCodec(codec, 0)
 	})
 }
@@ -197,7 +197,7 @@ func DialWebsocketWithDialer(ctx context.Context, endpoint, origin string, diale
 			}
 			return nil, hErr
 		}
-		return newWebsocketCodec(conn), nil
+		return newWebsocketCodec(conn, endpoint, header), nil
 	})
 }
 
@@ -235,12 +235,13 @@ func wsClientHeaders(endpoint, origin string) (string, http.Header, error) {
 type websocketCodec struct {
 	*jsonCodec
 	conn *websocket.Conn
+	info PeerInfo
 
 	wg        sync.WaitGroup
 	pingReset chan struct{}
 }
 
-func newWebsocketCodec(conn *websocket.Conn) ServerCodec {
+func newWebsocketCodec(conn *websocket.Conn, host string, req http.Header) ServerCodec {
 	conn.SetReadLimit(wsMessageSizeLimit)
 	conn.SetPongHandler(func(appData string) error {
 		conn.SetReadDeadline(time.Time{})
@@ -250,7 +251,16 @@ func newWebsocketCodec(conn *websocket.Conn) ServerCodec {
 		jsonCodec: NewFuncCodec(conn, conn.WriteJSON, conn.ReadJSON).(*jsonCodec),
 		conn:      conn,
 		pingReset: make(chan struct{}, 1),
+		info: PeerInfo{
+			Transport:  "ws",
+			RemoteAddr: conn.RemoteAddr().String(),
+		},
 	}
+	// Fill in connection details.
+	wc.info.HTTP.Host = host
+	wc.info.HTTP.Origin = req.Get("Origin")
+	wc.info.HTTP.UserAgent = req.Get("User-Agent")
+	// Start pinger.
 	wc.wg.Add(1)
 	go wc.pingLoop()
 	return wc
@@ -261,6 +271,10 @@ func (wc *websocketCodec) close() {
 	wc.wg.Wait()
 }
 
+func (wc *websocketCodec) peerInfo() PeerInfo {
+	return wc.info
+}
+
 func (wc *websocketCodec) writeJSON(ctx context.Context, v interface{}) error {
 	err := wc.jsonCodec.writeJSON(ctx, v)
 	if err == nil {