Unit test for DNS fallback in configure_nameservers

src/feature/relay/dns.c

@@ -1357,6 +1357,36 @@ evdns_err_is_transient(int err)
   }
 }
 
+/**
+ * Return number of configured nameservers in <b>the_evdns_base</b>.
+ */
+size_t
+number_of_configured_nameservers(void)
+{
+  return evdns_base_count_nameservers(the_evdns_base);
+}
+
+/**
+ * Return address of configured nameserver in <b>the_evdns_base</b>
+ * at index <b>idx</b>.
+ */
+tor_addr_t *
+configured_nameserver_address(const size_t idx)
+{
+ struct sockaddr_storage sa;
+ ev_socklen_t sa_len = sizeof(sa);
+
+ if (evdns_base_get_nameserver_addr(the_evdns_base, (int)idx,
+                                    (struct sockaddr *)&sa,
+                                    sa_len) > 0) {
+   tor_addr_t *tor_addr = tor_malloc(sizeof(tor_addr_t));
+   tor_addr_from_sockaddr(tor_addr, (const struct sockaddr *)&sa, NULL);
+   return tor_addr;
+ }
+
+ return NULL;
+}
+
 /** Configure eventdns nameservers if force is true, or if the configuration
  * has changed since the last time we called this function, or if we failed on
  * our last attempt.  On Unix, this reads from /etc/resolv.conf or

src/feature/relay/dns.h

@@ -45,6 +45,9 @@ size_t dns_cache_handle_oom(time_t now, size_t min_remove_bytes);
 #ifdef DNS_PRIVATE
 #include "feature/relay/dns_structs.h"
 
+size_t number_of_configured_nameservers(void);
+tor_addr_t *configured_nameserver_address(const size_t idx);
+
 MOCK_DECL(STATIC int,dns_resolve_impl,(edge_connection_t *exitconn,
 int is_resolve,or_circuit_t *oncirc, char **hostname_out,
 int *made_connection_pending_out, cached_resolve_t **resolve_out));

src/test/test_dns.c

@@ -13,9 +13,69 @@
 
 #include "core/or/edge_connection_st.h"
 #include "core/or/or_circuit_st.h"
+#include "app/config/or_options_st.h"
+#include "app/config/config.h"
+
+#include <event2/event.h>
+#include <event2/dns.h>
 
 #define NS_MODULE dns
 
+#define NS_SUBMODULE configure_nameservers_fallback
+
+static or_options_t options = {
+  .ORPort_set = 1,
+};
+
+static const or_options_t *
+mock_get_options(void)
+{
+  return &options;
+}
+
+static void
+NS(test_main)(void *arg)
+{
+  (void)arg;
+  tor_addr_t *nameserver_addr = NULL;
+
+  MOCK(get_options, mock_get_options);
+
+  options.ServerDNSResolvConfFile = (char *)"no_such_file!!!";
+
+  dns_init(); // calls configure_nameservers()
+
+  tt_int_op(number_of_configured_nameservers(), OP_EQ, 1);
+
+  nameserver_addr = configured_nameserver_address(0);
+
+  tt_assert(tor_addr_family(nameserver_addr) == AF_INET);
+  tt_assert(tor_addr_eq_ipv4h(nameserver_addr, 0x7f000001));
+
+#ifndef _WIN32
+  tor_free(nameserver_addr);
+
+  options.ServerDNSResolvConfFile = (char *)"/dev/null";
+
+  dns_init();
+
+  tt_int_op(number_of_configured_nameservers(), OP_EQ, 1);
+
+  nameserver_addr = configured_nameserver_address(0);
+
+  tt_assert(tor_addr_family(nameserver_addr) == AF_INET);
+  tt_assert(tor_addr_eq_ipv4h(nameserver_addr, 0x7f000001));
+#endif
+
+  UNMOCK(get_options);
+
+ done:
+  tor_free(nameserver_addr);
+  return;
+}
+
+#undef NS_SUBMODULE
+
 #define NS_SUBMODULE clip_ttl
 
 static void
@@ -736,6 +796,7 @@ NS(test_main)(void *arg)
 #undef NS_SUBMODULE
 
 struct testcase_t dns_tests[] = {
+   TEST_CASE(configure_nameservers_fallback),
    TEST_CASE(clip_ttl),
    TEST_CASE(resolve),
    TEST_CASE_ASPECT(resolve_impl, addr_is_ip_no_need_to_resolve),