From 0ce73d80dc0c3996eca0b73c76bf513a33c1dab4 Mon Sep 17 00:00:00 2001
From: Felix Fietkau <nbd@nbd.name>
Date: Wed, 28 May 2025 23:48:18 +0200
Subject: [PATCH] dns: add cache/queue for outgoing queries

Batch outgoing questions and drop redundant ones.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
 cache.c | 27 ++++++++----------------
 dns.c   | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 dns.h   |  3 ++-
 3 files changed, 73 insertions(+), 21 deletions(-)

diff --git a/cache.c b/cache.c
index 51eb707..0ccac49 100644
--- a/cache.c
+++ b/cache.c
@@ -143,26 +143,17 @@ void
 cache_update(void)
 {
 	struct cache_service *s;
-	int count = 2;
 
-	dns_packet_init();
-	dns_packet_question(C_DNS_SD, TYPE_ANY);
-	dns_packet_question(C_DNS_SD, TYPE_PTR);
+	dns_query(C_DNS_SD, TYPE_ANY);
+	dns_query(C_DNS_SD, TYPE_PTR);
 	avl_for_each_element(&services, s, avl) {
 		if (s->host) {
-			dns_packet_question(s->host, TYPE_A);
-			dns_packet_question(s->host, TYPE_AAAA);
+			dns_query(s->host, TYPE_A);
+			dns_query(s->host, TYPE_AAAA);
 		} else {
-			dns_packet_question(s->entry, TYPE_PTR);
+			dns_query(s->entry, TYPE_PTR);
 		}
-		if (++count < 16)
-			continue;
-		dns_packet_broadcast();
-		count = 0;
 	}
-
-	if (count)
-		dns_packet_broadcast();
 }
 
 static struct cache_service*
@@ -203,14 +194,12 @@ cache_service(struct interface *iface, char *entry, int hlen, int ttl)
 		s->avl.key = type;
 	avl_insert(&services, &s->avl);
 
-	dns_packet_init();
 	if (hlen) {
-		dns_packet_question(s->host, TYPE_A);
-		dns_packet_question(s->host, TYPE_AAAA);
+		dns_query(s->host, TYPE_A);
+		dns_query(s->host, TYPE_AAAA);
 	} else {
-		dns_packet_question(entry, TYPE_PTR);
+		dns_query(entry, TYPE_PTR);
 	}
-	dns_packet_broadcast();
 
 	return s;
 }
diff --git a/dns.c b/dns.c
index 715125b..7c24ddc 100644
--- a/dns.c
+++ b/dns.c
@@ -31,6 +31,7 @@
 #include <libubox/uloop.h>
 #include <libubox/usock.h>
 #include <libubox/utils.h>
+#include <libubox/avl-cmp.h>
 
 #include "announce.h"
 #include "util.h"
@@ -39,6 +40,15 @@
 #include "service.h"
 #include "interface.h"
 
+#define QUERY_BATCH_SIZE	16
+
+struct query_entry {
+	struct avl_node node;
+	uint16_t type;
+	char name[];
+};
+
+static AVL_TREE(queries, avl_strcmp, true, NULL);
 static char name_buffer[MAX_NAME_LEN + 1];
 
 static struct {
@@ -185,7 +195,7 @@ void dns_packet_send(struct interface *iface, struct sockaddr *to, bool query, i
 		perror("failed to send answer");
 }
 
-void dns_packet_broadcast(void)
+static void dns_packet_broadcast(void)
 {
 	struct interface *iface;
 
@@ -202,6 +212,58 @@ dns_send_question(struct interface *iface, struct sockaddr *to,
 	dns_packet_send(iface, to, true, multicast);
 }
 
+static void
+dns_query_pending(struct uloop_timeout *t)
+{
+	struct query_entry *e, *tmp;
+	int count = 0;
+
+	dns_packet_init();
+	avl_remove_all_elements(&queries, e, node, tmp) {
+		dns_packet_question(e->name, e->type);
+		free(e);
+
+		if (++count < QUERY_BATCH_SIZE)
+			continue;
+
+		count = 0;
+		dns_packet_broadcast();
+	}
+
+	if (count)
+		dns_packet_broadcast();
+}
+
+void dns_query(const char *name, uint16_t type)
+{
+	static struct uloop_timeout timer = {
+		.cb = dns_query_pending
+	};
+	struct query_entry *e;
+
+	e = avl_find_element(&queries, name, e, node);
+	while (e) {
+		if (e->type == type)
+			return;
+
+		e = avl_next_element(e, node);
+		if (strcmp(e->name, name) != 0)
+			break;
+	}
+
+	e = calloc(1, sizeof(*e) + strlen(name) + 1);
+	e->type = type;
+	e->node.key = e->name;
+	strcpy(e->name, name);
+	avl_insert(&queries, &e->node);
+
+	if (queries.count > QUERY_BATCH_SIZE)
+		timer.cb(&timer);
+
+	if (!timer.pending)
+		uloop_timeout_set(&timer, 100);
+}
+
 void
 dns_reply_a(struct interface *iface, struct sockaddr *to, int ttl, const char *hostname)
 {
diff --git a/dns.h b/dns.h
index 65efcf7..fde049f 100644
--- a/dns.h
+++ b/dns.h
@@ -77,7 +77,8 @@ void dns_packet_init(void);
 bool dns_packet_question(const char *name, int type);
 void dns_packet_answer(const char *name, int type, const uint8_t *rdata, uint16_t rdlength, int ttl);
 void dns_packet_send(struct interface *iface, struct sockaddr *to, bool query, int multicast);
-void dns_packet_broadcast(void);
+
+void dns_query(const char *name, uint16_t type);
 
 void dns_send_question(struct interface *iface, struct sockaddr *to,
 		       const char *question, int type, int multicast);
-- 
2.30.2