PBandK Service Generator and Kotlin Multiplatform Runtime for Twirp

This project is a service generator plugin for PBandK that generates Kotlin client integration for Twirp services. The generated client code leverages PBandK for protobuf messages, kotlinx.serialization for JSON handling of Twirp service errors, and Ktor for HTTP. All of these choices enable the generated client code to be leveraged in Kotlin Multiplatform projects, sharing the network integration layer with compatible platform targets.

There are two parts to this project - the generator itself, and the supporting runtime for leveraging the generated service code.

Generator

In general, follow PBandK Usage instructions, but supply the twirp-kmp-generator as the kotlin_service_gen option as described in PBandK's Service Code Generation documentation.

Usage

Download the latest release, currently 0.4.0, and pass it to protoc via pbandk:

# Download the library to ~
cd ~/
curl -OL https://github.com/collectiveidea/twirp-kmp/releases/download/0.4.0/twirp-kmp-generator-0.4.0.jar

Pass the jar and generator class name as the kotlin_service_gen option to pbandk_out:

cd ~/exampleProject
protoc --pbandk_out=kotlin_service_gen='~/twirp-kmp-generator-0.4.0.jar|com.collectiveidea.twirp.Generator',kotlin_package=com.example.api:src/main/kotlin src/main/proto/example.proto

Build

To build the library locally, run:

./gradlew build

This creates the versioned .jar file, e.g. generator/build/libs/twirp-kmp-generator-0.4.0-SNAPSHOT.jar

Then, the built version can be used, instead of the latest release, by supplying the path to the built .jar, e.g.:

protoc --pbandk_out=kotlin_service_gen='/Users/darron/Development/twirp-kmp/generator/build/libs/twirp-kmp-generator-0.4.0-SNAPSHOT.jar|com.collectiveidea.twirp.Generator',kotlin_package=com.example.api:shared/src/commonMain/kotlin shared/src/commonMain/proto/example.proto

Runtime

The runtime provides an installTwirp helper to configure a Ktor HttpClient for Twirp integration.

First, add the runtime as a dependency:

implementation "com.collectiveidea.twirp:twirp-kmp-runtime:0.4.0"

Then, configure the HttpClient and pass the client into the generated service constructor:

val client = HttpClient(engine) {    
    installTwirp(baseUrl)
}

val exampleService = ExampleServiceImpl(client)

Service methods throw a ServiceException on error. The ServiceException contains the parsed error response from the Twirp service JSON body.