Lay the groundwork for enabling EDNS0 in queries.
This change does not enable EDNS0, so it should not
result in any behavior change. However, enabling EDNS0
should now be possible with only a small additional change
to "flip the switch".
This change has also landed in NetBSD upstream
(http://gnats.netbsd.org/52578) so this change reduces
divergence from upstream.
Most of the code in this change is for caching of queries that contain
an additional section.
Bug: 15132200
Test: Added integration tests for fallback to the netd suite.
Change-Id: Ic64bed0754e1d529dc0c0ab6a5e2f1ea201ff0d5
diff --git a/libc/dns/net/getaddrinfo.c b/libc/dns/net/getaddrinfo.c
index 418bf6d..c0a2fdb 100644
--- a/libc/dns/net/getaddrinfo.c
+++ b/libc/dns/net/getaddrinfo.c
@@ -2171,8 +2171,12 @@
int class, type;
u_char *answer;
int anslen;
+ u_int oflags;
hp = (HEADER *)(void *)t->answer;
+ oflags = res->_flags;
+
+again:
hp->rcode = NOERROR; /* default */
/* make it easier... */
@@ -2188,7 +2192,8 @@
n = res_nmkquery(res, QUERY, name, class, type, NULL, 0, NULL,
buf, sizeof(buf));
#ifdef RES_USE_EDNS0
- if (n > 0 && (res->options & RES_USE_EDNS0) != 0)
+ if (n > 0 && (res->_flags & RES_F_EDNS0ERR) == 0 &&
+ (res->options & (RES_USE_EDNS0|RES_USE_DNSSEC)) != 0)
n = res_nopt(res, n, buf, sizeof(buf), anslen);
#endif
if (n <= 0) {
@@ -2213,6 +2218,18 @@
if (n < 0 || hp->rcode != NOERROR || ntohs(hp->ancount) == 0) {
rcode = hp->rcode; /* record most recent error */
+#ifdef RES_USE_EDNS0
+ /* if the query choked with EDNS0, retry without EDNS0 */
+ if ((res->options & (RES_USE_EDNS0|RES_USE_DNSSEC)) != 0 &&
+ ((oflags ^ res->_flags) & RES_F_EDNS0ERR) != 0) {
+ res->_flags |= RES_F_EDNS0ERR;
+#ifdef DEBUG
+ if (res->options & RES_DEBUG)
+ printf(";; res_nquery: retry without EDNS0\n");
+#endif
+ goto again;
+ }
+#endif
#ifdef DEBUG
if (res->options & RES_DEBUG)
printf(";; rcode = %u, ancount=%u\n", hp->rcode,