DerHeader(
        tagClass = DerHeader.TAG_CLASS_UNIVERSAL,
        tag = DerHeader.TAG_END_OF_CONTENTS,
        constructed = false,
        length = -1L,
      )
  }

  /** A source that keeps track of how many bytes it's consumed. */
  private class CountingSource(source: Source) : ForwardingSource(source) {
    var bytesRead = 0L

    override fun read(
      sink: Buffer,
      byteCount: Long,