provide a way for systemd-supervised services to listen on TLS via socket activation

daemon/main.c

@@ -510,6 +510,8 @@ int main(int argc, char **argv)
 		}
 		if (!strcasecmp("control",socket_names[i])) {
 			control_fd = fd;
+		} else if (!strcasecmp("tls",socket_names[i])) {
+			array_push(tls_fd_set, fd);
 		} else {
 			array_push(fd_set, fd);
 		}

systemd/knot-resolver-tls.socket

+[Unit]
+Description=Knot DNS Resolver TLS network listener
+Documentation=man:kresd(8)
+Before=sockets.target
+
+[Socket]
+ListenStream=853
+FileDescriptorName=tls
+Service=knot-resolver.service
+
+[Install]
+WantedBy=sockets.target