Implement Stream.Read(Span<byte>) overloads.

The default Stream implementation of this method has to rent an array so it can call the overload that accepts an array, and then copy the output over. This is because the array overload is required and the span overload was only added more recently.

We can avoid the overhead of this by implementing the span overload and working with the destination span directly. Do so for all classes we have that derive from Stream, and redirect their array overload to the span overload for code reuse.

OpenRA.Game/Primitives/MergedStream.cs

@@ -80,18 +80,23 @@ namespace OpenRA.Primitives
 		}
 
 		public override int Read(byte[] buffer, int offset, int count)
+		{
+			return Read(buffer.AsSpan(offset, count));
+		}
+
+		public override int Read(Span<byte> buffer)
 		{
 			int bytesRead;
 
 			if (position >= Stream1.Length)
-				bytesRead = Stream2.Read(buffer, offset, count);
-			else if (count > Stream1.Length)
+				bytesRead = Stream2.Read(buffer);
+			else if (buffer.Length > Stream1.Length)
 			{
-				bytesRead = Stream1.Read(buffer, offset, (int)Stream1.Length);
-				bytesRead += Stream2.Read(buffer, (int)Stream1.Length, count - (int)Stream1.Length);
+				bytesRead = Stream1.Read(buffer[..(int)Stream1.Length]);
+				bytesRead += Stream2.Read(buffer[(int)Stream1.Length..]);
 			}
 			else
-				bytesRead = Stream1.Read(buffer, offset, count);
+				bytesRead = Stream1.Read(buffer);
 
 			position += bytesRead;
 
@@ -108,6 +113,11 @@ namespace OpenRA.Primitives
 			throw new NotSupportedException();
 		}
 
+		public override void Write(ReadOnlySpan<byte> buffer)
+		{
+			throw new NotSupportedException();
+		}
+
 		public override bool CanRead => Stream1.CanRead && Stream2.CanRead;
 
 		public override bool CanSeek => Stream1.CanSeek && Stream2.CanSeek;