Don't warn about Android native handler with grpc-web

src/Grpc.Net.Client/GrpcChannel.cs

@@ -431,13 +431,15 @@ private HttpMessageInvoker CreateInternalHttpInvoker(HttpMessageHandler? handler
             // in advanced gRPC scenarios. We want Android to use SocketsHttpHandler. Throw an error if:
             // 1. Client is running on Android.
             // 2. Channel is created with HttpClientHandler.
-            // 3. UseNativeHttpHandler switch is true.
+            // 3. Channel is not using GrpcWebHandler. grpc-web is compatible with the native handler.
+            // 4. UseNativeHttpHandler switch is true.
             if (OperatingSystem.IsAndroid)
             {
                 // GetHttpHandlerType recurses through DelegatingHandlers that may wrap the HttpClientHandler.
                 var httpClientHandler = HttpRequestHelpers.GetHttpHandlerType<HttpClientHandler>(handler);
+                var grpcWebHandler = HttpRequestHelpers.GetHttpHandlerType(handler, "Grpc.Net.Client.Web.GrpcWebHandler");
 
-                if (httpClientHandler != null && RuntimeHelpers.QueryRuntimeSettingSwitch("System.Net.Http.UseNativeHttpHandler", defaultValue: false))
+                if (httpClientHandler != null && grpcWebHandler == null && RuntimeHelpers.QueryRuntimeSettingSwitch("System.Net.Http.UseNativeHttpHandler", defaultValue: false))
                 {
                     throw new InvalidOperationException("The channel configuration isn't valid on Android devices. " +
                         "The channel is configured to use HttpClientHandler and Android's native HTTP/2 library. " +

test/Grpc.Net.Client.Tests/Grpc.Net.Client.Tests.csproj

@@ -30,6 +30,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\..\src\Grpc.Net.Client\Grpc.Net.Client.csproj" />
+    <ProjectReference Include="..\..\src\Grpc.Net.Client.Web\Grpc.Net.Client.Web.csproj" />
 
     <PackageReference Include="Google.Protobuf" Version="$(GoogleProtobufPackageVersion)" />
     <PackageReference Include="Grpc.Tools" Version="$(GrpcToolsPackageVersion)" PrivateAssets="All" />

test/Grpc.Net.Client.Tests/GrpcChannelTests.cs

@@ -26,7 +26,7 @@
 using Microsoft.Extensions.Logging.Testing;
 using NUnit.Framework;
 using Grpc.Net.Client.Internal;
-using System.Net;
+using Grpc.Net.Client.Web;
 #if SUPPORT_LOAD_BALANCING
 using Grpc.Net.Client.Balancer;
 using Grpc.Net.Client.Balancer.Internal;
@@ -402,7 +402,7 @@ public async Task Dispose_CalledWhileActiveCalls_ActiveCallsDisposed()
         Assert.AreEqual(0, channel.ActiveCalls.Count);
     }
 
-    [TestCase(null)]
+    [TestCase(true)]
     [TestCase(false)]
     public void HttpHandler_HttpClientHandlerOverNativeOnAndroid_ThrowError(bool useDelegatingHandlers)
     {
@@ -415,6 +415,8 @@ public void HttpHandler_HttpClientHandlerOverNativeOnAndroid_ThrowError(bool use
             services.AddSingleton<IOperatingSystem>(new TestOperatingSystem { IsAndroid = true });
 
             HttpMessageHandler handler = new HttpClientHandler();
+
+            // Add an extra handler to verify that test successfully recurses down custom handlers.
             if (useDelegatingHandlers)
             {
                 handler = new TestDelegatingHandler(handler);
@@ -443,6 +445,43 @@ public void HttpHandler_HttpClientHandlerOverNativeOnAndroid_ThrowError(bool use
         }
     }
 
+    [TestCase(true)]
+    [TestCase(false)]
+    public void HttpHandler_HttpClientHandlerOverNativeOnAndroid_HasGrpcWebHandler_ThrowError(bool useDelegatingHandlers)
+    {
+        // Arrange
+        AppContext.SetSwitch("System.Net.Http.UseNativeHttpHandler", true);
+
+        try
+        {
+            var services = new ServiceCollection();
+            services.AddSingleton<IOperatingSystem>(new TestOperatingSystem { IsAndroid = true });
+
+            HttpMessageHandler handler = new HttpClientHandler();
+            handler = new GrpcWebHandler(handler);
+
+            // Add an extra handler to verify that test successfully recurses down custom handlers.
+            if (useDelegatingHandlers)
+            {
+                handler = new TestDelegatingHandler(handler);
+            }
+
+            var channel = GrpcChannel.ForAddress("https://localhost", new GrpcChannelOptions
+            {
+                HttpHandler = handler,
+                ServiceProvider = services.BuildServiceProvider()
+            });
+
+            // Assert
+            Assert.IsTrue(channel.OperatingSystem.IsAndroid);
+        }
+        finally
+        {
+            // Reset switch for other tests.
+            AppContext.SetSwitch("System.Net.Http.UseNativeHttpHandler", false);
+        }
+    }
+
     private class TestDelegatingHandler : DelegatingHandler
     {
         public TestDelegatingHandler(HttpMessageHandler innerHandler) : base(innerHandler)