RFC 2308 says a lot about negative answer caching.
Here is patch, that discloses TTL of negative answer (if possible) to
the library user.
--
WBRBW, Leonid Evdokimov
xmpp:l...@darkk.net.ru && http://darkk.net.ru
tel:+79816800702 && tel:+79050965222
From c903d9db417d2d8478eb7371e46dbc5ef60f650b Mon Sep 17 00:00:00 2001
From: Leonid Evdokimov <da...@yandex-team.ru>
Date: Wed, 31 Aug 2011 00:56:45 +0400
Subject: [PATCH 7/7] DNS: add ttl for negative answers using RFC 2308 idea.
---
evdns.c | 42 ++++++++++++++++++++++++++++++++++++------
1 files changed, 36 insertions(+), 6 deletions(-)
diff --git a/evdns.c b/evdns.c
index d7a3093..5f11772 100644
--- a/evdns.c
+++ b/evdns.c
@@ -135,6 +135,7 @@
#define TYPE_A EVDNS_TYPE_A
#define TYPE_CNAME 5
#define TYPE_PTR EVDNS_TYPE_PTR
+#define TYPE_SOA EVDNS_TYPE_SOA
#define TYPE_AAAA EVDNS_TYPE_AAAA
#define CLASS_INET EVDNS_CLASS_INET
@@ -762,7 +763,7 @@ reply_run_callback(struct deferred_cb *d, void *user_pointer)
cb->reply.data.a.addresses,
user_pointer);
else
- cb->user_callback(cb->err, 0, 0, 0, NULL, user_pointer);
+ cb->user_callback(cb->err, 0, 0, cb->ttl, NULL, user_pointer);
break;
case TYPE_PTR:
if (cb->have_reply) {
@@ -770,7 +771,7 @@ reply_run_callback(struct deferred_cb *d, void *user_pointer)
cb->user_callback(DNS_ERR_NONE, DNS_PTR, 1, cb->ttl,
&name, user_pointer);
} else {
- cb->user_callback(cb->err, 0, 0, 0, NULL, user_pointer);
+ cb->user_callback(cb->err, 0, 0, cb->ttl, NULL, user_pointer);
}
break;
case TYPE_AAAA:
@@ -780,7 +781,7 @@ reply_run_callback(struct deferred_cb *d, void *user_pointer)
cb->reply.data.aaaa.addresses,
user_pointer);
else
- cb->user_callback(cb->err, 0, 0, 0, NULL, user_pointer);
+ cb->user_callback(cb->err, 0, 0, cb->ttl, NULL, user_pointer);
break;
default:
EVUTIL_ASSERT(0);
@@ -901,7 +902,7 @@ reply_handle(struct request *const req, u16 flags, u32 ttl, struct reply *reply)
}
/* all else failed. Pass the failure up */
- reply_schedule_callback(req, 0, error, NULL);
+ reply_schedule_callback(req, ttl, error, NULL);
request_finished(req, &REQ_HEAD(req->base, req->trans_id), 1);
} else {
/* all ok, tell the user */
@@ -1004,8 +1005,8 @@ reply_parse(struct evdns_base *base, u8 *packet, int length) {
/* If it's not an answer, it doesn't correspond to any request. */
if (!(flags & 0x8000)) return -1; /* must be an answer */
- if (flags & 0x020f) {
- /* there was an error */
+ if ((flags & 0x020f) && (flags & 0x020f) != DNS_ERR_NOTEXIST) {
+ /* there was an error and it's not NXDOMAIN */
goto err;
}
/* if (!answers) return; */ /* must have an answer of some form */
@@ -1127,6 +1128,35 @@ reply_parse(struct evdns_base *base, u8 *packet, int length) {
}
}
+ if (!reply.have_answer) {
+ for (i = 0; i < authority; ++i) {
+ u16 type, class;
+ SKIP_NAME;
+ GET16(type);
+ GET16(class);
+ GET32(ttl);
+ GET16(datalength);
+ if (type == TYPE_SOA && class == CLASS_INET) {
+ u32 serial, refresh, retry, expire, minimum;
+ SKIP_NAME;
+ SKIP_NAME;
+ GET32(serial);
+ GET32(refresh);
+ GET32(retry);
+ GET32(expire);
+ GET32(minimum);
+ ttl_r = MIN(ttl_r, ttl);
+ ttl_r = MIN(ttl_r, minimum);
+ } else {
+ /* skip over any other type of resource */
+ j += datalength;
+ }
+ }
+ }
+
+ if (ttl_r == 0xffffffff)
+ ttl_r = 0;
+
reply_handle(req, flags, ttl_r, &reply);
return 0;
err:
--
1.7.4.1
