Add rich error handling

go/README.md

@@ -2,6 +2,11 @@
 
 ## Instructions
 
+Install the go protobuf plugin required:
+
+	$ go get github.com/golang/protobuf/protoc-gen-go
+	$ go install github.com/golang/protobuf/protoc-gen-go
+
 Generate protobuf files:
 
     $ protoc -I ../ ../hello.proto --go_out=plugins=grpc:./hello

go/client.go

@@ -48,9 +48,32 @@ func main() {
 		// Want to take specific action based on specific error?
 		if codes.InvalidArgument == errStatus.Code() {
 			// do your stuff here
-			log.Fatal()
 		}
 	}
 
+	resp, err = c.SayHelloAdvanced(
+		context.Background(),
+		&api.HelloReq{Name: "Leonhard Euler"},
+	)
+
+	if err != nil {
+		// this is advanced error handling. Everything works exactly like the previous example, but in this one you also
+		// get extra error information
+		errStatus, _ := status.FromError(err)
+		fmt.Println(errStatus.Message())
+		// lets print the error code which is `INVALID_ARGUMENT`
+		fmt.Println(errStatus.Code())
+		// now lets get the advanced error info!
+		for _, d := range errStatus.Details() {
+			switch errProto := d.(type) {
+			// in some languages, you may need to unwrap the obj from an any.Any. However, Go grpc lib have done that already for us
+			case *api.Error:
+				// following prints the error desc, "Your name contains 14 characters, ..."
+				fmt.Println(errProto.Description)
+			default:
+				log.Fatal("Unexpected type: ", errProto)
+			}
+		}
+	}
 	fmt.Println(resp.GetResult())
 }

go/server.go

@@ -28,6 +28,24 @@ func (s *HelloServer) SayHelloStrict(ctx context.Context, req *api.HelloReq) (*a
 	return &api.HelloResp{Result: fmt.Sprintf("Hey, %s!", req.GetName())}, nil
 }
 
+func (s *HelloServer) SayHelloAdvanced(ctx context.Context, req *api.HelloReq) (*api.HelloResp, error) {
+	if len(req.GetName()) >= 10 {
+		// with the error, you can also send any proto object as metadata. We will use the one we defined in the
+		// proto definition
+		// so create an api.Error obj and send that along with the error.
+		detail := &api.Error{
+			Description: fmt.Sprintf("Your name contains %d characters, but you cannot use more than 10 characters in this API request", len(req.Name)),
+		}
+		st := status.New(codes.InvalidArgument, "Length of `Name` cannot be more than 10 characters")
+		// following attaches the extra error metadata to the error
+		// in other languages, you may need to wrap the obj within an any.Any. Following `WithDetails` method does that
+		// for us
+		st, _ = st.WithDetails(detail)
+		return nil, st.Err()
+	}
+	return &api.HelloResp{Result: fmt.Sprintf("Hey, %s!", req.GetName())}, nil
+}
+
 func Serve() {
 	addr := fmt.Sprintf(":%d", 50051)
 	conn, err := net.Listen("tcp", addr)

hello.proto

@@ -9,6 +9,8 @@ service HelloService {
     // Strict Version responds only to requests which have `Name` length
     // less than 10 characters
     rpc SayHelloStrict(HelloReq) returns (HelloResp) {};
+    // Same like previous one, but returns an advanced error, an instance of Error message defined below
+    rpc SayHelloAdvanced(HelloReq) returns (HelloResp) {};
 }
 
 message HelloReq {
@@ -17,4 +19,8 @@ message HelloReq {
 
 message HelloResp {
     string Result = 1;
+}
+
+message Error {
+    string Description = 1;
 }