evdns: add ability to get CNAME

Add new flag (DNS_CNAME_CALLBACK) for
evdns_base_resolve_ipv4()/evdns_base_resolve_ipv6().

If set, you will get one more callback with type == DNS_CNAME and CNAME
in addrs argument.

evdns.c

@@ -209,6 +209,7 @@ struct request {
 	u16 trans_id;  /* the transaction id */
 	unsigned request_appended :1;	/* true if the request pointer is data which follows this struct */
 	unsigned transmit_me :1;  /* needs to be transmitted */
+	unsigned need_cname :1;   /* make a separate callback for CNAME */
 
 	/* XXXX This is a horrible hack. */
 	char **put_cname_in_ptr; /* store the cname here if we get one. */
@@ -228,6 +229,7 @@ struct reply {
 		char *ptr_name;
 		void *raw;
 	} data;
+	char *cname;
 };
 
 enum tcp_state {
@@ -986,12 +988,15 @@ reply_run_callback(struct event_callback *d, void *user_pointer)
 
 	switch (cb->request_type) {
 	case TYPE_A:
-		if (cb->have_reply)
+		if (cb->have_reply) {
 			cb->user_callback(DNS_ERR_NONE, DNS_IPv4_A,
 			    cb->reply.rr_count, cb->ttl,
 			    cb->reply.data.a,
 			    user_pointer);
-		else
+			if (cb->reply.cname)
+				cb->user_callback(DNS_ERR_NONE, DNS_CNAME, 1,
+				    cb->ttl, cb->reply.cname, user_pointer);
+		} else
 			cb->user_callback(cb->err, 0, 0, cb->ttl, NULL, user_pointer);
 		break;
 	case TYPE_PTR:
@@ -1004,12 +1009,15 @@ reply_run_callback(struct event_callback *d, void *user_pointer)
 		}
 		break;
 	case TYPE_AAAA:
-		if (cb->have_reply)
+		if (cb->have_reply) {
 			cb->user_callback(DNS_ERR_NONE, DNS_IPv6_AAAA,
 			    cb->reply.rr_count, cb->ttl,
 			    cb->reply.data.aaaa,
 			    user_pointer);
-		else
+			if (cb->reply.cname)
+				cb->user_callback(DNS_ERR_NONE, DNS_CNAME, 1,
+				    cb->ttl, cb->reply.cname, user_pointer);
+		} else
 			cb->user_callback(cb->err, 0, 0, cb->ttl, NULL, user_pointer);
 		break;
 	default:
@@ -1024,6 +1032,10 @@ reply_run_callback(struct event_callback *d, void *user_pointer)
 		mm_free(cb->reply.data.raw);
 	}
 
+	if (cb->reply.cname) {
+		mm_free(cb->reply.cname);
+	}
+
 	mm_free(cb);
 }
 
@@ -1383,13 +1395,13 @@ reply_parse(struct evdns_base *base, u8 *packet, int length)
 			break;
 		} else if (type == TYPE_CNAME) {
 			char cname[HOST_NAME_MAX];
-			if (!req->put_cname_in_ptr || *req->put_cname_in_ptr) {
-				j += datalength; continue;
-			}
 			if (name_parse(packet, length, &j, cname,
 				sizeof(cname))<0)
 				goto err;
-			*req->put_cname_in_ptr = mm_strdup(cname);
+			if (req->need_cname)
+				reply.cname = mm_strdup(cname);
+			if (req->put_cname_in_ptr && !*req->put_cname_in_ptr)
+				*req->put_cname_in_ptr = mm_strdup(cname);
 		} else if (type == TYPE_AAAA && class == CLASS_INET) {
 			int addrcount;
 			if (req->request_type != TYPE_AAAA) {
@@ -3555,6 +3567,9 @@ request_new(struct evdns_base *base, struct evdns_request *handle, int type,
 		handle->base = base;
 	}
 
+	if (flags & DNS_CNAME_CALLBACK)
+		req->need_cname = 1;
+
 	return req;
 err1:
 	mm_free(req);

include/event2/dns.h

@@ -182,6 +182,7 @@ extern "C" {
 #define DNS_IPv4_A 1
 #define DNS_PTR 2
 #define DNS_IPv6_AAAA 3
+#define DNS_CNAME 4
 
 /** Disable searching for the query. */
 #define DNS_QUERY_NO_SEARCH 0x01
@@ -189,6 +190,8 @@ extern "C" {
 #define DNS_QUERY_USEVC 0x02
 /** Ignore trancation flag in responses (don't fallback to TCP connections). */
 #define DNS_QUERY_IGNTC 0x04
+/** Make a separate callback for CNAME in answer */
+#define DNS_CNAME_CALLBACK 0x80
 
 /* Allow searching */
 #define DNS_OPTION_SEARCH 1

test/regress_dns.c

@@ -512,7 +512,7 @@ generic_dns_callback(int result, char type, int count, int ttl, void *addresses,
 		len = count * 4;
 	else if (type == DNS_IPv6_AAAA)
 		len = count * 16;
-	else if (type == DNS_PTR)
+	else if (type == DNS_PTR || type == DNS_CNAME)
 		len = strlen(addresses)+1;
 	else {
 		res->addrs_len = len = 0;
@@ -551,6 +551,7 @@ static struct regress_dns_server_table search_table[] = {
 	{ "hostn.a.example.com", "errsoa", "0", 0, 0 },
 	{ "hostn.b.example.com", "errsoa", "3", 0, 0 },
 	{ "hostn.c.example.com", "err", "0", 0, 0 },
+	{ "hostc.c.example.com", "CNAME", "cname.c.example.com", 0, 0 },
 	{ "host", "err", "3", 0, 0 },
 	{ "host2", "err", "3", 0, 0 },
 	{ "*", "err", "3", 0, 0 },
@@ -586,7 +587,7 @@ dns_search_test_impl(void *arg, int lower)
 	ev_uint16_t portnum = 0;
 	char buf[64];
 
-	struct generic_dns_callback_result r[8];
+	struct generic_dns_callback_result r[9];
 	size_t i;
 
 	for (i = 0; i < ARRAY_SIZE(table); ++i) {
@@ -604,7 +605,7 @@ dns_search_test_impl(void *arg, int lower)
 	evdns_base_search_add(dns, "b.example.com");
 	evdns_base_search_add(dns, "c.example.com");
 
-	n_replies_left = ARRAY_SIZE(r);
+	n_replies_left = ARRAY_SIZE(r)+1;	/* CNAME gives us 2 callbacks for 1 request */
 	exit_base = base;
 
 	evdns_base_resolve_ipv4(dns, "host", 0, generic_dns_callback, &r[0]);
@@ -615,6 +616,8 @@ dns_search_test_impl(void *arg, int lower)
 	evdns_base_resolve_ipv4(dns, "hostn.a.example.com", DNS_NO_SEARCH, generic_dns_callback, &r[5]);
 	evdns_base_resolve_ipv4(dns, "hostn.b.example.com", DNS_NO_SEARCH, generic_dns_callback, &r[6]);
 	evdns_base_resolve_ipv4(dns, "hostn.c.example.com", DNS_NO_SEARCH, generic_dns_callback, &r[7]);
+	evdns_base_resolve_ipv4(dns, "hostc.c.example.com", DNS_NO_SEARCH | DNS_CNAME_CALLBACK,
+				generic_dns_callback, &r[8]);
 
 	event_base_dispatch(base);
 
@@ -633,6 +636,9 @@ dns_search_test_impl(void *arg, int lower)
 	tt_int_op(r[6].ttl, ==, 42);
 	tt_int_op(r[7].result, ==, DNS_ERR_NODATA);
 	tt_int_op(r[7].ttl, ==, 0);
+	tt_int_op(r[8].type, ==, DNS_CNAME);
+	tt_int_op(r[8].count, ==, 1);
+	tt_str_op(r[8].addrs, ==, "cname.c.example.com");
 
 end:
 	if (dns)

test/regress_testutils.c

@@ -257,6 +257,11 @@ regress_dns_server_cb(struct evdns_server_request *req, void *data)
 		}
 		evdns_server_request_add_aaaa_reply(req,
 		    question, 1, &in6.s6_addr, 100);
+	} else if (!strcmp(tab->anstype, "CNAME")) {
+		struct in_addr in;
+		evutil_inet_pton(AF_INET, "11.22.33.44", &in);
+		evdns_server_request_add_a_reply(req, question, 1, &in, 100);
+		evdns_server_request_add_cname_reply(req, question, tab->ans, 100);
 	} else {
 		TT_DIE(("Weird table entry with type '%s'", tab->anstype));
 	}