public Task<DriverReadResult> ReadAsync(long position, long maxBytes, CancellationToken cancel = new CancellationToken())
{
var events = new List<RawEvent>();
if (position >= _file.Length)
return Task.FromResult(new DriverReadResult(_file.Length, events));
_file.Seek(position, SeekOrigin.Begin);
var readBytes = 0L;
using (var r = new BinaryReader(_file, Encoding.UTF8, true))
{
var availableBytes = _file.Length - position;
while (readBytes < availableBytes)
{
var evt = EventFormat.Read(r);
var newReadBytes = _file.Position - position;
if (events.Count == 0 || newReadBytes < maxBytes)
{
events.Add(evt);
readBytes = newReadBytes;
}
if (newReadBytes >= maxBytes)
break;
}
}
return Task.FromResult(new DriverReadResult(position + readBytes, events));
}
internal DriverReadResult Read(long position, long maxBytes)
{
var events = new List <RawEvent>();
if (position >= _file.Length)
{
return(new DriverReadResult(_file.Length, events));
}
_file.Seek(position, SeekOrigin.Begin);
var readBytes = 0L;
using (var r = new BinaryReader(_file, Encoding.UTF8, true))
{
var availableBytes = _file.Length - position;
while (readBytes < availableBytes)
{
var evt = EventFormat.Read(r);
var newReadBytes = _file.Position - position;
if (events.Count == 0 || newReadBytes < maxBytes)
{
events.Add(evt);
readBytes = newReadBytes;
}
if (newReadBytes >= maxBytes)
{
break;
}
}
}
return(new DriverReadResult(position + readBytes, events));
}
public async Task <DriverReadResult> ReadAsync(long position, long maxBytes, CancellationToken cancel = new CancellationToken())
{
// STEP 1: PRELIMINARY CHECKS
// ==========================
// The local cache tells us there is no data available at the provided position,
// so start by refreshing the cache.
if (_blobs.Count == 0 || position >= _lastKnownPosition)
{
await RefreshCache(cancel);
}
// Even with a fresh cache, our position is beyond any available data:
// return that there is no more data available.
if (_blobs.Count == 0 || position >= _lastKnownPosition)
{
return(new DriverReadResult(_lastKnownPosition, new RawEvent[0]));
}
// STEP 2: IDENTIFY BLOB
// =====================
CloudAppendBlob blob = null;
long firstPosition = 0;
long blobSize = 0;
for (var i = _blobs.Count - 1; i >= 0; --i)
{
if (_firstPosition[i] <= position)
{
blob = _blobs[i];
firstPosition = _firstPosition[i];
blobSize = (i == _blobs.Count - 1 ? _lastKnownPosition : _firstPosition[i + 1]) - firstPosition;
break;
}
}
if (blob == null)
{
// Since _firstPosition[0] == 0, this means the position is negative
throw new ArgumentOutOfRangeException("Invalid position:" + position, "position");
}
// STEP 3: READ RAW DATA
// =====================
var startPos = position - firstPosition;
maxBytes = Math.Min(maxBytes, Math.Min(_buffer.Length, blobSize - startPos));
if (maxBytes == 0)
{
return(new DriverReadResult(_lastKnownPosition, new RawEvent[0]));
}
var length = await ReadRangeAsync(blob, startPos, maxBytes, cancel);
// STEP 4: PARSE DATA
// ==================
var events = new List <RawEvent>();
var readBytes = 0L;
using (var ms = new MemoryStream(_buffer, 0, length))
using (var reader = new BinaryReader(ms))
{
while (true)
{
try
{
events.Add(EventFormat.Read(reader));
// Only update after finishing a full read !
readBytes = ms.Position;
}
catch (EndOfStreamException)
{
break;
}
catch (InvalidDataException e)
{
throw new InvalidDataException($"{e.Message} at {position + readBytes}");
}
}
}
return(new DriverReadResult(position + readBytes, events));
}
