C Klib

CKlib is a gradle plugin that will build and package C/C++/Objective-C code for Kotlin/Native.

The Problem

When you want to access C-etc code from Kotlin/Native, you point the cinterop process at it. That will create Kotlin code to enable calling the native code. That's only one part of the process, though. You also need to build and link binaries to implement the native calls. Configuring native builds can be complex because of the number of options that need to be correctly configured, as well as the need to package and link the complied binaries.

The Solution

This problem is already kind of solved by Kotlin/Native itself. The platform is based largely on C and C++. There's a Gradle plugin and set of tasks embedded within Kotlin/Native and the broader Kotlin platform that configures and builds native C-etc code. That plugin is not published in an accessible way, unfortunately. CKlib extracts that Clang Gradle plugin to be used externally.

For packaging, the problem is already solved there as well. You can just insert the compiled binary into your klib. CKlib is configured to do that for you.

Status

This plugin hasn't been designed for all use cases. We needed to compile and embed C code with no real external dependencies. You may want to build and embed C-etc code for other use cases we haven't considered, and this plugin will almost certainly need to be modified for your particular situation. Please start conversations and/or submit PRs if you add anything significant.

Usage

Add the plugin to your buildscript path:

buildscript {
  repositories {
    mavenCentral() // <- need this
    google()
    gradlePluginPortal()
  }
  dependencies {
    classpath("co.touchlab:cklib-gradle-plugin:1.5.31.3") // <- Replace with current version
  }
}

Apply the plugin. You will also need to have the Kotlin Multiplatform plugin applied. CKlib depends on it.

plugins {
  kotlin("multiplatform")
  id("co.touchlab.cklib")
}

To create compilations, add the cklib block and then point at C-etc source.

cklib {
  create("somecode") {
    language = C
    compilerArgs.addAll(
      listOf(
        "-Wno-unused-function"
      )
    )
  }
}

By default, the C-etc code is built and packaged in compatible Kotlin/Native klibs. You can specify source folders and you will likely need to add some compiler args. Anything more custom will probably require tweaking the plugin itself, as it was really designed for a very particular use case.

Versioning

The underlying code comes from the Kotlin repo, and references local dependencies that are tightly coupled with Kotlin versions. As such, we have a 4 number version system. The first 3 are the Kotlin version, and the last is our point version.

So, for Kotlin 1.5.31, we have CKlib 1.5.31.3, which is the 3rd point release.

We're Hiring!

Touchlab is looking for a Mobile Developer, with Android/Kotlin experience, who is eager to dive into Kotlin Multiplatform Mobile (KMM) development. Come join the remote-first team putting KMM in production. More info here.

Primary Maintainer

Kevin Galligan

Ping me on twitter @kpgalligan if you don't get a timely reply! -Kevin

License

Copyright 2021 Touchlab, Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.