/// <summary>
/// If available, overwrites the space allocated to the previous file first to save space.
/// </summary>
/// <param name="index"></param>
/// <param name="fileId"></param>
/// <param name="data"></param>
public void WriteFileData(Index index, int fileId, byte[] data)
{
if (this.ReadOnly)
{
throw new InvalidOperationException("Can't write data in readonly mode.");
}
lock (this._ioLock)
{
// Obtain possibly existing sector positions to overwrite
int[] existingSectorPositions;
try
{
existingSectorPositions = this.ReadSectors(index, fileId)
.Select(sector => sector.Position)
.ToArray();
}
catch (Exception ex) when(ex is FileNotFoundException)
{
// Assume there are no existing sectors when the method fails
existingSectorPositions = new int[0];
}
var sectors = Sector.FromData(data, index, fileId);
var dataWriter = new BinaryWriter(this._dataStream);
foreach (var sector in sectors)
{
// Overwrite existing sector data if available, otherwise append to file
sector.Position = sector.ChunkId < existingSectorPositions.Length
? existingSectorPositions[sector.ChunkId]
: (int)(dataWriter.BaseStream.Length / Sector.Length);
// Set position of next sector
sector.NextSectorPosition = sector.ChunkId + 1 < existingSectorPositions.Length
? existingSectorPositions[sector.ChunkId + 1]
: (int)(dataWriter.BaseStream.Length / Sector.Length);
// Happens if both positions were based on the stream length
if (sector.NextSectorPosition == sector.Position)
{
sector.NextSectorPosition++;
}
// Add to index
if (sector.ChunkId == 0)
{
var pointer = new IndexPointer
{
FirstSectorPosition = sector.Position,
Filesize = data.Length
};
// Create index file if it does not exist yet
if (!this._indexStreams.ContainsKey(index))
{
this._indexStreams.Add(index, File.Open(
Path.Combine(this.CacheDirectory, "main_file_cache.idx" + (int)index),
FileMode.OpenOrCreate,
FileAccess.ReadWrite));
}
var indexWriter = new BinaryWriter(this._indexStreams[index]);
var pointerPosition = fileId * IndexPointer.Length;
// Write zeroes up to the desired position of the index stream if it is larger than its size
if (indexWriter.BaseStream.Length < pointerPosition)
{
indexWriter.BaseStream.Position = indexWriter.BaseStream.Length;
indexWriter.Write(Enumerable.Repeat((byte)0, (int)(pointerPosition - indexWriter.BaseStream.Length)).ToArray());
}
else
{
indexWriter.BaseStream.Position = pointerPosition;
}
pointer.Encode(indexWriter.BaseStream);
}
// Write the encoded sector
dataWriter.BaseStream.Position = sector.Position * Sector.Length;
dataWriter.Write(sector.Encode());
}
}
}
private IEnumerable <Sector> ReadSectors(Index index, int fileId, out int filesize)
{
if (!this._indexStreams.ContainsKey(index))
{
throw new FileNotFoundException($"Index does not exist for {(int)index}/{fileId}.");
}
var indexReader = new BinaryReader(this._indexStreams[index]);
var indexPosition = (long)fileId * IndexPointer.Length;
if (indexPosition < 0 || indexPosition >= indexReader.BaseStream.Length)
{
throw new FileNotFoundException($"{(int)index}/{fileId} is outside of the index file's bounds.");
}
var sectors = new List <Sector>();
// Lock stream, to allow multiple threads from calling this method at the same time
lock (this._ioLock)
{
indexReader.BaseStream.Position = indexPosition;
var indexPointer = IndexPointer.Decode(indexReader.BaseStream);
filesize = indexPointer.Filesize;
if (indexPointer.Filesize <= 0)
{
throw new FileNotFoundException($"{index}/{fileId} has no size, which means it is not stored in the cache.");
}
var chunkId = 0;
var remaining = indexPointer.Filesize;
var dataReader = new BinaryReader(this._dataStream);
var dataPosition = (long)indexPointer.FirstSectorPosition * Sector.Length;
do
{
dataReader.BaseStream.Position = dataPosition;
var sectorBytes = dataReader.ReadBytes(Sector.Length);
if (sectorBytes.Length != Sector.Length)
{
throw new EndOfStreamException($"One of {index}/{fileId}'s sectors could not be fully read.");
}
var sector = new Sector((int)(dataPosition / Sector.Length), index, fileId, chunkId++, sectorBytes);
var bytesRead = Math.Min(sector.Data.Length, remaining);
remaining -= bytesRead;
dataPosition = (long)sector.NextSectorPosition * Sector.Length;
sectors.Add(sector);
}while (remaining > 0);
}
return(sectors);
}
