Calling any WCF service Task-based Async methods from Xamarin fails

[PhilPJL]

I have hit the same issue noted here https://bugzilla.xamarin.com/show_bug.cgi?id=51959

To reproduce

1. Using VS 2017 15.5.2
2. Create a Xamarin cross platform app and select '.NET standard option' and 'Android'
3. Since it's not possible to add a web service reference to the shared assembly (will open separate bug) add a .NET standard 2.0 class library project to host the web service reference.
4. Create a reference to a WCF service from the class library. Using basicHttpBinding will do.
5. All methods in the service are async, which is fine, except calling one (called GetVersion in this case) results in:

Error in deserializing body of request message for operation 'GetVersion'. OperationFormatter encountered an invalid Message body. Expected to find node type 'Element' with name 'GetVersion' and namespace 'hexcel.com'. Found node type 'Element' with name 'GetVersionAsync' and namespace 'hexcel.com'

[PhilPJL]

I've created a sample project showing the issue.
You'll need to publish WcfService - which is pretty much the default WCF service project created by VS - to IIS and then recreate the web reference in the XamarinTestServices project.

XamarinTest2.zip

[mlacouture]

Hi @PhilPJL
I'll take a look at this problem and report back as soon as I have the chance to. Thank you for reporting this issue.

Miguel Lacouture

[zhenlan]

WCF Connected Service generates the modern task-based asynchronous (TBA) client proxy code. The code can be compiled fine in a .NET Standard library. When this library is used at the runtime, it requires the WCF implementation of the actual runtime framework supports TBA. TBA is supported by WCF on .NET Core and .NET Framework. After discussing with @mconnew, we believe the root-cause of the issue is that the WCF implementation in Xamarin/mono does not support TBA. Xamarin/mono implementation supports the old style async programming model (APM Begin/End) only.

To solve this issue, the WCF implementation in Xamarin/mono needs to be updated to catch up what .NET Framework has for many years. Add @marek-safar and @akoeplinger from Xamarin team. Is this something you can plan for Xamarin/mono? There are quite a few reports of this issue recently. In the latest VS2017 update, Xamarin project offers to create .NET Standard library by default template, so more customers may run into this issue in the future.

[marek-safar]

Updating Xamarin implementation of WCF is something we'd certainly like to do but it's not a simple task. Due to its complexity and amount of work needed we have been postponing the work for some time.