_2019-06-26_

**This release upgrades OkHttp to Kotlin.** We tried our best to make fast and safe to upgrade
from OkHttp 3.x. We wrote an [upgrade guide][upgrading_to_okhttp_4] to help with the migration and a
[blog post][okhttp4_blog_post] to explain it.

 *  Fix: Target Java 8 bytecode for Java and Kotlin.


## Version 4.0.0-RC3

_2019-06-24_

    // our connection coalescing requirements are met. See also:
    // https://hpbn.co/optimizing-application-delivery/#eliminate-domain-sharding
    // https://daniel.haxx.se/blog/2016/08/18/http2-connection-coalescing/

    // 1. This connection must be HTTP/2.
    if (http2Connection == null) return false

    // 2. The routes must share an IP address.

    assertInvalid("http://.a/", "Invalid URL host: \".a\"")
    assertInvalid("http://../", "Invalid URL host: \"..\"")
  }

  @Test
  fun hostnameTelephone() {
    // https://www.gosecure.net/blog/2020/10/27/weakness-in-java-tls-host-verification/

    // Map the single character telephone symbol (℡) to the string "tel".
    assertThat(parse("http://\u2121").host).isEqualTo("tel")

 *
 * Using a yubikey device as a SSL key store.
 * https://lauri.võsandi.com/2017/03/yubikey-for-ssh-auth.html
 *
 * Using PKCS11 support in the JDK.
 * https://tersesystems.com/blog/2018/09/08/keymanagers-and-keystores/
 *
 * Install OpenSC separately. On a mac `brew cast install opensc`.
 */
@SuppressSignatureCheck
class YubikeyClientAuth {
  fun run() {

          if (!buffer.isProbablyUtf8()) {
            logger.log("")
            logger.log("<-- END HTTP (${totalMs}ms, binary ${buffer.size}-byte body omitted)")
            return response
          }

          if (contentLength != 0L) {
            logger.log("")
            logger.log(buffer.clone().readString(charset))
          }

          logger.log(
            buildString {

    }
    val multimap = mapOf("Set-Cookie" to cookieStrings)
    try {
      cookieHandler.put(url.toUri(), multimap)
    } catch (e: IOException) {
      Platform.get().log("Saving cookies failed for " + url.resolve("/...")!!, WARN, e)
    }
  }

  override fun loadForRequest(url: HttpUrl): List<Cookie> {
    val cookieHeaders =
      try {

    address: InetSocketAddress,
    connectTimeout: Int,
  ) {
    socket.connect(address, connectTimeout)
  }

  open fun log(
    message: String,
    level: Int = INFO,
    t: Throwable? = null,
  ) {
    val logLevel = if (level == WARN) Level.WARNING else Level.INFO
    logger.log(logLevel, message, t)
  }

  open fun isCleartextTrafficPermitted(hostname: String): Boolean = true

  /**

  val showHeaders: Boolean by option("-i", "--include", help = "Include protocol headers in the output").flag()

  val showHttp2Frames: Boolean by option("--frames", help = "Log HTTP/2 frames to STDERR").flag()

  val referer: String? by option("-e", "--referer", help = "Referer URL")

  val verbose: Boolean by option("-v", "--verbose", help = "Makes $NAME verbose during the operation").flag()

This [sample factory](https://github.com/square/okhttp/blob/master/samples/guide/src/main/java/okhttp3/recipes/PrintEvents.java) creates a unique ID for each call and uses that ID to differentiate calls in log messages.

```java
class PrintingEventListener extends EventListener {
  public static final Factory FACTORY = new Factory() {
    final AtomicLong nextCallId = new AtomicLong(1L);

          responseCallback.onResponse(this@RealCall, response)
        } catch (e: IOException) {
          if (signalledCallback) {
            // Do not signal the callback twice!
            Platform.get().log("Callback failure for ${toLoggableString()}", Platform.INFO, e)
          } else {
            responseCallback.onFailure(this@RealCall, e)
          }
        } catch (t: Throwable) {
          cancel()