tl;dr:
I have a .NET Framework 4.7.2 project consuming a NuGet package which supports .NET Standard 2.0. That package, in turn, requires another package which supports .NET Standard 2.0. However, when run, the latter package uses net461 binaries rather than netstandard2.0.
How do I force a NuGet package & its dependencies to use .NET Standard 2.0?
Are there special steps required to consume a .NET Standard package from a .NET Framework 4.7.2 project?
Specifics:
I am trying to get the NuGet package for SparkplugNet (which uses the MQTTNet package) working in a .NET Framework 4.7.2 project - just the basic "How to use" SparkplugB example. Both projects support .NET Standard 2.0. After some debugging (details below), it appears MQTTNet is trying to use code paths specific to .NET Framework 4.6.1, rather than .NET Standard 2.0, and crashing with no feedback whatsoever.
To troubleshoot, I built SparkplugNet and MQTTNet from source. As far as I can tell, the crash comes from hitting .NET 4.5/4.6.1-specific code in CrossPlatformSocket.ConnectAsync(), specifically this line (in context):
await Task.Factory.FromAsync(_socket.BeginConnect, _socket.EndConnect, host, port, null).ConfigureAwait(false)
When I debug, _socket is a System.Net.Sockets.Socket which doesn't appears to have a BeginConnect() method, at least in the source file my debugger pulled. I am not sure why it branches to that code when .NET Standard 2.0 would be a better fit.
Back to a 4.7.2 project consuming SparkplugNet & MQTTNet via NuGet package.... If I look at the reference paths, SparkplugNet is properly pointed at the netstandard2.0 folder, but MQTTNet points to packages\MQTTnet.4.1.3.436\lib\net461\MQTTnet.dll. If I change the hint path manually in the project file, MSBuild appears to pull from the netstandard2.0 folder, but it still crashes. I assume it is the same cause, though I'm having trouble debugging using NuGet packages. Also, I'm hoping for a better solution than hacking hint paths.
