DiscUtils: Fat: Fix an issue with no long path name support in the upstream library

DiscUtils/DiscUtils.Fat/ClusterReader.cs

@@ -0,0 +1,95 @@
+//
+// Copyright (c) 2008-2011, Kenneth Bell
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+//
+
+using System;
+using System.IO;
+using DiscUtils.Streams;
+
+namespace DiscUtils.Fat
+{
+    internal sealed class ClusterReader
+    {
+        private readonly int _bytesPerSector;
+
+        /// <summary>
+        /// Pre-calculated value because of number of uses of this externally.
+        /// </summary>
+        private readonly int _clusterSize;
+
+        private readonly int _firstDataSector;
+        private readonly int _sectorsPerCluster;
+        private readonly Stream _stream;
+
+        public ClusterReader(Stream stream, int firstDataSector, int sectorsPerCluster, int bytesPerSector)
+        {
+            _stream = stream;
+            _firstDataSector = firstDataSector;
+            _sectorsPerCluster = sectorsPerCluster;
+            _bytesPerSector = bytesPerSector;
+
+            _clusterSize = _sectorsPerCluster * _bytesPerSector;
+        }
+
+        public int ClusterSize
+        {
+            get { return _clusterSize; }
+        }
+
+        public void ReadCluster(uint cluster, byte[] buffer, int offset)
+        {
+            if (offset + ClusterSize > buffer.Length)
+            {
+                throw new ArgumentOutOfRangeException(nameof(offset),
+                    "buffer is too small - cluster would overflow buffer");
+            }
+
+            uint firstSector = (uint)((cluster - 2) * _sectorsPerCluster + _firstDataSector);
+
+            _stream.Position = firstSector * _bytesPerSector;
+            StreamUtilities.ReadExact(_stream, buffer, offset, _clusterSize);
+        }
+
+        internal void WriteCluster(uint cluster, byte[] buffer, int offset)
+        {
+            if (offset + ClusterSize > buffer.Length)
+            {
+                throw new ArgumentOutOfRangeException(nameof(offset),
+                    "buffer is too small - cluster would overflow buffer");
+            }
+
+            uint firstSector = (uint)((cluster - 2) * _sectorsPerCluster + _firstDataSector);
+
+            _stream.Position = firstSector * _bytesPerSector;
+
+            _stream.Write(buffer, offset, _clusterSize);
+        }
+
+        internal void WipeCluster(uint cluster)
+        {
+            uint firstSector = (uint)((cluster - 2) * _sectorsPerCluster + _firstDataSector);
+
+            _stream.Position = firstSector * _bytesPerSector;
+
+            _stream.Write(new byte[_clusterSize], 0, _clusterSize);
+        }
+    }
+}