BUG/MINOR: resolvers: answser item list was randomly purged or errors

In case of SRV records, The answer item list was purged by the
error callback of the first requester which considers the error
could not be safely ignored. It makes this item list unavailable
for subsequent requesters even if they consider the error
could be ignored.

On A resolution or do_resolve action error, the answer items were
never trashed.

This patch re-work the error callbacks and the code to check the return code
If a callback return 1, we consider the error was ignored and
the answer item list must be kept. At the opposite, If all error callbacks
of all requesters of the same resolution returns 0 the list will be purged

This patch should be backported as far as 2.0.

src/action.c

@@ -157,6 +157,12 @@ int act_resolution_cb(struct resolv_requester *requester, struct dns_counters *c
 	return 0;
 }
 
+/*
+ * Do resolve error management callback
+ * returns:
+ *  0 if we can trash answser items.
+ *  1 when safely ignored and we must kept answer items
+ */
 int act_resolution_error_cb(struct resolv_requester *requester, int error_code)
 {
 	struct stream *stream;

src/resolvers.c

@@ -1900,6 +1900,7 @@ static int resolv_process_responses(struct dns_nameserver *ns)
 	unsigned short query_id;
 	struct eb32_node *eb;
 	struct resolv_requester *req;
+	int keep_answer_items;
 
 	resolvers = ns->parent;
 	HA_SPIN_LOCK(DNS_LOCK, &resolvers->lock);
@@ -2034,8 +2035,11 @@ static int resolv_process_responses(struct dns_nameserver *ns)
 		goto report_res_success;
 
 	report_res_error:
+		keep_answer_items = 0;
 		list_for_each_entry(req, &res->requesters, list)
-			req->requester_error_cb(req, dns_resp);
+			keep_answer_items |= req->requester_error_cb(req, dns_resp);
+		if (!keep_answer_items)
+			resolv_purge_resolution_answer_records(res);
 		resolv_reset_resolution(res);
 		LIST_DELETE(&res->list);
 		LIST_APPEND(&resolvers->resolutions.wait, &res->list);
@@ -2097,12 +2101,15 @@ static struct task *process_resolvers(struct task *t, void *context, unsigned in
 		 * the list */
 		if (!res->try) {
 			struct resolv_requester *req;
+			int keep_answer_items = 0;
 
 			/* Notify the result to the requesters */
 			if (!res->nb_responses)
 				res->status = RSLV_STATUS_TIMEOUT;
 			list_for_each_entry(req, &res->requesters, list)
-				req->requester_error_cb(req, res->status);
+				keep_answer_items |= req->requester_error_cb(req, res->status);
+			if (!keep_answer_items)
+				resolv_purge_resolution_answer_records(res);
 
 			/* Clean up resolution info and remove it from the
 			 * current list */

src/server.c

@@ -3436,8 +3436,8 @@ int snr_resolution_cb(struct resolv_requester *requester, struct dns_counters *c
 /*
  * SRV record error management callback
  * returns:
- *  0 on error
+ *  0 if we can trash answser items.
- *  1 when no error or safe ignore
+ *  1 when safely ignored and we must kept answer items
  *
  * Grabs the server's lock.
  */
@@ -3452,7 +3452,7 @@ int srvrq_resolution_error_cb(struct resolv_requester *requester, int error_code
 	/* SRV records */
 	srvrq = objt_resolv_srvrq(requester->owner);
 	if (!srvrq)
-		return 1;
+		return 0;
 
 	resolvers = srvrq->resolvers;
 	res = requester->resolution;
@@ -3502,16 +3502,14 @@ int srvrq_resolution_error_cb(struct resolv_requester *requester, int error_code
 		HA_SPIN_UNLOCK(SERVER_LOCK, &s->lock);
 	}
 
-	resolv_purge_resolution_answer_records(res);
+	return 0;
-
-	return 1;
 }
 
 /*
  * Server Name Resolution error management callback
  * returns:
- *  0 on error
+ *  0 if we can trash answser items.
- *  1 when no error or safe ignore
+ *  1 when safely ignored and we must kept answer items
  *
  * Grabs the server's lock.
  */
@@ -3521,11 +3519,16 @@ int snr_resolution_error_cb(struct resolv_requester *requester, int error_code)
 
 	s = objt_server(requester->owner);
 	if (!s)
-		return 1;
+		return 0;
+
 	HA_SPIN_LOCK(SERVER_LOCK, &s->lock);
-	if (!snr_update_srv_status(s, 1))
+	if (!snr_update_srv_status(s, 1)) {
 		memset(&s->addr, 0, sizeof(s->addr));
+		HA_SPIN_UNLOCK(SERVER_LOCK, &s->lock);
+		return 0;
+	}
 	HA_SPIN_UNLOCK(SERVER_LOCK, &s->lock);
+
 	return 1;
 }