* The [exchange] field is assigned to null when its streams end, which may be before or after the
   * network interceptors return.
   */
  internal var interceptorScopedExchange: Exchange? = null
    private set

  // These properties are guarded by [lock]. They are typically only accessed by the thread executing
  // the call, but they may be accessed by other threads for duplex requests.

  // These properties are guarded by [lock].

  /**
   * If true, no new exchanges can be created on this connection. It is necessary to set this to
   * true when removing a connection from the pool; otherwise a racing caller might get it from the
   * pool when it shouldn't. Symmetrically, this must always be checked before returning a
   * connection from the pool.
   *
   * Once true this is always true. Guarded by this.

  /**
   * Returns a request that includes a credential to satisfy an authentication challenge in
   * [response]. Returns null if the challenge cannot be satisfied.
   *
   * The route is best effort, it currently may not always be provided even when logically
   * available. It may also not be provided when an authenticator is re-used manually in an
   * application interceptor, such as when implementing client-specific retries.
   */

 * addresses nor hostnames; they will be verified as IP addresses (which is a more strict
 * verification).
 */
private val VERIFY_AS_IP_ADDRESS = "([0-9a-fA-F]*:[0-9a-fA-F:.]*)|([\\d.]+)".toRegex()

/** Returns true if this string is not a host name and might be an IP address. */
fun String.canParseAsIpAddress(): Boolean = VERIFY_AS_IP_ADDRESS.matches(this)

/**

   */
  class AddressPolicy(
    /**
     * 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,

      assertThat(expected.message).isEqualTo("Code must be in range [1000,5000): 98724976")
    }
  }

  @Test fun closeReservedThrows() {
    assertFailsWith<IllegalArgumentException> {
      clientWriter.writeClose(1005, "Hello".encodeUtf8())
    }.also { expected ->
      assertThat(expected.message).isEqualTo("Code 1005 is reserved and may not be used.")
    }
  }

  @Test fun serverEmptyPing() {

   *
   *  * 16 bytes: either `OkHttp cache v1\n` if the persisted file is complete. This is another
   *    sequence of bytes if the file is incomplete and should not be used.
   *  * 8 bytes: *n*: upstream data size
   *  * 8 bytes: *m*: metadata size
   *  * *n* bytes: upstream data
   *  * *m* bytes: metadata
   *

   * qualifier are not unique and should only be used in development environments. If you create
   * custom builds of OkHttp please include a qualifier your version name, like "4.7.0-mycompany.3".
   * The version string is configured in the root project's `build.gradle`.
   *
   * Note that OkHttp's runtime version may be different from the version specified in your

 * 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
   * connection to an address fails, OkHttp will retry the connection with the next address until

makes HTTP and HTTPS calls. It lets you specify which responses to return and
then verify that requests were made as expected.

Because it exercises your full HTTP stack, you can be confident that you're
testing everything. You can even copy & paste HTTP responses from your real web
server to create representative test cases. Or test that your code survives in