Proguard

If you have some restrictions on your JAR size (for example when deploying a free application to heroku),you can use proguard to shrink it. If you are using gradle, it is pretty straightforward to use theproguard-gradle plugin. You only have to remember to keep: your main module method, the EngineMainclass, and the Kotlin reflect classes. You can then fine-tune it as required:

build.gradle

  1. buildscript {
  2.     ext.proguard_version = '6.0.1'
  3.     dependencies {
  4.         classpath "net.sf.proguard:proguard-gradle:$proguard_version"
  5.     }
  6. }
  8. task minimizedJar(type: proguard.gradle.ProGuardTask, dependsOn: shadowJar) {
  9.     injars "build/libs/my-application.jar"
  10.     outjars "build/libs/my-application.min.jar"
  11.     libraryjars System.properties.'java.home' + "/lib/rt.jar"
  12.     printmapping "build/libs/my-application.map"
  13.     ignorewarnings
  14.     dontobfuscate
  15.     dontoptimize
  16.     dontwarn
  18.     def keepClasses = [
  19.             'io.ktor.server.netty.EngineMain', // The EngineMain you use, netty in this case.
  20.             'kotlin.reflect.jvm.internal.**',
  21.             'io.ktor.samples.hello.HelloApplicationKt', // The class containing your module defined in the application.conf
  22.             'kotlin.text.RegexOption'
  23.     ]
  25.     for (keepClass in keepClasses) {
  26.         keep access: 'public', name: keepClass, {
  27.             method access: 'public'
  28.             method access: 'private'
  29.         }
  30.     }
  31. }

You have a full example on: https://github.com/ktorio/ktor-samples/tree/master/other/proguard