Add configure option AuthDirHasIPv6Connectivity.

Implements enhancement 5974.

changes/bug5974

@@ -0,0 +1,4 @@
+  o Minor features:
+
+    - Add new configure option AuthDirHasIPv6Connectivity.  Implements
+      feature #5974.

doc/tor.1.txt

@@ -1728,6 +1728,14 @@ DIRECTORY AUTHORITY SERVER OPTIONS
     votes on whether to accept relays as hidden service directories.
     (Default: 1)
 
+**AuthDirHasIPv6Connectivity** **0**|**1**|**auto**::
+
+    Authoritative directories only. When set to 0, OR ports with an
+    IPv6 address are being accepted without reachability testing.
+    When set to 1, IPv6 OR ports are being tested just like IPv4 OR
+    ports.  When set to auto, Tor tries to find out if the authority
+    relay has IPv6 connectivity or not. (Default: auto)
+
 HIDDEN SERVICE OPTIONS
 ----------------------
 

src/or/config.c

@@ -201,6 +201,7 @@ static config_var_t _option_vars[] = {
   V(AuthDirListBadExits,         BOOL,     "0"),
   V(AuthDirMaxServersPerAddr,    UINT,     "2"),
   V(AuthDirMaxServersPerAuthAddr,UINT,     "5"),
+  V(AuthDirHasIPv6Connectivity,  AUTOBOOL, "auto"),
   VAR("AuthoritativeDirectory",  BOOL, AuthoritativeDir,    "0"),
   V(AutomapHostsOnResolve,       BOOL,     "0"),
   V(AutomapHostsSuffixes,        CSV,      ".onion,.exit"),

src/or/dirserv.c

@@ -2470,11 +2470,12 @@ set_routerstatus_from_routerinfo(routerstatus_t *rs,
   rs->dir_port = ri->dir_port;
   if (authdir_mode_bridge(options) &&
       !tor_addr_is_null(&ri->ipv6_addr) &&
-      node->last_reachable6 >= now - REACHABLE_TIMEOUT) {
+      (options->AuthDirHasIPv6Connectivity == 0 ||
+       node->last_reachable6 >= now - REACHABLE_TIMEOUT)) {
     /* We're a bridge authority (we're not ready for IPv6 relays in
        the consensus quite yet).  There's an IPv6 OR port and it's
-       reachable so copy it to the routerstatus.  FIXME: If we're not
-       on IPv6, copy it regardless of reachability.  */
+       reachable (or we know that we're not on IPv6) so copy it to the
+       routerstatus.  */
     tor_addr_copy(&rs->ipv6_addr, &ri->ipv6_addr);
     rs->ipv6_orport = ri->ipv6_orport;
   }

src/or/or.h

@@ -3273,6 +3273,7 @@ typedef struct {
   int AuthDirMaxServersPerAuthAddr; /**< Do not permit more than this
                                      * number of servers per IP address shared
                                      * with an authority. */
+  int AuthDirHasIPv6Connectivity; /**< Autoboolean: are we on IPv6?  */
 
   /** If non-zero, always vote the Fast flag for any relay advertising
    * this amount of capacity or more. */