private static StreamCopyHelper ConstructCopyHelperForCommand(Command command, Stream input, Stream delta)
{
switch (command.Kind)
{
case CommandKind.Literal:
// for a literal command, we copy bytes from the delta stream
return new StreamCopyHelper(command.Parameter1, delta);
case CommandKind.Copy:
// for a copy command, we seek to the specified point and copy from the input stream
input.Seek(command.Parameter1, SeekOrigin.Begin);
return new StreamCopyHelper(command.Parameter2, input);
case CommandKind.End:
return null;
default:
throw new InvalidDataException(string.Format("Unknown command {0}", command.Parameter1));
}
}
private static Command ReadCommand(BinaryReader s)
{
// the first byte indicates which kind and format it is
var commandFormat = GetCommandFormat(s.ReadByte());
// then we might have to read the parameters in
Command result = new Command();
result.Kind = commandFormat.Kind;
if (commandFormat.Length1 > 0)
{
result.Parameter1 = StreamHelpers.ConvertFromBigEndian(s.ReadBytes(commandFormat.Length1));
}
else
{
// some of the commands encode the parameter directly into the command byte
result.Parameter1 = commandFormat.ImmediateValue;
}
if (commandFormat.Length2 > 0)
{
result.Parameter2 = StreamHelpers.ConvertFromBigEndian(s.ReadBytes(commandFormat.Length2));
}
return result;
}