1 files changed, 52 insertions, 0 deletions
diff --git a/crypto/src/util/io/PushbackStream.cs b/crypto/src/util/io/PushbackStream.cs
new file mode 100644
index 000000000..954694259
--- /dev/null
+++ b/crypto/src/util/io/PushbackStream.cs
@@ -0,0 +1,52 @@
+using System;
+using System.IO;
+
+using Org.BouncyCastle.Asn1.Utilities;
+
+namespace Org.BouncyCastle.Utilities.IO
+{
+	public class PushbackStream
+		: FilterStream
+	{
+		private int buf = -1;
+
+		public PushbackStream(
+			Stream s)
+			: base(s)
+		{
+		}
+
+		public override int ReadByte()
+		{
+			if (buf != -1)
+			{
+				int tmp = buf;
+				buf = -1;
+				return tmp;
+			}
+
+			return base.ReadByte();
+		}
+
+		public override int Read(byte[] buffer, int offset, int count)
+		{
+			if (buf != -1 && count > 0)
+			{
+				// TODO Can this case be made more efficient?
+				buffer[offset] = (byte) buf;
+				buf = -1;
+				return 1;
+			}
+
+			return base.Read(buffer, offset, count);
+		}
+
+		public virtual void Unread(int b)
+		{
+			if (buf != -1)
+				throw new InvalidOperationException("Can only push back one byte");
+
+			buf = b & 0xFF;
+		}
+	}
+}