Do you like WCF-like approach and need to cover communication in between ASP.NET Core service and Blazor WebAssembly client? Use code-first with gRPC-Web! You can try the it right now by following a few simple steps (GitHub repo):

1. Blazor.Server – Prepare the ASP.NET Core host

Add NuGet packages:

1. Grpc.AspNetCore.Web (prerelease)
2. protobuf-net.Grpc.AspNetCore

Register CodeFirstGrpc() and GrpcWeb() services in Startup.cs ConfigureServices() method:

services.AddCodeFirstGrpc(config => { config.ResponseCompressionLevel = System.IO.Compression.CompressionLevel.Optimal; });

Add GrpcWeb middleware in between UseRouting() and UseEndpoints():

app.UseGrpcWeb(new GrpcWebOptions() { DefaultEnabled = true });

2. Blazor.Shared – Define the service contract (code-first)

Add System.ServiceModel.Primitives NuGet package.

Define the interface of your service:

[ServiceContract]
public interface IMyService
{
	Task DoSomething(MyServiceRequest request);

}

[DataContract]
public class MyServiceResult
{
	[DataMember(Order = 1)]
	public string NewText { get; set; }

	[DataMember(Order = 2)]
	public int NewValue { get; set; }
}

[DataContract]
public class MyServiceRequest
{
	[DataMember(Order = 1)]
	public string Text { get; set; }

	[DataMember(Order = 2)]
	public int Value { get; set; }
}

3. Blazor.Server – Implement and publish the service

Implement your service:

public class MyService : IMyService
{
	public Task DoSomething(MyServiceRequest request)
	{
		return Task.FromResult(new MyServiceResult()
		{
			NewText = request.Text + " from server",
			NewValue = request.Value + 1
		});
	}
}

Publish the service in Startup.cs:

app.UseEndpoints(endpoints =>
{
	endpoints.MapGrpcService();
	// ...
}

4. Blazor.Client (Blazor Web Assembly) – consume the service

Add NuGet packages:

1. Grpc.Net.Client
2. Grpc.Net.Client.Web (prerelease)
3. protobuf-net.Grpc

Consume the service in your razor file:

var handler = new Grpc.Net.Client.Web.GrpcWebHandler(Grpc.Net.Client.Web.GrpcWebMode.GrpcWeb, new HttpClientHandler());
using (var channel = Grpc.Net.Client.GrpcChannel.ForAddress("https://localhost:44383/", new Grpc.Net.Client.GrpcChannelOptions() { HttpClient = new HttpClient(handler) }))
{
	var testFacade = channel.CreateGrpcService();
	this.result = await testFacade.DoSomething(request);
}

(You can move the plumbing to ConfigureServices() and use pure dependency injection in your razor files.)

References

1. Steve Sanderson: Using gRPC-Web with Blazor WebAssembly
2. Use gRPC in browser apps | Microsoft Docs
3. protobuf-net.Grpc – Getting Started