Microsoft.AspNetCore.SignalR.Client is not working with Xamarin.Mac application

[Semptra]

Describe the bug

Cannot build HubConnection due to exception:

System.MissingMethodException: Method not found: int System.Text.Encodings.Web.TextEncoder.FindFirstCharacterToEncodeUtf8(System.ReadOnlySpan`1<byte>)
  at System.Text.Json.JsonEncodedText.EncodeHelper (System.ReadOnlySpan`1[T] utf8Value, System.Text.Encodings.Web.JavaScriptEncoder encoder) [0x00000] in <90ed82de44024ca1bc6b68be1a1a7e32>:0
  at System.Text.Json.JsonEncodedText.TranscodeAndEncode (System.ReadOnlySpan`1[T] value, System.Text.Encodings.Web.JavaScriptEncoder encoder) [0x00033] in <90ed82de44024ca1bc6b68be1a1a7e32>:0
  at System.Text.Json.JsonEncodedText.Encode (System.ReadOnlySpan`1[T] value, System.Text.Encodings.Web.JavaScriptEncoder encoder) [0x00014] in <90ed82de44024ca1bc6b68be1a1a7e32>:0
  at System.Text.Json.JsonEncodedText.Encode (System.String value, System.Text.Encodings.Web.JavaScriptEncoder encoder) [0x00014] in <90ed82de44024ca1bc6b68be1a1a7e32>:0
  at Microsoft.AspNetCore.SignalR.Protocol.JsonHubProtocol..cctor () [0x00000] in <98d61c04d1b44672b33d354f73c63eae>:0

To Reproduce

1. Create a new Xamarin.Mac application with Target Framework = Xamarin.Mac 2.0 (Modern)
2. Add Microsoft.AspNetCore.SignalR.Client NuGet package
3. Add this code to AppDelegate:

using AppKit;
using Foundation;
using Microsoft.AspNetCore.SignalR.Client;

namespace SampleApp
{
    [Register("AppDelegate")]
    public class AppDelegate : NSApplicationDelegate
    {
        public override void DidFinishLaunching(NSNotification notification)
        {
            var connection = new HubConnectionBuilder()
                .WithUrl("http://localhost:5000/")
                .Build();
        }
    }
}

Further technical details

.NET Core version:

.NET Core SDK (reflecting any global.json):
 Version:   3.1.100-preview3-014645
 Commit:    b32d27f4b3

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  10.14
 OS Platform: Darwin
 RID:         osx.10.14-x64
 Base Path:   /usr/local/share/dotnet/sdk/3.1.100-preview3-014645/

Host (useful for support):
  Version: 3.1.0-preview3.19553.2
  Commit:  13f35c3d86

.NET Core SDKs installed:
  3.0.100 [/usr/local/share/dotnet/sdk]
  3.1.100-preview3-014645 [/usr/local/share/dotnet/sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.App 3.0.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.0-preview3.19555.2 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.13 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.0-preview3.19553.2 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

VS for Mac version: Visual Studio Enterprise 2019 for Mac Version 8.3.10 (build 2)
Xamarin.Mac version: Xamarin.Mac 5.16.1.24 (d16-3 / 08809f5b)
Microsoft.AspNetCore.SignalR.Client NuGet version: 3.1.0

[analogrelay]

Looks like System.Text.Json is not working in Xamarin.Mac? @ahsonkhan @marek-safar any thoughts from your respective sides here?

(Since it came up in Triage, the .NET Core version info isn't necessarily relevant here because this is a Xamarin.Mac app using the SignalR Client via NuGet. Just in case any other viewers of this issue get worried by the "preview3" branding references)

[analogrelay]

I'm going to move this to dotnet/runtime for now. It looks like this is an issue in System.Text.Json on Xamarin.Mac and not specific to ASP.NET Core SignalR

[ericstj]

FindFirstCharacterToEncodeUtf8 was a new API that was added during 3.0.
dotnet/corefx@bbbcac5

For this error to occur it means you must be using an old copy of System.Text.Encodings.Web. Can you double check that you are referencing package version 4.7.0 of System.Text.Encodings.Web? This is a declared dependency of System.Text.Json
https://www.nuget.org/packages/System.Text.Json/

It's possible you downgraded that dependency and suppressed a warning about the downgrade. If the package reference looks correct, you can double check that the API is present in that nuget package. If it is, then follow up with Xamarin.Mac owners about why they don't honor that package. For many .NET packages Xamarin tooling ignores the assembly in preference of their own, but this should not be one of them. /cc @mhutch

[ericstj]

I took a closer look at this with @ahsonkhan who had VS for Mac and we could debug.

It turns out this is happening because the Xamarin.Mac project is allowing the System.Memory dll from the package to win out over the framework copy. This causes System.Text.Json and System.Text.Encodings.Web to disagree on where ReadOnlySpan lives.

System.Text.Json thinks it lives in System.Memory, which has a type definition.
System.Text.Encodings.Web is built against netstandard2.1, so it thinks ROS lives in netstandard.dll which has a typeforward to mscorlib.

This results in the MissingMethodException since the runtime can't find the method on TextEncoder that takes a System.Memory-defined ROS.

The bug here is that Xamarin.Mac isn't preferring it's own copy of System.Memory: it should, this is what .NETCoreApp does. The version of System.Memory in the package is 4.0.1.1, where the version in Xamarin.Mac is 4.0.99.0.

I found a similar bug which is caused by the same root issue here:
dotnet/macios#5687
dotnet/macios#6412

Closing this as a dup and adding my analysis.

[ericstj]

To workaround:

If the project is using packages.config, then delete the <Reference for System.Memory from the Csproj. If the project is using PackageReference add <PackageReference Include="System.Memory" Version="4.5.3" IncludeAssets="None" />

[ChrisAllisonMalta]

I don't know if this is a similar issue but I'm getting the following error

/Users/chris/Projects/Odyssey/Odyssey.Mac/MMP: Error MM2002: Failed to resolve "Microsoft.AspNetCore.SignalR.Client.IConnectionFactory" reference from "Microsoft.AspNetCore.SignalR.Client.Core, Version=3.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60" (MM2002) (Odyssey.Mac)

I added a MacOS project to my existing Xamarin Forms (iOS) project and afgter going through all of the dependency issues and adding references from nuget, I get stuck with this one. The above workaround didn't work unfortunately.