private static Block ReadBlock(FileStream stream, BlockHandle handle)
{
uint n = (uint)handle.Size;
stream.Position = (long)handle.Offset;
using (var reader = new BinaryReader(stream, Encoding.UTF8, true))
{
var buf = reader.ReadBytes(unchecked ((int)n + 1));
var encoding = buf[n];
var crc32c = reader.ReadInt32();
// TODO: validate crc32c here?
switch (encoding)
{
case kNoCompression:
return(new Block(new Slice(buf, 0, n)));
case kSnappyCompression:
buf = SnappyDecompressor.Decompress(buf, 0, unchecked ((int)n));
return(new Block(new Slice(buf)));
}
}
throw new Exception("bad block type");
}
private Block GetBlock(byte[] key)
{
if (m_stream != null)
{
var handle = BlockHandle.DecodeFrom(new Slice(key));
if (m_blockCache != null && m_blockCache.TryGetValue(handle, out var block))
{
return(block);
}
block = ReadBlock(m_stream, handle);
m_blockCache?.Add(handle, block);
return(block);
}
throw new Exception("TableFile not open");
}
public static Footer DecodeFrom(Slice slice)
{
uint startOffset = slice.Offset;
uint startLength = slice.Length;
uint magic_lo = Coding.DecodeFixed32(slice.NewSlice(kEncodedLength - 8, 4));
uint magic_hi = Coding.DecodeFixed32(slice.NewSlice(kEncodedLength - 4, 4));
ulong magic = (unchecked ((ulong)magic_hi) << 32) | unchecked ((ulong)magic_lo);
if (magic != kTableMagicNumber)
{
throw new Exception("not an sstable (bad magic number)");
}
var metaIndexHandle = BlockHandle.DecodeFrom(slice);
var indexHandle = BlockHandle.DecodeFrom(slice);
slice.Update(startOffset + kEncodedLength, startLength - kEncodedLength);
return(new Footer(metaIndexHandle, indexHandle));
}
public Footer(BlockHandle metaIndexHandle, BlockHandle indexHandle)
{
MetaIndexHandle = metaIndexHandle;
IndexHandle = indexHandle;
}