Add option to export ROMs as ZIP files.

RomRepoMgr.Core/StreamWithLength.cs

@@ -0,0 +1,43 @@
+using System;
+using System.IO;
+
+namespace RomRepoMgr.Core
+{
+    internal sealed class StreamWithLength : Stream
+    {
+        readonly Stream _baseStream;
+
+        public StreamWithLength(Stream baseStream, long length)
+        {
+            _baseStream = baseStream;
+            Length      = length;
+        }
+
+        public override bool CanRead  => _baseStream.CanRead;
+        public override bool CanSeek  => _baseStream.CanSeek;
+        public override bool CanWrite => _baseStream.CanWrite;
+        public override long Length   { get; }
+
+        public override long Position
+        {
+            get => throw new NotSupportedException();
+            set => throw new NotSupportedException();
+        }
+
+        public override void Flush() => _baseStream.Flush();
+
+        public override int Read(byte[] buffer, int offset, int count) => _baseStream.Read(buffer, offset, count);
+
+        public override long Seek(long offset, SeekOrigin origin) => throw new NotSupportedException();
+
+        public override void SetLength(long value) => throw new NotSupportedException();
+
+        public override void Write(byte[] buffer, int offset, int count) => throw new NotSupportedException();
+
+        public override void Close()
+        {
+            _baseStream.Close();
+            base.Close();
+        }
+    }
+}