feat: verify RpcPath on startup (#2159)

* feat: verify RpcPath on startup

* feat: support http header Grpc-Timeout

gateway/internal/descriptorsource.go

@@ -0,0 +1,34 @@
+package internal
+
+import (
+	"fmt"
+
+	"github.com/fullstorydev/grpcurl"
+	"github.com/jhump/protoreflect/desc"
+)
+
+// GetMethods returns all methods of the given grpcurl.DescriptorSource.
+func GetMethods(source grpcurl.DescriptorSource) ([]string, error) {
+	svcs, err := source.ListServices()
+	if err != nil {
+		return nil, err
+	}
+
+	var methods []string
+	for _, svc := range svcs {
+		d, err := source.FindSymbol(svc)
+		if err != nil {
+			return nil, err
+		}
+
+		switch val := d.(type) {
+		case *desc.ServiceDescriptor:
+			svcMethods := val.GetMethods()
+			for _, method := range svcMethods {
+				methods = append(methods, fmt.Sprintf("%s/%s", svc, method.GetName()))
+			}
+		}
+	}
+
+	return methods, nil
+}