1 files changed, 212 insertions, 0 deletions

diff --git a/src/dtf/WixToolset.Dtf.Compression/DuplicateStream.cs b/src/dtf/WixToolset.Dtf.Compression/DuplicateStream.cs
new file mode 100644
index 00000000..50e62e73
--- /dev/null
+++ b/src/dtf/WixToolset.Dtf.Compression/DuplicateStream.cs
@@ -0,0 +1,212 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information.
+
+namespace WixToolset.Dtf.Compression
+{
+    using System;
+    using System.IO;
+
+    /// <summary>
+    /// Duplicates a source stream by maintaining a separate position.
+    /// </summary>
+    /// <remarks>
+    /// WARNING: duplicate streams are not thread-safe with respect to each other or the original stream.
+    /// If multiple threads use duplicate copies of the same stream, they must synchronize for any operations.
+    /// </remarks>
+    public class DuplicateStream : Stream
+    {
+        private Stream source;
+        private long position;
+
+        /// <summary>
+        /// Creates a new duplicate of a stream.
+        /// </summary>
+        /// <param name="source">source of the duplicate</param>
+        public DuplicateStream(Stream source)
+        {
+            if (source == null)
+            {
+                throw new ArgumentNullException("source");
+            }
+
+            this.source = DuplicateStream.OriginalStream(source);
+        }
+
+        /// <summary>
+        /// Gets the original stream that was used to create the duplicate.
+        /// </summary>
+        public Stream Source
+        {
+            get
+            {
+                return this.source;
+            }
+        }
+
+        /// <summary>
+        /// Gets a value indicating whether the source stream supports reading.
+        /// </summary>
+        /// <value>true if the stream supports reading; otherwise, false.</value>
+        public override bool CanRead
+        {
+            get
+            {
+                return this.source.CanRead;
+            }
+        }
+
+        /// <summary>
+        /// Gets a value indicating whether the source stream supports writing.
+        /// </summary>
+        /// <value>true if the stream supports writing; otherwise, false.</value>
+        public override bool CanWrite
+        {
+            get
+            {
+                return this.source.CanWrite;
+            }
+        }
+
+        /// <summary>
+        /// Gets a value indicating whether the source stream supports seeking.
+        /// </summary>
+        /// <value>true if the stream supports seeking; otherwise, false.</value>
+        public override bool CanSeek
+        {
+            get
+            {
+                return this.source.CanSeek;
+            }
+        }
+
+        /// <summary>
+        /// Gets the length of the source stream.
+        /// </summary>
+        public override long Length
+        {
+            get
+            {
+                return this.source.Length;
+            }
+        }
+
+        /// <summary>
+        /// Gets or sets the position of the current stream,
+        /// ignoring the position of the source stream.
+        /// </summary>
+        public override long Position
+        {
+            get
+            {
+                return this.position;
+            }
+
+            set
+            {
+                this.position = value;
+            }
+        }
+
+        /// <summary>
+        /// Retrieves the original stream from a possible duplicate stream.
+        /// </summary>
+        /// <param name="stream">Possible duplicate stream.</param>
+        /// <returns>If the stream is a DuplicateStream, returns
+        /// the duplicate's source; otherwise returns the same stream.</returns>
+        public static Stream OriginalStream(Stream stream)
+        {
+            DuplicateStream dupStream = stream as DuplicateStream;
+            return dupStream != null ? dupStream.Source : stream;
+        }
+
+        /// <summary>
+        /// Flushes the source stream.
+        /// </summary>
+        public override void Flush()
+        {
+            this.source.Flush();
+        }
+
+        /// <summary>
+        /// Sets the length of the source stream.
+        /// </summary>
+        /// <param name="value">The desired length of the stream in bytes.</param>
+        public override void SetLength(long value)
+        { 
+            this.source.SetLength(value);
+        }
+
+        /// <summary>
+        /// Closes the underlying stream, effectively closing ALL duplicates.
+        /// </summary>
+        public override void Close()
+        {
+            this.source.Close();
+        }
+
+        /// <summary>
+        /// Reads from the source stream while maintaining a separate position
+        /// and not impacting the source stream's position.
+        /// </summary>
+        /// <param name="buffer">An array of bytes. When this method returns, the buffer
+        /// contains the specified byte array with the values between offset and
+        /// (offset + count - 1) replaced by the bytes read from the current source.</param>
+        /// <param name="offset">The zero-based byte offset in buffer at which to begin
+        /// storing the data read from the current stream.</param>
+        /// <param name="count">The maximum number of bytes to be read from the current stream.</param>
+        /// <returns>The total number of bytes read into the buffer. This can be less
+        /// than the number of bytes requested if that many bytes are not currently available,
+        /// or zero (0) if the end of the stream has been reached.</returns>
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            long saveSourcePosition = this.source.Position;
+            this.source.Position = this.position;
+            int read = this.source.Read(buffer, offset, count);
+            this.position = this.source.Position;
+            this.source.Position = saveSourcePosition;
+            return read;
+        }
+
+        /// <summary>
+        /// Writes to the source stream while maintaining a separate position
+        /// and not impacting the source stream's position.
+        /// </summary>
+        /// <param name="buffer">An array of bytes. This method copies count
+        /// bytes from buffer to the current stream.</param>
+        /// <param name="offset">The zero-based byte offset in buffer at which
+        /// to begin copying bytes to the current stream.</param>
+        /// <param name="count">The number of bytes to be written to the
+        /// current stream.</param>
+        public override void Write(byte[] buffer, int offset, int count)
+        {
+            long saveSourcePosition = this.source.Position;
+            this.source.Position = this.position;
+            this.source.Write(buffer, offset, count);
+            this.position = this.source.Position;
+            this.source.Position = saveSourcePosition;
+        }
+
+        /// <summary>
+        /// Changes the position of this stream without impacting the
+        /// source stream's position.
+        /// </summary>
+        /// <param name="offset">A byte offset relative to the origin parameter.</param>
+        /// <param name="origin">A value of type SeekOrigin indicating the reference
+        /// point used to obtain the new position.</param>
+        /// <returns>The new position within the current stream.</returns>
+        public override long Seek(long offset, SeekOrigin origin)
+        {
+            long originPosition = 0;
+            if (origin == SeekOrigin.Current)
+            {
+                originPosition = this.position;
+            }
+            else if (origin == SeekOrigin.End)
+            {
+                originPosition = this.Length;
+            }
+
+            this.position = originPosition + offset;
+            return this.position;
+        }
+    }
+}