* Apply inbound settings and send an acknowledgement to the peer that provided them.
     *
     * We need to apply the settings and ack them atomically. This is because some HTTP/2
     * implementations (nghttp2) forbid peers from taking advantage of settings before they have
     * acknowledged! In particular, we shouldn't send frames that assume a new `initialWindowSize`
     * until we send the frame that acknowledges this new size.
     *

  /**
   * The reason why this stream was closed, or null if it closed normally or has not yet been
   * closed.
   *
   * If there are multiple reasons to abnormally close this stream (such as both peers closing it
   * near-simultaneously) then this is the first reason known to this peer.
   */
  internal var errorCode: ErrorCode? = null
    get() = this.withLock { field }