# 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][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):

```sh
$ # Clone the repository at the latest release to get the example code:
$ git clone -b 1.0.0-alpha.20 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

   ```sh
   $ swift run HelloWorldServer
   server started on port 52200
   $ # Note: the port may be different on your machine.
   ```

2. In another terminal, compile and run the client

   ```sh
   $ swift run HelloWorldClient 52200
   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?][grpc-guides]. 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:

```proto
// 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:

```proto
// 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

```sh
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:

```swift
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:

```swift
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

   ```sh
   $ swift run HelloWorldServer
   server started on port 52416
   $ # Note: the port may be different on your machine.
   ```

2. In another terminal, compile and run the client

   ```sh
   $ swift run HelloWorldClient 52416
   Greeter received: Hello stranger!
   Greeter received: Hello again stranger!
   ```

### What's next

- Read a full explanation of how gRPC works in [What is gRPC?][grpc-guides] and
  [gRPC Concepts][grpc-concepts]
- Work through a more detailed tutorial in [gRPC Basics: Swift][basic-tutorial]

[grpc-guides]: https://grpc.io/docs/guides/
[grpc-concepts]: https://grpc.io/docs/guides/concepts/
[protobuf-releases]: https://github.com/google/protobuf/releases
[basic-tutorial]: ./basic-tutorial.md