it against OkHttp 4.x. We’re using the excellent [japicmp][japicmp] library via its
   [Gradle plugin][japicmp_gradle] to enforce binary compatibility.

 * **Java source compatibility** is the ability to upgrade Java uses of OkHttp 3.x to 4.x without
   changing `.java` files.

 * **Kotlin source compatibility** is the ability to upgrade Kotlin uses of OkHttp 3.x to 4.x

    private val timeout = Timeout()

    /** The operator to read and write the shared file. Null if this source is closed. */
    private var fileOperator: FileOperator? = FileOperator(file!!.channel)

    /** The next byte to read. This is always less than or equal to [upstreamPos]. */
    private var sourcePos = 0L

    /**
     * Selects where to find the bytes for a read and read them. This is one of three sources.
     *

    coders call this and we don't want their users to suffer.


## Version 4.0.0

_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.

    /**
     * How many concurrent calls should be possible to make at any time.
     * The pool will routinely try to pre-emptively open connections to satisfy this minimum.
     * Connections will still be closed if they idle beyond the keep-alive but will be replaced.
     */
    @JvmField val minimumConcurrentCalls: Int = 0,
    /** How long to wait to retry pre-emptive connection attempts that fail. */

 * or both.
 *
 * ## Authentication Retries
 *
 * If your authentication may be flaky and requires retries you should apply some policy
 * to limit the retries by the class of errors and number of attempts.  To get the number of
 * attempts to the current point use this function.
 *
 * ```java
 * private int responseCount(Response response) {
 *   int result = 1;

 * implementation to use a different DNS server, to prefer IPv6 addresses, to prefer IPv4 addresses,
 * or to force a specific known IP address.
 *
 * Implementations of this interface must be safe for concurrent use.
 */
fun interface Dns {
  /**
   * Returns the IP addresses of `hostname`, in the order they will be attempted by OkHttp. If a

### EventListener.Factory

In the preceding example we used a field, `callStartNanos`, to track the elapsed time of each event. This is handy, but it won’t work if multiple calls are executing concurrently. To accommodate this, use a `Factory` to create a new `EventListener` instance for each `Call`. This allows each listener to keep call-specific state.

A wildcard rule was added with a wildcard that is not in leftmost position! We'll need to change the ${PublicSuffixDatabase::class.java.name} to handle this."""
    }
    check(rule.indexOf(WILDCARD_CHAR, 1) == -1) {
      """Wildcard Assertion Failure: '$rule'
A wildcard rule was added with multiple wildcards! We'll need to change ${PublicSuffixDatabase::class.java.name} to handle this."""
    }
    check(rule.length != 1) {

 *
 * ### Trust Manager Extraction
 *
 * Supported on Android 2.3+ and OpenJDK 7+. There are no public APIs to recover the trust
 * manager that was used to create an [SSLSocketFactory].
 *
 * Not supported by choice on JDK9+ due to access checks.
 *
 * ### Android Cleartext Permit Detection
 *
 * Supported on Android 6.0+ via `NetworkSecurityPolicy`.
 */
open class Platform {

  /** Finds an exchange to send the next request and receive the next response. */
  private var exchangeFinder: ExchangeFinder? = null

  var connection: RealConnection? = null
    private set
  private var timeoutEarlyExit = false

  /**
   * This is the same value as [exchange], but scoped to the execution of the network interceptors.