Avoid infinite log resending if exceptions happen during the log-sending process

src/AWS.Logger.Core/Core/AWSLoggerCore.cs

@@ -435,6 +435,37 @@ private async Task Monitor(CancellationToken token)
                     LogLibraryServiceError(ex);
                 }
             }
+        }
+
+        private static readonly TimeSpan MaxLogEventBatchAllowedTimeRange = TimeSpan.FromHours(24);
+        private void PrepareLogEventBatchForSending()
+        {
+            //Make sure the log events are in order from the oldest to the newest.
+            _repo._request.LogEvents.Sort((ev1, ev2) =>
+                ev1.Timestamp.GetValueOrDefault().CompareTo(ev2.Timestamp.GetValueOrDefault()));
+            if (_repo._request.LogEvents.Count > 0)
+            {
+                DateTime latestLogDateTime = _repo._request.LogEvents.Last().Timestamp ?? DateTime.UtcNow;
+                //Avoid the error that log events must be within a 24-hour window.
+                //https://docs.aws.amazon.com/AmazonCloudWatchLogs/latest/APIReference/API_PutLogEvents.html
+                int lastInvalidEventIndexToRemove = -1;
+                for (int i = 0; i < _repo._request.LogEvents.Count; i++)
+                {
+                    var logEvent = _repo._request.LogEvents[i];
+                    if (!logEvent.Timestamp.HasValue || (latestLogDateTime - logEvent.Timestamp.Value) > MaxLogEventBatchAllowedTimeRange)
+                    {
+                        lastInvalidEventIndexToRemove = i;
+                    }
+                    else
+                    {
+                        break; // Events are in order, so we can stop checking once we find a valid event
+                    }
+                }
+                if (lastInvalidEventIndexToRemove >= 0)
+                {
+                    _repo.RemoveMessages(0, lastInvalidEventIndexToRemove + 1);
+                }
+            }
         }
 
         /// <summary>
@@ -446,10 +477,13 @@ private async Task SendMessages(CancellationToken token)
         {
             try
             {
-                //Make sure the log events are in the right order.
-                _repo._request.LogEvents.Sort((ev1, ev2) => 
-                    ev1.Timestamp.GetValueOrDefault().CompareTo(ev2.Timestamp.GetValueOrDefault()));
-                var response = await _client.Value.PutLogEventsAsync(_repo._request, token).ConfigureAwait(false);
+                PrepareLogEventBatchForSending();
+                if (_repo._request.LogEvents.Count == 0)
+                {
+                    _repo.Reset();
+                    return;
+                }
+                await _client.Value.PutLogEventsAsync(_repo._request, token).ConfigureAwait(false);
                 _repo.Reset();
             }
             catch (ResourceNotFoundException ex)
@@ -458,6 +492,12 @@ private async Task SendMessages(CancellationToken token)
                 LogLibraryServiceError(ex);
 
                 _currentStreamName = await LogEventTransmissionSetup(token).ConfigureAwait(false);
+            }
+            catch (InvalidParameterException ex)
+            {
+                // Bad log events, log error and discard batch
+                LogLibraryServiceError(ex);
+                _repo.Reset();
             }
         }
 
@@ -683,6 +723,21 @@ public void AddMessage(InputLogEvent ev)
                 _request.LogEvents.Add(ev);
             }
 
+            public void RemoveMessages(int startIndex, int count)
+            {
+                if (startIndex < 0 || startIndex >= _request.LogEvents.Count || count < 0 || (startIndex + count) > _request.LogEvents.Count)
+                {
+                    return;
+                }
+                Encoding unicode = Encoding.Unicode;
+                for (int i = startIndex; i < startIndex + count; i++)
+                {
+                    InputLogEvent ev = _request.LogEvents[i];
+                    _totalMessageSize -= unicode.GetMaxByteCount(ev.Message.Length);
+                }
+                _request.LogEvents.RemoveRange(startIndex, count);
+            }
+
             public void Reset()
             {
                 _request.LogEvents.Clear();