@get:JvmName("boundary") val boundary: String,
  ) : Closeable {
    /** This delimiter typically precedes the first part. */
    private val dashDashBoundary =
      Buffer()
        .writeUtf8("--")
        .writeUtf8(boundary)
        .readByteString()

    /**
     * This delimiter typically precedes all subsequent parts. It may also precede the first part
     * if the body contains a preamble.