gsockaddr: V4-mapped addresses should be formatted as an IPv4 address

V4-mapped address space is a compatibility feature of dual-stack TCP/IP
stacks, where IPv4 connections can be established to IPv6 capable sockets.

When this happens, the client IP address would be a V4-mapped address,
as determined by the IN6_IS_ADDR_V4MAPPED() function, which
is equivalent to an "::FFFF:<ipv4>" address (see RFC3493)

This change would trickle into how we fill $HOST if we didn't find a
hostname there, previously these would have the form of "::FFFF:ipv4",
with this one they would become "ipv4" just as if we received them using
an ipv4 specific source.

Signed-off-by: Balazs Scheidler <balazs.scheidler@axoflow.com>

lib/gsockaddr.c

@@ -377,7 +377,10 @@ g_sockaddr_inet6_format(GSockAddr *s, gchar *text, gulong n, gint format)
     }
   else if (format == GSA_ADDRESS_ONLY)
     {
-      inet_ntop(AF_INET6, &self->sin6.sin6_addr, text, n);
+      if (IN6_IS_ADDR_V4MAPPED(&self->sin6.sin6_addr))
+        inet_ntop(AF_INET, &self->sin6.sin6_addr.s6_addr32[3], text, n);
+      else
+        inet_ntop(AF_INET6, &self->sin6.sin6_addr, text, n);
     }
   else
     g_assert_not_reached();