add knock option for probe resistance

Author: ginuerzh

cmd/gost/route.go

@@ -438,6 +438,7 @@ func (r *route) GenRouters() ([]router, error) {
 			gost.RetryHandlerOption(node.GetInt("retry")), // override the global retry option.
 			gost.TimeoutHandlerOption(time.Duration(node.GetInt("timeout"))*time.Second),
 			gost.ProbeResistHandlerOption(node.Get("probe_resist")),
+			gost.KnockingHandlerOption(node.Get("knock")),
 			gost.NodeHandlerOption(node),
 			gost.IPsHandlerOption(ips),
 		)

handler.go

@@ -34,6 +34,7 @@ type HandlerOptions struct {
 	Resolver      Resolver
 	Hosts         *Hosts
 	ProbeResist   string
+	KnockingHost  string
 	Node          Node
 	Host          string
 	IPs           []string
@@ -150,6 +151,13 @@ func ProbeResistHandlerOption(pr string) HandlerOption {
 	}
 }
 
+// KnockingHandlerOption adds the knocking host for probe resistance.
+func KnockingHandlerOption(host string) HandlerOption {
+	return func(opts *HandlerOptions) {
+		opts.KnockingHost = host
+	}
+}
+
 // NodeHandlerOption set the server node for server handler.
 func NodeHandlerOption(node Node) HandlerOption {
 	return func(opts *HandlerOptions) {

http.go

@@ -302,8 +302,9 @@ func (h *httpHandler) authenticate(conn net.Conn, req *http.Request, resp *http.
 		return true
 	}
 
-	// probing resistance is enabled
-	if ss := strings.SplitN(h.options.ProbeResist, ":", 2); len(ss) == 2 {
+	// probing resistance is enabled, and knocking host is mismatch.
+	if ss := strings.SplitN(h.options.ProbeResist, ":", 2); len(ss) == 2 &&
+		(h.options.KnockingHost == "" || !strings.EqualFold(req.URL.Hostname(), h.options.KnockingHost)) {
 		resp.StatusCode = http.StatusServiceUnavailable // default status code
 
 		switch ss[0] {

http2.go

@@ -461,8 +461,9 @@ func (h *http2Handler) authenticate(w http.ResponseWriter, r *http.Request, resp
 		return true
 	}
 
-	// probing resistance is enabled
-	if ss := strings.SplitN(h.options.ProbeResist, ":", 2); len(ss) == 2 {
+	// probing resistance is enabled, and knocking host is mismatch.
+	if ss := strings.SplitN(h.options.ProbeResist, ":", 2); len(ss) == 2 &&
+		(h.options.KnockingHost == "" || !strings.EqualFold(r.URL.Hostname(), h.options.KnockingHost)) {
 		resp.StatusCode = http.StatusServiceUnavailable // default status code
 		w.Header().Del("Proxy-Agent")