Add networkstatus_consensus_has_ipv6() and unit tests

networkstatus_consensus_has_ipv6() tells us whether the consensus method of
our current consensus supports IPv6 ORPorts in the consensus.

Part of #23827.

src/or/networkstatus.c

@@ -1507,6 +1507,32 @@ networkstatus_consensus_is_already_downloading(const char *resource)
   return answer;
 }
 
+/* Does the current, reasonably live consensus have IPv6 addresses?
+ * Returns 1 if there is a reasonably live consensus and its consensus method
+ * includes IPv6 addresses in the consensus.
+ * Otherwise, if there is no consensus, or the method does not include IPv6
+ * addresses, returns 0. */
+int
+networkstatus_consensus_has_ipv6(const or_options_t* options)
+{
+  const networkstatus_t *cons = networkstatus_get_reasonably_live_consensus(
+                                                    approx_time(),
+                                                    usable_consensus_flavor());
+
+  /* If we have no consensus, we have no IPv6 in it */
+  if (!cons) {
+    return 0;
+  }
+
+  /* Different flavours of consensus gained IPv6 at different times */
+  if (we_use_microdescriptors_for_circuits(options)) {
+    return
+       cons->consensus_method >= MIN_METHOD_FOR_A_LINES_IN_MICRODESC_CONSENSUS;
+  } else {
+    return cons->consensus_method >= MIN_METHOD_FOR_A_LINES;
+  }
+}
+
 /** Given two router status entries for the same router identity, return 1 if
  * if the contents have changed between them. Otherwise, return 0. */
 static int

src/or/networkstatus.h

@@ -93,6 +93,7 @@ int networkstatus_consensus_can_use_multiple_directories(
 MOCK_DECL(int, networkstatus_consensus_can_use_extra_fallbacks,(
                                                 const or_options_t *options));
 int networkstatus_consensus_is_already_downloading(const char *resource);
+int networkstatus_consensus_has_ipv6(const or_options_t* options);
 
 #define NSSET_FROM_CACHE 1
 #define NSSET_WAS_WAITING_FOR_CERTS 2

src/test/test_dir.c

@@ -6174,6 +6174,101 @@ test_dir_platform_str(void *arg)
   ;
 }
 
+static networkstatus_t *mock_networkstatus;
+
+static networkstatus_t *
+mock_networkstatus_get_latest_consensus_by_flavor(consensus_flavor_t f)
+{
+  (void)f;
+  return mock_networkstatus;
+}
+
+static void
+test_dir_networkstatus_consensus_has_ipv6(void *arg)
+{
+  (void)arg;
+
+  int has_ipv6 = 0;
+
+  /* Init options and networkstatus */
+  or_options_t our_options;
+  mock_options = &our_options;
+  reset_options(mock_options, &mock_get_options_calls);
+  MOCK(get_options, mock_get_options);
+
+  networkstatus_t our_networkstatus;
+  mock_networkstatus = &our_networkstatus;
+  memset(mock_networkstatus, 0, sizeof(*mock_networkstatus));
+  MOCK(networkstatus_get_latest_consensus_by_flavor,
+       mock_networkstatus_get_latest_consensus_by_flavor);
+
+  /* A live consensus */
+  mock_networkstatus->valid_after = time(NULL) - 3600;
+  mock_networkstatus->valid_until = time(NULL) + 3600;
+
+  /* Test the bounds for A lines in the NS consensus */
+  mock_options->UseMicrodescriptors = 0;
+
+  mock_networkstatus->consensus_method = MIN_METHOD_FOR_A_LINES;
+  has_ipv6 = networkstatus_consensus_has_ipv6(get_options());
+  tt_assert(has_ipv6);
+
+  mock_networkstatus->consensus_method = MIN_METHOD_FOR_A_LINES + 1;
+  has_ipv6 = networkstatus_consensus_has_ipv6(get_options());
+  tt_assert(has_ipv6);
+
+  mock_networkstatus->consensus_method = MIN_METHOD_FOR_A_LINES + 20;
+  has_ipv6 = networkstatus_consensus_has_ipv6(get_options());
+  tt_assert(has_ipv6);
+
+  mock_networkstatus->consensus_method = MIN_METHOD_FOR_A_LINES - 1;
+  has_ipv6 = networkstatus_consensus_has_ipv6(get_options());
+  tt_assert(!has_ipv6);
+
+  /* Test the bounds for A lines in the microdesc consensus */
+  mock_options->UseMicrodescriptors = 1;
+
+  mock_networkstatus->consensus_method = MIN_METHOD_FOR_A_LINES_IN_MICRODESC_CONSENSUS;
+  has_ipv6 = networkstatus_consensus_has_ipv6(get_options());
+  tt_assert(has_ipv6);
+
+  mock_networkstatus->consensus_method = MIN_METHOD_FOR_A_LINES_IN_MICRODESC_CONSENSUS + 1;
+  has_ipv6 = networkstatus_consensus_has_ipv6(get_options());
+  tt_assert(has_ipv6);
+
+  mock_networkstatus->consensus_method = MIN_METHOD_FOR_A_LINES_IN_MICRODESC_CONSENSUS + 20;
+  has_ipv6 = networkstatus_consensus_has_ipv6(get_options());
+  tt_assert(has_ipv6);
+
+  mock_networkstatus->consensus_method = MIN_METHOD_FOR_A_LINES_IN_MICRODESC_CONSENSUS - 1;
+  has_ipv6 = networkstatus_consensus_has_ipv6(get_options());
+  tt_assert(!has_ipv6);
+
+  /* Test the edge cases */
+  mock_options->UseMicrodescriptors = 1;
+  mock_networkstatus->consensus_method = MIN_METHOD_FOR_A_LINES_IN_MICRODESC_CONSENSUS;
+
+  /* Reasonably live */
+  mock_networkstatus->valid_until = time(NULL) - 60;
+  has_ipv6 = networkstatus_consensus_has_ipv6(get_options());
+  tt_assert(has_ipv6);
+
+  /* Not reasonably live */
+  mock_networkstatus->valid_after = time(NULL) - 24*60*60 - 3600;
+  mock_networkstatus->valid_until = time(NULL) - 24*60*60 - 60;
+  has_ipv6 = networkstatus_consensus_has_ipv6(get_options());
+  tt_assert(!has_ipv6);
+
+  /* NULL consensus */
+  mock_networkstatus = NULL;
+  has_ipv6 = networkstatus_consensus_has_ipv6(get_options());
+  tt_assert(!has_ipv6);
+
+ done:
+  UNMOCK(get_options);
+  UNMOCK(networkstatus_get_latest_consensus_by_flavor);
+}
+
 #define DIR_LEGACY(name)                             \
   { #name, test_dir_ ## name , TT_FORK, NULL, NULL }
 
@@ -6241,6 +6336,7 @@ struct testcase_t dir_tests[] = {
   DIR(assumed_flags, 0),
   DIR(networkstatus_compute_bw_weights_v10, 0),
   DIR(platform_str, 0),
+  DIR(networkstatus_consensus_has_ipv6, 0),
   END_OF_TESTCASES
 };