support EDNS0 (RFC2671) buffer size notification on DNS queries.

"options edns0" in /etc/resolv.conf will enable the behavior.  no behavior
change if you don't have the line.  see resolv.conf(5) for more details.

EDNS0 is useful for avoiding TCP DNS queries/replies on larger DNS responses.
also, draft-ietf-dnsext-message-size-* plans to mandate EDNS0 support for DNS
clients that support IPv6 transport.

1 files changed, 5 insertions, 2 deletions

diff --git a/src/lib/libc/net/res_query.c b/src/lib/libc/net/res_query.c
index 01d1f691cb..433e80f648 100644
--- a/src/lib/libc/net/res_query.c
+++ b/src/lib/libc/net/res_query.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: res_query.c,v 1.13 1999/09/27 23:58:26 alex Exp $     */
+/*      $OpenBSD: res_query.c,v 1.14 2001/06/11 10:06:01 itojun Exp $   */
 
 /*
  * ++Copyright++ 1988, 1993
@@ -60,7 +60,7 @@
 static char sccsid[] = "@(#)res_query.c 8.1 (Berkeley) 6/4/93";
 static char rcsid[] = "$From: res_query.c,v 8.9 1996/09/22 00:13:28 vixie Exp $";
 #else
-static char rcsid[] = "$OpenBSD: res_query.c,v 1.13 1999/09/27 23:58:26 alex Exp $";
+static char rcsid[] = "$OpenBSD: res_query.c,v 1.14 2001/06/11 10:06:01 itojun Exp $";
 #endif
 #endif /* LIBC_SCCS and not lint */
 
@@ -87,6 +87,7 @@ static char rcsid[] = "$OpenBSD: res_query.c,v 1.13 1999/09/27 23:58:26 alex Exp
 
 const char *hostalias __P((const char *));
 int h_errno;
+extern int res_opt __P((int, u_char *, int, int));
 
 /*
  * Formulate a normal query, send, and await answer.
@@ -122,6 +123,8 @@ res_query(name, class, type, answer, anslen)
 
         n = res_mkquery(QUERY, name, class, type, NULL, 0, NULL,
                         buf, sizeof(buf));
+        if (n > 0 && (_res.options & RES_USE_EDNS0) != 0)
+                n = res_opt(n, buf, sizeof(buf), anslen);
         if (n <= 0) {
 #ifdef DEBUG
                 if (_res.options & RES_DEBUG)