SabreTools/SabreTools.Helper/Skippers/SkipperRule.cs

using System;
using System.Collections.Generic;

using SabreTools.Helper.Data;

#if mono
using System.IO;
#else
using Alphaleonis.Win32.Filesystem;
#endif

using BinaryReader = System.IO.BinaryReader;
using BinaryWriter = System.IO.BinaryWriter;
using FileAccess = System.IO.FileAccess;
using FileMode = System.IO.FileMode;
using FileShare = System.IO.FileShare;
using FileStream = System.IO.FileStream;
using SeekOrigin = System.IO.SeekOrigin;
using Stream = System.IO.Stream;

namespace SabreTools.Helper.Skippers
{
	public class SkipperRule
	{
		// Public variables
		public long? StartOffset; // null is EOF
		public long? EndOffset; // null if EOF
		public HeaderSkipOperation Operation;
		public List<SkipperTest> Tests;
		public string SourceFile;

		/// <summary>
		/// Transform an input file using the given rule
		/// </summary>
		/// <param name="input">Input file name</param>
		/// <param name="output">Output file name</param>
		/// <param name="logger">Logger object for file and console output</param>
		/// <returns>True if the file was transformed properly, false otherwise</returns>
		public bool TransformFile(string input, string output, Logger logger)
		{
			bool success = true;

			// If the input file doesn't exist, fail
			if (!File.Exists(input))
			{
				logger.Error("I'm sorry but '" + input + "' doesn't exist!");
				return false;
			}

			// Create the output directory if it doesn't already
			if (!Directory.Exists(Path.GetDirectoryName(output)))
			{
				Directory.CreateDirectory(Path.GetDirectoryName(output));
			}

			logger.User("Attempting to apply rule to '" + input + "'");
			success = TransformStream(File.Open(input, FileMode.Open, FileAccess.Read, FileShare.ReadWrite), File.OpenWrite(output), logger);

			// If the output file has size 0, delete it
			if (new FileInfo(output).Length == 0)
			{
				try
				{
					File.Delete(output);
					success = false;
				}
				catch
				{
					// Don't log this file deletion error
				}
			}

			return success;
		}

		/// <summary>
		/// Transform an input stream using the given rule
		/// </summary>
		/// <param name="input">Input stream</param>
		/// <param name="output">Output stream</param>
		/// <param name="logger">Logger object for file and console output</param>
		/// <param name="keepReadOpen">True if the underlying read stream should be kept open, false otherwise</param>
		/// <param name="keepWriteOpen">True if the underlying write stream should be kept open, false otherwise</param>
		/// <returns>True if the file was transformed properly, false otherwise</returns>
		public bool TransformStream(Stream input, Stream output, Logger logger, bool keepReadOpen = false, bool keepWriteOpen = false)
		{
			bool success = true;

			// If the sizes are wrong for the values, fail
			long extsize = input.Length;
			if ((Operation > HeaderSkipOperation.Bitswap && (extsize % 2) != 0)
				|| (Operation > HeaderSkipOperation.Byteswap && (extsize % 4) != 0)
				|| (Operation > HeaderSkipOperation.Bitswap && (StartOffset == null || StartOffset % 2 == 0)))
			{
				logger.Error("The stream did not have the correct size to be transformed!");
				return false;
			}

			// Now read the proper part of the file and apply the rule
			BinaryWriter bw = null;
			BinaryReader br = null;
			try
			{
				logger.User("Applying found rule to input stream");
				bw = new BinaryWriter(output);
				br = new BinaryReader(input);

				// Seek to the beginning offset
				if (StartOffset == null)
				{
					success = false;
				}
				else if (Math.Abs((long)StartOffset) > input.Length)
				{
					success = false;
				}
				else if (StartOffset > 0)
				{
					input.Seek((long)StartOffset, SeekOrigin.Begin);
				}
				else if (StartOffset < 0)
				{
					input.Seek((long)StartOffset, SeekOrigin.End);
				}

				// Then read and apply the operation as you go
				if (success)
				{
					byte[] buffer = new byte[4];
					int pos = 0;
					while (input.Position < (EndOffset != null ? EndOffset : input.Length)
						&& input.Position < input.Length)
					{
						byte b = br.ReadByte();
						switch (Operation)
						{
							case HeaderSkipOperation.Bitswap:
								// http://stackoverflow.com/questions/3587826/is-there-a-built-in-function-to-reverse-bit-order
								uint r = b;
								int s = 7;
								for (b >>= 1; b != 0; b >>= 1)
								{
									r <<= 1;
									r |= (byte)(b & 1);
									s--;
								}
								r <<= s;
								buffer[pos] = (byte)r;
								break;
							case HeaderSkipOperation.Byteswap:
								if (pos % 2 == 1)
								{
									buffer[pos - 1] = b;
								}
								if (pos % 2 == 0)
								{
									buffer[pos + 1] = b;
								}
								break;
							case HeaderSkipOperation.Wordswap:
								buffer[3 - pos] = b;
								break;
							case HeaderSkipOperation.WordByteswap:
								buffer[(pos + 2) % 4] = b;
								break;
							case HeaderSkipOperation.None:
							default:
								buffer[pos] = b;
								break;
						}

						// Set the buffer position to default write to
						pos = (pos + 1) % 4;

						// If we filled a buffer, flush to the stream
						if (pos == 0)
						{
							bw.Write(buffer);
							bw.Flush();
							buffer = new byte[4];
						}
					}
					// If there's anything more in the buffer, write only the left bits
					for (int i = 0; i < pos; i++)
					{
						bw.Write(buffer[i]);
					}
				}
			}
			catch (Exception ex)
			{
				logger.Error(ex.ToString());
				return false;
			}
			finally
			{
				// If we're not keeping the read stream open, dispose of the binary reader
				if (!keepReadOpen)
				{
					br?.Dispose();
				}

				// If we're not keeping the write stream open, dispose of the binary reader
				if (!keepWriteOpen)
				{
					bw?.Dispose();
				}
			}

			return success;
		}
	}

	/// <summary>
	/// Intermediate class for storing Skipper Test information
	/// </summary>
	public struct SkipperTest
	{
		public HeaderSkipTest Type;
		public long? Offset; // null is EOF
		public byte[] Value;
		public bool Result;
		public byte[] Mask;
		public long? Size; // null is PO2, "power of 2" filesize
		public HeaderSkipTestFileOperator Operator;
	}
}