/// <summary>
/// Decodes an original stream and a delta stream, writing to a target stream.
/// The original stream may be null, so long as the delta stream never
/// refers to it. The original and delta streams must be readable, and the
/// original stream (if any) and the target stream must be seekable.
/// The target stream must be writable and readable. The original and target
/// streams are rewound to their starts before any data is read; the relevant data
/// must occur at the beginning of the original stream, and any data already present
/// in the target stream may be overwritten. The delta data must begin
/// wherever the delta stream is currently positioned. The delta stream must end
/// after the last window. The streams are not disposed by this method.
/// </summary>
/// <param name="original">Stream containing delta. May be null.</param>
/// <param name="delta">Stream containing delta data.</param>
/// <param name="output">Stream to write resulting data to.</param>
public static void Decode(Stream original, Stream delta, Stream output)
{
#region Simple argument checking
if (original != null && (!original.CanRead || !original.CanSeek))
{
throw new ArgumentException("Must be able to read and seek in original stream", "original");
}
if (delta == null)
{
throw new ArgumentNullException(nameof(delta));
}
if (!delta.CanRead)
{
throw new ArgumentException("Unable to read from delta stream");
}
if (output == null)
{
throw new ArgumentNullException(nameof(output));
}
if (!output.CanWrite || !output.CanRead || !output.CanSeek)
{
throw new ArgumentException("Must be able to read, write and seek in output stream", "output");
}
#endregion
// Now the arguments are checked, we construct an instance of the
// class and ask it to do the decoding.
VcdiffDecoder instance = new VcdiffDecoder(original, delta, output);
instance.Decode();
}
/// <summary>
/// Reads the custom code table, if there is one
/// </summary>
void ReadCodeTable()
{
// The length given includes the nearSize and sameSize bytes
int compressedTableLength = IOHelper.ReadBigEndian7BitEncodedInt(delta) - 2;
int nearSize = IOHelper.CheckedReadByte(delta);
int sameSize = IOHelper.CheckedReadByte(delta);
byte[] compressedTableData = IOHelper.CheckedReadBytes(delta, compressedTableLength);
byte[] defaultTableData = CodeTable.Default.GetBytes();
MemoryStream tableOriginal = new MemoryStream(defaultTableData, false);
MemoryStream tableDelta = new MemoryStream(compressedTableData, false);
byte[] decompressedTableData = new byte[1536];
MemoryStream tableOutput = new MemoryStream(decompressedTableData, true);
VcdiffDecoder.Decode(tableOriginal, tableDelta, tableOutput);
if (tableOutput.Position != 1536)
{
throw new VcdiffFormatException("Compressed code table was incorrect size");
}
_codeTable = new CodeTable(decompressedTableData);
_cache = new AddressCache(nearSize, sameSize);
}