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Repeated ICMP packets are generated when poll() keeps returning SLIRP_POLL_HUP revent for UDP sockets

I’m seeing many copies of the same ICMP packet generated by libslirp when poll() keeps returning revent POLLHUP(SLIRP_POLL_HUP) for UDP sockets. Those ICMP packets are for the same latest outbound UDP packet. This problem is found on iPhone intermittently.

Questions:

  • Is there a reason why libslirp doesn’t close the UDP socket for revent SLIRP_POLL_HUP but only generating an ICMP?
  • Can this problem be addressed in libslirp? Or any suggestions on how to handle in my application?

Here are some details when the issue happens.

  • When my app calls slirp_pollfds_fill(), add_poll() callback receives the fds with event SLIRP_POLL_IN | SLIRP_POLL_HUP | SLIRP_POLL_ERR.
  • My app calls poll().
  • Poll() returns immediately.
  • My app calls slirp_pollfds_poll() with revent SLIRP_POLL_IN | SLIRP_POLL_HUP received on those fds.
  • Libslirp attempts to read from recvfrom(), gets -1, then generates the ICMP packet.
  • The UDP sockets are not closed. When my app calls slirp_pollfds_fill() in the next round, the same thing happens again.