It assumes that you have read the [Getting started](https://github.com/grpc/grpc/tree/master/examples) guide and are familiar with [protocol buffers] (https://developers.google.com/protocol-buffers/docs/overview). Note that the example in this tutorial only uses the proto2 version of the protocol buffers language, as proto3 support for C# is not ready yet (see [protobuf C# README](https://github.com/google/protobuf/tree/master/csharp#proto2--proto3)).
This isn't a comprehensive guide to using gRPC in C#: more reference documentation is coming soon.
## 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 implement clients and servers in any of gRPC's supported languages, which in turn can be run in environments ranging from servers inside Google 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.
The example code for our tutorial is in [examples/csharp/route_guide](.). To download the example, clone this repository by running the following command:
On Linux (or MacOS), you will first need to install protobuf and gRPC C Core using Linuxbrew (or Homebrew) tool in order to be
able to generate the server and client interface code and run the examples. Follow the instructions for [Linux](https://github.com/grpc/grpc/tree/master/src/csharp#usage-linux-mono) or [MacOS](https://github.com/grpc/grpc/tree/master/src/csharp#usage-macos-mono).
Our first step (as you'll know from [Getting started](https://github.com/grpc/grpc/tree/master/examples)) is to define the gRPC *service* and the method *request* and *response* types using [protocol buffers] (https://developers.google.com/protocol-buffers/docs/overview). You can see the complete .proto file in [`RouteGuide/protos/route_guide.proto`](RouteGuide/protos/route_guide.proto).
To define a service, you specify a named `service` in your .proto file:
```protobuf
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 stub and waits for a response to come back, just like a normal function call.
```protobuf
// 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.
```protobuf
// 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
- 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 server-side streaming method by placing the `stream` keyword before the *request* type.
```protobuf
// Accepts a stream of Points on a route being traversed, returning a
- 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.
```protobuf
// Accepts a stream of RouteNotes sent while a route is being traversed,
// while receiving other RouteNotes (e.g. from other users).
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:
```protobuf
// 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. We do this using the protocol buffer compiler `protoc` with a special gRPC C# plugin.
To generate the code on Windows, we use `protoc.exe` from the `Google.Protobuf` NuGet package and `grpc_csharp_plugin.exe` from the `Grpc.Tools` NuGet package (both under the `tools` directory).
Normally you would need to add the `Grpc.Tools` package to the solution yourself, but in this tutorial it has been already done for you. Following command should be run from the `csharp/route_guide` directory:
-`RouteGuide/RouteGuide.cs` defines a namespace `examples`
- This contains all the protocol buffer code to populate, serialize, and retrieve our request and response message types
-`RouteGuide/RouteGuideGrpc.cs`, provides stub and service classes
- an interface `RouteGuide.IRouteGuide` to inherit from when defining RouteGuide service implementations
- a class `RouteGuide.RouteGuideClient` that can be used to access remote RouteGuide instances
<aname="server"></a>
## 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](#client) (though you might find it interesting anyway!).
There are two parts to making our `RouteGuide` service do its job:
- Implementing the service interface 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 [RouteGuideServer/RouteGuideImpl.cs](RouteGuideServer/RouteGuideServerImpl.cs). Let's take a closer look at how it works.
`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`.
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.
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.
As you can see, here the request object is a `Rectangle` in which our client wants to find `Feature`s, but instead of returning a simple response we need to write responses to an asynchronous stream `IServerStreamWriter` using async method `WriteAsync`.
Similarly, the client-side streaming method `RecordRoute` uses an [IAsyncEnumerator](https://github.com/Reactive-Extensions/Rx.NET/blob/master/Ix.NET/Source/System.Interactive.Async/IAsyncEnumerator.cs), to read the stream of requests using the async method `MoveNext` and the `Current` property.
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`.
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:
```csharp
var features = RouteGuideUtil.ParseFeatures(RouteGuideUtil.DefaultFeaturesFile);
3. Register our service implementation by adding its service definition to `Services` collection (We obtain the service definition from the generated `RouteGuide.BindService` method).
2. Specify the address and port we want to use to listen for client requests. This is done by adding `ServerPort` to `Ports` collection.
In this section, we'll look at creating a C# client for our `RouteGuide` service. You can see our complete example client code in [RouteGuideClient/Program.cs](RouteGuideClient/Program.cs).
First, we need to create a gRPC client channel that will connect to gRPC server. Then, we use the `RouteGuide.NewClient` method of the `RouteGuide` class generated from our .proto.
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`) will be returned. Otherwise, an exception of type `RpcException` will be thrown, indicating the status code of the problem.
Alternatively, if you are in async context, you can call an asynchronous version of the method (and use `await` keyword to await the result):
Now let's look at our streaming methods. If you've already read [Creating the server](#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, that provides access to request/response streams and/or asynchronous result (depending on the streaming type you are using).
Here's where we call the server-side streaming method `ListFeatures`, which has property `ReponseStream` of type `IAsyncEnumerator<Feature>`
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 request will be send using `CompleteAsync`. The method result can be obtained through the property
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.
