v0.80.65

AssetStudio/OffsetStream.cs

@@ -0,0 +1,75 @@
+using System;
+using System.IO;
+
+namespace AssetStudio
+{
+    public class OffsetStream : Stream
+    {
+        private readonly Stream _baseStream;
+        private long _offset;
+
+        public override bool CanRead => _baseStream.CanRead;
+        public override bool CanSeek => _baseStream.CanSeek;
+        public override bool CanWrite => false;
+
+        public long Offset
+        {
+            get => _offset;
+            set
+            {
+                if (value < 0 || value > _baseStream.Length)
+                {
+                    throw new IOException($"{nameof(Offset)} is out of stream bound");
+                }
+                _offset = value;
+                Seek(0, SeekOrigin.Begin);
+            }
+        }
+        public long AbsolutePosition => _baseStream.Position;
+        public long Remaining => Length - Position;
+
+        public override long Length => _baseStream.Length - _offset;
+        public override long Position
+        {
+            get => _baseStream.Position - _offset;
+            set => Seek(value, SeekOrigin.Begin);
+        }
+
+        public OffsetStream(Stream stream, long offset)
+        {
+            _baseStream = stream;
+
+            Offset = offset;
+        }
+
+        public override long Seek(long offset, SeekOrigin origin)
+        {
+            if (offset > _baseStream.Length)
+            {
+                throw new IOException("Unable to seek beyond stream bound");
+            }
+
+            var target = origin switch
+            {
+                SeekOrigin.Begin => offset + _offset,
+                SeekOrigin.Current => offset + Position,
+                SeekOrigin.End => offset + _baseStream.Length,
+                _ => throw new NotSupportedException()
+            };
+
+            _baseStream.Seek(target, SeekOrigin.Begin);
+            return Position;
+        }
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            if (offset > _baseStream.Length || Position + count > _baseStream.Length)
+            {
+                throw new IOException("Unable to read beyond stream bound");
+            }
+            return _baseStream.Read(buffer, offset, count);
+        }
+        public override void Write(byte[] buffer, int offset, int count) => throw new NotImplementedException();
+        public override void SetLength(long value) => throw new NotImplementedException();
+        public override void Flush() => throw new NotImplementedException();
+    }
+}