Extension methods to Typesafe Config to support Docker Swarm secrets

ConfigExtensions.scala

package com.typesafe.config.impl

import com.typesafe.config.ConfigFactory.parseMap
import com.typesafe.config.{Config, ConfigFactory}

import scala.collection.JavaConverters._
import scala.io.Source
import scala.util.Try

// discussion: https://groups.google.com/forum/#!topic/play-framework-dev/t2g-TWbqtzY 
trait ConfigExtensions {

  implicit class ExtConfig(config: Config) {
    val rawConfig: Config = ConfigFactory.defaultApplication()

    def withSecretAt(path: String*): Config = {
      val secretConfig = parseMap(path.map(p => (p, Try(getSecretUnsafe(p)).toOption.orNull)).filterNot(_._2 == null).toMap.asJava)
      secretConfig.withFallback(config)
    }

    def getSecret(path: String): String =
      Try {
        getSecretUnsafe(path)
      }.recover {
        case _ => config.getString(path)
      }.get

    private def getSecretUnsafe(path: String) = {
      val p: Path      = Path.newPath(path)
      val last: String = p.last()
      val rs           = new ResolveSource(rawConfig.getObject(path.stripSuffix(s".$last")).asInstanceOf[AbstractConfigObject])

      val envVarName = rs.root.get(last) match {
        case cr: ConfigReference =>
          cr.expression.path.render
        case cdm: ConfigDelayedMerge =>
          cdm.unmergedValues().iterator().next().render().stripPrefix("${").stripPrefix("?").stripSuffix("}")
      }

      String.valueOf(Source.fromFile(s"/run/secrets/$envVarName").toArray)
    }

  }

}