sink: Buffer,
        byteCount: Long,
      ): Long {
        require(byteCount >= 0L) { "byteCount < 0: $byteCount" }
        check(currentPart == this) { "closed" }

        return source.timeout().intersectWith(timeout) {
          when (val limit = currentPartBytesRemaining(maxByteCount = byteCount)) {
            0L -> -1L

            // No more bytes in this part.
            else -> source.read(sink, limit)