Regression in net9.0 when calling a ServiceClient from a dynamically loaded Assembly

[hdocsek]

Description

We have a plugin loaded using AssemblyLoadContext. This plugin calls a WCF service orignially generated by dotnet-svcutil.

Under net9.0 we noticed what appears to be a regression. When the channel is created System.ServiceModel tries to generate a proxy. This fails with a FileNotFoundException indicating that the plugin assembly cannot be found. The error message shows a PublicKeyToken with a random value on each attempt.

The PublicKeyToken value is unexpected, it should be null since none of the assemblies are signed.

We tried various combinations of TargetFramework values for the involved projects. The results are summarized below.

ConsoleApp1	Contracts	Plugin1	Result
net8.0	net8.0	net8.0	✅ WORKS
net8.0	netstandard2.0	net8.0	✅ WORKS
net9.0	net9.0	net8.0	🚨 FAILS
net9.0	netstandard2.0	net9.0	🚨FAILS

Reproduction Steps

I attached a minimal repro extracted from the actual application which is impacted by this issue.

NET9WcfRepro.zip

It contains the following:

• ConsoleApp1: loads and calls the plugin Plugin1
• Plugin1: contains the WCF call
• WcfServiceSimulator: contains a web api which returns a mocked SOAP response

To reproduce the issue:

1. Install .NET SDK 9.0 RC1 (net9.0.100-rc.1.24452.12)
2. cd ./WcfServiceSimulator and dotnet run
3. cd ./ConsoleApp1 and dotnet run

Expected behavior

The expected output when running dotnet run --project .\ConsoleApp1 using net8.0 is:

TargetFramework is .NET 8.0.
Plugin "PluginId@1.0" dynamically loaded from "Plugin1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"
Calling WCF Service using a dynamically loaded Assembly.
Response from http://localhost:7261/sdk was successful. Info.Name: Simulator

Actual behavior

When executing dotnet run --project .\ConsoleApp1 using net9.0, an unhandled exception is thrown.

TargetFramework is .NET 9.0.
Plugin "PluginId@1.0" dynamically loaded from "Plugin1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"
Calling WCF Service using a dynamically loaded Assembly.
Unhandled exception. System.IO.FileNotFoundException: Could not load file or assembly 'Plugin1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=10000000fc7f0000'. The system cannot find the file specified.
File name: 'Plugin1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=10000000fc7f0000'
   at System.Reflection.Emit.RuntimeTypeBuilder.CreateTypeNoLock()
   at System.Reflection.Emit.RuntimeTypeBuilder.CreateTypeInfoImpl()
   at System.Reflection.DispatchProxyGenerator.ProxyBuilder.CreateType()
   at System.Reflection.DispatchProxyGenerator.ProxyAssembly.GetProxyType(Type baseType, Type interfaceType, String interfaceParameter, String proxyParameter)
   at System.Reflection.DispatchProxyGenerator.CreateProxyInstance(Type baseType, Type interfaceType, String interfaceParameter, String proxyParameter)
   at System.Reflection.DispatchProxy.Create[T,TProxy]()
   at System.ServiceModel.Channels.ServiceChannelProxy.CreateProxy[TChannel](MessageDirection direction, ServiceChannel serviceChannel)
   at System.ServiceModel.Channels.ServiceChannelFactory.CreateProxy[TChannel](MessageDirection direction, ServiceChannel serviceChannel)
   at System.ServiceModel.Channels.ServiceChannelFactory.CreateChannel[TChannel](EndpointAddress address, Uri via)
   at System.ServiceModel.ChannelFactory`1.CreateChannel(EndpointAddress address, Uri via)
   at System.ServiceModel.ChannelFactory`1.CreateChannel()
   at System.ServiceModel.ClientBase`1.CreateChannel()
   at System.ServiceModel.ClientBase`1.CreateChannelInternal()
   at System.ServiceModel.ClientBase`1.get_Channel()
   at DummyServiceClient.RetrieveServiceContent(ManagedObjectReference _this) in C:\Repos\Issues\ne9-wcf-proxy\ConsoleApp1\Plugin1\DummyService.cs:line 102
   at Plugin1.Plugin1Entrypoint.HandleRequest() in C:\Repos\Issues\ne9-wcf-proxy\ConsoleApp1\Plugin1\Plugin1Entrypoint.cs:line 44
   at Program.<Main>$(String[] args) in C:\Repos\Issues\ne9-wcf-proxy\ConsoleApp1\ConsolePlugin\Program.cs:line 35

Regression?

This worked as expected on net8.0.

Known Workarounds

No response

Configuration

• .NET: net9.0.100-rc.1.24452.12
• OS: Windows 11 Pro
• Arch: ARM64, x64

Other information

No response

[dotnet-policy-service]

Tagging subscribers to this area: @vitek-karas, @agocke, @VSadov
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Tagging subscribers to this area: @dotnet/area-system-reflection
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[nil4]

This regression still reproduces with .NET SDK 9.0 RC2 (9.0.100-rc.2.24474.11)

@ericstj @tmat as Reflection area owners, do you think a fix before RTM next month is feasible?

[steveharter]

Currently investigating