Merge branch '3132-add-send-timeout' into 'main'

Add timeout when writing TCP data

Closes #3132

See merge request isc-projects/bind9!5848

CHANGES

@@ -1,3 +1,7 @@
+5807.	[bug]		Add a TCP "write" timer, and time out writing
+			connections after the "tcp-idle-timeout" period
+			has elapsed. [GL #3132]
+
 5806.	[bug]		An error in checking the "blackhole" ACL could cause
 			DNS requests sent by named to fail if the
 			destination address or prefix was specifically

bin/tests/system/timeouts/setup.sh

@@ -20,6 +20,11 @@ copy_setports ns1/named.conf.in ns1/named.conf
 # tcp-initial-timeout interval
 #
 $PYTHON -c "
+print('large IN TXT', end=' ')
+for a in range(128):
+    print('\"%s\"' % ('A' * 240), end=' ')
+print('')
+
 for a in range(150000):
     print('%s IN NS a' % (a))
     print('%s IN NS b' % (a))" > ns1/large.db

bin/tests/system/timeouts/tests-tcp.py

@@ -51,7 +51,7 @@ def test_initial_timeout(port):
             try:
                 (sbytes, stime) = dns.query.send_tcp(sock, msg, timeout())
                 (response, rtime) = dns.query.receive_tcp(sock, timeout())
-            except ConnectionResetError as e:
+            except ConnectionError as e:
                 raise EOFError from e
 
 
@@ -83,7 +83,7 @@ def test_idle_timeout(port):
             try:
                 (sbytes, stime) = dns.query.send_tcp(sock, msg, timeout())
                 (response, rtime) = dns.query.receive_tcp(sock, timeout())
-            except ConnectionResetError as e:
+            except ConnectionError as e:
                 raise EOFError from e
 
 
@@ -152,7 +152,7 @@ def test_pipelining_timeout(port):
             try:
                 (sbytes, stime) = dns.query.send_tcp(sock, msg, timeout())
                 (response, rtime) = dns.query.receive_tcp(sock, timeout())
-            except ConnectionResetError as e:
+            except ConnectionError as e:
                 raise EOFError from e
 
 
@@ -190,3 +190,33 @@ def test_long_axfr(port):
             if soa is not None:
                 break
         assert soa is not None
+
+
+@pytest.mark.dnspython
+@pytest.mark.dnspython2
+def test_send_timeout(port):
+    import dns.query
+
+    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
+        sock.connect(("10.53.0.1", port))
+
+        # Send and receive single large RDATA over TCP
+        msg = create_msg("large.example.", "TXT")
+        (sbytes, stime) = dns.query.send_tcp(sock, msg, timeout())
+        (response, rtime) = dns.query.receive_tcp(sock, timeout())
+
+        # Send and receive 28 large (~32k) DNS queries that should
+        # fill the default maximum 208k TCP send buffer
+        for n in range(28):
+            (sbytes, stime) = dns.query.send_tcp(sock, msg, timeout())
+
+        # configure idle interval is 5 seconds, sleep 6 to make sure we are
+        # above the interval
+        time.sleep(6)
+
+        with pytest.raises(EOFError):
+            try:
+                (sbytes, stime) = dns.query.send_tcp(sock, msg, timeout())
+                (response, rtime) = dns.query.receive_tcp(sock, timeout())
+            except ConnectionError as e:
+                raise EOFError from e

doc/notes/notes-current.rst

@@ -70,3 +70,9 @@ Bug Fixes
   to ``none``.  ``blackhole`` worked correctly when it was left unset, or
   if only positive-match elements were included. This has now been fixed.
   :gl:`#3157`
+
+- TCP connections could hang indefinitely if the TCP write buffers
+  were full because of the other party not reading sent data.  This has
+  been fixed by adding a "write" timer. Connections that are hung
+  while writing will now time out after the ``tcp-idle-timeout`` period
+  has elapsed. :gl:`#3132`

lib/isc/include/isc/netmgr.h

@@ -697,3 +697,6 @@ isc__nm_force_tid(int tid);
  * Force the thread ID to 'tid'. This is STRICTLY for use in unit
  * tests and should not be used in any production code.
  */
+
+void
+isc_nmhandle_setwritetimeout(isc_nmhandle_t *handle, uint64_t write_timeout);

lib/isc/netmgr/netmgr-int.h

@@ -950,10 +950,17 @@ struct isc_nmsocket {
 	/*%
 	 * TCP read/connect timeout timers.
 	 */
-	uv_timer_t timer;
+	uv_timer_t read_timer;
 	uint64_t read_timeout;
 	uint64_t connect_timeout;
 
+	/*%
+	 * TCP write timeout timer.
+	 */
+	uv_timer_t write_timer;
+	uint64_t write_timeout;
+	int64_t writes;
+
 	/*% outer socket is for 'wrapped' sockets - e.g. tcpdns in tcp */
 	isc_nmsocket_t *outer;
 
@@ -2071,12 +2078,25 @@ isc__nm_failed_connect_cb(isc_nmsocket_t *sock, isc__nm_uvreq_t *req,
 void
 isc__nm_failed_read_cb(isc_nmsocket_t *sock, isc_result_t result, bool async);
 
-void
-isc__nmsocket_connecttimeout_cb(uv_timer_t *timer);
-
 void
 isc__nm_accept_connection_log(isc_result_t result, bool can_log_quota);
 
+/*
+ * Timeout callbacks
+ */
+void
+isc__nmsocket_connecttimeout_cb(uv_timer_t *timer);
+void
+isc__nmsocket_readtimeout_cb(uv_timer_t *timer);
+void
+isc__nmsocket_writetimeout_cb(uv_timer_t *timer);
+
+/*%<
+ *
+ * Maximum number of simultaneous handles in flight supported for a single
+ * connected TCPDNS socket. This value was chosen arbitrarily, and may be
+ * changed in the future.
+ */
 #define STREAM_CLIENTS_PER_CONN 23
 
 #define UV_RUNTIME_CHECK(func, ret)                                           \

lib/isc/netmgr/netmgr.c

@@ -604,6 +604,14 @@ isc_nm_maxudp(isc_nm_t *mgr, uint32_t maxudp) {
 	atomic_store(&mgr->maxudp, maxudp);
 }
 
+void
+isc_nmhandle_setwritetimeout(isc_nmhandle_t *handle, uint64_t write_timeout) {
+	REQUIRE(VALID_NMHANDLE(handle));
+	REQUIRE(VALID_NMSOCK(handle->sock));
+
+	handle->sock->write_timeout = write_timeout;
+}
+
 void
 isc_nm_settimeouts(isc_nm_t *mgr, uint32_t init, uint32_t idle,
 		   uint32_t keepalive, uint32_t advertised) {
@@ -1977,7 +1985,7 @@ isc__nm_failed_connect_cb(isc_nmsocket_t *sock, isc__nm_uvreq_t *req,
 	REQUIRE(req->cb.connect != NULL);
 
 	isc__nmsocket_timer_stop(sock);
-	uv_handle_set_data((uv_handle_t *)&sock->timer, sock);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
 
 	INSIST(atomic_compare_exchange_strong(&sock->connecting,
 					      &(bool){ true }, false));
@@ -2070,7 +2078,21 @@ isc__nm_accept_connection_log(isc_result_t result, bool can_log_quota) {
 		      isc_result_totext(result));
 }
 
-static void
+void
+isc__nmsocket_writetimeout_cb(uv_timer_t *timer) {
+	isc_nmsocket_t *sock = uv_handle_get_data((uv_handle_t *)timer);
+
+	int r = uv_timer_stop(&sock->write_timer);
+	UV_RUNTIME_CHECK(uv_timer_stop, r);
+
+	/* The shutdown will be handled in the respective close functions */
+	r = uv_tcp_close_reset(&sock->uv_handle.tcp, NULL);
+	UV_RUNTIME_CHECK(uv_tcp_close_reset, r);
+
+	isc__nmsocket_shutdown(sock);
+}
+
+void
 isc__nmsocket_readtimeout_cb(uv_timer_t *timer) {
 	isc_nmsocket_t *sock = uv_handle_get_data((uv_handle_t *)timer);
 
@@ -2108,7 +2130,7 @@ isc__nmsocket_timer_restart(isc_nmsocket_t *sock) {
 			return;
 		}
 
-		r = uv_timer_start(&sock->timer,
+		r = uv_timer_start(&sock->read_timer,
 				   isc__nmsocket_connecttimeout_cb,
 				   sock->connect_timeout + 10, 0);
 		UV_RUNTIME_CHECK(uv_timer_start, r);
@@ -2120,7 +2142,8 @@ isc__nmsocket_timer_restart(isc_nmsocket_t *sock) {
 			return;
 		}
 
-		r = uv_timer_start(&sock->timer, isc__nmsocket_readtimeout_cb,
+		r = uv_timer_start(&sock->read_timer,
+				   isc__nmsocket_readtimeout_cb,
 				   sock->read_timeout, 0);
 		UV_RUNTIME_CHECK(uv_timer_start, r);
 	}
@@ -2130,7 +2153,7 @@ bool
 isc__nmsocket_timer_running(isc_nmsocket_t *sock) {
 	REQUIRE(VALID_NMSOCK(sock));
 
-	return (uv_is_active((uv_handle_t *)&sock->timer));
+	return (uv_is_active((uv_handle_t *)&sock->read_timer));
 }
 
 void
@@ -2152,7 +2175,7 @@ isc__nmsocket_timer_stop(isc_nmsocket_t *sock) {
 
 	/* uv_timer_stop() is idempotent, no need to check if running */
 
-	r = uv_timer_stop(&sock->timer);
+	r = uv_timer_stop(&sock->read_timer);
 	UV_RUNTIME_CHECK(uv_timer_stop, r);
 }
 
@@ -2404,7 +2427,7 @@ isc_nmhandle_cleartimeout(isc_nmhandle_t *handle) {
 	default:
 		handle->sock->read_timeout = 0;
 
-		if (uv_is_active((uv_handle_t *)&handle->sock->timer)) {
+		if (uv_is_active((uv_handle_t *)&handle->sock->read_timer)) {
 			isc__nmsocket_timer_stop(handle->sock);
 		}
 	}
@@ -2446,6 +2469,8 @@ isc_nmhandle_keepalive(isc_nmhandle_t *handle, bool value) {
 		atomic_store(&sock->keepalive, value);
 		sock->read_timeout = value ? atomic_load(&sock->mgr->keepalive)
 					   : atomic_load(&sock->mgr->idle);
+		sock->write_timeout = value ? atomic_load(&sock->mgr->keepalive)
+					    : atomic_load(&sock->mgr->idle);
 		break;
 #if HAVE_LIBNGHTTP2
 	case isc_nm_tlssocket:

lib/isc/netmgr/tcp.c

@@ -140,8 +140,13 @@ tcp_connect_direct(isc_nmsocket_t *sock, isc__nm_uvreq_t *req) {
 	UV_RUNTIME_CHECK(uv_tcp_init, r);
 	uv_handle_set_data(&sock->uv_handle.handle, sock);
 
-	r = uv_timer_init(&worker->loop, &sock->timer);
+	r = uv_timer_init(&worker->loop, &sock->read_timer);
 	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
+
+	r = uv_timer_init(&worker->loop, &sock->write_timer);
+	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&sock->write_timer, sock);
 
 	r = uv_tcp_open(&sock->uv_handle.tcp, sock->fd);
 	if (r != 0) {
@@ -170,7 +175,8 @@ tcp_connect_direct(isc_nmsocket_t *sock, isc__nm_uvreq_t *req) {
 	}
 	isc__nm_incstats(sock, STATID_CONNECT);
 
-	uv_handle_set_data((uv_handle_t *)&sock->timer, &req->uv_req.connect);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer,
+			   &req->uv_req.connect);
 	isc__nmsocket_timer_start(sock);
 
 	atomic_store(&sock->connected, true);
@@ -231,7 +237,7 @@ tcp_connect_cb(uv_connect_t *uvreq, int status) {
 	REQUIRE(sock->tid == isc_nm_tid());
 
 	isc__nmsocket_timer_stop(sock);
-	uv_handle_set_data((uv_handle_t *)&sock->timer, sock);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
 
 	if (!atomic_load(&sock->connecting)) {
 		return;
@@ -527,10 +533,13 @@ isc__nm_async_tcplisten(isc__networker_t *worker, isc__netievent_t *ev0) {
 	/* This keeps the socket alive after everything else is gone */
 	isc__nmsocket_attach(sock, &(isc_nmsocket_t *){ NULL });
 
-	r = uv_timer_init(&worker->loop, &sock->timer);
+	r = uv_timer_init(&worker->loop, &sock->read_timer);
 	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
 
-	uv_handle_set_data((uv_handle_t *)&sock->timer, sock);
+	r = uv_timer_init(&worker->loop, &sock->write_timer);
+	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&sock->write_timer, sock);
 
 	LOCK(&sock->parent->lock);
 
@@ -974,9 +983,13 @@ accept_connection(isc_nmsocket_t *ssock, isc_quota_t *quota) {
 	UV_RUNTIME_CHECK(uv_tcp_init, r);
 	uv_handle_set_data(&csock->uv_handle.handle, csock);
 
-	r = uv_timer_init(&worker->loop, &csock->timer);
+	r = uv_timer_init(&worker->loop, &csock->read_timer);
 	UV_RUNTIME_CHECK(uv_timer_init, r);
-	uv_handle_set_data((uv_handle_t *)&csock->timer, csock);
+	uv_handle_set_data((uv_handle_t *)&csock->read_timer, csock);
+
+	r = uv_timer_init(&worker->loop, &csock->write_timer);
+	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&csock->write_timer, csock);
 
 	r = uv_accept(&ssock->uv_handle.stream, &csock->uv_handle.stream);
 	if (r != 0) {
@@ -1071,6 +1084,13 @@ isc__nm_tcp_send(isc_nmhandle_t *handle, const isc_region_t *region,
 	uvreq->cb.send = cb;
 	uvreq->cbarg = cbarg;
 
+	if (sock->write_timeout == 0) {
+		sock->write_timeout =
+			(atomic_load(&sock->keepalive)
+				 ? atomic_load(&sock->mgr->keepalive)
+				 : atomic_load(&sock->mgr->idle));
+	}
+
 	ievent = isc__nm_get_netievent_tcpsend(sock->mgr, sock, uvreq);
 	isc__nm_maybe_enqueue_ievent(&sock->mgr->workers[sock->tid],
 				     (isc__netievent_t *)ievent);
@@ -1081,11 +1101,17 @@ isc__nm_tcp_send(isc_nmhandle_t *handle, const isc_region_t *region,
 static void
 tcp_send_cb(uv_write_t *req, int status) {
 	isc__nm_uvreq_t *uvreq = (isc__nm_uvreq_t *)req->data;
+
 	REQUIRE(VALID_UVREQ(uvreq));
 	REQUIRE(VALID_NMHANDLE(uvreq->handle));
 
 	isc_nmsocket_t *sock = uvreq->sock;
 
+	if (--sock->writes == 0) {
+		int r = uv_timer_stop(&sock->write_timer);
+		UV_RUNTIME_CHECK(uv_timer_stop, r);
+	}
+
 	if (status < 0) {
 		isc__nm_incstats(sock, STATID_SENDFAIL);
 		failed_send_cb(sock, uvreq, isc__nm_uverr2result(status));
@@ -1129,6 +1155,11 @@ tcp_send_direct(isc_nmsocket_t *sock, isc__nm_uvreq_t *req) {
 		return (ISC_R_CANCELED);
 	}
 
+	r = uv_timer_start(&sock->write_timer, isc__nmsocket_writetimeout_cb,
+			   sock->write_timeout, 0);
+	UV_RUNTIME_CHECK(uv_timer_start, r);
+	RUNTIME_CHECK(sock->writes++ >= 0);
+
 	r = uv_write(&req->uv_req.write, &sock->uv_handle.stream, &req->uvbuf,
 		     1, tcp_send_cb);
 	if (r < 0) {
@@ -1192,7 +1223,7 @@ tcp_close_cb(uv_handle_t *handle) {
 }
 
 static void
-timer_close_cb(uv_handle_t *handle) {
+read_timer_close_cb(uv_handle_t *handle) {
 	isc_nmsocket_t *sock = uv_handle_get_data(handle);
 	uv_handle_set_data(handle, NULL);
 
@@ -1205,6 +1236,17 @@ timer_close_cb(uv_handle_t *handle) {
 	}
 }
 
+static void
+write_timer_close_cb(uv_handle_t *timer) {
+	isc_nmsocket_t *sock = uv_handle_get_data(timer);
+	uv_handle_set_data(timer, NULL);
+
+	REQUIRE(VALID_NMSOCK(sock));
+
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
+	uv_close((uv_handle_t *)&sock->read_timer, read_timer_close_cb);
+}
+
 static void
 stop_tcp_child(isc_nmsocket_t *sock) {
 	REQUIRE(sock->type == isc_nm_tcpsocket);
@@ -1257,6 +1299,8 @@ stop_tcp_parent(isc_nmsocket_t *sock) {
 
 static void
 tcp_close_direct(isc_nmsocket_t *sock) {
+	int r;
+
 	REQUIRE(VALID_NMSOCK(sock));
 	REQUIRE(sock->tid == isc_nm_tid());
 	REQUIRE(atomic_load(&sock->closing));
@@ -1278,8 +1322,10 @@ tcp_close_direct(isc_nmsocket_t *sock) {
 	isc__nmsocket_timer_stop(sock);
 	isc__nm_stop_reading(sock);
 
-	uv_handle_set_data((uv_handle_t *)&sock->timer, sock);
+	r = uv_timer_stop(&sock->write_timer);
-	uv_close((uv_handle_t *)&sock->timer, timer_close_cb);
+	UV_RUNTIME_CHECK(uv_timer_stop, r);
+	uv_handle_set_data((uv_handle_t *)&sock->write_timer, sock);
+	uv_close((uv_handle_t *)&sock->write_timer, write_timer_close_cb);
 }
 
 void
@@ -1401,7 +1447,7 @@ isc__nm_async_tcpcancel(isc__networker_t *worker, isc__netievent_t *ev0) {
 	REQUIRE(sock->tid == isc_nm_tid());
 	UNUSED(worker);
 
-	uv_timer_stop(&sock->timer);
+	uv_timer_stop(&sock->read_timer);
 
 	isc__nm_tcp_failed_read_cb(sock, ISC_R_EOF);
 }

lib/isc/netmgr/tcpdns.c

@@ -37,13 +37,6 @@
 #include "netmgr-int.h"
 #include "uv-compat.h"
 
-/*%<
- *
- * Maximum number of simultaneous handles in flight supported for a single
- * connected TCPDNS socket. This value was chosen arbitrarily, and may be
- * changed in the future.
- */
-
 static atomic_uint_fast32_t last_tcpdnsquota_log = ATOMIC_VAR_INIT(0);
 
 static bool
@@ -105,8 +98,13 @@ tcpdns_connect_direct(isc_nmsocket_t *sock, isc__nm_uvreq_t *req) {
 	UV_RUNTIME_CHECK(uv_tcp_init, r);
 	uv_handle_set_data(&sock->uv_handle.handle, sock);
 
-	r = uv_timer_init(&worker->loop, &sock->timer);
+	r = uv_timer_init(&worker->loop, &sock->read_timer);
 	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
+
+	r = uv_timer_init(&worker->loop, &sock->write_timer);
+	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&sock->write_timer, sock);
 
 	if (isc__nm_closing(sock)) {
 		result = ISC_R_SHUTTINGDOWN;
@@ -144,7 +142,8 @@ tcpdns_connect_direct(isc_nmsocket_t *sock, isc__nm_uvreq_t *req) {
 	}
 	isc__nm_incstats(sock, STATID_CONNECT);
 
-	uv_handle_set_data((uv_handle_t *)&sock->timer, &req->uv_req.connect);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer,
+			   &req->uv_req.connect);
 	isc__nmsocket_timer_start(sock);
 
 	atomic_store(&sock->connected, true);
@@ -205,7 +204,7 @@ tcpdns_connect_cb(uv_connect_t *uvreq, int status) {
 	REQUIRE(sock->tid == isc_nm_tid());
 
 	isc__nmsocket_timer_stop(sock);
-	uv_handle_set_data((uv_handle_t *)&sock->timer, sock);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
 
 	if (!atomic_load(&sock->connecting)) {
 		return;
@@ -497,9 +496,13 @@ isc__nm_async_tcpdnslisten(isc__networker_t *worker, isc__netievent_t *ev0) {
 	/* This keeps the socket alive after everything else is gone */
 	isc__nmsocket_attach(sock, &(isc_nmsocket_t *){ NULL });
 
-	r = uv_timer_init(&worker->loop, &sock->timer);
+	r = uv_timer_init(&worker->loop, &sock->read_timer);
 	UV_RUNTIME_CHECK(uv_timer_init, r);
-	uv_handle_set_data((uv_handle_t *)&sock->timer, sock);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
+
+	r = uv_timer_init(&worker->loop, &sock->write_timer);
+	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&sock->write_timer, sock);
 
 	LOCK(&sock->parent->lock);
 
@@ -966,9 +969,13 @@ accept_connection(isc_nmsocket_t *ssock, isc_quota_t *quota) {
 	UV_RUNTIME_CHECK(uv_tcp_init, r);
 	uv_handle_set_data(&csock->uv_handle.handle, csock);
 
-	r = uv_timer_init(&worker->loop, &csock->timer);
+	r = uv_timer_init(&worker->loop, &csock->read_timer);
 	UV_RUNTIME_CHECK(uv_timer_init, r);
-	uv_handle_set_data((uv_handle_t *)&csock->timer, csock);
+	uv_handle_set_data((uv_handle_t *)&csock->read_timer, csock);
+
+	r = uv_timer_init(&worker->loop, &csock->write_timer);
+	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&csock->write_timer, csock);
 
 	r = uv_accept(&ssock->uv_handle.stream, &csock->uv_handle.stream);
 	if (r != 0) {
@@ -1086,6 +1093,13 @@ isc__nm_tcpdns_send(isc_nmhandle_t *handle, isc_region_t *region,
 	uvreq->cb.send = cb;
 	uvreq->cbarg = cbarg;
 
+	if (sock->write_timeout == 0) {
+		sock->write_timeout =
+			(atomic_load(&sock->keepalive)
+				 ? atomic_load(&sock->mgr->keepalive)
+				 : atomic_load(&sock->mgr->idle));
+	}
+
 	ievent = isc__nm_get_netievent_tcpdnssend(sock->mgr, sock, uvreq);
 	isc__nm_maybe_enqueue_ievent(&sock->mgr->workers[sock->tid],
 				     (isc__netievent_t *)ievent);
@@ -1103,6 +1117,11 @@ tcpdns_send_cb(uv_write_t *req, int status) {
 
 	sock = uvreq->sock;
 
+	if (--sock->writes == 0) {
+		int r = uv_timer_stop(&sock->write_timer);
+		UV_RUNTIME_CHECK(uv_timer_stop, r);
+	}
+
 	if (status < 0) {
 		isc__nm_incstats(sock, STATID_SENDFAIL);
 		isc__nm_failed_send_cb(sock, uvreq,
@@ -1169,6 +1188,11 @@ isc__nm_async_tcpdnssend(isc__networker_t *worker, isc__netievent_t *ev0) {
 		goto fail;
 	}
 
+	r = uv_timer_start(&sock->write_timer, isc__nmsocket_writetimeout_cb,
+			   sock->write_timeout, 0);
+	UV_RUNTIME_CHECK(uv_timer_start, r);
+	RUNTIME_CHECK(sock->writes++ >= 0);
+
 	r = uv_write(&uvreq->uv_req.write, &sock->uv_handle.stream, bufs, nbufs,
 		     tcpdns_send_cb);
 	if (r < 0) {
@@ -1238,7 +1262,7 @@ tcpdns_close_cb(uv_handle_t *handle) {
 }
 
 static void
-timer_close_cb(uv_handle_t *timer) {
+read_timer_close_cb(uv_handle_t *timer) {
 	isc_nmsocket_t *sock = uv_handle_get_data(timer);
 	uv_handle_set_data(timer, NULL);
 
@@ -1253,6 +1277,17 @@ timer_close_cb(uv_handle_t *timer) {
 	}
 }
 
+static void
+write_timer_close_cb(uv_handle_t *timer) {
+	isc_nmsocket_t *sock = uv_handle_get_data(timer);
+	uv_handle_set_data(timer, NULL);
+
+	REQUIRE(VALID_NMSOCK(sock));
+
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
+	uv_close((uv_handle_t *)&sock->read_timer, read_timer_close_cb);
+}
+
 static void
 stop_tcpdns_child(isc_nmsocket_t *sock) {
 	REQUIRE(sock->type == isc_nm_tcpdnssocket);
@@ -1305,6 +1340,7 @@ stop_tcpdns_parent(isc_nmsocket_t *sock) {
 
 static void
 tcpdns_close_direct(isc_nmsocket_t *sock) {
+	int r;
 	REQUIRE(VALID_NMSOCK(sock));
 	REQUIRE(sock->tid == isc_nm_tid());
 	REQUIRE(atomic_load(&sock->closing));
@@ -1320,8 +1356,10 @@ tcpdns_close_direct(isc_nmsocket_t *sock) {
 	isc__nmsocket_timer_stop(sock);
 	isc__nm_stop_reading(sock);
 
-	uv_handle_set_data((uv_handle_t *)&sock->timer, sock);
+	r = uv_timer_stop(&sock->write_timer);
-	uv_close((uv_handle_t *)&sock->timer, timer_close_cb);
+	UV_RUNTIME_CHECK(uv_timer_stop, r);
+	uv_handle_set_data((uv_handle_t *)&sock->write_timer, sock);
+	uv_close((uv_handle_t *)&sock->write_timer, write_timer_close_cb);
 }
 
 void

lib/isc/netmgr/tlsdns.c

@@ -38,13 +38,6 @@
 #include "openssl_shim.h"
 #include "uv-compat.h"
 
-/*%<
- *
- * Maximum number of simultaneous handles in flight supported for a single
- * connected TLSDNS socket. This value was chosen arbitrarily, and may be
- * changed in the future.
- */
-
 static atomic_uint_fast32_t last_tlsdnsquota_log = ATOMIC_VAR_INIT(0);
 
 static void
@@ -121,9 +114,13 @@ tlsdns_connect_direct(isc_nmsocket_t *sock, isc__nm_uvreq_t *req) {
 	UV_RUNTIME_CHECK(uv_tcp_init, r);
 	uv_handle_set_data(&sock->uv_handle.handle, sock);
 
-	r = uv_timer_init(&worker->loop, &sock->timer);
+	r = uv_timer_init(&worker->loop, &sock->read_timer);
 	UV_RUNTIME_CHECK(uv_timer_init, r);
-	uv_handle_set_data((uv_handle_t *)&sock->timer, sock);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
+
+	r = uv_timer_init(&worker->loop, &sock->write_timer);
+	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&sock->write_timer, sock);
 
 	if (isc__nm_closing(sock)) {
 		result = ISC_R_SHUTTINGDOWN;
@@ -161,7 +158,8 @@ tlsdns_connect_direct(isc_nmsocket_t *sock, isc__nm_uvreq_t *req) {
 	}
 	isc__nm_incstats(sock, STATID_CONNECT);
 
-	uv_handle_set_data((uv_handle_t *)&sock->timer, &req->uv_req.connect);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer,
+			   &req->uv_req.connect);
 	isc__nmsocket_timer_start(sock);
 
 	atomic_store(&sock->connected, true);
@@ -569,9 +567,13 @@ isc__nm_async_tlsdnslisten(isc__networker_t *worker, isc__netievent_t *ev0) {
 	/* This keeps the socket alive after everything else is gone */
 	isc__nmsocket_attach(sock, &(isc_nmsocket_t *){ NULL });
 
-	r = uv_timer_init(&worker->loop, &sock->timer);
+	r = uv_timer_init(&worker->loop, &sock->read_timer);
 	UV_RUNTIME_CHECK(uv_timer_init, r);
-	uv_handle_set_data((uv_handle_t *)&sock->timer, sock);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
+
+	r = uv_timer_init(&worker->loop, &sock->write_timer);
+	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&sock->write_timer, sock);
 
 	LOCK(&sock->parent->lock);
 
@@ -1107,7 +1109,8 @@ tls_cycle_input(isc_nmsocket_t *sock) {
 			sock->tls.pending_req = NULL;
 
 			isc__nmsocket_timer_stop(sock);
-			uv_handle_set_data((uv_handle_t *)&sock->timer, sock);
+			uv_handle_set_data((uv_handle_t *)&sock->read_timer,
+					   sock);
 
 			INSIST(atomic_compare_exchange_strong(
 				&sock->connecting, &(bool){ true }, false));
@@ -1163,6 +1166,11 @@ tls_write_cb(uv_write_t *req, int status) {
 	isc__nm_uvreq_t *uvreq = (isc__nm_uvreq_t *)req->data;
 	isc_nmsocket_t *sock = uvreq->sock;
 
+	if (--sock->writes == 0) {
+		int r = uv_timer_stop(&sock->write_timer);
+		UV_RUNTIME_CHECK(uv_timer_stop, r);
+	}
+
 	free_senddata(sock);
 
 	isc__nm_uvreq_put(&uvreq, sock);
@@ -1236,6 +1244,12 @@ tls_cycle_output(isc_nmsocket_t *sock) {
 			break;
 		}
 
+		r = uv_timer_start(&sock->write_timer,
+				   isc__nmsocket_writetimeout_cb,
+				   sock->write_timeout, 0);
+		UV_RUNTIME_CHECK(uv_timer_start, r);
+		RUNTIME_CHECK(sock->writes++ >= 0);
+
 		r = uv_write(&req->uv_req.write, &sock->uv_handle.stream,
 			     &req->uvbuf, 1, tls_write_cb);
 		if (r < 0) {
@@ -1476,9 +1490,13 @@ accept_connection(isc_nmsocket_t *ssock, isc_quota_t *quota) {
 	UV_RUNTIME_CHECK(uv_tcp_init, r);
 	uv_handle_set_data(&csock->uv_handle.handle, csock);
 
-	r = uv_timer_init(&worker->loop, &csock->timer);
+	r = uv_timer_init(&worker->loop, &csock->read_timer);
 	UV_RUNTIME_CHECK(uv_timer_init, r);
-	uv_handle_set_data((uv_handle_t *)&csock->timer, csock);
+	uv_handle_set_data((uv_handle_t *)&csock->read_timer, csock);
+
+	r = uv_timer_init(&worker->loop, &csock->write_timer);
+	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&csock->write_timer, csock);
 
 	r = uv_accept(&ssock->uv_handle.stream, &csock->uv_handle.stream);
 	if (r != 0) {
@@ -1627,6 +1645,13 @@ isc__nm_tlsdns_send(isc_nmhandle_t *handle, isc_region_t *region,
 	uvreq->cb.send = cb;
 	uvreq->cbarg = cbarg;
 
+	if (sock->write_timeout == 0) {
+		sock->write_timeout =
+			(atomic_load(&sock->keepalive)
+				 ? atomic_load(&sock->mgr->keepalive)
+				 : atomic_load(&sock->mgr->idle));
+	}
+
 	ievent = isc__nm_get_netievent_tlsdnssend(sock->mgr, sock, uvreq);
 	isc__nm_enqueue_ievent(&sock->mgr->workers[sock->tid],
 			       (isc__netievent_t *)ievent);
@@ -1804,7 +1829,7 @@ tlsdns_close_cb(uv_handle_t *handle) {
 }
 
 static void
-timer_close_cb(uv_handle_t *handle) {
+read_timer_close_cb(uv_handle_t *handle) {
 	isc_nmsocket_t *sock = uv_handle_get_data(handle);
 	uv_handle_set_data(handle, NULL);
 
@@ -1819,6 +1844,17 @@ timer_close_cb(uv_handle_t *handle) {
 	}
 }
 
+static void
+write_timer_close_cb(uv_handle_t *timer) {
+	isc_nmsocket_t *sock = uv_handle_get_data(timer);
+	uv_handle_set_data(timer, NULL);
+
+	REQUIRE(VALID_NMSOCK(sock));
+
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
+	uv_close((uv_handle_t *)&sock->read_timer, read_timer_close_cb);
+}
+
 static void
 stop_tlsdns_child(isc_nmsocket_t *sock) {
 	REQUIRE(sock->type == isc_nm_tlsdnssocket);
@@ -1872,6 +1908,8 @@ stop_tlsdns_parent(isc_nmsocket_t *sock) {
 
 static void
 tlsdns_close_direct(isc_nmsocket_t *sock) {
+	int r;
+
 	REQUIRE(VALID_NMSOCK(sock));
 	REQUIRE(sock->tid == isc_nm_tid());
 	REQUIRE(atomic_load(&sock->closing));
@@ -1889,8 +1927,10 @@ tlsdns_close_direct(isc_nmsocket_t *sock) {
 	isc__nmsocket_timer_stop(sock);
 	isc__nm_stop_reading(sock);
 
-	uv_handle_set_data((uv_handle_t *)&sock->timer, sock);
+	r = uv_timer_stop(&sock->write_timer);
-	uv_close((uv_handle_t *)&sock->timer, timer_close_cb);
+	UV_RUNTIME_CHECK(uv_timer_stop, r);
+	uv_handle_set_data((uv_handle_t *)&sock->write_timer, sock);
+	uv_close((uv_handle_t *)&sock->write_timer, write_timer_close_cb);
 }
 
 void

lib/isc/netmgr/udp.c

@@ -74,7 +74,10 @@ static void
 udp_close_cb(uv_handle_t *handle);
 
 static void
-timer_close_cb(uv_handle_t *handle);
+read_timer_close_cb(uv_handle_t *handle);
+
+static void
+write_timer_close_cb(uv_handle_t *handle);
 
 static void
 udp_close_direct(isc_nmsocket_t *sock);
@@ -265,9 +268,13 @@ route_connect_direct(isc_nmsocket_t *sock) {
 	UV_RUNTIME_CHECK(uv_udp_init, r);
 	uv_handle_set_data(&sock->uv_handle.handle, sock);
 
-	r = uv_timer_init(&worker->loop, &sock->timer);
+	r = uv_timer_init(&worker->loop, &sock->read_timer);
 	UV_RUNTIME_CHECK(uv_timer_init, r);
-	uv_handle_set_data((uv_handle_t *)&sock->timer, sock);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
+
+	r = uv_timer_init(&worker->loop, &sock->write_timer);
+	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&sock->write_timer, sock);
 
 	if (isc__nm_closing(sock)) {
 		result = ISC_R_SHUTTINGDOWN;
@@ -441,9 +448,13 @@ isc__nm_async_udplisten(isc__networker_t *worker, isc__netievent_t *ev0) {
 	/* This keeps the socket alive after everything else is gone */
 	isc__nmsocket_attach(sock, &(isc_nmsocket_t *){ NULL });
 
-	r = uv_timer_init(&worker->loop, &sock->timer);
+	r = uv_timer_init(&worker->loop, &sock->read_timer);
 	UV_RUNTIME_CHECK(uv_timer_init, r);
-	uv_handle_set_data((uv_handle_t *)&sock->timer, sock);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
+
+	r = uv_timer_init(&worker->loop, &sock->write_timer);
+	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&sock->write_timer, sock);
 
 	LOCK(&sock->parent->lock);
 
@@ -857,9 +868,13 @@ udp_connect_direct(isc_nmsocket_t *sock, isc__nm_uvreq_t *req) {
 	UV_RUNTIME_CHECK(uv_udp_init, r);
 	uv_handle_set_data(&sock->uv_handle.handle, sock);
 
-	r = uv_timer_init(&worker->loop, &sock->timer);
+	r = uv_timer_init(&worker->loop, &sock->read_timer);
 	UV_RUNTIME_CHECK(uv_timer_init, r);
-	uv_handle_set_data((uv_handle_t *)&sock->timer, sock);
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
+
+	r = uv_timer_init(&worker->loop, &sock->write_timer);
+	UV_RUNTIME_CHECK(uv_timer_init, r);
+	uv_handle_set_data((uv_handle_t *)&sock->write_timer, sock);
 
 	if (isc__nm_closing(sock)) {
 		result = ISC_R_SHUTTINGDOWN;
@@ -1210,7 +1225,7 @@ udp_close_cb(uv_handle_t *handle) {
 }
 
 static void
-timer_close_cb(uv_handle_t *handle) {
+read_timer_close_cb(uv_handle_t *handle) {
 	isc_nmsocket_t *sock = uv_handle_get_data(handle);
 	uv_handle_set_data(handle, NULL);
 
@@ -1221,6 +1236,17 @@ timer_close_cb(uv_handle_t *handle) {
 	}
 }
 
+static void
+write_timer_close_cb(uv_handle_t *timer) {
+	isc_nmsocket_t *sock = uv_handle_get_data(timer);
+	uv_handle_set_data(timer, NULL);
+
+	REQUIRE(VALID_NMSOCK(sock));
+
+	uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
+	uv_close((uv_handle_t *)&sock->read_timer, read_timer_close_cb);
+}
+
 static void
 stop_udp_child(isc_nmsocket_t *sock) {
 	REQUIRE(sock->type == isc_nm_udpsocket);
@@ -1273,10 +1299,14 @@ stop_udp_parent(isc_nmsocket_t *sock) {
 
 static void
 udp_close_direct(isc_nmsocket_t *sock) {
+	int r;
 	REQUIRE(VALID_NMSOCK(sock));
 	REQUIRE(sock->tid == isc_nm_tid());
 
-	uv_close((uv_handle_t *)&sock->timer, timer_close_cb);
+	r = uv_timer_stop(&sock->write_timer);
+	UV_RUNTIME_CHECK(uv_timer_stop, r);
+	uv_handle_set_data((uv_handle_t *)&sock->write_timer, sock);
+	uv_close((uv_handle_t *)&sock->write_timer, write_timer_close_cb);
 }
 
 void

lib/isc/netmgr/uv-compat.c

@@ -42,6 +42,24 @@ isc_uv_udp_connect(uv_udp_t *handle, const struct sockaddr *addr) {
 }
 #endif /* UV_VERSION_HEX < UV_VERSION(1, 27, 0) */
 
+#if UV_VERSION_HEX < UV_VERSION(1, 32, 0)
+int
+uv_tcp_close_reset(uv_tcp_t *handle, uv_close_cb close_cb) {
+	if (setsockopt(handle->io_watcher.fd, SOL_SOCKET, SO_LINGER,
+		       &(struct linger){ 1, 0 }, sizeof(struct linger)) == -1)
+	{
+#if UV_VERSION_HEX >= UV_VERSION(1, 10, 0)
+		return (uv_translate_sys_error(errno));
+#else
+		return (-errno);
+#endif /* UV_VERSION_HEX >= UV_VERSION(1, 10, 0) */
+	}
+
+	uv_close((uv_handle_t *)handle, close_cb);
+	return (0);
+}
+#endif /* UV_VERSION_HEX < UV_VERSION(1, 32, 0) */
+
 int
 isc_uv_udp_freebind(uv_udp_t *handle, const struct sockaddr *addr,
 		    unsigned int flags) {

lib/isc/netmgr/uv-compat.h

@@ -23,6 +23,10 @@
 
 #define UV_VERSION(major, minor, patch) ((major << 16) | (minor << 8) | (patch))
 
+#if !defined(UV__ERR)
+#define UV__ERR(x) (-(x))
+#endif
+
 #if UV_VERSION_HEX < UV_VERSION(1, 19, 0)
 static inline void *
 uv_handle_get_data(const uv_handle_t *handle) {
@@ -45,6 +49,11 @@ uv_req_set_data(uv_req_t *req, void *data) {
 }
 #endif /* UV_VERSION_HEX < UV_VERSION(1, 19, 0) */
 
+#if UV_VERSION_HEX < UV_VERSION(1, 32, 0)
+int
+uv_tcp_close_reset(uv_tcp_t *handle, uv_close_cb close_cb);
+#endif
+
 #if UV_VERSION_HEX < UV_VERSION(1, 34, 0)
 #define uv_sleep(msec) usleep(msec * 1000)
 #endif /* UV_VERSION_HEX < UV_VERSION(1, 34, 0) */

lib/isc/tests/netmgr_test.c

@@ -437,6 +437,7 @@ connect_send(isc_nmhandle_t *handle) {
 	isc_nmhandle_t *sendhandle = NULL;
 	isc_refcount_increment0(&active_csends);
 	isc_nmhandle_attach(handle, &sendhandle);
+	isc_nmhandle_setwritetimeout(handle, T_IDLE);
 	if (atomic_fetch_sub(&nsends, 1) > 1) {
 		isc_nm_send(sendhandle, (isc_region_t *)&send_msg,
 			    connect_send_cb, NULL);
@@ -548,6 +549,7 @@ listen_read_cb(isc_nmhandle_t *handle, isc_result_t eresult,
 			isc_nmhandle_t *sendhandle = NULL;
 			isc_nmhandle_attach(handle, &sendhandle);
 			isc_refcount_increment0(&active_ssends);
+			isc_nmhandle_setwritetimeout(sendhandle, T_IDLE);
 			isc_nm_send(sendhandle, (isc_region_t *)&send_msg,
 				    listen_send_cb, cbarg);
 		}