.Net 6/7 IAsyncDisposable uses wrong DisposeAsync method

[roddone]

Steps to reproduce

1. Create a project targeting .net 6 or higher
2. use ZipOutputStream with "await using"
3. Or call directly .DisposeAsync() on previously created ZipOutputStream

Expected behavior

When Disposing, or calling .DisposeAsync(), it uses DeflaterOutputStream.DisposeAsync()

Actual behavior

When Disposing, it uses the base class Stream.DisposeAsync() instead of DeflaterOutputStream.DisposeAsync() method.
This is caused by a compilation directive #if NETSTANDARD2_1 that does not take in consideration recent .net versions (.Net 6 and 7, and probably 5, I have not tested this version)

Version of SharpZipLib

• Compiled from source (latest commit on master)

full sample to reproduce (must create a .net 6 project) :

using ICSharpCode.SharpZipLib.Zip;
using System.Text;

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/", async (HttpContext context) =>
{
	await using (var outputStream = new MemoryStream())
	{
		await using (var stream = new ZipOutputStream(outputStream))
		{
			//add file without compression
			await stream.PutNextEntryAsync(new ZipEntry("test.txt") { CompressionMethod = CompressionMethod.Stored });

			var bytes = Encoding.UTF8.GetBytes("ah ah !");
			await stream.WriteAsync(bytes);

			await stream.FinishAsync(CancellationToken.None);
			outputStream.Position = 0;
			await outputStream.CopyToAsync(context.Response.Body);
		}
	}
});

app.Run();

[piksel]

Good catch, it should be NETSTANDARD2_1_OR_GREATER instead. It shouldn't happen unless you change the TargetFrameworks in the .csproj though? Right now we are only targeting netstandard2.0, netstandard2.1 and net45, so it shouldn't be a problem.

[roddone]

It also happens when you generate the nuget package from source and reference it in a .net 6 project. That's how I spotted the issue.
To find what caused it, I've added the .net6.0 in targetframeworks (for testing only) ;)

[piksel]

When running the example you provided above, I don't get any errors and it seems to work fine.
The compiler directives are interpreted when you are building the library, and since the targets does not include net6.0 you should get the library targeting netstandard2.1 when using it with a NET 6.0 project.

[piksel]

In any case, this is fixed in #755 that actually adds support for .NET 6.0 target.