public IEnumerable <TapeRecord> ReadRecords(long afterVersion, int maxCount)
{
if (afterVersion < 0)
{
throw new ArgumentOutOfRangeException("afterVersion", "Must be zero or greater.");
}
if (maxCount <= 0)
{
throw new ArgumentOutOfRangeException("maxCount", "Must be more than zero.");
}
// afterVersion + maxCount > long.MaxValue, but transformed to avoid overflow
if (afterVersion > long.MaxValue - maxCount)
{
throw new ArgumentOutOfRangeException("maxCount", "Version will exceed long.MaxValue.");
}
var blob = _container.GetBlockBlobReference(_blobName);
var dataExists = blob.Exists();
// we return empty result if writer didn't even start writing to the storage.
if (!dataExists)
{
return(Enumerable.Empty <TapeRecord>());
}
var blockList = blob.DownloadBlockList();
var range = GetReadRange(blockList, afterVersion, maxCount);
if (range.Item4 == 0)
{
return(new TapeRecord[0]);
}
using (var s = blob.OpenRead())
{
s.ReadAheadSize = range.Item2;
s.Seek(range.Item1, SeekOrigin.Begin);
using (var reader = new BinaryReader(s))
{
var bytes = reader.ReadBytes(range.Item2);
using (var ms = new MemoryStream(bytes))
{
TapeStreamSerializer.SkipRecords(range.Item3, ms);
var records = Enumerable.Range(0, range.Item4)
.Select(i => TapeStreamSerializer.ReadRecord(ms))
.ToArray();
return(records);
}
}
}
}
public IEnumerable <TapeRecord> ReadRecords(long afterVersion, int maxCount)
{
if (afterVersion < 0)
{
throw new ArgumentOutOfRangeException("afterVersion", "Must be zero or greater.");
}
if (maxCount <= 0)
{
throw new ArgumentOutOfRangeException("maxCount", "Must be more than zero.");
}
// afterVersion + maxCount > long.MaxValue, but transformed to avoid overflow
if (afterVersion > long.MaxValue - maxCount)
{
throw new ArgumentOutOfRangeException("maxCount", "Version will exceed long.MaxValue.");
}
if (!_data.Exists)
{
// file could've been created since the last check
_data.Refresh();
if (!_data.Exists)
{
yield break;
}
}
using (var file = OpenForRead())
{
if (!TapeStreamSerializer.SkipRecords(afterVersion, file))
{
yield break;
}
for (var i = 0; i < maxCount; i++)
{
if (file.Position == file.Length)
{
yield break;
}
var record = TapeStreamSerializer.ReadRecord(file);
yield return(record);
}
}
}