特性六：grpc内 errors使用

原理:

使用status包对grpc内的错误进行识别！

代码：

r, err := c.SayHello(ctx, &pb.HelloRequest{Name: "world"})
    if err != nil {
        s := status.Convert(err)
        for _, d := range s.Details() {
            switch info := d.(type) {
            case *epb.QuotaFailure:
                log.Printf("Quota failure: %s", info)
            default:
                log.Printf("Unexpected type: %s", info)
            }
        }
        os.Exit(1)
    }

服务端：

st := status.New(codes.ResourceExhausted, "Request limit exceeded.")
        ds, err := st.WithDetails(
            &epb.QuotaFailure{
                Violations: []*epb.QuotaFailure_Violation{{
                    Subject:     fmt.Sprintf("name:%s", in.Name),
                    Description: "Limit one greeting per person",
                }},
            },
        )
        if err != nil {
            return nil, st.Err()
        }