LibHac/libhac/XTSSharp/RandomAccessSectorStream.cs

// Copyright (c) 2010 Gareth Lennox (garethl@dwakn.com)
// All rights reserved.

// Redistribution and use in source and binary forms, with or without modification,
// are permitted provided that the following conditions are met:

//     * Redistributions of source code must retain the above copyright notice,
//       this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above copyright notice,
//       this list of conditions and the following disclaimer in the documentation
//       and/or other materials provided with the distribution.
//     * Neither the name of Gareth Lennox nor the names of its
//       contributors may be used to endorse or promote products derived from this
//       software without specific prior written permission.

// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
// THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

using System;
using System.Collections.Generic;
using System.IO;

namespace libhac.XTSSharp
{
    /// <summary>
    /// A wraps a sector based stream and provides random access to it
    /// </summary>
    public class RandomAccessSectorStream : Stream
    {
        private byte[] _buffer;
        private readonly int _bufferSize;
        private readonly SectorStream _s;
        private readonly bool _keepOpen;
        private bool _bufferDirty;
        private bool _bufferLoaded;
        private int _bufferPos;
        private int _currentBufferSize;

        private long PhysicalRead { get; set; }
        private long VirtualRead { get; set; }
        private int CacheMisses { get; set; }
        private int CacheHits { get; set; }

        // List should work just fine for a tiny cache
        private List<Sector> Cache { get; }
        private const int CacheSize = 4;

        /// <summary>
        /// Creates a new stream
        /// </summary>
        /// <param name="s">Base stream</param>
        public RandomAccessSectorStream(SectorStream s)
            : this(s, true)
        {
        }

        /// <summary>
        /// Creates a new stream
        /// </summary>
        /// <param name="s">Base stream</param>
        /// <param name="keepOpen">Should this stream leave the base stream open when disposed?</param>
        public RandomAccessSectorStream(SectorStream s, bool keepOpen)
        {
            _s = s;
            _keepOpen = keepOpen;
            _buffer = new byte[s.SectorSize];
            _bufferSize = s.SectorSize;

            Cache = new List<Sector>(CacheSize);

            for (int i = 0; i < CacheSize; i++)
            {
                Cache.Add(new Sector
                {
                    Position = -1,
                    Data = new byte[_bufferSize]
                });
            }
        }

        /// <summary>
        /// Gets a value indicating whether the current stream supports reading.
        /// </summary>
        /// <returns>true if the stream supports reading; otherwise, false.</returns>
        public override bool CanRead
        {
            get { return _s.CanRead; }
        }

        /// <summary>
        /// Gets a value indicating whether the current stream supports seeking.
        /// </summary>
        /// <returns>true if the stream supports seeking; otherwise, false.</returns>
        public override bool CanSeek
        {
            get { return _s.CanSeek; }
        }

        /// <summary>
        /// Gets a value indicating whether the current stream supports writing.
        /// </summary>
        /// <returns>true if the stream supports writing; otherwise, false.</returns>
        public override bool CanWrite
        {
            get { return _s.CanWrite; }
        }

        /// <summary>
        /// Gets the length in bytes of the stream.
        /// </summary>
        /// <returns>A long value representing the length of the stream in bytes.</returns>
        public override long Length
        {
            get { return _s.Length; }
        }

        /// <summary>
        /// Gets or sets the position within the current stream.
        /// </summary>
        /// <returns>The current position within the stream.</returns>
        public override long Position
        {
            get { return _bufferLoaded ? (_s.Position - _currentBufferSize + _bufferPos) : _s.Position + _bufferPos; }
            set
            {
                if (value < 0L)
                    throw new ArgumentOutOfRangeException("value");

                var sectorPosition = (value % _bufferSize);
                var position = value - sectorPosition;

                //see if its within the current sector
                if (_bufferLoaded)
                {
                    var basePosition = _s.Position - _bufferSize;
                    if (value > basePosition && value < basePosition + _bufferSize)
                    {
                        _bufferPos = (int)sectorPosition;
                        return;
                    }
                }
                //outside the current buffer

                //write it
                if (_bufferDirty)
                    WriteSector();

                _s.Position = position;

                //read this sector
                ReadSector();

                //bump us forward if need be
                _bufferPos = (int)sectorPosition;
            }
        }

        /// <summary>
        /// Releases the unmanaged resources used by the <see cref="T:System.IO.Stream"/> and optionally releases the managed resources.
        /// </summary>
        /// <param name="disposing">true to release both managed and unmanaged resources; false to release only unmanaged resources. </param>
        protected override void Dispose(bool disposing)
        {
            Flush();

            base.Dispose(disposing);

            if (!_keepOpen)
                _s.Dispose();
        }

        /// <summary>
        /// Clears all buffers for this stream and causes any buffered data to be written to the underlying device.
        /// </summary>
        public override void Flush()
        {
            if (_bufferDirty)
                WriteSector();
        }

        /// <summary>
        /// Sets the position within the current stream.
        /// </summary>
        /// <returns>
        /// The new position within the current stream.
        /// </returns>
        /// <param name="offset">A byte offset relative to the <paramref name="origin"/> parameter.</param>
        /// <param name="origin">A value of type <see cref="T:System.IO.SeekOrigin"/> indicating the reference point used to obtain the new position.</param>
        public override long Seek(long offset, SeekOrigin origin)
        {
            long newPosition;
            switch (origin)
            {
                case SeekOrigin.Begin:
                    newPosition = offset;
                    break;
                case SeekOrigin.End:
                    newPosition = Length - offset;
                    break;
                default:
                    newPosition = Position + offset;
                    break;
            }

            Position = newPosition;

            return newPosition;
        }

        /// <summary>
        /// Sets the length of the current stream.
        /// </summary>
        /// <param name="value">The desired length of the current stream in bytes.</param>
        public override void SetLength(long value)
        {
            var remainder = value % _s.SectorSize;

            if (remainder > 0)
            {
                value = (value - remainder) + _bufferSize;
            }

            _s.SetLength(value);
        }

        /// <summary>
        /// Reads a sequence of bytes from the current stream and advances the position within the stream by the number of bytes read.
        /// </summary>
        /// <returns>The total number of bytes read into the buffer. This can be less than the number of bytes requested if that many bytes are not currently available, or zero (0) if the end of the stream has been reached.</returns>
        /// <param name="buffer">An array of bytes. When this method returns, the buffer contains the specified byte array with the values between <paramref name="offset"/> and (<paramref name="offset"/> + <paramref name="count"/> - 1) replaced by the bytes read from the current source. </param>
        /// <param name="offset">The zero-based byte offset in <paramref name="buffer"/> at which to begin storing the data read from the current stream.</param>
        /// <param name="count">The maximum number of bytes to be read from the current stream.</param>
        public override int Read(byte[] buffer, int offset, int count)
        {
            var position = Position;

            if (position + count > _s.Length)
            {
                count = (int)(_s.Length - position);
            }

            if (!_bufferLoaded)
                ReadSector();

            var totalBytesRead = 0;
            while (count > 0)
            {
                var bytesToRead = Math.Min(count, _bufferSize - _bufferPos);

                Buffer.BlockCopy(_buffer, _bufferPos, buffer, offset, bytesToRead);

                offset += bytesToRead;
                _bufferPos += bytesToRead;
                count -= bytesToRead;

                totalBytesRead += bytesToRead;

                if (_bufferPos == _bufferSize)
                    ReadSector();
            }

            VirtualRead += totalBytesRead;

            return totalBytesRead;
        }

        /// <summary>
        /// Writes a sequence of bytes to the current stream and advances the current position within this stream by the number of bytes written.
        /// </summary>
        /// <param name="buffer">An array of bytes. This method copies <paramref name="count"/> bytes from <paramref name="buffer"/> to the current stream.</param>
        /// <param name="offset">The zero-based byte offset in <paramref name="buffer"/> at which to begin copying bytes to the current stream.</param>
        /// <param name="count">The number of bytes to be written to the current stream.</param>
        public override void Write(byte[] buffer, int offset, int count)
        {
            while (count > 0)
            {
                if (!_bufferLoaded)
                    ReadSector();

                var bytesToWrite = Math.Min(count, _bufferSize - _bufferPos);

                Buffer.BlockCopy(buffer, offset, _buffer, _bufferPos, bytesToWrite);

                offset += bytesToWrite;
                _bufferPos += bytesToWrite;
                count -= bytesToWrite;
                _bufferDirty = true;

                if (_bufferPos == _bufferSize)
                    WriteSector();
            }
        }

        /// <summary>
        /// Reads a sector
        /// </summary>
        private void ReadSector()
        {
            if (_bufferLoaded && _bufferDirty)
            {
                WriteSector();
            }

            if (_s.Position == _s.Length)
            {
                return;
            }

            var sectorPosition = _s.Position;

            for (int i = 0; i < CacheSize; i++)
            {
                var sector = Cache[i];
                if (sector.Position == sectorPosition)
                {
                    if (i != 0)
                    {
                        Cache.RemoveAt(i);
                        Cache.Insert(0, sector);
                    }

                    _buffer = sector.Data;

                    _bufferLoaded = true;
                    _bufferPos = 0;
                    _bufferDirty = false;
                    _currentBufferSize = sector.Length;
                    CacheHits++;
                    _s.Position += _bufferSize;
                    return;
                }
            }

            var item = Cache[CacheSize - 1];
            Cache.RemoveAt(CacheSize - 1);
            _buffer = item.Data;

            var bytesRead = _s.Read(_buffer, 0, _buffer.Length);
            PhysicalRead += bytesRead;

            //clean the end of it
            if (bytesRead != _bufferSize)
                Array.Clear(_buffer, bytesRead, _buffer.Length - bytesRead);

            _bufferLoaded = true;
            _bufferPos = 0;
            _bufferDirty = false;
            _currentBufferSize = bytesRead;

            item.Position = sectorPosition;
            item.Length = bytesRead;
            Cache.Insert(0, item);
            CacheMisses++;
        }

        /// <summary>
        /// Writes a sector
        /// </summary>
        private void WriteSector()
        {
            if (_bufferLoaded)
            {
                //go back to beginning of the current sector
                _s.Seek(-_bufferSize, SeekOrigin.Current);
            }

            //write it
            _s.Write(_buffer, 0, _bufferSize);
            _bufferDirty = false;
            _bufferLoaded = false;
            _bufferPos = 0;
            Array.Clear(_buffer, 0, _bufferSize);
        }

        private class Sector
        {
            public long Position { get; set; }
            public byte[] Data { get; set; }
            public int Length { get; set; }
        }
    }
}