Adjust the rules for warning about too many connections.

Previously we tolerated up to 1.5 connections for every relay we
were connected to, and didn't warn if we had fewer than 5
connections total.

Now we tolerate up to 1.5 connections per relay, and up to 4
connections per authority, and we don't warn at all when we have
fewer than 25 connections total.

Fixes bug 33880, which seems to have been provoked by our #17592
change in 0.3.5.

changes/ticket33880

+  o Minor bugfixes (relay, usability):
+    - Adjust the rules for when to warn about having too many connections
+      to other relays. Previously we'd tolerate up to 1.5 connections
+      per relay on average.  Now we tolerate more connections for directory
+      authorities, and raise the number of total connections we need
+      to see before we warn.  Fixes bug 33880; bugfix on 0.3.1.1-alpha.

src/core/or/channel.c

@@ -72,6 +72,7 @@
 #include "core/or/relay.h"
 #include "core/or/scheduler.h"
 #include "feature/client/entrynodes.h"
+#include "feature/nodelist/dirlist.h"
 #include "feature/nodelist/networkstatus.h"
 #include "feature/nodelist/nodelist.h"
 #include "feature/nodelist/routerlist.h"
@@ -749,6 +750,7 @@ channel_check_for_duplicates(void)
 {
   channel_idmap_entry_t **iter;
   channel_t *chan;
+  int total_dirauth_connections = 0, total_dirauths = 0;
   int total_relay_connections = 0, total_relays = 0, total_canonical = 0;
   int total_half_canonical = 0;
   int total_gt_one_connection = 0, total_gt_two_connections = 0;
@@ -756,13 +758,18 @@ channel_check_for_duplicates(void)
 
   HT_FOREACH(iter, channel_idmap, &channel_identity_map) {
     int connections_to_relay = 0;
+    const char *id_digest = (char *) (*iter)->digest;
 
     /* Only consider relay connections */
-    if (!connection_or_digest_is_known_relay((char*)(*iter)->digest))
+    if (!connection_or_digest_is_known_relay(id_digest))
       continue;
 
     total_relays++;
 
+    const bool is_dirauth = router_digest_is_trusted_dir(id_digest);
+    if (is_dirauth)
+      total_dirauths++;
+
     for (chan = TOR_LIST_FIRST(&(*iter)->channel_list); chan;
         chan = channel_next_with_rsa_identity(chan)) {
 
@@ -771,6 +778,8 @@ channel_check_for_duplicates(void)
 
       connections_to_relay++;
       total_relay_connections++;
+      if (is_dirauth)
+        total_dirauth_connections++;
 
       if (chan->is_canonical(chan, 0)) total_canonical++;
 
@@ -785,11 +794,28 @@ channel_check_for_duplicates(void)
     if (connections_to_relay > 4) total_gt_four_connections++;
   }
 
-#define MIN_RELAY_CONNECTIONS_TO_WARN 5
+  /* Don't bother warning about excessive connections unless we have
+   * at least this many connections, total.
+   */
+#define MIN_RELAY_CONNECTIONS_TO_WARN 25
+  /* If the average number of connections for a regular relay is more than
+   * this, that's too high.
+   */
+#define MAX_AVG_RELAY_CONNECTIONS 1.5
+  /* If the average number of connections for a dirauth is more than
+   * this, that's too high.
+   */
+#define MAX_AVG_DIRAUTH_CONNECTIONS 4
+
+  /* How many connections total would be okay, given the number of
+   * relays and dirauths that we have connections to? */
+  const int max_tolerable_connections = (int)(
+    (total_relays-total_dirauths) * MAX_AVG_RELAY_CONNECTIONS +
+    total_dirauths * MAX_AVG_DIRAUTH_CONNECTIONS);
 
   /* If we average 1.5 or more connections per relay, something is wrong */
   if (total_relays > MIN_RELAY_CONNECTIONS_TO_WARN &&
-          total_relay_connections >= 1.5*total_relays) {
+      total_relay_connections > max_tolerable_connections) {
     log_notice(LD_OR,
         "Your relay has a very large number of connections to other relays. "
         "Is your outbound address the same as your relay address? "