Grebe

This repository is intended to improve and simplify the gRPC development workflow for iOS apps and provides a small wrapper to incorporate Swift Combine in gRPC. The Swift Package contains the following parts:

• A Swift Combine gRPC wrapper. Read more about it in this section.
• A code generator to generate Swift code using the previously stated library.
• A CLI tool to simplify the development workflow. You can import the library without using the CLI tool. Read more about it in this section

Installation

You can install the Grebe CLI executable via Homebrew. To install run the following command in your command line:

brew install apodini/tap/grebe

Of course you can simply clone the repository or install it via the Swift Package Manager.

Usage

The recommended way to use Grebe is to first define an API using the Protocol Buffer language.

Setting up Grebe

To use Grebe you need to install the Protocol Buffer Compiler, the Swift Protobuf Code Generator Plugin and Swift gRPC plugins to generate the necessary support code. To do all this in one step, run the following command in your command line. Make sure to specify your shell path.

grebe setup -e <your shell path>

Building the Grebe Swift Package

This step generates a Swift Package that contains the Protocol Buffer support code, the gRPC interface code and the Grebe interface code. It hides the complete gRPC implementation and exposes only the methods, services and message types defined in your proto file. You can easily intergrate it into your project via drag and drop. It is not part of the main target and therefore offers a clear public interface.

After you run the setup command described in the previous step you are ready to build the Swift Package:

grebe generate -p <proto file path>

This command will do the following:

1. Load the latest version of the Grebe code generator (unless otherwise stated) to generate Swift code which projects the service methods defined in your proto file to simple Swift methods using our library.
2. Invoke the protoc-gen-swift and protoc-gen-swiftgrpc plugins on your proto file.
3. Bundle all generated code in a Swift Package.

Parameters

Using the generated Swift Package

Drag the package folder into your Xcode project. Then click the Plus button in the "Link Binary with Libraries" section, locate the package in the modal dialog, select the gray library icon inside the package, and add this one. In all files you would like to use the package import Grebe_Generated.

Example

Consider the following protobuf definition for a simple echo service. The service defines one unary RPC. You send one message and it echoes the message back to you.

syntax = "proto3";

service EchoService {
  rpc echo (EchoRequest) returns (EchoResponse);
}

message EchoRequest {
  string message = 1;
}

message EchoResponse {
  string message = 1;
}

The code generator will create following Swift file:

extension EchoServiceService: GRPCClientInitializable {
  func echo(
    request: EchoRequest, 
    callOptions: CallOptions? = defaultCallOptions
  ) -> AnyPublisher<EchoResponse, GRPCStatus> {
    GUnaryCall(request: request, callOptions: callOptions, closure: echo).execute()
  }
}

Now just call the generated method:

echo(request: EchoRequest.with { $0.message = "hello"})

Swift Combine gRPC Wrapper

This library provides a Swift-Combine wrapper for Swift-gRPC. It is a generic abstraction layer above the nio layer provided by the Swift-gRPC implementation. It supports all four gRPC API styles (Unary, Server Streaming, Client Streaming, and Bidirectional Streaming).

Example

Again consider the following protobuf definition for a simple echo service.

syntax = "proto3";

service EchoService {
  rpc echo (EchoRequest) returns (EchoResponse);
}

message EchoRequest {
  string message = 1;
}

message EchoResponse {
  string message = 1;
}

Let's set up the client:

let client = GClient<EchoServiceServiceClient>(target: .hostAndPort("localhost", 62801))

To call the service, create a GUnaryCall and use it's execute method. You provide it with a EchoRequest and get back a stream AnyPublisher<EchoResponse, GRPCStatus of responses (in this case only one) from the server.

let call = GUnaryCall(request: EchoRequest.with { $0.message = "hello"}, closure: client.service.echo)
call.execute()

License

Grebe is licensed under the MIT License. See License for more information.

Contributing

Contributions to this projects are welcome. Please make sure to read the contribution guidelines first.