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) {

  }

  /**
   * Returns a plan to reuse a pooled connection, or null if the pool doesn't have a connection for
   * this address.
   *
   * If [planToReplace] is non-null, this will swap it for a pooled connection if that pooled
   * connection uses HTTP/2. That results in fewer sockets overall and thus fewer TCP slow starts.
   */
  internal fun planReusePooledConnection(