add onRetryCallback callback function

interceptors/retry/options.go

@@ -26,6 +26,9 @@ var (
 		backoffFunc: BackoffFuncContext(func(ctx context.Context, attempt uint) time.Duration {
 			return BackoffLinearWithJitter(50*time.Millisecond /*jitter*/, 0.10)(attempt)
 		}),
+		onRetryCallback: OnRetryCallback(func(ctx context.Context, attempt uint, err error) {
+			logTrace(ctx, "grpc_retry attempt: %d, backoff for %v", attempt, err)
+		}),
 	}
 )
 
@@ -45,6 +48,9 @@ type BackoffFunc func(attempt uint) time.Duration
 // with the next iteration. The context can be used to extract request scoped metadata and context values.
 type BackoffFuncContext func(ctx context.Context, attempt uint) time.Duration
 
+// OnRetryCallback is the type of function called when a retry occurs.
+type OnRetryCallback func(ctx context.Context, attempt uint, err error)
+
 // Disable disables the retry behaviour on this call, or this interceptor.
 //
 // Its semantically the same to `WithMax`
@@ -75,6 +81,15 @@ func WithBackoffContext(bf BackoffFuncContext) CallOption {
 	}}
 }
 
+// WithOnRetryCallback sets the callback to use when a retry occurs.
+//
+// By default, when no callback function provided, we will just print a log to trace
+func WithOnRetryCallback(fn OnRetryCallback) CallOption {
+	return CallOption{applyFunc: func(o *options) {
+		o.onRetryCallback = fn
+	}}
+}
+
 // WithCodes sets which codes should be retried.
 //
 // Please *use with care*, as you may be retrying non-idempotent calls.
@@ -105,11 +120,12 @@ func WithPerRetryTimeout(timeout time.Duration) CallOption {
 }
 
 type options struct {
-	max            uint
-	perCallTimeout time.Duration
-	includeHeader  bool
-	codes          []codes.Code
-	backoffFunc    BackoffFuncContext
+	max             uint
+	perCallTimeout  time.Duration
+	includeHeader   bool
+	codes           []codes.Code
+	backoffFunc     BackoffFuncContext
+	onRetryCallback OnRetryCallback
 }
 
 // CallOption is a grpc.CallOption that is local to grpc_retry.

interceptors/retry/retry.go

@@ -48,7 +48,7 @@ func UnaryClientInterceptor(optFuncs ...CallOption) grpc.UnaryClientInterceptor
 			if lastErr == nil {
 				return nil
 			}
-			logTrace(parentCtx, "grpc_retry attempt: %d, got err: %v", attempt, lastErr)
+			callOpts.onRetryCallback(parentCtx, attempt, lastErr)
 			if isContextError(lastErr) {
 				if parentCtx.Err() != nil {
 					logTrace(parentCtx, "grpc_retry attempt: %d, parent context error: %v", attempt, parentCtx.Err())
@@ -110,8 +110,7 @@ func StreamClientInterceptor(optFuncs ...CallOption) grpc.StreamClientIntercepto
 				}
 				return retryingStreamer, nil
 			}
-
-			logTrace(parentCtx, "grpc_retry attempt: %d, got err: %v", attempt, lastErr)
+			callOpts.onRetryCallback(parentCtx, attempt, lastErr)
 			if isContextError(lastErr) {
 				if parentCtx.Err() != nil {
 					logTrace(parentCtx, "grpc_retry attempt: %d, parent context error: %v", attempt, parentCtx.Err())
@@ -189,6 +188,7 @@ func (s *serverStreamingRetryingStream) RecvMsg(m interface{}) error {
 		if err := waitRetryBackoff(attempt, s.parentCtx, s.callOpts); err != nil {
 			return err
 		}
+		s.callOpts.onRetryCallback(s.parentCtx, attempt, lastErr)
 		// TODO(bwplotka): Close cancel as it might leak some resources.
 		callCtx, _ := perCallContext(s.parentCtx, s.callOpts, attempt) //nolint
 		newStream, err := s.reestablishStreamAndResendBuffer(callCtx)

interceptors/retry/retry_test.go

@@ -215,6 +215,21 @@ func (s *RetrySuite) TestUnary_PerCallDeadline_FailsOnParent() {
 	require.Equal(s.T(), codes.DeadlineExceeded, status.Code(err), "failre code must be a gRPC error of Deadline class")
 }
 
+func (s *RetrySuite) TestUnary_OnRetryCallbackCalled() {
+	retryCallbackCount := 0
+
+	s.srv.resetFailingConfiguration(3, codes.Unavailable, noSleep) // see retriable_errors
+	out, err := s.Client.Ping(s.SimpleCtx(), testpb.GoodPing,
+		retry.WithOnRetryCallback(func(ctx context.Context, attempt uint, err error) {
+			retryCallbackCount++
+		}),
+	)
+
+	require.NoError(s.T(), err, "the third invocation should succeed")
+	require.NotNil(s.T(), out, "Pong must be not nil")
+	require.EqualValues(s.T(), 2, retryCallbackCount, "two retry callbacks should be called")
+}
+
 func (s *RetrySuite) TestServerStream_SucceedsOnRetriableError() {
 	s.srv.resetFailingConfiguration(3, codes.DataLoss, noSleep) // see retriable_errors
 	stream, err := s.Client.PingList(s.SimpleCtx(), testpb.GoodPingList)
@@ -266,6 +281,21 @@ func (s *RetrySuite) TestServerStream_PerCallDeadline_FailsOnParent() {
 	require.Equal(s.T(), codes.DeadlineExceeded, status.Code(err), "failre code must be a gRPC error of Deadline class")
 }
 
+func (s *RetrySuite) TestServerStream_OnRetryCallbackCalled() {
+	retryCallbackCount := 0
+
+	s.srv.resetFailingConfiguration(3, codes.Unavailable, noSleep) // see retriable_errors
+	stream, err := s.Client.PingList(s.SimpleCtx(), testpb.GoodPingList,
+		retry.WithOnRetryCallback(func(ctx context.Context, attempt uint, err error) {
+			retryCallbackCount++
+		}),
+	)
+
+	require.NoError(s.T(), err, "establishing the connection must always succeed")
+	s.assertPingListWasCorrect(stream)
+	require.EqualValues(s.T(), 2, retryCallbackCount, "two retry callbacks should be called")
+}
+
 func (s *RetrySuite) TestServerStream_CallFailsOnOutOfRetries() {
 	restarted := s.RestartServer(3 * retryTimeout)
 	_, err := s.Client.PingList(s.SimpleCtx(), testpb.GoodPingList)