Add a PDS_ flag to exclude authorities from which we are fetching descs.

Yes, this is maybe a little overspecific.  Part of a bug 366 fix.

svn:r17593

src/or/directory.c

@@ -368,6 +368,22 @@ directory_get_from_dirserver(uint8_t dir_purpose, uint8_t router_purpose,
       if (prefer_authority || type == BRIDGE_AUTHORITY) {
         /* only ask authdirservers, and don't ask myself */
         rs = router_pick_trusteddirserver(type, pds_flags);
+        if (rs == NULL && (pds_flags & PDS_NO_EXISTING_SERVERDESC_FETCH)) {
+          /* We don't want to fetch from any authorities that we're currently
+           * fetching server descriptors from, and we got no match.  Did we
+           * get no match because all the authorities have connections
+           * fetching server descriptors (in which case we should just
+           * return,) or because all the authorities are down or on fire or
+           * unreachable or something (in which case we should go on with
+           * our fallback code)? */
+          pds_flags &= ~PDS_NO_EXISTING_SERVERDESC_FETCH;
+          rs = router_pick_trusteddirserver(type, pds_flags);
+          if (rs) {
+            log_debug(LD_DIR, "Deferring serverdesc fetch: all authorities "
+                      "are in use.");
+            return;
+          }
+        }
       }
       if (!rs && type != BRIDGE_AUTHORITY) {
         /* anybody with a non-zero dirport will do */

src/or/or.h

@@ -4191,9 +4191,26 @@ int router_reload_router_list(void);
 smartlist_t *router_get_trusted_dir_servers(void);
 
 /* Flags for pick_directory_server and pick_trusteddirserver. */
+/** Flag to indicate that we should not automatically be willing to use
+ * ourself to answer a directory request.
+ * Passed to router_pick_directory_server (et al).*/
 #define PDS_ALLOW_SELF                 (1<<0)
+/** Flag to indicate that if no servers seem to be up, we should mark all
+ * directory servers as up and try again.
+ * Passed to router_pick_directory_server (et al).*/
 #define PDS_RETRY_IF_NO_SERVERS        (1<<1)
+/** Flag to indicate that we should not exclude directory servers that
+ * our ReachableAddress settings would exclude.  This usually means that
+ * we're going to connect to the server over Tor, and so we don't need to
+ * worry about our firewall telling us we can't.
+ * Passed to router_pick_directory_server (et al).*/
 #define PDS_IGNORE_FASCISTFIREWALL     (1<<2)
+/** Flag to indicate that we should not use any directory authority to which
+ * we have an existing directory connection for downloading server descriptors
+ * or extrainfo documents.  [NOTE: Only implemented for
+ * router_pick_trusteddirserver, not router_pick_directory_server.]
+ * Passed to router_pick_directory_server (et al).*/
+#define PDS_NO_EXISTING_SERVERDESC_FETCH (1<<3)
 #define _PDS_PREFER_TUNNELED_DIR_CONNS (1<<16)
 routerstatus_t *router_pick_directory_server(authority_type_t type, int flags);
 trusted_dir_server_t *router_get_trusteddirserver_by_digest(const char *d);

src/or/routerlist.c

@@ -24,7 +24,7 @@ const char routerlist_c_id[] =
 static routerstatus_t *router_pick_directory_server_impl(
                                            authority_type_t auth, int flags);
 static routerstatus_t *router_pick_trusteddirserver_impl(
-                                           authority_type_t auth, int flags);
+                          authority_type_t auth, int flags, int *n_busy_out);
 static void mark_all_trusteddirservers_up(void);
 static int router_nickname_matches(routerinfo_t *router, const char *nickname);
 static void trusted_dir_server_free(trusted_dir_server_t *ds);
@@ -979,17 +979,25 @@ routerstatus_t *
 router_pick_trusteddirserver(authority_type_t type, int flags)
 {
   routerstatus_t *choice;
+  int busy = 0;
   if (get_options()->PreferTunneledDirConns)
     flags |= _PDS_PREFER_TUNNELED_DIR_CONNS;
 
-  choice = router_pick_trusteddirserver_impl(type, flags);
+  choice = router_pick_trusteddirserver_impl(type, flags, &busy);
   if (choice || !(flags & PDS_RETRY_IF_NO_SERVERS))
     return choice;
+  if (busy) {
+    /* If the reason that we got no server is that servers are "busy",
+     * we must be excluding good servers because we already have serverdesc
+     * fetches with them.  Do not mark down servers up because of this. */
+    tor_assert((flags & PDS_NO_EXISTING_SERVERDESC_FETCH));
+    return NULL;
+  }
 
   log_info(LD_DIR,
            "No trusted dirservers are reachable. Trying them all again.");
   mark_all_trusteddirservers_up();
-  return router_pick_trusteddirserver_impl(type, flags);
+  return router_pick_trusteddirserver_impl(type, flags, NULL);
 }
 
 /** How long do we avoid using a directory server after it's given us a 503? */
@@ -1095,16 +1103,19 @@ router_pick_directory_server_impl(authority_type_t type, int flags)
  * are as for router_pick_directory_server_impl().
  */
 static routerstatus_t *
-router_pick_trusteddirserver_impl(authority_type_t type, int flags)
+router_pick_trusteddirserver_impl(authority_type_t type, int flags,
+                                  int *n_busy_out)
 {
   smartlist_t *direct, *tunnel;
   smartlist_t *overloaded_direct, *overloaded_tunnel;
   routerinfo_t *me = router_get_my_routerinfo();
   routerstatus_t *result;
   time_t now = time(NULL);
-  int requireother = ! (flags & PDS_ALLOW_SELF);
-  int fascistfirewall = ! (flags & PDS_IGNORE_FASCISTFIREWALL);
-  int prefer_tunnel = (flags & _PDS_PREFER_TUNNELED_DIR_CONNS);
+  const int requireother = ! (flags & PDS_ALLOW_SELF);
+  const int fascistfirewall = ! (flags & PDS_IGNORE_FASCISTFIREWALL);
+  const int prefer_tunnel = (flags & _PDS_PREFER_TUNNELED_DIR_CONNS);
+  const int no_serverdesc_fetching =(flags & PDS_NO_EXISTING_SERVERDESC_FETCH);
+  int n_busy = 0;
 
   if (!trusted_dir_servers)
     return NULL;
@@ -1131,6 +1142,18 @@ router_pick_trusteddirserver_impl(authority_type_t type, int flags)
       /* XXXX021 IP6 proposal 118 */
       tor_addr_from_ipv4h(&addr, d->addr);
 
+      if (no_serverdesc_fetching) {
+        if (connection_get_by_type_addr_port_purpose(
+            CONN_TYPE_DIR, &addr, d->dir_port, DIR_PURPOSE_FETCH_SERVERDESC)
+         || connection_get_by_type_addr_port_purpose(
+             CONN_TYPE_DIR, &addr, d->dir_port, DIR_PURPOSE_FETCH_EXTRAINFO)) {
+          //log_debug(LD_DIR, "We have an existing connection to fetch "
+          //           "descriptor from %s; delaying",d->description);
+          ++n_busy;
+          continue;
+        }
+      }
+
       if (prefer_tunnel &&
           d->or_port &&
           (!fascistfirewall ||
@@ -1154,6 +1177,9 @@ router_pick_trusteddirserver_impl(authority_type_t type, int flags)
     result = smartlist_choose(overloaded_direct);
   }
 
+  if (n_busy_out)
+    *n_busy_out = n_busy;
+
   smartlist_free(direct);
   smartlist_free(tunnel);
   smartlist_free(overloaded_direct);