Providing streaming AudFormat data.

AudFormat.GetPCMInputStream now returns data that is streamed, rather than a MemoryStream.

OpenRA.Game/Primitives/SegmentStream.cs

@@ -21,6 +21,15 @@ namespace OpenRA.Primitives
 		public readonly long BaseOffset;
 		public readonly long BaseCount;
 
+		/// <summary>
+		/// Creates a new <see cref="SegmentStream"/> that wraps a subset of the source stream. This takes ownership of
+		/// the source stream. The <see cref="SegmentStream"/> is dependent on the source and changes its underlying
+		/// position.
+		/// </summary>
+		/// <param name="stream">The source stream, of which only a segment should be exposed. Ownership is transferred
+		/// to the <see cref="SegmentStream"/>.</param>
+		/// <param name="offset">The offset at which the segment starts.</param>
+		/// <param name="count">The length of the segment.</param>
 		public SegmentStream(Stream stream, long offset, long count)
 		{
 			if (stream == null)
@@ -90,7 +99,7 @@ namespace OpenRA.Primitives
 			base.Dispose(disposing);
 		}
 
-		public static long GetOverallNestedOffset(Stream stream, out Stream overallBaseStream)
+		static long GetOverallNestedOffset(Stream stream, out Stream overallBaseStream)
 		{
 			var offset = 0L;
 			overallBaseStream = stream;
@@ -99,5 +108,34 @@ namespace OpenRA.Primitives
 				offset += segmentStream.BaseOffset + GetOverallNestedOffset(segmentStream.BaseStream, out overallBaseStream);
 			return offset;
 		}
+
+		/// <summary>
+		/// Creates a new <see cref="Stream"/> that wraps a subset of the source stream without taking ownership of it,
+		/// allowing it to be reused by the caller. The <see cref="Stream"/> is independent of the source stream and
+		/// won't affect its position.
+		/// </summary>
+		/// <param name="stream">The source stream, of which only a segment should be exposed. Ownership is retained by
+		/// the caller.</param>
+		/// <param name="offset">The offset at which the segment starts.</param>
+		/// <param name="count">The length of the segment.</param>
+		public static Stream CreateWithoutOwningStream(Stream stream, long offset, int count)
+		{
+			Stream parentStream;
+			var nestedOffset = offset + GetOverallNestedOffset(stream, out parentStream);
+
+			// Special case FileStream - instead of creating an in-memory copy,
+			// just reference the portion of the on-disk file that we need to save memory.
+			// We use GetType instead of 'is' here since we can't handle any derived classes of FileStream.
+			if (parentStream.GetType() == typeof(FileStream))
+			{
+				var path = ((FileStream)parentStream).Name;
+				return new SegmentStream(File.OpenRead(path), nestedOffset, count);
+			}
+
+			// For all other streams, create a copy in memory.
+			// This uses more memory but is the only way in general to ensure the returned streams won't clash.
+			stream.Seek(offset, SeekOrigin.Begin);
+			return new MemoryStream(stream.ReadBytes(count));
+		}
 	}
 }