quick-start.md

gRPC Swift Quick Start

Before you begin

Prerequisites

Swift Version

gRPC requires Swift 5.0 or higher.

Install Protocol Buffers v3

Install the protoc compiler that is used to generate gRPC service code. The simplest way to do this is to download pre-compiled binaries for your platform (protoc-<version>-<platform>.zip) from here: https://github.com/google/protobuf/releases.

• Unzip this file.
• Update the environment variable PATH to include the path to the protoc binary file.

Download the example

You'll need a local copy of the example code to work through this quickstart. Download the example code from our GitHub repository (the following command clones the entire repository, but you just need the examples for this quickstart and other tutorials):

$ # Clone the repository at the latest release to get the example code:
$ git clone -b 1.0.0 https://github.com/grpc/grpc-swift
$ # Navigate to the repository
$ cd grpc-swift/

Run a gRPC application

From the grpc-swift directory:

1. Compile and run the server

   $ swift run HelloWorldServer

2. In another terminal, compile and run the client

   $ swift run HelloWorldClient
   Greeter received: Hello stranger!

Congratulations! You've just run a client-server application with gRPC.

Update a gRPC service

Now let's look at how to update the application with an extra method on the server for the client to call. Our gRPC service is defined using protocol buffers; you can find out lots more about how to define a service in a .proto file in What is gRPC?. For now all you need to know is that both the server and the client "stub" have a SayHello RPC method that takes a HelloRequest parameter from the client and returns a HelloReply from the server, and that this method is defined like this:

// The greeting service definition.
service Greeter {
  // Sends a greeting.
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings.
message HelloReply {
  string message = 1;
}

Let's update this so that the Greeter service has two methods. Edit Sources/Examples/HelloWorld/Model/helloworld.proto and update it with a new SayHelloAgain method, with the same request and response types:

// The greeting service definition.
service Greeter {
  // Sends a greeting.
  rpc SayHello (HelloRequest) returns (HelloReply) {}
  // Sends another greeting.
  rpc SayHelloAgain (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings.
message HelloReply {
  string message = 1;
}

(Don't forget to save the file!)

Update and run the application

We need to regenerate Sources/Examples/HelloWorld/Model/helloworld.grpc.swift, which contains our generated gRPC client and server classes.

From the grpc-swift directory run

make generate-helloworld

This also regenerates classes for populating, serializing, and retrieving our request and response types.

However, we still need to implement and call the new method in the human-written parts of our example application.

Update the server

In the same directory, open Sources/Examples/HelloWorld/Server/GreeterProvider.swift. Implement the new method like this:

class GreeterProvider: Helloworld_GreeterProvider {
  func sayHello(
    request: Helloworld_HelloRequest,
    context: StatusOnlyCallContext
  ) -> EventLoopFuture<Helloworld_HelloReply> {
    let recipient = request.name.isEmpty ? "stranger" : request.name
    let response = Helloworld_HelloReply.with {
      $0.message = "Hello \(recipient)!"
    }
    return context.eventLoop.makeSucceededFuture(response)
  }

  func sayHelloAgain(
    request: Helloworld_HelloRequest,
    context: StatusOnlyCallContext
  ) -> EventLoopFuture<Helloworld_HelloReply> {
    let recipient = request.name.isEmpty ? "stranger" : request.name
    let response = Helloworld_HelloReply.with {
      $0.message = "Hello again \(recipient)!"
    }
    return context.eventLoop.makeSucceededFuture(response)
  }
}

Update the client

In the same directory, open Sources/Examples/HelloWorld/Client/main.swift. Call the new method like this:

func greet(name: String?, client greeter: Helloworld_GreeterClient) {
  // Form the request with the name, if one was provided.
  let request = Helloworld_HelloRequest.with {
    $0.name = name ?? ""
  }

  // Make the RPC call to the server.
  let sayHello = greeter.sayHello(request)

  // wait() on the response to stop the program from exiting before the response is received.
  do {
    let response = try sayHello.response.wait()
    print("Greeter received: \(response.message)")
  } catch {
    print("Greeter failed: \(error)")
    return
  }

  let sayHelloAgain = greeter.sayHelloAgain(request)
  do {
    let response = try sayHelloAgain.response.wait()
    print("Greeter received: \(response.message)")
  } catch {
    print("Greeter failed: \(error)")
    return
  }
}

Run!

Just like we did before, from the top level grpc-swift directory:

1. Compile and run the server

   $ swift run HelloWorldServer

2. In another terminal, compile and run the client

   $ swift run HelloWorldClient
   Greeter received: Hello stranger!
   Greeter received: Hello again stranger!

What's next

• Read a full explanation of how gRPC works in What is gRPC? and gRPC Concepts
• Work through a more detailed tutorial in gRPC Basics: Swift