refactor(contrib/rpc/grpcx): optimize server unary interceptor error handling

Author: bandl

contrib/rpc/grpcx/grpcx_interceptor_server.go

@@ -43,13 +43,21 @@ func (s modServer) UnaryError(
 	ctx context.Context, req any, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler,
 ) (any, error) {
 	res, err := handler(ctx, req)
-	if err != nil {
+	if err == nil {
+		return res, nil
+	}
+	switch {
+	// Case 1: Error already implements GRPCStatus, it's already a gRPC standard error
+	case err.(interface{ GRPCStatus() *status.Status }) != nil:
+		return res, err
+	// Case 2: Error contains a valid custom error code, convert to gRPC status error
+	case gerror.Code(err).Code() != -1:
 		code := gerror.Code(err)
-		if code.Code() != -1 {
-			err = status.Error(codes.Code(code.Code()), err.Error())
-		}
+		return res, status.Error(codes.Code(code.Code()), err.Error())
+	// Case 3: Invalid error code or other cases, keep the original error
+	default:
+		return res, err
 	}
-	return res, err
 }
 
 // UnaryRecover is the first interceptor that keep server not down from panics.