public void Decode(Window window)
{
// Clear cache
codeTable.Cache.Initialize();
// Set the target window offset
window.TargetWindowOffset = (uint)output.Position;
// For each instruction
Instruction firstInstruction, secondInstruction;
while (!window.Instructions.Eof) {
byte codeIndex = window.Instructions.ReadByte();
codeTable.GetInstructions(codeIndex, out firstInstruction, out secondInstruction);
firstInstruction.Decode(window, input, output);
secondInstruction.Decode(window, input, output);
}
// Check all data has been decoded
if (output.Position - window.TargetWindowOffset != window.TargetWindowLength)
throw new Exception("Target window not fully decoded");
// Check checksum
if (window.Source.Contains(WindowFields.Adler32)) {
output.Position = window.TargetWindowOffset;
uint newAdler = Adler32.Run(1, output, window.TargetWindowLength);
if (newAdler != window.Checksum)
throw new Exception("Invalid checksum");
}
}
public void Decode(Window window, Stream input, Stream output)
{
if (Type != InstructionType.Noop && SizeInTable == 0)
Size = window.Instructions.ReadInteger();
DecodeInstruction(window, input, output);
}
public void Run()
{
WindowReader windowReader = new WindowReader(Patch, Header);
WindowDecoder windowDecoder = new WindowDecoder(Input, Output);
// Decode windows until there are no more bytes to process
while (Patch.Position < Patch.Length) {
DisposeLastWindow();
Window window = windowReader.Read();
LastWindow = window;
windowDecoder.Decode(window);
OnProgressChanged(1.0 * Patch.Position / Patch.Length);
}
OnFinished();
}
private Window ReadWindow()
{
Window window = new Window();
// Get window indicator
window.Source = (WindowFields)vcdReader.ReadByte();
if (window.Source.Contains(WindowFields.NotSupported))
throw new FormatException("unrecognized window indicator bits set");
if (window.Source.Contains(WindowFields.Source | WindowFields.Target)) {
window.SourceSegmentLength = vcdReader.ReadInteger();
window.SourceSegmentOffset = vcdReader.ReadInteger();
}
// Copy offset and copy length may not overflow
if (window.SourceSegmentOffset.CheckOverflow(window.SourceSegmentLength))
throw new FormatException("decoder copy window overflows a file offset");
// Check copy window bounds
if (window.Source.Contains(WindowFields.Target) &&
window.SourceSegmentOffset + window.SourceSegmentLength > lastWindowOffset)
throw new FormatException("VCD_TARGET window out of bounds");
// Start of Delta Encoding Data
vcdReader.ReadInteger(); // Length of the delta encoding (following data)
// Get the length of target window
window.TargetWindowLength = vcdReader.ReadInteger();
lastWindowLength = window.TargetWindowLength;
// Set the maximum decoder position, beyond which we should not
// decode any data. This may not exceed the size of a UInt32.
if (window.SourceSegmentLength.CheckOverflow(window.TargetWindowLength))
throw new FormatException("decoder target window overflows a UInt32");
// Check for malicious files
if (window.TargetWindowLength > HardMaxWindowSize)
throw new FormatException("Hard window size exceeded");
// Get compressed / delta fields
window.CompressedFields = (WindowCompressedFields)vcdReader.ReadByte();
if (window.CompressedFields.Contains(WindowCompressedFields.Invalid))
throw new FormatException("unrecognized delta indicator bits set");
// Compressed fields is only used with secondary compression
if (window.CompressedFields != WindowCompressedFields.None &&
header.SecondaryCompressor == SecondaryCompressor.None)
throw new FormatException("invalid delta indicator bits set");
// Read section lengths
uint dataLength = vcdReader.ReadInteger();
uint instructionsLength = vcdReader.ReadInteger();
uint addressesLength = vcdReader.ReadInteger();
// Read checksum if so (it's in big-endian-non-integer)
if (window.Source.Contains(WindowFields.Adler32)) {
byte[] checksum = vcdReader.ReadBytes(4);
window.Checksum = (uint)((checksum[0] << 24) | (checksum[1] << 16) |
(checksum[2] << 8) | checksum[3]);
}
// Read sections
MemoryStream data = new MemoryStream(vcdReader.ReadBytes(dataLength));
MemoryStream instructions = new MemoryStream(vcdReader.ReadBytes(instructionsLength));
MemoryStream addresses = new MemoryStream(vcdReader.ReadBytes(addressesLength));
window.Data = new VcdReader(data);
window.Instructions = new VcdReader(instructions);
window.Addresses = new VcdReader(addresses);
return window;
}
private void DisposeLastWindow()
{
if (LastWindow != null) {
LastWindow.Data.BaseStream.Dispose();
LastWindow.Data = null;
LastWindow.Instructions.BaseStream.Dispose();
LastWindow.Instructions = null;
LastWindow.Addresses.BaseStream.Dispose();
LastWindow.Addresses = null;
LastWindow = null;
}
}
public abstract void DecodeInstruction(Window window, Stream input, Stream output);
