Mark Andrews writes:
>
> In message <[email protected]>, Andrew Sullivan writes:
> > On Thu, Feb 06, 2014 at 04:31:38AM +0000, Viktor Dukhovni wrote:
> > > I must plead ignorance of the obstacle, what do you have in mind?
> >
> > I am repeatedly informed by my man pages, RFC 3493, and every web
> > browser implementer I've ever spoken to that getting the TTL on an RR
> > coming to you from the system resolver is hard. I'd be more delighted
> > than I can express to be misinformed, so if you know otherwise please
> > say so.
>
> And I say BS. If you are using a layer above the resolver
> (gethostbyname, getaddrinfo) yes it may be hard but for TLSA *there
> is no layer above the resolver*.
>
> libresolv/libbind have provided access to the TTL since the 1980's.
>
> Even Microsoft Windows programmers don't have a excuse as DnsQuery
> returns the ttl in its results.
>
> http://msdn.microsoft.com/en-us/library/windows/desktop/ms682016(v=vs.85).asp
> x
And as for getaddrinfo/RFC 3493, the api was designed to be extendable.
We should just extend it to return the ttl. Something like the following
would do.
e.g.
In <netdb.h>
struct addrinfo {
int ai_flags; /* AI_PASSIVE, AI_CANONNAME,
AI_NUMERICHOST, .. */
int ai_family; /* AF_xxx */
int ai_socktype; /* SOCK_xxx */
int ai_protocol; /* 0 or IPPROTO_xxx for IPv4 and IPv6 */
socklen_t ai_addrlen; /* length of ai_addr */
char *ai_canonname; /* canonical name for nodename */
struct sockaddr *ai_addr; /* binary address */
struct addrinfo *ai_next; /* next structure in linked list */
/* RFC XXXX */
#define AI_TTL 1
#define AI_NOTTL 0xffffffffu /* No TTL available */
unsigned int ai_ttl; /* DNS TTL */
};
In the application
unsigned int ttl;
#ifdef AI_TTL
if (addrinfo->ai_ttl == AI_NOTTL)
ttl = addrinfo->ai_ttl;
else
#else
ttl = 0;
#endif
Mark
--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: [email protected]
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