/// <summary>
/// Reads data from the stream.
/// </summary>
/// <param name="buffer">The buffer to fill</param>
/// <param name="offset">The first byte in buffer to fill</param>
/// <param name="count">The requested number of bytes to read</param>
/// <returns>The actual number of bytes read</returns>
public override int Read(byte[] buffer, int offset, int count)
{
lock (_common)
{
SparseStream wrapped = Wrapped;
wrapped.Position = _position;
int numRead = wrapped.Read(buffer, offset, count);
_position += numRead;
return(numRead);
}
}
public override int Read(byte[] buffer, int offset, int count)
{
return(_wrapped.Read(buffer, offset, count));
}
internal override int Read(long diskOffset, byte[] block, int offset, int count)
{
_stream.Position = diskOffset - Start;
return(_stream.Read(block, offset, count));
}
/// <summary>
/// Reads data from the stream.
/// </summary>
/// <param name="buffer">The buffer to fill</param>
/// <param name="offset">The buffer offset to start from</param>
/// <param name="count">The number of bytes to read</param>
/// <returns>The number of bytes read</returns>
public override int Read(byte[] buffer, int offset, int count)
{
CheckDisposed();
if (_position >= Length)
{
if (_atEof)
{
throw new IOException("Attempt to read beyond end of stream");
}
else
{
_atEof = true;
return(0);
}
}
_stats.TotalReadsIn++;
if (count > _settings.LargeReadSize)
{
_stats.LargeReadsIn++;
_stats.TotalReadsOut++;
_wrappedStream.Position = _position;
int numRead = _wrappedStream.Read(buffer, offset, count);
_position = _wrappedStream.Position;
if (_position >= Length)
{
_atEof = true;
}
return(numRead);
}
int totalBytesRead = 0;
bool servicedFromCache = false;
bool servicedOutsideCache = false;
int blockSize = _settings.BlockSize;
long firstBlock = _position / blockSize;
int offsetInNextBlock = (int)(_position % blockSize);
long endBlock = Utilities.Ceil(Math.Min(_position + count, Length), blockSize);
int numBlocks = (int)(endBlock - firstBlock);
if (offsetInNextBlock != 0)
{
_stats.UnalignedReadsIn++;
}
int blocksRead = 0;
while (blocksRead < numBlocks)
{
Block block;
// Read from the cache as much as possible
while (blocksRead < numBlocks && _cache.TryGetBlock(firstBlock + blocksRead, out block))
{
int bytesToRead = Math.Min(count - totalBytesRead, block.Available - offsetInNextBlock);
Array.Copy(block.Data, offsetInNextBlock, buffer, offset + totalBytesRead, bytesToRead);
offsetInNextBlock = 0;
totalBytesRead += bytesToRead;
_position += bytesToRead;
blocksRead++;
servicedFromCache = true;
}
// Now handle a sequence of (one or more) blocks that are not cached
if (blocksRead < numBlocks && !_cache.ContainsBlock(firstBlock + blocksRead))
{
servicedOutsideCache = true;
// Figure out how many blocks to read from the wrapped stream
int blocksToRead = 0;
while (blocksRead + blocksToRead < numBlocks &&
blocksToRead < _blocksInReadBuffer &&
!_cache.ContainsBlock(firstBlock + blocksRead + blocksToRead))
{
++blocksToRead;
}
// Allow for the end of the stream not being block-aligned
long readPosition = (firstBlock + blocksRead) * (long)blockSize;
int bytesToRead = (int)Math.Min(blocksToRead * (long)blockSize, Length - readPosition);
// Do the read
_stats.TotalReadsOut++;
_wrappedStream.Position = readPosition;
int bytesRead = Utilities.ReadFully(_wrappedStream, _readBuffer, 0, bytesToRead);
if (bytesRead != bytesToRead)
{
throw new IOException("Short read before end of stream");
}
// Cache the read blocks
for (int i = 0; i < blocksToRead; ++i)
{
int copyBytes = Math.Min(blockSize, bytesToRead - (i * blockSize));
block = _cache.GetBlock(firstBlock + blocksRead + i);
Array.Copy(_readBuffer, i * blockSize, block.Data, 0, copyBytes);
block.Available = copyBytes;
if (copyBytes < blockSize)
{
Array.Clear(_readBuffer, (i * blockSize) + copyBytes, blockSize - copyBytes);
}
}
blocksRead += blocksToRead;
// Propogate the data onto the caller
int bytesToCopy = Math.Min(count - totalBytesRead, bytesRead - offsetInNextBlock);
Array.Copy(_readBuffer, offsetInNextBlock, buffer, offset + totalBytesRead, bytesToCopy);
totalBytesRead += bytesToCopy;
_position += bytesToCopy;
offsetInNextBlock = 0;
}
}
if (_position >= Length && totalBytesRead == 0)
{
_atEof = true;
}
if (servicedFromCache)
{
_stats.ReadCacheHits++;
}
if (servicedOutsideCache)
{
_stats.ReadCacheMisses++;
}
return(totalBytesRead);
}
/// <summary>
/// Reads from the buffer into a byte array.
/// </summary>
/// <param name="pos">The offset within the buffer to start reading.</param>
/// <param name="buffer">The destination byte array.</param>
/// <param name="offset">The start offset within the destination buffer.</param>
/// <param name="count">The number of bytes to read.</param>
/// <returns>The actual number of bytes read</returns>
public override int Read(long pos, byte[] buffer, int offset, int count)
{
_stream.Position = pos;
return(_stream.Read(buffer, offset, count));
}