RedirectHackPlugin.scala

import java.net.{HttpURLConnection, URI, URL}

import sbt.plugins.IvyPlugin
import sbt.{AllRequirements, AutoPlugin, Keys, Logger, MavenRepository, Patterns, PluginTrigger, Plugins, Resolver, URLRepository}

import scala.collection.mutable
import scala.util.control.NonFatal

object RedirectHackPlugin extends AutoPlugin {

  private val redirectCache: mutable.Map[String, Option[String]] = mutable.Map.empty

  override def trigger: PluginTrigger = AllRequirements

  override def requires: Plugins = IvyPlugin

  override def projectSettings = Seq(
    Keys.fullResolvers := {
      Keys.fullResolvers.value.map(resolveRedirectUrl(_, Keys.streams.value.log))
    }
  )

  private def resolveRedirectUrl(r: Resolver, logger: Logger): Resolver = {
    r match {
      case MavenRepository(name, root) =>
        findRedirectUrl(root, logger).map(MavenRepository(name, _)).getOrElse(r)
      case URLRepository(name, patterns) =>
        val ivyPatterns = patterns.ivyPatterns.map(p => findRedirectPattern(p, logger).getOrElse(p))
        val ppp = patterns.artifactPatterns.map(p => findRedirectPattern(p, logger).getOrElse(p))
        URLRepository(name, new Patterns(ivyPatterns, ppp, patterns.isMavenCompatible, patterns.descriptorOptional, patterns.skipConsistencyCheck))
      case _ => r
    }
  }

  private def findRedirectPattern(pattern: String, logger: Logger): Option[String] = {
    val ary = pattern.split("\\[", 2)
    findRedirectUrl(ary.head, logger).map(r => (Array(r) ++ ary.tail).mkString("["))
  }

  private def findRedirectUrl(root: String, logger: Logger) = {
    redirectCache.getOrElseUpdate(root, {
      new URL(root).openConnection() match {
        case conn: HttpURLConnection =>
          conn.setInstanceFollowRedirects(false)
          conn.getResponseCode match {
            case HttpURLConnection.HTTP_MOVED_PERM | HttpURLConnection.HTTP_MOVED_TEMP | HttpURLConnection.HTTP_SEE_OTHER =>
              val location = Option(conn.getHeaderField("Location"))
                .filter(isBintray)
              location.foreach(l => logger.debug(s"Redirect: $root -> $l"))
              location
            case _ =>
              None
          }
        case _ => None
      }
    })
  }

  private def isBintray(s: String): Boolean = {
    try {
      new URI(s).getHost == "dl.bintray.com"
    } catch {
      case NonFatal(_) => false
    }
  }
}

dl.bintray.com へのリダイレクト時間を省略するために最初に fullResolvers を書き換えるハック