mono/mcs/class/corlib/System.IO/IntPtrStream.cs

//
// System.IO.IntPtrStream: A stream that is backed up by unmanaged memory
//
// Author:
//   Miguel de Icaza ([email protected])
//
// Based on the code for MemoryStream.cs:
//
// Authors:	Marcin Szczepanski ([email protected])
//		Patrik Torstensson
//		Gonzalo Paniagua Javier ([email protected])
//
// (c) 2001,2002 Marcin Szczepanski, Patrik Torstensson
// (c) 2003 Ximian, Inc. (http://www.ximian.com)
//

using System.Runtime.InteropServices;
namespace System.IO {

	internal class IntPtrStream : Stream {
		unsafe byte *base_address;
		int size;
		int position;
		bool closed;

		public event EventHandler Closed;
		
		public IntPtrStream (IntPtr base_address, int size)
		{
			unsafe {
				this.base_address = (byte*)((void *)base_address);
			}
			this.size = size;
			position = 0;
		}

		public override bool CanRead {
			get {
				return true;
			}
		}

		public override bool CanSeek {
			get {
				return true;
			}
		}

		public override bool CanWrite {
			get {
				return false;
			}
		}

		public override long Position {
			get {
				return position;
			}

			set {
				if (position < 0)
					throw new ArgumentOutOfRangeException ("Position", "Can not be negative");
				if (position > size)
					throw new ArgumentOutOfRangeException ("Position", "Pointer falls out of range");

				position = (int) value;
			}
		}

		public override long Length {
			get {
				return size;
			}
		}

		public override int Read (byte [] buffer, int offset, int count)
		{
			if (buffer == null)
				throw new ArgumentNullException ("buffer");

			if (offset < 0 || count < 0)
				throw new ArgumentOutOfRangeException ("offset or count less than zero.");

			if (buffer.Length - offset < count )
				throw new ArgumentException ("offset+count",
							      "The size of the buffer is less than offset + count.");

			if (closed)
				throw new ObjectDisposedException ("Stream has been closed");

			if (position >= size || count == 0)
				return 0;

			if (position > size - count)
				count = size - position;

			unsafe {
				Marshal.Copy ((IntPtr) (base_address + position), buffer, offset, count);
			}
			position += count;
			return count;
		}

		public override int ReadByte ()
		{
			if (position >= size)
				return -1;

			if (closed)
				throw new ObjectDisposedException ("Stream has been closed");

			unsafe {
				return base_address [position++];
			}
		}

		public override long Seek (long offset, SeekOrigin loc)
		{
			// It's funny that they don't throw this exception for < Int32.MinValue
			if (offset > (long) Int32.MaxValue)
				throw new ArgumentOutOfRangeException ("Offset out of range. " + offset);

			if (closed)
				throw new ObjectDisposedException ("Stream has been closed");

			int ref_point;
			switch (loc) {
			case SeekOrigin.Begin:
				if (offset < 0)
					throw new IOException ("Attempted to seek before start of MemoryStream.");
				ref_point = 0;
				break;
			case SeekOrigin.Current:
				ref_point = position;
				break;
			case SeekOrigin.End:
				ref_point = size;
				break;
			default:
				throw new ArgumentException ("loc", "Invalid SeekOrigin");
			}

			checked {
				try {
					ref_point += (int) offset;
				} catch {
					throw new ArgumentOutOfRangeException ("Too large seek destination");
				}
				
				if (ref_point < 0)
					throw new IOException ("Attempted to seek before start of MemoryStream.");
			}

			position = ref_point;
			return position;
		}
		
		public override void SetLength (long value)
		{
			throw new NotSupportedException ("This stream can not change its size");
		}

		public override void Write (byte [] buffer, int offset, int count)
		{
			throw new NotSupportedException ("This stream can not change its size");
		}

		public override void WriteByte (byte value)
		{
			throw new NotSupportedException ("This stream can not change its size");
		}
		
		public override void Flush ()
		{
		}

		public override void Close ()
		{
			closed = true;

			if (Closed != null)
				Closed (this, null);
		}
	}
}