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Exception Type Return Values

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1. Introduction

This document demonstrates how to handle error type responses during RPC calls. You can view the complete example source code here.

2. Example Details

2.1 Server

Server proto file

Source file path: dubbo-go-sample/error/proto/greet.proto

syntax = "proto3";

package greet;

option go_package = "github.com/apache/dubbo-go-samples/error/proto;greet";

message GreetRequest {
  string name = 1;
}

message GreetResponse {
  string greeting = 1;
}

service GreetService {
  rpc Greet(GreetRequest) returns (GreetResponse) {}
}

Server handler file

Note that in this program design, the Greet method will only consider the request valid if it receives name="right name"; otherwise, it will return an error.

Source file path: dubbo-go-sample/context/go-server/main.go

package main

import (
	"context"
	"fmt"
	"github.com/pkg/errors"

	_ "dubbo.apache.org/dubbo-go/v3/imports"
	"dubbo.apache.org/dubbo-go/v3/protocol"
	"dubbo.apache.org/dubbo-go/v3/server"
	greet "github.com/apache/dubbo-go-samples/helloworld/proto"
	"github.com/dubbogo/gost/log/logger"
)

type GreetTripleServer struct {
}

func (srv *GreetTripleServer) Greet(ctx context.Context, req *greet.GreetRequest) (*greet.GreetResponse, error) {
	name := req.Name
	if name != "right name" {
		errInfo := fmt.Sprintf("name is not right: %s", name)
		logger.Error(errInfo)
		return nil, errors.New(errInfo)
	}

	resp := &greet.GreetResponse{Greeting: req.Name}
	return resp, nil
}

func main() {
	srv, err := server.NewServer(
		server.WithServerProtocol(
			protocol.WithPort(20000),
			protocol.WithTriple(),
		),
	)
	if err != nil {
		panic(err)
	}

	if err = greet.RegisterGreetServiceHandler(srv, &GreetTripleServer{}); err != nil {
		panic(err)
	}

	if err = srv.Serve(); err != nil {
		logger.Error(err)
	}
}

From the RPC method signature, we can see that func (srv *GreetTripleServer) Greet(ctx context.Context, req *greet.GreetRequest) (*greet.GreetResponse, error) includes an error return value.

2.2 Client

The client makes two calls, one with a valid request and one with an invalid request.

Source file path: dubbo-go-sample/context/go-client/main.go

package main

import (
	"context"

	"dubbo.apache.org/dubbo-go/v3/client"
	_ "dubbo.apache.org/dubbo-go/v3/imports"
	greet "github.com/apache/dubbo-go-samples/helloworld/proto"
	"github.com/dubbogo/gost/log/logger"
)

func main() {
	cli, err := client.NewClient(
		client.WithClientURL("127.0.0.1:20000"),
	)
	if err != nil {
		panic(err)
	}

	svc, err := greet.NewGreetService(cli)
	if err != nil {
		panic(err)
	}

	resp, err := svc.Greet(context.Background(), &greet.GreetRequest{Name: "right name"})
	if err != nil {
		logger.Error(err)
	}
	logger.Infof("call Greet success: %s", resp.Greeting)

	resp, err = svc.Greet(context.Background(), &greet.GreetRequest{Name: "wrong name"})
	if err != nil {
		logger.Errorf("call Greet failed, err: %s", err.Error())
	}
}

2.3 Case Effect

Start the server first, then the client. You can observe that the client's first call succeeds, while the second call fails, and the server returns an error.

2024-02-28 17:49:40	INFO	logger/logging.go:42	call Greet success: [right name]
2024-02-28 17:49:40	ERROR	logger/logging.go:52	call Greet failed, err: [Failed to invoke the method Greet in the service greet.GreetService. Tried 2 times of the providers [tri://:@127.0.0.1:20000/?interface=greet.GreetService&group=&version= tri://:@127.0.0.1:20000/?interface=greet.GreetService&group=&version= tri://:@127.0.0.1:20000/?interface=greet.GreetService&group=&version=] (3/1)from the registry tri://127.0.0.1:20000/greet.GreetService?app.version=&application=dubbo.io&async=false&bean.name=greet.GreetService&cluster=failover&config.tracing=&environment=&generic=&group=&interface=greet.GreetService&loadbalance=&metadata-type=local&module=sample&name=dubbo.io&organization=dubbo-go&owner=dubbo-go&peer=true&provided-by=&reference.filter=cshutdown&registry.role=0&release=dubbo-golang-3.2.0&remote.timestamp=&retries=&serialization=protobuf&side=consumer&sticky=false&timestamp=1709113780&version= on the consumer 30.221.146.234 using the dubbo version 3.2.0. Last error is unknown: name is not right: wrong name.: unknown: name is not right: wrong name]