**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_

 *  Fix: Retain binary-compatibility in `okhttp3.internal.HttpMethod`. Naughty third party SDKs

In OkHttp we expose a blocking API over a framed protocol. This document explains the code and policy that makes that work.

### Threads

#### Application's calling thread

## Version 3.13.0

_2019-02-04_

 *  **This release bumps our minimum requirements to Java 8+ or Android 5+.** Cutting off old
    devices is a serious change and we don't do it lightly! [This post][require_android_5] explains
    why we're doing this and how to upgrade.

    The OkHttp 3.12.x branch will be our long-term branch for Android 2.3+ (API level 9+) and Java

   * near-simultaneously) then this is the first reason known to this peer.
   */
  internal var errorCode: ErrorCode? = null
    get() = this.withLock { field }

  /** The exception that explains [errorCode]. Null if no exception was provided. */
  internal var errorException: IOException? = null

  init {
    if (headers != null) {

        }
        else -> throw expected
      }
    }
  }

  /**
   * Not checking the CA bit created a vulnerability in old OkHttp releases. It is exploited by
   * triggering different chains to be discovered by the TLS engine and our chain cleaner. In this
   * attack there's several different chains.
   *
   *