DNS resolution does not respect local configuration (/etc/hosts, avahi *.local, nsswitch.conf, etc)
afcady opened this issue · comments
There is an issue in baresip which results from the DNS client code in re.
re implements its own asynchronous DNS resolver in src/dns/client.c. It uses this to resolve all names in SIP addresses.
On systems where the only source of name resolution is DNS, that is alright. But desktop OSes typically support both /etc/hosts and some form of LAN discovery (such as MDNS, implemented by avahi/bonjour on Linux/Mac OS X). In a correctly functioning SIP client on these platforms, two machines on a LAN that have locally-propagated *.local MDNS names will be able to make SIP calls to one another using these names.
On Linux, the re library needs to use getaddrinfo or getaddrinfo_a to get the correct behavior.
I looked at src/dns/client.c to see what would need to be changed to switch to getaddrinfo_a.
At present the creation of the struct dnsc in dnscalloc() is also installing a udp_listen callback udp_recv_handler for DNS replies.
Then in query() either send_udp or send_tcp is used to send the DNS request. Here, a third option would be added, when DNS_TYPE_A or AAAA, to call getaddrinfo_a with a callback that is equivalent to what the reply_recv does, which is ultimately to call the dns_query_h *qh callback from the struct dns_query (in query_handler). This accepts a const struct dnshdr *hdr which could maybe be NULL, with only the struct list *ansl 3rd argument containing a value derived from the lookup. I suppose this needs to be called in the same context as the udp_recv_handler so the callback actually passed to getaddrinfo_a would only add the response to a list protected by a mutex. Then the part of the loop that runs udp_recv_handler would be modified to check this list and call the dns_query_h.
Sound good? Would this be acceptable if I submitted a patch?
due to the current policy, this will not be accepted: