/// <inheritdoc />
public async Task <IImmutableList <Message> > FetchMessagesAsync(string topicName, int partitionId, long offset, int maxCount, CancellationToken cancellationToken)
{
if (offset < 0)
{
throw new ArgumentOutOfRangeException(nameof(offset), offset, "must be >= 0");
}
// Previously fetched messages may contain everything we need
var localIndex = _localMessages.FindIndex(m => m.Offset == offset);
if (0 <= localIndex && localIndex + maxCount <= _localMessages.Count)
{
return(_localMessages.GetRange(localIndex, maxCount));
}
var localCount = (0 <= localIndex && localIndex < _localMessages.Count) ? _localMessages.Count - localIndex : 0;
var request = new FetchRequest(new FetchRequest.Topic(topicName, partitionId, offset + localCount, Configuration.MaxPartitionFetchBytes),
Configuration.MaxFetchServerWait, Configuration.MinFetchBytes, Configuration.MaxFetchBytes);
var response = await _brokerRouter.SendAsync(request, topicName, partitionId, cancellationToken).ConfigureAwait(false);
var topic = response.Topics.SingleOrDefault();
if (topic?.Messages?.Count == 0)
{
return(ImmutableList <Message> .Empty);
}
if (localCount > 0)
{
// Previously fetched messages contain some of what we need, so append
_localMessages = (ImmutableList <Message>)_localMessages.AddNotNullRange(topic?.Messages);
}
else
{
localIndex = 0;
_localMessages = topic?.Messages?.ToImmutableList() ?? ImmutableList <Message> .Empty;
}
return(_localMessages.GetRange(localIndex, Math.Min(maxCount, _localMessages.Count)));
}
