server.Serve returns error after GracefulStop

[jsha]

Steps to reproduce:

1. Set up a gRPC server listening in a goroutine.
2. At some later time, call server.GracefulStop()

Expected result:

server.Serve() returns nil error

Actual result:

server.Serve() returns accept tcp [::]:50051: use of closed network connection

// testServer is used to implement InterceptorTest
type testServer struct{}

// Chill implements InterceptorTest.Chill
func (s *testServer) Chill(ctx context.Context, in *Time) (*Time, error) {
	start := time.Now()
	time.Sleep(time.Duration(*in.Time) * time.Nanosecond)
	spent := int64(time.Since(start) / time.Nanosecond)
	return &Time{Time: &spent}, nil
}

func TestGracefulStopNoError(t *testing.T) {
	const port = ":50051"

	lis, err := net.Listen("tcp", port)
	if err != nil {
		log.Fatalf("failed to listen: %v", err)
	}
	s := grpc.NewServer()
	RegisterInterceptorTestServer(s, &testServer{})
	go func() {
		start := time.Now()
		if err := s.Serve(lis); err != nil {
			t.Fatalf("s.Serve: %v after %s", err, time.Since(start))
		}
	}()

	// Set up a connection to the server.
	conn, err := grpc.Dial("localhost"+port, grpc.WithInsecure())
	if err != nil {
		t.Fatalf("did not connect: %v", err)
	}
	defer conn.Close()
	c := NewInterceptorTestClient(conn)
	var second int64 = time.Second.Nanoseconds()
	spent, err := c.Chill(context.Background(), &Time{Time: &second})
	if err != nil {
		t.Fatal("Calling Chill: %s", err)
	}
	t.Logf("Successfully chilled for %s", time.Duration(*spent.Time)*time.Nanosecond)

	s.GracefulStop()
}

syntax = "proto2";

option go_package = "grpc";

service InterceptorTest {
  // Sleep for the given amount of time, and return the amount of time slept.
  rpc Chill(Time) returns (Time) {}
}

message Time {
  optional int64 time = 1; // In nanoseconds
}

Output:

            interceptors_test.go:115: s.Serve: accept tcp [::]:50051: use of closed network connection after 1.001130858s

[menghanl]

Serve() returns the fatal error returned by lis.Accept.
And lis.Accept returns use of closed network connection error when it's closed.

[jsha]

@menghanl: So, assuming that I log all errors returned from Serve(), how do I accomplish a clean shutdown that does not log any errors?

Also, is there any situation in which Serve() will return without an error? If not, that should be documented.

[menghanl]

Serve() always returns non-nil error. I will create a PR to document that.

One way to get a clean log is to filter errors with use of closed network connection, because error net.errClosing is not exported.

[menghanl]

#1018 created