Xamarin iOS native linking failed for grpc.core

Question

I've been attempting to make grpc work (ssl http2) on Xamarin Forms and after some pain I managed to get it to work on Android using Grpc.Core. However I couldn't get iOS to compile. Working through this problem I was trying to get anything grpc related to work on iOS, and eventually found the grpc experimental xamarin demo, HelloworldXamarin. Found here:

https://github.com/grpc/grpc/tree/master/examples/csharp/HelloworldXamarin

I downloaded the solution, but when I try to compile it I get the following errors:

Error Text:

Native linking failed, undefined symbol: operator delete(void*). Please verify that all the necessary frameworks have been referenced and native libraries are properly linked in.

Native linking failed. Please review the build log and the user flags provided to gcc: -LC:/g/examples/csharp/HelloworldXamarin/packages/Grpc.Core.2.23.0/build/Xamarin.iOS10/../../native/ios/universal -lgrpc_csharp_ext -force_load C:/g/examples/csharp/HelloworldXamarin/packages/Grpc.Core.2.23.0/build/Xamarin.iOS10/../../native/ios/universal/libgrpc_csharp_ext.a -LC:/g/examples/csharp/HelloworldXamarin/packages/Grpc.Core.2.23.0/build/Xamarin.iOS10/../../native/ios/universal -lgrpc -force_load C:/g/examples/csharp/HelloworldXamarin/packages/Grpc.Core.2.23.0/build/Xamarin.iOS10/../../native/ios/universal/libgrpc.a

linker command failed with exit code 1 (use -v to see invocation)

For the warning regarding not being able to find libgrpc_csharp_ext.a, I verified that the file was there.

There appears to be some issue with native linking, which I am very unfamiliar with. I'm using nearly the latest Visual Studio (well, 16.5.3), a mac build host with latest OS and XCode updated to latest. Didn't make any changes to the files pulled from git. I only just started working with Xamarin iOS this week, so everything should be in a fairly "default" state.

What could be wrong with my setup/system that makes this not work? I understand that this is an experimental feature still, but I can't tell if I've done something stupid or if there's been some change in something (like XCode? or it needing VS 2017?) that makes this no longer work? Is anyone else able to get this example to compile?

I've also tried newer versions of the grpc nuget packages and that only resulted in more errors.

Ultimately I'm trying to get latest Grpc.Core to work in iOS on Xamarin.Forms, though I have very little experience working with iOS. If there are issues with the latest versions of XCode/Visual Studio/Grpc.Core that are causing this, I'm willing to try to work through them, if someone can point me in the right direction.

Answer 1

It is not at all related to your versions or something that you did or didn't do.

First for some theory: If someone wants to use Objective-C libraries or CocoaPods packages in their Xamarin project, they will need to create a binding library for this. Take it as some sort of a "bridge" between the native implementation and the later exposed C# code that you can use. You can learn more about the binding from the official documentation here and more specifically here.

To sum up the info - after the bindings have been created, you see a .lib or .a file. This is exactly what they have done - exposed some native code into the libgrpc_csharp_ext.a. Unfortunately, there are some bindings that are not correct. This is exactly what you are seeing here - the aftermath of an incorrect binding.

Looking a bit into the project I got to the following conclusions:

1. There is an open issue from May 2019 about this - https://github.com/grpc/grpc/issues/19172 Unfortunately, the issue is still active and there is no movement there.
2. I have confirmed that after version 1.21 (incl.) the build is not working. For now, you can downgrade to version 1.20.1 (last known to work). I have successfully built the solution with it. Please review the changelog and release notes for this specific version (if any) so that you know if it will fit your needs.

Basically, you have 2 options:

1. Downgrade to the last good version in order to use it;

2. If you want to use the latest version either wait for the issue to be fixed, or fork the repo and help with the fixing.

If you want to see their build script and help fix the issue, you can start from here.

Another useful resource is this video from the official Xamarin channel.