Merge branch '4038-resize-send-buffers-to-avoid-excessive-memory-allocation' into 'main'

Use appropriately sized send buffers for DNS messages over TCP

Closes #4038

See merge request isc-projects/bind9!8004

CHANGES

@@ -1,3 +1,7 @@
+6188.	[performance]	Reduce memory consumption by allocating properly
+			sized send buffers for stream-based transports.
+			[GL #4038]
+
 6187.	[bug]		Address view shutdown INSIST when accessing the
 			zonetable. [GL #4093]
 

doc/notes/notes-current.rst

@@ -64,6 +64,10 @@ Bug Fixes
   a delegation from cache was returned to the client. This has now been fixed.
   :gl:`#3950`
 
+- BIND could allocate too big buffers when sending data via
+  stream-based DNS transports, leading to increased memory usage.
+  This has been fixed. :gl:`#4038`
+
 Known Issues
 ~~~~~~~~~~~~
 

lib/ns/client.c

@@ -331,6 +331,7 @@ client_allocsendbuf(ns_client_t *client, isc_buffer_t *buffer,
 		INSIST(client->tcpbuf == NULL);
 		client->tcpbuf = isc_mem_get(client->manager->mctx,
 					     NS_CLIENT_TCP_BUFFER_SIZE);
+		client->tcpbuf_size = NS_CLIENT_TCP_BUFFER_SIZE;
 		data = client->tcpbuf;
 		isc_buffer_init(buffer, data, NS_CLIENT_TCP_BUFFER_SIZE);
 	} else {
@@ -363,7 +364,17 @@ client_sendpkg(ns_client_t *client, isc_buffer_t *buffer) {
 
 	REQUIRE(client->sendhandle == NULL);
 
-	isc_buffer_usedregion(buffer, &r);
+	if (isc_buffer_base(buffer) == client->tcpbuf) {
+		size_t used = isc_buffer_usedlength(buffer);
+		client->tcpbuf = isc_mem_reget(client->manager->mctx,
+					       client->tcpbuf,
+					       client->tcpbuf_size, used);
+		client->tcpbuf_size = used;
+		r.base = client->tcpbuf;
+		r.length = used;
+	} else {
+		isc_buffer_usedregion(buffer, &r);
+	}
 	isc_nmhandle_attach(client->handle, &client->sendhandle);
 
 	if (isc_nm_is_http_handle(client->handle)) {
@@ -434,8 +445,7 @@ ns_client_sendraw(ns_client_t *client, dns_message_t *message) {
 done:
 	if (client->tcpbuf != NULL) {
 		isc_mem_put(client->manager->mctx, client->tcpbuf,
-			    NS_CLIENT_TCP_BUFFER_SIZE);
-		client->tcpbuf = NULL;
+			    client->tcpbuf_size);
 	}
 
 	ns_client_drop(client, result);
@@ -719,8 +729,7 @@ renderend:
 cleanup:
 	if (client->tcpbuf != NULL) {
 		isc_mem_put(client->manager->mctx, client->tcpbuf,
-			    NS_CLIENT_TCP_BUFFER_SIZE);
-		client->tcpbuf = NULL;
+			    client->tcpbuf_size);
 	}
 
 	if (cleanup_cctx) {
@@ -1609,7 +1618,7 @@ ns__client_reset_cb(void *client0) {
 	ns_client_endrequest(client);
 	if (client->tcpbuf != NULL) {
 		isc_mem_put(client->manager->mctx, client->tcpbuf,
-			    NS_CLIENT_TCP_BUFFER_SIZE);
+			    client->tcpbuf_size);
 	}
 
 	if (client->keytag != NULL) {

lib/ns/include/ns/client.h

@@ -171,6 +171,7 @@ struct ns_client {
 					 (query, update, notify) */
 	isc_nmhandle_t *updatehandle; /* Waiting for update callback */
 	unsigned char  *tcpbuf;
+	size_t		tcpbuf_size;
 	dns_message_t  *message;
 	unsigned char  *sendbuf;
 	dns_rdataset_t *opt;