Basics tutorial

This tutorial provides a basic C# programmer’s introduction to working with gRPC.

By walking through this example you’ll learn how to:

• Define a service in a .proto file.
• Generate server and client code using the protocol buffer compiler.
• Use the C# gRPC API to write a simple client and server for your service.

It assumes that you have read the Introduction to gRPC and are familiar with protocol buffers. Note that the example in this tutorial uses the proto3 version of the protocol buffers language: you can find out more in the proto3 language guide and C# generated code reference.

Why use gRPC?

Our example is a simple route mapping application that lets clients get information about features on their route, create a summary of their route, and exchange route information such as traffic updates with the server and other clients.

With gRPC we can define our service once in a .proto file and generate clients and servers in any of gRPC’s supported languages, which in turn can be run in environments ranging from servers inside a large data center to your own tablet — all the complexity of communication between different languages and environments is handled for you by gRPC. We also get all the advantages of working with protocol buffers, including efficient serialization, a simple IDL, and easy interface updating.

Example code and setup

The example code for our tutorial is in grpc/grpc/examples/csharp/RouteGuide. To download the example, clone the grpc repository by running the following command:

$ git clone -b v1.35.0 https://github.com/grpc/grpc
$ cd grpc

All the files for this tutorial are in the directory examples/csharp/RouteGuide. Open the solution examples/csharp/RouteGuide/RouteGuide.sln from Visual Studio (Windows or Mac) or Visual Studio Code. For additional installation details, see the How to use instructions.

Defining the service

Our first step (as you’ll know from the Introduction to gRPC) is to define the gRPC service and the method request and response types using protocol buffers. You can see the complete .proto file in examples/protos/route_guide.proto.

To define a service, you specify a named service in your .proto file:

service RouteGuide {
   ...
}

Then you define rpc methods inside your service definition, specifying their request and response types. gRPC lets you define four kinds of service method, all of which are used in the RouteGuide service:

• A simple RPC where the client sends a request to the server using the client object and waits for a response to come back, just like a normal function call.

  // Obtains the feature at a given position.
  rpc GetFeature(Point) returns (Feature) {}
  

• A server-side streaming RPC where the client sends a request to the server and gets a stream to read a sequence of messages back. The client reads from the returned stream until there are no more messages. As you can see in our example, you specify a server-side streaming method by placing the stream keyword before the response type.

  // Obtains the Features available within the given Rectangle.  Results are
  // streamed rather than returned at once (e.g. in a response message with a
  // repeated field), as the rectangle may cover a large area and contain a
  // huge number of features.
  rpc ListFeatures(Rectangle) returns (stream Feature) {}
  

• A client-side streaming RPC where the client writes a sequence of messages and sends them to the server, again using a provided stream. Once the client has finished writing the messages, it waits for the server to read them all and return its response. You specify a client-side streaming method by placing the stream keyword before the request type.

  // Accepts a stream of Points on a route being traversed, returning a
  // RouteSummary when traversal is completed.
  rpc RecordRoute(stream Point) returns (RouteSummary) {}
  

• A bidirectional streaming RPC where both sides send a sequence of messages using a read-write stream. The two streams operate independently, so clients and servers can read and write in whatever order they like: for example, the server could wait to receive all the client messages before writing its responses, or it could alternately read a message then write a message, or some other combination of reads and writes. The order of messages in each stream is preserved. You specify this type of method by placing the stream keyword before both the request and the response.

  // Accepts a stream of RouteNotes sent while a route is being traversed,
  // while receiving other RouteNotes (e.g. from other users).
  rpc RouteChat(stream RouteNote) returns (stream RouteNote) {}
  

Our .proto file also contains protocol buffer message type definitions for all the request and response types used in our service methods - for example, here’s the Point message type:

// Points are represented as latitude-longitude pairs in the E7 representation
// (degrees multiplied by 10**7 and rounded to the nearest integer).
// Latitudes should be in the range +/- 90 degrees and longitude should be in
// the range +/- 180 degrees (inclusive).
message Point {
  int32 latitude = 1;
  int32 longitude = 2;
}

Generating client and server code

Next we need to generate the gRPC client and server interfaces from our .proto service definition. This can be done by invoking the protocol buffer compiler protoc with a special gRPC C# plugin from the command line, but starting from version 1.17 the Grpc.Tools NuGet package integrates with MSBuild to provide automatic C# code generation from .proto files, which gives much better developer experience by running the right commands for you as part of the build.

This example already has a dependency on Grpc.Tools NuGet package and the route_guide.proto has already been added to the project, so the only thing needed to generate the client and server code is to build the solution. That can be done by running dotnet build RouteGuide.sln or building directly in Visual Studio.

The build regenerates the following files under the RouteGuide/obj/Debug/TARGET_FRAMEWORK directory:

• RouteGuide.cs contains all the protocol buffer code to populate, serialize, and retrieve our request and response message types
• RouteGuideGrpc.cs provides generated client and server classes, including:
  • an abstract class RouteGuide.RouteGuideBase to inherit from when defining RouteGuide service implementations
  • a class RouteGuide.RouteGuideClient that can be used to access remote RouteGuide instances

Creating the server

First let’s look at how we create a RouteGuide server. If you’re only interested in creating gRPC clients, you can skip this section and go straight to Creating the client (though you might find it interesting anyway!).

There are two parts to making our RouteGuide service do its job:

• Implementing the service functionality by inheriting from the base class generated from our service definition: doing the actual “work” of our service.
• Running a gRPC server to listen for requests from clients and return the service responses.

You can find our example RouteGuide server in examples/csharp/RouteGuide/RouteGuideServer/RouteGuideImpl.cs. Let’s take a closer look at how it works.

Implementing RouteGuide

As you can see, our server has a RouteGuideImpl class that inherits from the generated RouteGuide.RouteGuideBase:

// RouteGuideImpl provides an implementation of the RouteGuide service.
public class RouteGuideImpl : RouteGuide.RouteGuideBase

Simple RPC

RouteGuideImpl implements all our service methods. Let’s look at the simplest type first, GetFeature, which just gets a Point from the client and returns the corresponding feature information from its database in a Feature.

public override Task<Feature> GetFeature(Point request, Grpc.Core.ServerCallContext context)
{
    return Task.FromResult(CheckFeature(request));
}

The method is passed a context for the RPC (which is empty in the alpha release), the client’s Point protocol buffer request, and returns a Feature protocol buffer. In the method we create the Feature with the appropriate information, and then return it. To allow asynchronous implementation, the method returns Task<Feature> rather than just Feature. You are free to perform your computations synchronously and return the result once you’ve finished, just as we do in the example.

Server-side streaming RPC

Now let’s look at something a bit more complicated - a streaming RPC. ListFeatures is a server-side streaming RPC, so we need to send back multiple Feature protocol buffers to our client.

// in RouteGuideImpl
public override async Task ListFeatures(Rectangle request,
    Grpc.Core.IServerStreamWriter<Feature> responseStream,
    Grpc.Core.ServerCallContext context)
{
    var responses = features.FindAll( (feature) => feature.Exists() && request.Contains(feature.Location) );
    foreach (var response in responses)
    {
        await responseStream.WriteAsync(response);
    }
}

As you can see, here the request object is a Rectangle in which our client wants to find Features, but instead of returning a simple response we need to write responses to an asynchronous stream IServerStreamWriter using async method WriteAsync.

Client-side streaming RPC

Similarly, the client-side streaming method RecordRoute uses an IAsyncEnumerator, to read the stream of requests using the async method MoveNext and the Current property.

public override async Task<RouteSummary> RecordRoute(Grpc.Core.IAsyncStreamReader<Point> requestStream,
    Grpc.Core.ServerCallContext context)
{
    int pointCount = 0;
    int featureCount = 0;
    int distance = 0;
    Point previous = null;
    var stopwatch = new Stopwatch();
    stopwatch.Start();

    while (await requestStream.MoveNext())
    {
        var point = requestStream.Current;
        pointCount++;
        if (CheckFeature(point).Exists())
        {
            featureCount++;
        }
        if (previous != null)
        {
            distance += (int) previous.GetDistance(point);
        }
        previous = point;
    }

    stopwatch.Stop();

    return new RouteSummary
    {
        PointCount = pointCount,
        FeatureCount = featureCount,
        Distance = distance,
        ElapsedTime = (int)(stopwatch.ElapsedMilliseconds / 1000)
    };
}

Bidirectional streaming RPC

Finally, let’s look at our bidirectional streaming RPC RouteChat.

public override async Task RouteChat(Grpc.Core.IAsyncStreamReader<RouteNote> requestStream,
    Grpc.Core.IServerStreamWriter<RouteNote> responseStream,
    Grpc.Core.ServerCallContext context)
{
    while (await requestStream.MoveNext())
    {
        var note = requestStream.Current;
        List<RouteNote> prevNotes = AddNoteForLocation(note.Location, note);
        foreach (var prevNote in prevNotes)
        {
            await responseStream.WriteAsync(prevNote);
        }
    }
}

Here the method receives both requestStream and responseStream arguments. Reading the requests is done the same way as in the client-side streaming method RecordRoute. Writing the responses is done the same way as in the server-side streaming method ListFeatures.

Starting the server

Once we’ve implemented all our methods, we also need to start up a gRPC server so that clients can actually use our service. The following snippet shows how we do this for our RouteGuide service:

var features = RouteGuideUtil.LoadFeatures();

Server server = new Server
{
    Services = { RouteGuide.BindService(new RouteGuideImpl(features)) },
    Ports = { new ServerPort("localhost", Port, ServerCredentials.Insecure) }
};
server.Start();

Console.WriteLine("RouteGuide server listening on port " + port);
Console.WriteLine("Press any key to stop the server...");
Console.ReadKey();

server.ShutdownAsync().Wait();

As you can see, we build and start our server using Grpc.Core.Server class. To do this, we:

1. Create an instance of Grpc.Core.Server.
2. Create an instance of our service implementation class RouteGuideImpl.
3. Register our service implementation by adding its service definition to the Services collection (We obtain the service definition from the generated RouteGuide.BindService method).
4. Specify the address and port we want to use to listen for client requests. This is done by adding ServerPort to the Ports collection.
5. Call Start on the server instance to start an RPC server for our service.

Creating the client

In this section, we’ll look at creating a C# client for our RouteGuide service. You can see our complete example client code in examples/csharp/RouteGuide/RouteGuideClient/Program.cs.

Creating a client object

To call service methods, we first need to create a client object (also referred to as stub for other gRPC languages).

First, we need to create a gRPC client channel that will connect to gRPC server. Then, we create an instance of the RouteGuide.RouteGuideClient class generated from our .proto, passing the channel as an argument.

Channel channel = new Channel("127.0.0.1:50052", ChannelCredentials.Insecure);
var client = new RouteGuide.RouteGuideClient(channel);

// YOUR CODE GOES HERE

channel.ShutdownAsync().Wait();

Calling service methods

Now let’s look at how we call our service methods. gRPC C# provides asynchronous versions of each of the supported method types. For convenience, gRPC C# also provides a synchronous method stub, but only for simple (single request/single response) RPCs.

Simple RPC

Calling the simple RPC GetFeature in a synchronous way is nearly as straightforward as calling a local method.

Point request = new Point { Latitude = 409146138, Longitude = -746188906 };
Feature feature = client.GetFeature(request);

As you can see, we create and populate a request protocol buffer object (in our case Point), and call the desired method on the client object, passing it the request. If the RPC finishes with success, the response protocol buffer (in our case Feature) is returned. Otherwise, an exception of type RpcException is thrown, indicating the status code of the problem.

Alternatively, if you are in an async context, you can call an asynchronous version of the method and use the await keyword to await the result:

Point request = new Point { Latitude = 409146138, Longitude = -746188906 };
Feature feature = await client.GetFeatureAsync(request);

Streaming RPCs

Now let’s look at our streaming methods. If you’ve already read Creating the server some of this may look very familiar - streaming RPCs are implemented in a similar way on both sides. The difference with respect to simple call is that the client methods return an instance of a call object. This provides access to request/response streams and/or the asynchronous result, depending on the streaming type you are using.

Here’s where we call the server-side streaming method ListFeatures, which has the property ReponseStream of type IAsyncEnumerator<Feature>

using (var call = client.ListFeatures(request))
{
    while (await call.ResponseStream.MoveNext())
    {
        Feature feature = call.ResponseStream.Current;
        Console.WriteLine("Received " + feature.ToString());
    }
}

The client-side streaming method RecordRoute is similar, except we use the property RequestStream to write the requests one by one using WriteAsync, and eventually signal that no more requests will be sent using CompleteAsync. The method result can be obtained through the property ResponseAsync.

using (var call = client.RecordRoute())
{
    foreach (var point in points)
    {
        await call.RequestStream.WriteAsync(point);
    }
    await call.RequestStream.CompleteAsync();

    RouteSummary summary = await call.ResponseAsync;
}

Finally, let’s look at our bidirectional streaming RPC RouteChat. In this case, we write the request to RequestStream and receive the responses from ResponseStream. As you can see from the example, the streams are independent of each other.

using (var call = client.RouteChat())
{
    var responseReaderTask = Task.Run(async () =>
    {
        while (await call.ResponseStream.MoveNext())
        {
            var note = call.ResponseStream.Current;
            Console.WriteLine("Received " + note);
        }
    });

    foreach (RouteNote request in requests)
    {
        await call.RequestStream.WriteAsync(request);
    }
    await call.RequestStream.CompleteAsync();
    await responseReaderTask;
}

Try it out!

Build the client and server:

Using Visual Studio (or Visual Studio For Mac)

Open the solution examples/csharp/RouteGuide/RouteGuide.sln and select Build.

Using dotnet command line tool

Run dotnet build RouteGuide.sln from the examples/csharp/RouteGuide directory. For additional instructions on building the gRPC example with the dotnet command line tool, see Quick start.

Run the server:

> cd RouteGuideServer
> dotnet run

From a different terminal, run the client:

> cd RouteGuideClient
> dotnet run

You can also run the server and client directly from Visual Studio.