Some code improvements

* Rewrite empty string checks more idiomatically.
* Change strings.ToLower comparisons to strings.EqualFold.
* Rewrite switch statement with only one case as if.

proxy/http/server.go

@@ -120,11 +120,11 @@ Start:
 	}
 
 	defaultPort := net.Port(80)
-	if strings.ToLower(request.URL.Scheme) == "https" {
+	if strings.EqualFold(request.URL.Scheme, "https") {
 		defaultPort = net.Port(443)
 	}
 	host := request.Host
-	if len(host) == 0 {
+	if host == "" {
 		host = request.URL.Host
 	}
 	dest, err := http_proto.ParseHost(host, defaultPort)
@@ -137,7 +137,7 @@ Start:
 		Status: log.AccessAccepted,
 	})
 
-	if strings.ToUpper(request.Method) == "CONNECT" {
+	if strings.EqualFold(request.Method, "CONNECT") {
 		return s.handleConnect(ctx, request, reader, conn, dest, dispatcher)
 	}
 
@@ -211,7 +211,7 @@ func (s *Server) handleConnect(ctx context.Context, request *http.Request, reade
 var errWaitAnother = newError("keep alive")
 
 func (s *Server) handlePlainHTTP(ctx context.Context, request *http.Request, writer io.Writer, dest net.Destination, dispatcher routing.Dispatcher) error {
-	if !s.config.AllowTransparent && len(request.URL.Host) <= 0 {
+	if !s.config.AllowTransparent && request.URL.Host == "" {
 		// RFC 2068 (HTTP/1.1) requires URL to be absolute URL in HTTP proxy.
 		response := &http.Response{
 			Status:        "Bad Request",
@@ -235,7 +235,7 @@ func (s *Server) handlePlainHTTP(ctx context.Context, request *http.Request, wri
 	http_proto.RemoveHopByHopHeaders(request.Header)
 
 	// Prevent UA from being set to golang's default ones
-	if len(request.Header.Get("User-Agent")) == 0 {
+	if request.Header.Get("User-Agent") == "" {
 		request.Header.Set("User-Agent", "")
 	}
 

proxy/vmess/inbound/inbound.go

@@ -167,7 +167,7 @@ func (h *Handler) AddUser(ctx context.Context, user *protocol.MemoryUser) error
 }
 
 func (h *Handler) RemoveUser(ctx context.Context, email string) error {
-	if len(email) == 0 {
+	if email == "" {
 		return newError("Email must not be empty.")
 	}
 	if !h.usersByEmail.Remove(email) {

proxy/vmess/validator.go

@@ -149,7 +149,7 @@ func (v *TimedUserValidator) Remove(email string) bool {
 	email = strings.ToLower(email)
 	idx := -1
 	for i, u := range v.users {
-		if strings.ToLower(u.user.Email) == email {
+		if strings.EqualFold(u.user.Email, email) {
 			idx = i
 			break
 		}