From 0aebad96b5376e59a01034f3b2cc923b33e4b183 Mon Sep 17 00:00:00 2001
From: Diego Fronza <diego@isc.org>
Date: Fri, 18 Dec 2020 16:24:56 -0300
Subject: [PATCH] Added option for disabling stale-answer-client-timeout

This commit allows to specify "disabled" or "off" in
stale-answer-client-timeout statement. The logic to support this
behavior will be added in the subsequent commits.

This commit also ensures an upper bound to stale-answer-client-timeout
which equals to one second less than 'resolver-query-timeout'.

(cherry picked from commit 0ad6f594f65c6f33879a6a942f8e8ed17ba14fef)
---
 bin/named/server.c     | 35 ++++++++++++++++++++++++++++++++++-
 lib/isccfg/namedconf.c | 25 ++++++++++++++++++++++++-
 2 files changed, 58 insertions(+), 2 deletions(-)

diff --git a/bin/named/server.c b/bin/named/server.c
index 1c0190f31df..6050e476c00 100644
--- a/bin/named/server.c
+++ b/bin/named/server.c
@@ -4402,7 +4402,19 @@ configure_view(dns_view_t *view, dns_viewlist_t *viewlist, cfg_obj_t *config,
 	obj = NULL;
 	result = named_config_get(maps, "stale-answer-client-timeout", &obj);
 	INSIST(result == ISC_R_SUCCESS);
-	view->staleanswerclienttimeout = cfg_obj_asuint32(obj);
+	if (cfg_obj_isstring(obj)) {
+		/*
+		 * The only string values available for this option
+		 * are "disabled" and "off".
+		 * We use (uint32_t) -1 to represent disabled since
+		 * a value of zero means that stale data can be used
+		 * to promptly answer the query, while an attempt to
+		 * refresh the RRset will still be made in background.
+		 */
+		view->staleanswerclienttimeout = (uint32_t)-1;
+	} else {
+		view->staleanswerclienttimeout = cfg_obj_asuint32(obj);
+	}
 
 	obj = NULL;
 	result = named_config_get(maps, "stale-refresh-time", &obj);
@@ -4693,6 +4705,27 @@ configure_view(dns_view_t *view, dns_viewlist_t *viewlist, cfg_obj_t *config,
 	query_timeout = cfg_obj_asuint32(obj);
 	dns_resolver_settimeout(view->resolver, query_timeout);
 
+	/*
+	 * Adjust stale-answer-client-timeout upper bound
+	 * to be resolver-query-timeout - 1s.
+	 * This assignment is safe as dns_resolver_settimeout()
+	 * ensures that resolver->querytimeout value will be in the
+	 * [MINIMUM_QUERY_TIMEOUT, MAXIMUM_QUERY_TIMEOUT] range and
+	 * MINIMUM_QUERY_TIMEOUT is > 1000 (in ms).
+	 */
+	if (view->staleanswerclienttimeout != (uint32_t)-1 &&
+	    view->staleanswerclienttimeout >
+		    (dns_resolver_gettimeout(view->resolver) - 1000))
+	{
+		view->staleanswerclienttimeout =
+			dns_resolver_gettimeout(view->resolver) - 1000;
+		isc_log_write(
+			named_g_lctx, NAMED_LOGCATEGORY_GENERAL,
+			NAMED_LOGMODULE_SERVER, ISC_LOG_WARNING,
+			"stale-answer-client-timeout adjusted to %" PRIu32,
+			view->staleanswerclienttimeout);
+	}
+
 	/* Specify whether to use 0-TTL for negative response for SOA query */
 	dns_resolver_setzeronosoattl(view->resolver, zero_no_soattl);
 
diff --git a/lib/isccfg/namedconf.c b/lib/isccfg/namedconf.c
index 43e1bd1183c..6875f6a9c13 100644
--- a/lib/isccfg/namedconf.c
+++ b/lib/isccfg/namedconf.c
@@ -1948,6 +1948,28 @@ static cfg_type_t cfg_type_dns64 = { "dns64",	    cfg_parse_netprefix_map,
 				     cfg_print_map, cfg_doc_map,
 				     &cfg_rep_map,  dns64_clausesets };
 
+static const char *staleanswerclienttimeout_enums[] = { "disabled", "off",
+							NULL };
+static isc_result_t
+parse_staleanswerclienttimeout(cfg_parser_t *pctx, const cfg_type_t *type,
+			       cfg_obj_t **ret) {
+	return (cfg_parse_enum_or_other(pctx, type, &cfg_type_uint32, ret));
+}
+
+static void
+doc_staleanswerclienttimeout(cfg_printer_t *pctx, const cfg_type_t *type) {
+	cfg_doc_enum_or_other(pctx, type, &cfg_type_uint32);
+}
+
+static cfg_type_t cfg_type_staleanswerclienttimeout = {
+	"staleanswerclienttimeout",
+	parse_staleanswerclienttimeout,
+	cfg_print_ustring,
+	doc_staleanswerclienttimeout,
+	&cfg_rep_string,
+	staleanswerclienttimeout_enums
+};
+
 /*%
  * Clauses that can be found within the 'view' statement,
  * with defaults in the 'options' statement.
@@ -2076,7 +2098,8 @@ static cfg_clausedef_t view_clauses[] = {
 	{ "servfail-ttl", &cfg_type_duration, 0 },
 	{ "sortlist", &cfg_type_bracketed_aml, 0 },
 	{ "stale-answer-enable", &cfg_type_boolean, 0 },
-	{ "stale-answer-client-timeout", &cfg_type_uint32, 0 },
+	{ "stale-answer-client-timeout", &cfg_type_staleanswerclienttimeout,
+	  0 },
 	{ "stale-answer-ttl", &cfg_type_duration, 0 },
 	{ "stale-cache-enable", &cfg_type_boolean, 0 },
 	{ "stale-refresh-time", &cfg_type_duration, 0 },
-- 
2.47.3