Copied from dotnet/android#3397

Steps to Reproduce

1. Use the ZipArchive and ZipArchiveEntry classes to open a stream to an entry in a zip file
2. Set up a GZipStream compressing to a MemoryStream
3. Copy the zip entry stream to the GZipStream
4. Observe the NotImplementedException

Repro project: https://github.com/mfeingol/repros/tree/master/Xamarin.Android-3397-CopyToAsync

Expected Behavior

Stream copy is successful, as it was in prior versions of the Mono runtime.

Actual Behavior

NotImplementedException:

  at System.IO.Compression.DeflateStream.WriteAsyncMemory (System.ReadOnlyMemory`1[T] source, System.Threading.CancellationToken cancellationToken) [0x00000] in <ca7419b40e504a6dbe088f6fe95d09aa>:0 
  at (wrapper remoting-invoke-with-check) System.IO.Compression.DeflateStream.WriteAsyncMemory(System.ReadOnlyMemory`1<byte>,System.Threading.CancellationToken)
  at System.IO.Compression.GZipStream.WriteAsync (System.ReadOnlyMemory`1[T] buffer, System.Threading.CancellationToken cancellationToken) [0x00026] in <ca7419b40e504a6dbe088f6fe95d09aa>:0 
  at System.IO.Stream.CopyToAsyncInternal (System.IO.Stream destination, System.Int32 bufferSize, System.Threading.CancellationToken cancellationToken) [0x000c7] in <ff07eae8184a40a08e79049bbcb31a0e>:0 
  at CopyToAsync.MainPage.Repro (System.Object sender, System.EventArgs args) [0x0008a] in C:\Users\mfeingol\source\Repos\CopyToAsync\CopyToAsync\CopyToAsync\MainPage.xaml.cs:35 

Example code:

ZipArchive archive = new ZipArchive(ZipFile, ZipArchiveMode.Read, true, Encoding.UTF8);
ZipArchiveEntry entry = archive.GetEntry("a4.jpg");
Stream src = entry.Open();

MemoryStream dest = new MemoryStream();

using (GZipStream gzip = new GZipStream(dest, CompressionLevel.Optimal, true))
    await src.CopyToAsync(gzip);

byte[] compressed = dest.ToArray();

Version Information

VS 16.2.0, fresh project from new project wizard, latest Xamarin.Forms Nuget packages (not that it's relevant)

Log File

log.txt