contract { callsInPlace(action, InvocationKind.EXACTLY_ONCE) }
    return lock.withLock(action)
  }

  inline fun <T> RealConnection.withLock(action: () -> T): T {
    contract { callsInPlace(action, InvocationKind.EXACTLY_ONCE) }
    return lock.withLock(action)
  }

  inline fun <T> RealCall.withLock(action: () -> T): T {
    contract { callsInPlace(action, InvocationKind.EXACTLY_ONCE) }
    return lock.withLock(action)
  }

  /**
   * Invoked as soon as a call is enqueued or executed by a client. In case of thread or stream
   * limits, this call may be executed well before processing the request is able to begin.
   *
   * This will be invoked only once for a single [Call]. Retries of different routes or redirects
   * will be handled within the boundaries of a single [callStart] and [callEnd]/[callFailed] pair.
   */
  open fun callStart(call: Call) {
  }

  /**

   */
  fun cancel()

  fun interface Factory {
    /**
     * Creates a new event source and immediately returns it. Creating an event source initiates an
     * asynchronous process to connect the socket. Once that succeeds or fails, `listener` will be
     * notified. The caller must cancel the returned event source when it is no longer in use.
     */
    fun newEventSource(
      request: Request,

        return headersQueue.removeFirst()
      }
      throw errorException ?: StreamResetException(errorCode!!)
    }
  }

  /**
   * Returns the trailers. It is only safe to call this once the source stream has been completely
   * exhausted.
   */
  @Throws(IOException::class)
  fun trailers(): Headers {
    this.withLock {

  fun commit(upstreamSize: Long) {
    // Write metadata to the end of the file.
    writeMetadata(upstreamSize)
    file!!.channel.force(false)

    // Once everything else is in place we can swap the dirty header for a clean one.
    writeHeader(PREFIX_CLEAN, upstreamSize, metadata.size.toLong())
    file!!.channel.force(false)

    // This file is complete.
    synchronized(this@Relay) {

          return block()
        }
      },
      delayNanos,
    )
  }

  /**
   * Executes [block] once on a task runner thread.
   *
   * TODO: make this inline once this is fixed: https://github.com/oracle/graal/issues/3466
   */
  fun execute(
    name: String,
    delayNanos: Long = 0L,
    cancelable: Boolean = true,
    block: () -> Unit,
  ) {
    schedule(

    assertThat(response.body.contentLength()).isEqualTo(0L)
    assertThat(response.body.byteString()).isEqualTo(EMPTY)
  }

  /**
   * Returns a new response body that refuses to be read once it has been closed. This is true of
   * most [BufferedSource] instances, but not of [Buffer].
   */
  private fun responseBody(content: String): ResponseBody {
    val data = Buffer().writeUtf8(content)

  /** True if there are more exchanges expected for this call. */
  private var expectMoreExchanges = true

  // These properties are accessed by canceling threads. Any thread can cancel a call, and once it's
  // canceled it's canceled forever.

  @Volatile private var canceled = false

  @Volatile private var exchange: Exchange? = null
  internal val plansToCancel = CopyOnWriteArrayList<RoutePlanner.Plan>()

 * used. HTTP/1.x connections can carry either zero or one streams. HTTP/2 connections can carry any
 * number of streams, dynamically configured with `SETTINGS_MAX_CONCURRENT_STREAMS`. A connection
 * currently carrying zero streams is an idle stream. We keep it alive because reusing an existing
 * connection is typically faster than establishing a new one.
 *

   */
  fun cancel()

  fun interface Factory {
    /**
     * Creates a new web socket and immediately returns it. Creating a web socket initiates an
     * asynchronous process to connect the socket. Once that succeeds or fails, `listener` will be
     * notified. The caller must either close or cancel the returned web socket when it is no longer
     * in use.
     */
    fun newWebSocket(
      request: Request,