Grpc.Net.Client.Web

The .NET gRPC client can be configured to make gRPC-Web calls. This is useful for Blazor WebAssembly apps, which are hosted in the browser and have the same HTTP limitations of JavaScript code. Calling gRPC-Web with a .NET client is the same as HTTP/2 gRPC. The only modification is how the channel is created.

To use gRPC-Web:

• Add a reference to the Grpc.Net.Client.Web package.
• Ensure the reference to Grpc.Net.Client package is 2.29.0 or greater.
• Configure the channel to use the GrpcWebHandler:

var channel = GrpcChannel.ForAddress("https://localhost:5001", new GrpcChannelOptions
    {
        HttpHandler = new GrpcWebHandler(new HttpClientHandler())
    });

var client = new Greeter.GreeterClient(channel);
var response = await client.SayHelloAsync(new HelloRequest { Name = ".NET" });

The preceding code:

• Configures a channel to use gRPC-Web.
• Creates a client and makes a call using the channel.

GrpcWebHandler has the following configuration options:

• InnerHandler: The underlying HttpMessageHandler that makes the gRPC HTTP request, for example, HttpClientHandler.
• GrpcWebMode: An enumeration type that specifies whether the gRPC HTTP request Content-Type is application/grpc-web or application/grpc-web-text.
  • GrpcWebMode.GrpcWeb configures content to be sent without encoding. Default value.
  • GrpcWebMode.GrpcWebText configures content to be base64 encoded. Required for server streaming calls in browsers.
• HttpVersion: HTTP protocol Version used to set HttpRequestMessage.Version on the underlying gRPC HTTP request. gRPC-Web doesn't require a specific version and doesn't override the default unless specified.

gRPC-Web and streaming

Traditional gRPC over HTTP/2 supports streaming in all directions. gRPC-Web offers limited support for streaming:

• gRPC-Web browser clients don't support calling client streaming and bidirectional streaming methods.
• gRPC-Web .NET clients don't support calling client streaming and bidirectional streaming methods over HTTP/1.1.
• ASP.NET Core gRPC services hosted on Azure App Service and IIS don't support bidirectional streaming.

When using gRPC-Web, we only recommend the use of unary methods and server streaming methods.

Links

• Documentation
• grpc-dotnet GitHub