source: branches/eraser6/pluginsRewrite/Eraser.Plugins/ExtensionPoints/IErasureMethod.cs @ 2439

/* 
 * $Id: ErasureMethod.cs 2085 2010-05-09 10:00:15Z lowjoel $
 * Copyright 2008-2010 The Eraser Project
 * Original Author: Joel Low <lowjoel@users.sourceforge.net>
 * Modified By:
 * 
 * This file is part of Eraser.
 * 
 * Eraser is free software: you can redistribute it and/or modify it under the
 * terms of the GNU General Public License as published by the Free Software
 * Foundation, either version 3 of the License, or (at your option) any later
 * version.
 * 
 * Eraser is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 * A PARTICULAR PURPOSE. See the GNU General Public License for more details.
 * 
 * A copy of the GNU General Public License can be found at
 * <http://www.gnu.org/licenses/>.
 */

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using System.IO;
using Eraser.Util;

namespace Eraser.Plugins.ExtensionPoints
{
    /// <summary>
    /// An interface class representing the method for erasure. If classes only
    /// inherit this class, then the method can only be used to erase abstract
    /// streams, not unused drive space.
    /// </summary>
    public abstract class IErasureMethod : IRegisterable
    {
        public override string ToString()
        {
            if (Passes == 0)
                return Name;
            return Passes == 1 ? S._("{0} (1 pass)", Name) :
                S._("{0} ({1} passes)", Name, Passes);
        }

        /// <summary>
        /// The name of this erase pass, used for display in the UI
        /// </summary>
        public abstract string Name
        {
            get;
        }

        /// <summary>
        /// The number of erase passes for this erasure method.
        /// </summary>
        public abstract int Passes
        {
            get;
        }

        /// <summary>
        /// The GUID for this erasure method.
        /// </summary>
        public abstract Guid Guid
        {
            get;
        }

        /// <summary>
        /// Calculates the total size of the erasure data that needs to be written.
        /// This is mainly for use by the Manager to determine how much data needs
        /// to be written to disk.
        /// </summary>
        /// <param name="paths">The list containing the file paths to erase. This
        /// may be null if the list of paths are unknown.</param>
        /// <param name="targetSize">The precomputed value of the total size of
        /// the files to be erased.</param>
        /// <returns>The total size of the files that need to be erased.</returns>
        /// <remarks>This function MAY be slow. Most erasure methods can
        /// calculate this amount fairly quickly as the number of files and the
        /// total size of the files (the ones that take most computation time)
        /// are already provided. However some exceptional cases may take a
        /// long time if the data set is large.</remarks>
        public abstract long CalculateEraseDataSize(ICollection<StreamInfo> paths, long targetSize);

        /// <summary>
        /// The main bit of the class! This function is called whenever data has
        /// to be erased. Erase the stream passed in, using the given PRNG for
        /// randomness where necessary.
        /// 
        /// This function should be implemented thread-safe as using the same
        /// instance, this function may be called across different threads.
        /// </summary>
        /// <param name="stream">The stream which needs to be erased.</param>
        /// <param name="erasureLength">The length of the stream to erase. If all
        /// data in the stream should be overwritten, then pass in the maximum
        /// value for long, the function will take the minimum.</param>
        /// <param name="prng">The PRNG source for random data.</param>
        /// <param name="callback">The progress callback function.</param>
        public abstract void Erase(Stream stream, long erasureLength, IPrng prng,
            ErasureMethodProgressFunction callback);

        /// <summary>
        /// Disk operation write unit. Chosen such that this value mod 3, 4, 512,
        /// and 1024 is 0
        /// </summary>
        public const int DiskOperationUnit = 1536 * 4096;

        /// <summary>
        /// Unused space erasure file size. Each of the files used in erasing
        /// unused space will be of this size.
        /// </summary>
        public const int FreeSpaceFileUnit = DiskOperationUnit * 36;

        /// <summary>
        /// Shuffles the passes in the input array, effectively randomizing the
        /// order or rewrites.
        /// </summary>
        /// <param name="passes">The input set of passes.</param>
        /// <returns>The shuffled set of passes.</returns>
        protected static ErasureMethodPass[] ShufflePasses(ErasureMethodPass[] passes)
        {
            //Make a copy.
            ErasureMethodPass[] result = new ErasureMethodPass[passes.Length];
            passes.CopyTo(result, 0);

            //Randomize.
            IPrng rand = Host.Instance.Prngs.ActivePrng;
            for (int i = 0; i < result.Length; ++i)
            {
                int val = rand.Next(result.Length - 1);
                ErasureMethodPass tmpPass = result[val];
                result[val] = result[i];
                result[i] = tmpPass;
            }

            return result;
        }

        /// <summary>
        /// Helper function. This function will write random data to the stream
        /// using the provided PRNG.
        /// </summary>
        /// <param name="strm">The buffer to populate with data to write to disk.</param>
        /// <param name="prng">The PRNG used.</param>
        public static void WriteRandom(byte[] buffer, object value)
        {
            ((IPrng)value).NextBytes(buffer);
        }

        /// <summary>
        /// Helper function. This function will write the repeating pass constant.
        /// to the provided buffer.
        /// </summary>
        /// <param name="strm">The buffer to populate with data to write to disk.</param>
        /// <param name="value">The byte[] to write.</param>
        public static void WriteConstant(byte[] buffer, object value)
        {
            byte[] constant = (byte[])value;
            for (int i = 0; i < buffer.Length; ++i)
                buffer[i] = constant[i % constant.Length];
        }

        /// A simple callback for clients to retrieve progress information from
        /// the erase method.
        /// </summary>
        /// <param name="lastWritten">The amount of data written to the stream since
        /// the last call to the delegate.</param>
        /// <param name="totalData">The total amount of data that must be written to
        /// complete the erasure.</param>
        /// <param name="currentPass">The current pass number. The total number
        /// of passes can be found from the Passes property.</param>
        public delegate void ErasureMethodProgressFunction(long lastWritten, long totalData,
            int currentPass);
    }

    /// <summary>
    /// <summary>
    /// This class adds functionality to the ErasureMethod class to erase
    /// unused drive space.
    /// </summary>
    public abstract class UnusedSpaceErasureMethod : IErasureMethod
    {
        /// <summary>
        /// This function will allow clients to erase a file in a set of files
        /// used to fill the disk, thus achieving disk unused space erasure.
        /// 
        /// By default, this function will simply call the Erase method inherited
        /// from the ErasureMethod class.
        /// 
        /// This function should be implemented thread-safe as using the same
        /// instance, this function may be called across different threads.
        /// </summary>
        /// <param name="strm">The stream which needs to be erased.</param>
        /// <param name="prng">The PRNG source for random data.</param>
        /// <param name="callback">The progress callback function.</param>
        public virtual void EraseUnusedSpace(Stream stream, IPrng prng, ErasureMethodProgressFunction callback)
        {
            Erase(stream, long.MaxValue, prng, callback);
        }
    }

    /// <summary>
    /// Pass-based erasure method. This subclass of erasure methods follow a fixed
    /// pattern (constant or random data) for every pass, although the order of
    /// passes can be randomized. This is to simplify definitions of classes in
    /// plugins.
    /// 
    /// Since instances of this class apply data by passes, they can by default
    /// erase unused drive space as well.
    /// </summary>
    public abstract class PassBasedErasureMethod : UnusedSpaceErasureMethod
    {
        public override int Passes
        {
            get { return PassesSet.Length; }
        }

        /// <summary>
        /// Whether the passes should be randomized before running them in random
        /// order.
        /// </summary>
        protected abstract bool RandomizePasses
        {
            get;
        }

        /// <summary>
        /// The set of Pass objects describing the passes in this erasure method.
        /// </summary>
        protected abstract ErasureMethodPass[] PassesSet
        {
            get;
        }

        public override long CalculateEraseDataSize(ICollection<StreamInfo> paths, long targetSize)
        {
            //Simple. Amount of data multiplied by passes.
            return targetSize * Passes;
        }

        public override void Erase(Stream stream, long erasureLength, IPrng prng,
            ErasureMethodProgressFunction callback)
        {
            //Randomize the order of the passes
            ErasureMethodPass[] randomizedPasses = PassesSet;
            if (RandomizePasses)
                randomizedPasses = ShufflePasses(randomizedPasses);

            //Remember the starting position of the stream.
            long strmStart = stream.Position;
            long strmLength = Math.Min(stream.Length - strmStart, erasureLength);
            long totalData = CalculateEraseDataSize(null, strmLength);

            //Allocate memory for a buffer holding data for the pass.
            byte[] buffer = new byte[Math.Min(DiskOperationUnit, strmLength)];

            //Run every pass!
            for (int pass = 0; pass < Passes; ++pass)
            {
                //Do a progress callback first.
                if (callback != null)
                    callback(0, totalData, pass + 1);

                //Start from the beginning again
                stream.Seek(strmStart, SeekOrigin.Begin);

                //Write the buffer to disk.
                long toWrite = strmLength;
                int dataStopped = buffer.Length;
                while (toWrite > 0)
                {
                    //Calculate how much of the buffer to write to disk.
                    int amount = (int)Math.Min(toWrite, buffer.Length - dataStopped);

                    //If we have no data left, get more!
                    if (amount == 0)
                    {
                        randomizedPasses[pass].Execute(buffer, prng);
                        dataStopped = 0;
                        continue;
                    }

                    //Write the data.
                    stream.Write(buffer, dataStopped, amount);
                    stream.Flush();
                    toWrite -= amount;

                    //Do a progress callback.
                    if (callback != null)
                        callback(amount, totalData, pass + 1);
                }
            }
        }
    }

    /// <summary>
    /// A pass object. This object holds both the pass function, as well as the
    /// data used for the pass (random, byte, or triplet)
    /// </summary>
    public class ErasureMethodPass
    {
        public override string ToString()
        {
            return OpaqueValue == null ? S._("Random") : OpaqueValue.ToString();
        }

        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="function">The delegate to the function.</param>
        /// <param name="opaqueValue">The opaque value passed to the function.</param>
        public ErasureMethodPass(ErasureMethodPassFunction function, object opaqueValue)
        {
            Function = function;
            OpaqueValue = opaqueValue;
        }

        /// <summary>
        /// Executes the pass.
        /// </summary>
        /// <param name="buffer">The buffer to populate with the data to write.</param>
        /// <param name="prng">The PRNG used for random passes.</param>
        public void Execute(byte[] buffer, IPrng prng)
        {
            Function(buffer, OpaqueValue == null ? prng : OpaqueValue);
        }

        /// <summary>
        /// The function to execute for this pass.
        /// </summary>
        public ErasureMethodPassFunction Function { get; set; }

        /// <summary>
        /// The value to be passed to the executing function.
        /// </summary>
        public object OpaqueValue { get; set; }

        /// <summary>
        /// The prototype of a pass.
        /// </summary>
        /// <param name="strm">The buffer to populate with data to write to disk.</param>
        /// <param name="opaque">An opaque value, depending on the type of callback.</param>
        public delegate void ErasureMethodPassFunction(byte[] buffer, object opaque);
    }
}