Starting in Mono 6.0 (2019-02), NotImplementedException prevents using StreamWriter with GZipStream for encodings that use a preamble

[brendanzagaeski]

Starting in Mono 6.0 (2019-02), NotImplementedException prevents using StreamWriter with GZipStream for encodings that use a preamble

This is a follow-up to: dotnet/android#3397 (comment) and #16122

Steps to reproduce

Build and run the following program:

using System.IO;
using System.IO.Compression;
using System.Text;


class Program {
	public static void Main (string [] args)
	{
		MemoryStream dest = new MemoryStream ();
		using (GZipStream gzip = new GZipStream (dest, CompressionLevel.Optimal, true))
		using (StreamWriter sw = new StreamWriter (gzip, Encoding.UTF8)) {
			sw.Flush ();
		}
	}
}

Current behavior

With Mono 6.0.0.319 (2019-02/52203786470) and higher, the program aborts due to the following exception:

Unhandled Exception:
System.NotImplementedException: The method or operation is not implemented.
  at System.IO.Compression.DeflateStream.WriteCore (System.ReadOnlySpan`1[T] source) [0x00000] in /Users/builder/jenkins/workspace/build-package-osx-mono/2019-02/external/bockbuild/builds/mono-x64/mcs/class/System/System.IO.Compression/DeflateStream.cs:183 
  at (wrapper remoting-invoke-with-check) System.IO.Compression.DeflateStream.WriteCore(System.ReadOnlySpan`1<byte>)
  at System.IO.Compression.GZipStream.Write (System.ReadOnlySpan`1[T] buffer) [0x00025] in /Users/builder/jenkins/workspace/build-package-osx-mono/2019-02/external/bockbuild/builds/mono-x64/external/corefx/src/System.IO.Compression/src/System/IO/Compression/GZipStream.cs:127 
  at System.IO.StreamWriter.Flush (System.Boolean flushStream, System.Boolean flushEncoder) [0x00048] in /Users/builder/jenkins/workspace/build-package-osx-mono/2019-02/external/bockbuild/builds/mono-x64/external/corefx/src/Common/src/CoreLib/System/IO/StreamWriter.cs:265 
  at System.IO.StreamWriter.Flush () [0x00006] in /Users/builder/jenkins/workspace/build-package-osx-mono/2019-02/external/bockbuild/builds/mono-x64/external/corefx/src/Common/src/CoreLib/System/IO/StreamWriter.cs:239 
  at MainClass.Main (System.String[] args) [0x0001d] in <69e647dabefa4ac185e6a93787396406>:0 

Expected behavior

With Mono 5.18.1.24 (2018-08/082e1a23463), the program completes successfully and exits without error.

(Note that on Mono 6.0 or higher, changing StreamWriter (gzip, Encoding.UTF8) to StreamWriter (gzip) also allows the program to complete successfully because StreamWriter uses new UTF8Encoding (encoderShouldEmitUTF8Identifier: false) by default, and that encoding has a 0-length Preamble.)

On which platforms did you notice this

[x] macOS
[x] Android

[marek-safar]

@steveisok regression in 6.0

[ronnyhash]

When can we expect this in a stable release?

[brendanzagaeski]

When can we expect this in a stable release?

If you're wondering about this mostly due to the item https://github.com/Azure/azure-mobile-apps-net-client/issues/514, note that this issue #16950 was also present in Xamarin.Android 9.4.1.1 in Visual Studio 2019 version 16.2 and Visual Studio 2019 for Mac version 8.2, so this issue would not be responsible for the appearance of https://github.com/Azure/azure-mobile-apps-net-client/issues/514 in Xamarin.Android 10.0.0.43 in Visual Studio 2019 version 16.3 and Visual Studio 2019 for Mac version 8.3.

For the question of when the fix for this issue #16950 will be included in a Xamarin.Android release, I don't yet have information to share, but I will keep this issue updated as information becomes available.

[ronnyhash]

Thank you for giving that explanation! I really appreciate it!

[brendanzagaeski]

Xamarin release status update

New Release versions of Xamarin.Android, Xamarin.iOS, and Xamarin.Mac have now been published that include the fix for this item.

Fix included in Xamarin.Android 10.0.3.0, Xamarin.iOS 13.2.0.47, and Xamarin.Mac 6.2.0.47

Fix included on Windows in Visual Studio 2019 version 16.3.3. To get the new version that includes the fix, check for the latest updates or install the latest version from https://visualstudio.microsoft.com/downloads/.

Fix included on macOS in Visual Studio 2019 for Mac version 8.3.2. To get the new version that includes the fix, check for the latest updates on the Stable updater channel.

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Verification notes: I did a quick local verification for Xamarin.Android 10.0.3.0 to make sure I could still reproduce the original problem before the update and could no longer reproduce the problem after the update.