[Bug][Naming] Parameter validation errors incorrectly return 500 (Internal Server Error) in gRPC API

[xiaomudk]

Describe the bug
When a gRPC subscribe service request contains invalid parameters (e.g., empty serviceName), the server returns error code 500 (FAIL) instead of a distinguishable client error code. This causes serious issues in SDK clients:

1. SDK cannot distinguish between client parameter errors (should not retry) and server errors (can retry)
2. Infinite retry loop: SDK keeps retrying the invalid request, exhausting retry attempts
3. Client becomes UNHEALTHY: After retry exhaustion, the entire RPC client status changes to UNHEALTHY
4. Cascading failures: Other valid service subscriptions fail because the client is UNHEALTHY
5. Frequent reconnections: The unhealthy client triggers frequent reconnect attempts

Related Issue: This is causing production issues as reported in nacos-sdk-go: #868

Expected behavior
The gRPC API should have at least 3 distinguishable response codes:

• 200 - Success (current: SUCCESS)
• 400 - Client error / Invalid parameter (currently missing, returns 500)
• 500 - Server internal error (current: FAIL)

When serviceName is blank:

• Server should return a client error code (e.g., 400) instead of 500
• SDK should NOT retry client parameter errors
• SDK should return error to caller immediately without affecting client health status

Actually behavior
Current ResponseCode enum only has 2 values:

public enum ResponseCode { 
       SUCCESS(200, "Response ok"), 
       FAIL(500, "Response fail");  // Used for ALL failures}

When parameter validation fails:

1. Server catches IllegalArgumentException in GrpcRequestAcceptor
2. ErrorResponse.build(Throwable) returns ResponseCode.FAIL (500) for all non-Nacos exceptions
3. SDK receives error code 500
4. SDK treats it as server error and retries (default 3 times)
5. After retries exhausted: Request retry exhausted, status changed: RUNNING -> UNHEALTHY
6. Client becomes UNHEALTHY, affecting all other operations

How to Reproduce

1. Use nacos-sdk-go v2.3.1 or nacos-client (Java) 2.4.3
2. Subscribe to a service with empty serviceName:

   namingClient.Subscribe(vo.SubscribeParam{
       ServiceName: "",           // Empty serviceName
       GroupName:   "group-a",
       Clusters:    []string{"cluster-a"},
       SubscribeCallback: callback,
   })

3. Observe server logs:

   java.lang.IllegalArgumentException: Param 'serviceName' is illegal, serviceName is blank

Observe client logs showing infinite retry and status change to UNHEALTHY:

   Send request fail, retryTimes=1, error=Param 'serviceName' is illegal, serviceName is blank
   Send request fail, retryTimes=2, error=Param 'serviceName' is illegal, serviceName is blank
   Send request fail, retryTimes=3, error=Param 'serviceName' is illegal, serviceName is blank
   Request retry exhausted, status changed: RUNNING -> UNHEALTHY

Stack Trace:

java.lang.IllegalArgumentException: Param 'serviceName' is illegal, serviceName is blank
    at com.alibaba.nacos.api.naming.utils.NamingUtils.getGroupedName(NamingUtils.java:61)
    at com.alibaba.nacos.naming.remote.rpc.handler.SubscribeServiceRequestHandler.handle(SubscribeServiceRequestHandler.java:76)
    at com.alibaba.nacos.core.remote.RequestHandler.handleRequest(RequestHandler.java:58)
    at com.alibaba.nacos.core.remote.grpc.GrpcRequestAcceptor.request(GrpcRequestAcceptor.java:195)

Desktop (please complete the following information):

• OS: Linux
• Version:
  • nacos-server: 2.4.3
  • nacos-client (Java): 2.4.3
  • nacos-sdk-go: v2.3.1
    Module: naming (gRPC)
    Impact: Production Critical - causes client instability and cascading failures

Root Cause Analysis

1. Limited ResponseCode enum - Only SUCCESS(200) and FAIL(500), no client error code
2. ErrorResponse.build() treats all non-Nacos exceptions as 500:

   public static Response build(Throwable exception) {
       int errorCode;
       if (exception instanceof NacosException) {
           errorCode = ((NacosException) exception).getErrCode();
       } else if (exception instanceof NacosRuntimeException) {
           errorCode = ((NacosRuntimeException) exception).getErrCode();
       } else {
           errorCode = ResponseCode.FAIL.getCode(); // Always 500!
       }
       // ...
   }

3. No parameter validation before calling NamingUtils.getGroupedName()
4. SDK retry logic cannot distinguish retryable vs non-retryable errors

[shichaoyuan]

针对 IllegalArgumentException 返回 400 ？