[PATCH 1/1] ping: Add support for IPv4-mapped IPv6 address format

[Steffen Nurpmeso]

David Leonard wrote in
 <1qs786o8-714q-23nn-649q-o331s404so3r at nqncgvir-ragrecevfrf.pbz>:
 |On Sun, 20 Oct 2024, Lars Uffmann wrote:
 |> As for the points David brings up:
 |> On 2024-10-20 13:51:32, Petr Vorel wrote:
 |>>>> I'm not a fan of this patch because ping is a low-level diagnostic \
 |>>>> tool.
 |> While I would acknowlege the low-level diagnostic part, I do think \
 |> it has 
 |> uses that go beyond that - since most operating systems can be configure\
 |> d to
 |
 |I spent some time with your application trying to understand what
 |networking it's doing and the motivating context... and I would
 |recommend you look at getaddrinfo() and getnodeinfo(). These are
 |supported by cygwin64 (mentioned in file comments). My general advice
 |to you is to try and make your application address agnostic.
 |
 |It seems clear that this patch to ping exists only because of your
 |application's deliberate construction of IPv4-mapped IPv6
 |addresses to fit a poor choice of type/represenation.
 |
 |I see that the code had previously been using uint32_t for addresses,
 |and switched to in6_addr for IPv6 support. The incorrect assumption is
 |that in6_addr is simply a superspace of IPv4. (It's not.) You would be
 |better off using something to track address families, such as
 |a struct sockaddr_storage or struct addrinfo (latter is more portable).

On the other hand Linux (and OpenIndiana/Solaris) just (seem to)
work neatlessly with IPv4-mapped addresses (for server sockets).
In a simple thing i thus used

  /* Whether we should open distinct IPv4 and IPv6 sockets */
  #undef a_DISTINCT_SOCKS
  #if defined __FreeBSD__ || defined __NetBSD__ || defined __OpenBSD__
  # define a_DISTINCT_SOCKS
  #endif

and then mess like

  #ifdef a_DISTINCT_SOCKS
          fd_set rfds;
          struct sockaddr_in soa4;
          int sofd4;
  #endif
          struct sockaddr_in6 soa6;
          int sofd6, es;

as well as

  #if defined a_DISTINCT_SOCKS && defined IPV6_V6ONLY
                  int one;

                  one = 1;
                  if(setsockopt(sofd6, IPPROTO_IPV6, IPV6_V6ONLY, (void*)&one, sizeof(one)) == -1){
                          fprintf(stderr, "IPv6 cannot set server socket option V6ONLY: %s\n", strerror(errno));
                          es = a_EX_OSERR;
                          goto jleave;
                  }
  #endif

ie, if relying on (the standardized) IPv4-mapped addresses one can
avoid a whole bunch of things, including polling/selection,
system-specific problems etc.

 ...

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)