Fix double announce/denounce/implicit withdrawals (#29)

Signed-off-by: Igor Shishkin <me@teran.dev>

service/service.go

@@ -2,6 +2,7 @@ package service
 
 import (
 	"context"
+	"sync/atomic"
 	"time"
 
 	"github.com/pkg/errors"
@@ -21,6 +22,8 @@ type service struct {
 	checks    []checkers.Checker
 	interval  time.Duration
 	metrics   Metrics
+
+	announced *atomic.Bool
 }
 
 func New(
@@ -36,6 +39,7 @@ func New(
 		checks:    checks,
 		interval:  interval,
 		metrics:   metrics,
+		announced: &atomic.Bool{},
 	}
 }
 
@@ -59,19 +63,27 @@ func (s *service) run(ctx context.Context) error {
 
 			s.metrics.ServiceDown(s.name)
 
-			if err := s.announcer.Denounce(ctx); err != nil {
-				log.Warnf("denounce failed: %s", err)
-				return nil
+			if s.announced.Load() {
+				if err := s.announcer.Denounce(ctx); err != nil {
+					log.Warnf("denounce failed: %s", err)
+					return nil
+				}
+				s.announced.Store(false)
 			}
 			return nil
 		}
 	}
 
 	s.metrics.ServiceUp(s.name)
 
-	if err := s.announcer.Announce(ctx); err != nil {
-		log.Warnf("announce failed: %s", err)
+	if !s.announced.Load() {
+		if err := s.announcer.Announce(ctx); err != nil {
+			log.Warnf("announce failed: %s", err)
+			return nil
+		}
 	}
 
+	s.announced.Store(true)
+
 	return nil
 }

service/service_test.go

@@ -31,8 +31,6 @@ func (s *serviceTestSuite) TestRunPass() {
 }
 
 func (s *serviceTestSuite) TestRunFail() {
-	s.announcerM.On("Denounce").Return(nil).Once()
-
 	s.checkM.On("Check").Return(errors.New("error")).Once()
 
 	s.metricsM.On("ServiceDown", "test_service").Return().Once()