Advertise dirport if accountingmax is large enough

When we have an effective bandwidthrate configured so that we cannot
exceed our bandwidth limit in one accounting interval, don't disable
advertising the dirport. Implements ticket 2434.

changes/bug2434

@@ -0,0 +1,6 @@
+  o Minor features:
+    - Don't disable the DirPort when we cannot exceed our AccountingMax
+      limit during this interval because the effective bandwidthrate is
+      low enough. This is useful in a situation where AccountMax is only
+      used as an additional safeguard or to provide statistics.
+

src/or/hibernate.c

@@ -242,6 +242,14 @@ accounting_is_enabled(const or_options_t *options)
   return 0;
 }
 
+/** If accounting is enabled, return how long (in seconds) this
+ * interval lasts. */
+int
+accounting_get_interval_length(void)
+{
+  return (int)(interval_end_time - interval_start_time);
+}
+
 /** Called from main.c to tell us that <b>seconds</b> seconds have
  * passed, <b>n_read</b> bytes have been read, and <b>n_written</b>
  * bytes have been written. */
@@ -504,7 +512,6 @@ accounting_set_wakeup_time(void)
 {
   char digest[DIGEST_LEN];
   crypto_digest_env_t *d_env;
-  int time_in_interval;
   uint64_t time_to_exhaust_bw;
   int time_to_consider;
 
@@ -538,22 +545,21 @@ accounting_set_wakeup_time(void)
     interval_wakeup_time = interval_start_time;
 
     log_notice(LD_ACCT,
-           "Configured hibernation.  This interval begins at %s "
-           "and ends at %s.  We have no prior estimate for bandwidth, so "
+           "Configured hibernation. This interval begins at %s "
+           "and ends at %s. We have no prior estimate for bandwidth, so "
            "we will start out awake and hibernate when we exhaust our quota.",
            buf1, buf2);
     return;
   }
 
-  time_in_interval = (int)(interval_end_time - interval_start_time);
-
   time_to_exhaust_bw =
     (get_options()->AccountingMax/expected_bandwidth_usage)*60;
   if (time_to_exhaust_bw > INT_MAX) {
     time_to_exhaust_bw = INT_MAX;
     time_to_consider = 0;
   } else {
-    time_to_consider = time_in_interval - (int)time_to_exhaust_bw;
+    time_to_consider = accounting_get_interval_length() -
+                       (int)time_to_exhaust_bw;
   }
 
   if (time_to_consider<=0) {

src/or/hibernate.h

@@ -14,6 +14,7 @@
 
 int accounting_parse_options(const or_options_t *options, int validate_only);
 int accounting_is_enabled(const or_options_t *options);
+int accounting_get_interval_length(void);
 void configure_accounting(time_t now);
 void accounting_run_housekeeping(time_t now);
 void accounting_add_bytes(size_t n_read, size_t n_written, int seconds);

src/or/router.c

@@ -823,9 +823,26 @@ decide_to_advertise_dirport(const or_options_t *options, uint16_t dir_port)
    * make us choose not to publish. */
 
   if (accounting_is_enabled(options)) {
-    /* if we might potentially hibernate */
-    new_choice = 0;
-    reason = "AccountingMax enabled";
+    /* Don't spend bytes for directory traffic if we could end up hibernating,
+     * but allow DirPort otherwise. Some people set AccountingMax because
+     * they're confused or to get statistics. */
+    int interval_length = accounting_get_interval_length();
+    uint32_t effective_bw = get_effective_bwrate(options);
+    if (!interval_length) {
+      log_warn(LD_BUG, "An accounting interval is not allowed to be zero "
+                       "seconds long. Raising to 1.");
+      interval_length = 1;
+    }
+    log_info(LD_GENERAL, "Calculating whether to disable dirport: effective "
+                         "bwrate: %u, AccountingMax: "U64_FORMAT", "
+                         "accounting interval length %d", effective_bw,
+                         U64_PRINTF_ARG(options->AccountingMax),
+                         interval_length);
+    if (effective_bw >=
+        options->AccountingMax / interval_length) {
+      new_choice = 0;
+      reason = "AccountingMax enabled";
+    }
 #define MIN_BW_TO_ADVERTISE_DIRPORT 51200
   } else if (options->BandwidthRate < MIN_BW_TO_ADVERTISE_DIRPORT ||
              (options->RelayBandwidthRate > 0 &&