* resolv/res_init.c (res_setoptions): Recognize edns0 option.

	* resolv/res_mkquery.c: Define __res_nopt.
	* resolv/res_query.c (__libc_res_nquery): If RES_USE_EDNS0 is set
	try adding EDNS0 record.
	* resolv/res_send.c (send_dg): If request failed with FORMERR and
	EDNS0 record was send make sure we don't try it again.
	* resolv/resolv.h: Define RES_F_EDNS0ERR and RES_USE_EDNS0.
	* include/resolv.h: Declare __res_nopt.

5 files changed, 90 insertions, 7 deletions

diff --git a/resolv/res_init.c b/resolv/res_init.c
index b5a03d1883..640e087920 100644
--- a/resolv/res_init.c
+++ b/resolv/res_init.c
@@ -510,6 +510,8 @@ res_setoptions(res_state statp, const char *options, const char *source) {
 		} else if (!strncmp(cp, "no-check-names",
 				    sizeof("no-check-names") - 1)) {
 			statp->options |= RES_NOCHECKNAME;
+                } else if (!strncmp(cp, "edns0", sizeof("edns0") - 1)) {
+			statp->options |= RES_USE_EDNS0;
 		} else {
 			/* XXX - print a warning here? */
 		}
diff --git a/resolv/res_mkquery.c b/resolv/res_mkquery.c
index fd80569fe2..3fa597fecd 100644
--- a/resolv/res_mkquery.c
+++ b/resolv/res_mkquery.c
@@ -208,3 +208,49 @@ res_nmkquery(res_state statp,
 	return (cp - buf);
 }
 libresolv_hidden_def (res_nmkquery)
+
+
+/* attach OPT pseudo-RR, as documented in RFC2671 (EDNS0). */
+#ifndef T_OPT
+#define T_OPT   41
+#endif
+
+int
+__res_nopt(res_state statp,
+	   int n0,                /* current offset in buffer */
+	   u_char *buf,           /* buffer to put query */
+	   int buflen,            /* size of buffer */
+	   int anslen)            /* UDP answer buffer size */
+{
+	u_int16_t flags = 0;
+
+#ifdef DEBUG
+	if ((statp->options & RES_DEBUG) != 0U)
+		printf(";; res_nopt()\n");
+#endif
+
+	HEADER *hp = (HEADER *) buf;
+	u_char *cp = buf + n0;
+	u_char *ep = buf + buflen;
+
+	if ((ep - cp) < 1 + RRFIXEDSZ)
+		return -1;
+
+	*cp++ = 0;	/* "." */
+
+	ns_put16(T_OPT, cp);	/* TYPE */
+	cp += INT16SZ;
+	ns_put16(anslen & 0xffff, cp);	/* CLASS = UDP payload size */
+	cp += INT16SZ;
+	*cp++ = NOERROR;	/* extended RCODE */
+	*cp++ = 0;		/* EDNS version */
+	/* XXX Once we support DNSSEC we change the flag value here.  */
+	ns_put16(flags, cp);
+	cp += INT16SZ;
+	ns_put16(0, cp);	/* RDLEN */
+	cp += INT16SZ;
+	hp->arcount = htons(ntohs(hp->arcount) + 1);
+
+	return cp - buf;
+}
+libresolv_hidden_def (__res_nopt)
diff --git a/resolv/res_query.c b/resolv/res_query.c
index 85bad97d2d..4371af5b05 100644
--- a/resolv/res_query.c
+++ b/resolv/res_query.c
@@ -120,10 +120,13 @@ __libc_res_nquery(res_state statp,
 	u_char *buf;
 	HEADER *hp = (HEADER *) answer;
 	int n, use_malloc = 0;
+        u_int oflags = statp->_flags;
 
-	hp->rcode = NOERROR;	/* default */
+	size_t bufsize = QUERYSIZE;
+	buf = alloca (bufsize);
 
-	buf = alloca (QUERYSIZE);
+ again:
+	hp->rcode = NOERROR;	/* default */
 
 #ifdef DEBUG
 	if (statp->options & RES_DEBUG)
@@ -131,18 +134,30 @@ __libc_res_nquery(res_state statp,
 #endif
 
 	n = res_nmkquery(statp, QUERY, name, class, type, NULL, 0, NULL,
-			 buf, QUERYSIZE);
-	if (__builtin_expect (n <= 0, 0)) {
+			 buf, bufsize);
+	if (n > 0
+	    && (oflags & RES_F_EDNS0ERR) == 0
+	    && (statp->options & RES_USE_EDNS0) != 0)
+		n = __res_nopt(statp, n, buf, bufsize, anslen);
+	if (__builtin_expect (n <= 0, 0) && !use_malloc) {
 		/* Retry just in case res_nmkquery failed because of too
 		   short buffer.  Shouldn't happen.  */
-		buf = malloc (MAXPACKET);
+		bufsize = MAXPACKET;
+		buf = malloc (bufsize);
 		if (buf != NULL) {
 			use_malloc = 1;
-			n = res_nmkquery(statp, QUERY, name, class, type, NULL,
-					 0, NULL, buf, MAXPACKET);
+			goto again;
 		}
 	}
 	if (__builtin_expect (n <= 0, 0)) {
+		/* If the query choked with EDNS0, retry without EDNS0.  */
+		if ((statp->options & RES_USE_EDNS0) != 0
+		    && ((oflags ^ statp->_flags) & RES_F_EDNS0ERR) != 0) {
+			statp->_flags |= RES_F_EDNS0ERR;
+			if (statp->options & RES_DEBUG)
+				printf(";; res_nquery: retry without EDNS0\n");
+                        goto again;
+		}
 #ifdef DEBUG
 		if (statp->options & RES_DEBUG)
 			printf(";; res_query: mkquery failed\n");
diff --git a/resolv/res_send.c b/resolv/res_send.c
index 887d048e19..f38c399ffd 100644
--- a/resolv/res_send.c
+++ b/resolv/res_send.c
@@ -986,6 +986,24 @@ send_dg(res_state statp,
 				ans, (resplen > anssiz) ? anssiz : resplen);
 			goto wait;
 		}
+#ifdef RES_USE_EDNS0
+		if (anhp->rcode == FORMERR
+		    && (statp->options & RES_USE_EDNS0) != 0U) {
+			/*
+			 * Do not retry if the server do not understand
+			 * EDNS0.  The case has to be captured here, as
+			 * FORMERR packet do not carry query section, hence
+			 * res_queriesmatch() returns 0.
+			 */
+			DprintQ(statp->options & RES_DEBUG,
+				(stdout,
+				 "server rejected query with EDNS0:\n"),
+				ans, (resplen > anssiz) ? anssiz : resplen);
+			/* record the error */
+			statp->_flags |= RES_F_EDNS0ERR;
+			goto err_out;
+        }
+#endif
 		if (!(statp->options & RES_INSECURE2) &&
 		    !res_queriesmatch(buf, buf + buflen,
 				      ans, ans + anssiz)) {
diff --git a/resolv/resolv.h b/resolv/resolv.h
index d7cda117fd..9aa09b8701 100644
--- a/resolv/resolv.h
+++ b/resolv/resolv.h
@@ -180,6 +180,7 @@ struct res_sym {
  */
 #define	RES_F_VC	0x00000001	/* socket is TCP */
 #define	RES_F_CONN	0x00000002	/* socket is connected */
+#define RES_F_EDNS0ERR	0x00000004	/* EDNS0 caused errors */
 
 /* res_findzonecut() options */
 #define	RES_EXHAUSTIVE	0x00000001	/* always do all queries */
@@ -209,6 +210,7 @@ struct res_sym {
 					   strings */
 #define RES_NOIP6DOTINT	0x00080000	/* Do not use .ip6.int in IPv6
 					   reverse lookup */
+#define RES_USE_EDNS0	0x00100000	/* Use EDNS0.  */
 
 #define RES_DEFAULT	(RES_RECURSE|RES_DEFNAMES|RES_DNSRCH|RES_NOIP6DOTINT)