Xamarin support: introduce PlatformApis.isXamarin*, working NativeMethods for Xamarin.Android, do not use System.Runtime.Loader on Android for the moment

src/csharp/Grpc.Core/Grpc.Core.csproj

@@ -46,8 +46,12 @@
       <PackagePath>runtimes/win/native/grpc_csharp_ext.x86.dll</PackagePath>
       <Pack>true</Pack>
     </Content>
-    <Content Include="Grpc.Core.targets">
-      <PackagePath>build/net45/</PackagePath>
+    <Content Include="..\nativelibs\csharp_ext_monoandroid81_x86\libgrpc_csharp_ext.so">
+      <PackagePath>runtimes/monoandroid/armeabi-v7a/libgrpc_csharp_ext.so</PackagePath>
+      <Pack>true</Pack>
+    </Content>
+    <Content Include="..\nativelibs\csharp_ext_monoandroid81_x64\libgrpc_csharp_ext.so">
+      <PackagePath>runtimes/monoandroid/arm64-v8a/libgrpc_csharp_ext.so</PackagePath>
       <Pack>true</Pack>
     </Content>
   </ItemGroup>
@@ -69,4 +73,11 @@
 
   <Import Project="NativeDeps.csproj.include" />
 
+  <ItemGroup>
+    <Content Include="build\**\*.*">
+      <Pack>true</Pack>
+      <PackagePath>build</PackagePath>
+    </Content>
+  </ItemGroup>
+
 </Project>

src/csharp/Grpc.Core/GrpcEnvironment.cs

@@ -423,7 +423,8 @@ namespace Grpc.Core
                     if (!hooksRegistered)
                     {
 #if NETSTANDARD1_5
-                        System.Runtime.Loader.AssemblyLoadContext.Default.Unloading += (assemblyLoadContext) => { HandleShutdown(); };
+                        // FIXME couldn't get around a "cannot resolve type" runtime exception on Xamarin.Android
+                        //System.Runtime.Loader.AssemblyLoadContext.Default.Unloading += (assemblyLoadContext) => { HandleShutdown(); };
 #else
                         AppDomain.CurrentDomain.ProcessExit += (sender, eventArgs) => { HandleShutdown(); };
                         AppDomain.CurrentDomain.DomainUnload += (sender, eventArgs) => { HandleShutdown(); };

src/csharp/Grpc.Core/Internal/NativeExtension.cs

@@ -106,7 +106,9 @@ namespace Grpc.Core.Internal
         /// </summary>
         private static NativeMethods LoadNativeMethods()
         {
-            return PlatformApis.IsUnity ? LoadNativeMethodsUnity() : new NativeMethods(LoadUnmanagedLibrary());
+            return PlatformApis.IsUnity ? LoadNativeMethodsUnity() :
+                PlatformApis.IsXamarin ? LoadNativeMethodsXamarin() :
+                    new NativeMethods(LoadUnmanagedLibrary());
         }
 
         /// <summary>
@@ -128,6 +130,20 @@ namespace Grpc.Core.Internal
             }
         }
 
+        /// <summary>
+        /// Return native method delegates when running on the Xamarin platform.
+        /// WARNING: Xamarin support is experimental and work-in-progress. Don't expect it to work.
+        /// </summary>
+        private static NativeMethods LoadNativeMethodsXamarin()
+        {
+            if (PlatformApis.IsXamarinAndroid)
+            {
+                return new NativeMethods(new NativeMethods.DllImportsFromSharedLib());
+            }
+            // not tested yet
+            return new NativeMethods(new NativeMethods.DllImportsFromStaticLib());
+        }
+
         private static string GetAssemblyPath()
         {
             var assembly = typeof(NativeExtension).GetTypeInfo().Assembly;

src/csharp/Grpc.Core/Internal/PlatformApis.cs

@@ -33,12 +33,17 @@ namespace Grpc.Core.Internal
     internal static class PlatformApis
     {
         const string UnityEngineApplicationClassName = "UnityEngine.Application, UnityEngine";
+        const string XamarinAndroidActivityClassName = "Android.App.Activity, Mono.Android";
+        const string XamariniOSEnumClassName = "Mono.CSharp.Enum, Mono.CSharp";
         static readonly bool isLinux;
         static readonly bool isMacOSX;
         static readonly bool isWindows;
         static readonly bool isMono;
         static readonly bool isNetCore;
         static readonly bool isUnity;
+        static readonly bool isXamarin;
+        static readonly bool isXamariniOS;
+        static readonly bool isXamarinAndroid;
 
         static PlatformApis()
         {
@@ -58,6 +63,9 @@ namespace Grpc.Core.Internal
 #endif
             isMono = Type.GetType("Mono.Runtime") != null;
             isUnity = Type.GetType(UnityEngineApplicationClassName) != null;
+            isXamariniOS = Type.GetType(XamariniOSEnumClassName) != null;
+            isXamarinAndroid = Type.GetType(XamarinAndroidActivityClassName) != null;
+            isXamarin = isXamariniOS || isXamarinAndroid;
         }
 
         public static bool IsLinux
@@ -88,6 +96,31 @@ namespace Grpc.Core.Internal
             get { return isUnity; }
         }
 
+        /// <summary>
+        /// true if running on a Xamarin platform (either Xamarin.Android or Xamarin.iOS),
+        /// false otherwise.
+        /// </summary>
+        public static bool IsXamarin
+        {
+            get { return isXamarin; }
+        }
+
+        /// <summary>
+        /// true if running on Xamarin.iOS, false otherwise.
+        /// </summary>
+        public static bool IsXamariniOS
+        {
+            get { return isXamariniOS; }
+        }
+
+        /// <summary>
+        /// true if running on Xamarin.Android, false otherwise.
+        /// </summary>
+        public static bool IsXamarinAndroid
+        {
+            get { return isXamarinAndroid; }
+        }
+
         /// <summary>
         /// true if running on .NET Core (CoreCLR), false otherwise.
         /// </summary>

src/csharp/Grpc.Core/Version.csproj.include

@@ -1,7 +1,7 @@
 <!-- This file is generated -->
 <Project>
   <PropertyGroup>
-    <GrpcCsharpVersion>1.14.0-dev</GrpcCsharpVersion>
+    <GrpcCsharpVersion>1.14.1-dev</GrpcCsharpVersion>
     <GoogleProtobufVersion>3.5.1</GoogleProtobufVersion>
   </PropertyGroup>
 </Project>

src/csharp/Grpc.Core/build/MonoAndroid/Grpc.Core.targets

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <_GrpcCoreNugetNativePath Condition="'$(_GrpcCoreNugetNativePath)' == ''">$(MSBuildThisFileDirectory)..\..\</_GrpcCoreNugetNativePath>
+  </PropertyGroup>
+
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == 'MonoAndroid'">
+    <AndroidNativeLibrary Include="$(_GrpcCoreNugetNativePath)runtimes\monoandroid\arm64-v8a\libgrpc_csharp_ext.so">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+      <Abi>arm64-v8a</Abi>
+    </AndroidNativeLibrary>
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == 'MonoAndroid'">
+    <AndroidNativeLibrary Include="$(_GrpcCoreNugetNativePath)runtimes\monoandroid\armeabi-v7a\libgrpc_csharp_ext.so">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+      <Abi>armeabi-v7a</Abi>
+    </AndroidNativeLibrary>
+  </ItemGroup>
+
+</Project>

src/csharp/experimental/build_native_ext_for_android.sh

@@ -23,17 +23,28 @@ mkdir -p build
 cd build
 
 # set to the location where Android SDK is installed
-# e.g. ANDROID_NDK_PATH="$HOME/android-ndk-r16b"
+ANDROID_SDK_PATH="$HOME/Android/Sdk"
 
-cmake ../.. \
-  -DCMAKE_SYSTEM_NAME=Android \
-  -DCMAKE_SYSTEM_VERSION=15 \
-  -DCMAKE_ANDROID_ARCH_ABI=armeabi-v7a \
+# set to location where Android NDK is installed, usually a subfolder of Android SDK
+# install the Android NDK through the Android SDK Manager
+ANDROID_NDK_PATH=${ANDROID_SDK_PATH}/ndk-bundle
+
+# set to location of the cmake executable
+# by default, use cmake binary from the Android SDK
+CMAKE_PATH="${ANDROID_SDK_PATH}/cmake/3.6.4111459/bin/cmake"
+
+# ANDROID_ABI in ('arm64-v8a', 'armeabi-v7a')
+${CMAKE_PATH} ../.. \
+  -DCMAKE_TOOLCHAIN_FILE="${ANDROID_NDK_PATH}/build/cmake/android.toolchain.cmake" \
   -DCMAKE_ANDROID_NDK="${ANDROID_NDK_PATH}" \
   -DCMAKE_ANDROID_STL_TYPE=c++_static \
   -DRUN_HAVE_POSIX_REGEX=0 \
   -DRUN_HAVE_STD_REGEX=0 \
   -DRUN_HAVE_STEADY_CLOCK=0 \
-  -DCMAKE_BUILD_TYPE=Release
+  -DCMAKE_BUILD_TYPE=Release \
+  -DANDROID_PLATFORM=android-28 \
+  -DANDROID_ABI=arm64-v8a \
+  -DANDROID_NDK="${ANDROID_NDK_PATH}"
 
 make -j4 grpc_csharp_ext
+