tilkinsc · September 10, 2022 23:03 · Sep 10, 2022
diff --git a/TwoWayMemoryStream.cs b/TwoWayMemoryStream.cs
@@ -0,0 +1,73 @@
+using System.Runtime.InteropServices;
+
+namespace Util;
+
+class TwoWayMemoryStream : MemoryStream
+{
+
+	private byte[] _buffer;
+
+	private TwoWayMemoryStream()
+			: base()
+	{
+		_buffer = new byte[0];
+	}
+
+	private TwoWayMemoryStream(int capacity)
+			: base(capacity)
+	{
+		_buffer = new byte[capacity];
+	}
+
+	public TwoWayMemoryStream(byte[] buffer)
+			: base(buffer)
+	{
+		_buffer = buffer;
+	}
+
+	private TwoWayMemoryStream(byte[] buffer, bool writable)
+			: base(buffer, writable)
+	{
+		_buffer = buffer;
+	}
+
+	public override int Read([In, Out] byte[] buffer, int offset, int count)
+	{
+		if (buffer == null)
+			throw new ArgumentNullException("Buffer can't be null.");
+		if (offset < 0)
+			throw new ArgumentOutOfRangeException("Can't have a negative offset.");
+		if (count < 0)
+			throw new ArgumentOutOfRangeException("Can't read less than 0 bytes.");
+		if (buffer.Length - offset < count)
+			throw new ArgumentOutOfRangeException("Not enough space to read count bytes at offset.");
+		if (!CanRead)
+			throw new ObjectDisposedException("Could not read; stream has been closed.");
+
+		long n = Length - Position;
+		if (n > count)
+			n = count;
+		if (n <= 0)
+			return 0;
+
+		if (n <= 8) {
+			long byteCount = n;
+			while (--byteCount >= 0)
+				buffer[offset + byteCount] = _buffer[Position + byteCount];
+		} else {
+			Buffer.BlockCopy(_buffer, (int) Position, buffer, offset, (int) n);
+		}
+		Position -= n;
+		return 0;
+	}
+
+	public override int ReadByte()
+	{
+		if (!CanRead)
+			throw new ObjectDisposedException("Could not read; stream has been closed.");
+		if (Position >= Length)
+			return -1;
+		return _buffer[Position--];
+	}
+
+}