Implementing gRPC Swift

Introduction

I’ve never had the chance to use this technology before. I’ve always wondered how gRPC operates. In this article, I will explore what gRPC is, how to install and use it, and when to use gRPC.

What is gRPC?

gRPC is an open-source, high-performance framework that facilitates efficient communication in distributed systems. gRPC is an implementation of the RPC (Remote Procedure Call) protocol, which enables services to call functions on other machines as if they were local software methods. gRPC was developed by Google in 2015, and it includes several features that enhance the way remote procedure calls are made. For instance, its use of Protocol Buffers (Protobuf) supports strongly typed service contracts, data serialization, and code generation in a variety of programming languages. It also uses HTTP/2 as its transport protocol, which facilitates bi-directional streaming and reduces latency.

Installation Process

Prerequisites

Swift Version

gRPC requires Swift 5.8 or higher.

Install Protocol Buffers

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 (replacing x.y.z with the latest release, for example 1.13.0):
git clone -b x.y.z https://github.com/grpc/grpc-swift
# Navigate to the repository
cd grpc-swift/

Implementation Process

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 Protos/upstream/grpc/examples/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/v1/HelloWorld/Model/helloworld.grpc.swift, which contains our generated gRPC client and server classes. From the grpc-swift directory run:

Protos/generate.sh

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/v1/HelloWorld/Server/GreeterProvider.swift. Implement the new method like this:

final class GreeterProvider: Helloworld_GreeterAsyncProvider {
  let interceptors: Helloworld_GreeterServerInterceptorFactoryProtocol? = nil

  func sayHello(
    request: Helloworld_HelloRequest,
    context: GRPCAsyncServerCallContext
  ) async throws -> Helloworld_HelloReply {
    let recipient = request.name.isEmpty ? "stranger" : request.name
    return Helloworld_HelloReply.with {
      $0.message = "Hello \(recipient)!"
    }
  }

  func sayHelloAgain(
    request: Helloworld_HelloRequest,
    context: GRPCAsyncServerCallContext
  ) async throws -> Helloworld_HelloReply {
    let recipient = request.name.isEmpty ? "stranger" : request.name
    return Helloworld_HelloReply.with {
      $0.message = "Hello again \(recipient)!"
    }
  }
}

Update the Client

In the same directory, open Sources/Examples/v1/HelloWorld/Client/HelloWorldClient.swift. Call the new method like this:

func run() async throws {
  // Setup an `EventLoopGroup` for the connection to run on.
  //
  // See: https://github.com/apple/swift-nio#eventloops-and-eventloopgroups
  let group = MultiThreadedEventLoopGroup(numberOfThreads: 1)

  // Make sure the group is shutdown when we're done with it.
  defer {
    try! group.syncShutdownGracefully()
  }

  // Configure the channel, we're not using TLS so the connection is `insecure`.
  let channel = try GRPCChannelPool.with(
    target: .host("localhost", port: self.port),
    transportSecurity: .plaintext,
    eventLoopGroup: group
  )

  // Close the connection when we're done with it.
  defer {
    try! channel.close().wait()
  }

  // Provide the connection to the generated client.
  let greeter = Helloworld_GreeterAsyncClient(channel: channel)

  // Form the request with the name, if one was provided.
  let request = Helloworld_HelloRequest.with {
    $0.name = self.name ?? ""
  }

  do {
    let greeting = try await greeter.sayHello(request)
    print("Greeter received: \(greeting.message)")
  } catch {
    print("Greeter failed: \(error)")
  }

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

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!
   

When to Use gRPC

gRPC was designed to support highly efficient, language-agnostic communication in distributed systems. It is therefore better suited than REST for microservice-based architectures, in which individual services may be developed in different programming languages and may face varying workloads. Additionally, gRPC’s use of Protobuf for binary data serialization makes it the better choice for applications that demand low latency and high throughput, while its support for different streaming patterns makes it ideal for real-time chat and video applications.

Resources

• gRPC vs. REST
• gRPC Swift Quick Start

Thank you for reading! 😊