reddit/codablerpc

A Swift RPC client & server implementation using Codable.

CodableRPC

CodableRPC is a general purpose RPC client & server implemented in Swift that uses Codable for serialization, enabling you to write idiomatic and type-safe procedure calls.

While a general purpose RPC implementation, Reddit uses CodableRPC to support ad hoc communication between XCTest UI tests and the iOS app.

Usage

// An RPCMethod enum defines the methods that can be performed by the server.
enum ExampleRPCMethod: RPCMethod {
  typealias Result = ExampleMethodResult

  case ping
}

// The method result enum defines the responses returned by the server.
enum ExampleMethodResult: Codable {
  case pong(TimeInterval)
}

// Construct external dependencies needed by the RPC methods. These objects would likely be
// provided by your dependency injection system.
struct MethodDependencies {
  let timeProvider = TimeProvider()

  struct TimeProvider {
    var currentTime: TimeInterval {
      Date().timeIntervalSinceReferenceDate
    }
  }
}

// Extend the 'RPCMethod' method type in your server target with 'RPCMethodPerformable' to
// implement the method that performs the methods.
extension ExampleRPCMethod: RPCMethodPerformable {
  func perform(dependencyProvider: MethodDependencies) async throws -> ExampleMethodResult {
    switch self {
    case .ping:
      return .pong(dependencyProvider.timeProvider.currentTime)
    }
  }
}

// Start the server.
let server = RPCServer<ExampleRPCMethod>(dependencyProvider: MethodDependencies())
try server.start(host: "127.0.0.1", port: 1234)

// Connect the client.
let client = RPCClient<ExampleRPCMethod>()
try client.connect(host: "127.0.0.1", port: 1234)

// Perform the 'ping' method.
let result = try client.call(.ping)

switch result {
case .pong(let currentTime):
  print(currentTime)
}

The included example project demonstrates using CodableRPC to communicate between a UI test and the iOS app under test. Notice that the example project declares the ExampleRPCMethod enum in a target that is imported by both the app target and the test target, whereas the RPCMethodPerformable conformance is declared in a target that is only imported by the app target. This setup is necessary to decouple your test target from the dependencies that implement the RPC methods.

Configuration

Both RPCServer and RPCClient can be initialized with custom configurations, though the defaults should be reasonable for simple workloads. See the documentation on RPCServerConfig and RPCClientConfig for details.