/// <summary>
/// Reads the custom code table, if there is one
/// </summary>
private void ReadCodeTable()
{
// The length given includes the nearSize and sameSize bytes
var compressedTableLength = IOUtils.ReadBigEndian7BitEncodedInt(delta) - 2;
var nearSize = IOUtils.CheckedReadByte(delta);
var sameSize = IOUtils.CheckedReadByte(delta);
var compressedTableData = IOUtils.CheckedReadBytes(delta, compressedTableLength);
var defaultTableData = CodeTable.Default.GetBytes();
var decompressedTableData = new byte[CodeTable.TableSize];
using (var tableOriginal = new MemoryStream(defaultTableData, false))
using (var tableDelta = new MemoryStream(compressedTableData, false))
using (var tableOutput = new MemoryStream(decompressedTableData, true))
{
var innerDecoder = new VcdiffDecoder(tableOriginal, tableDelta, tableOutput);
innerDecoder.Decode();
if (tableOutput.Position != CodeTable.TableSize)
{
throw new VcdiffFormatException("Compressed code table was incorrect size");
}
}
codeTable = new CodeTable(decompressedTableData);
cache = new AddressCache(nearSize, sameSize);
}
private void ReadHeader()
{
var header = IOUtils.CheckedReadBytes(delta, 4);
if (header[0] != 0xd6 || header[1] != 0xc3 || header[2] != 0xc4)
{
throw new VcdiffFormatException("Invalid VCDIFF header in delta stream, should start with 0xd6c3c4");
}
if (header[3] != 0)
{
throw new VcdiffFormatException("Only version 0 delta stream are supported by this version");
}
// Load the header indicator
var hdrIndicator = IOUtils.CheckedReadByte(delta);
if ((hdrIndicator & VCD_MASK) != 0)
{
throw new VcdiffFormatException("Invalid header indicator - only bits 1 and 2 can be set.");
}
if ((hdrIndicator & VCD_DECOMPRESS) != 0)
{
throw new VcdiffFormatException("This implementation does not support delta stream with secondary compressors");
}
if ((hdrIndicator & VCD_CODETABLE) != 0)
{
ReadCodeTable();
}
else
{
cache = new AddressCache(4, 3);
}
}