PredictedCircsRelevanceTime: limit how long we predict a port will be used

By default, after you've made a connection to port XYZ, we assume
you might still want to have an exit ready to connect to XYZ for one
hour. This patch lets you lower that interval.

Implements ticket 91

3 files changed, 16 insertions, 8 deletions

diff --git a/src/or/config.c b/src/or/config.c
index 5ce7bad493..460bf3ec41 100644
--- a/src/or/config.c
+++ b/src/or/config.c
@@ -314,6 +314,7 @@ static config_var_t option_vars_[] = {
   V(NATDListenAddress,           LINELIST, NULL),
   VPORT(NATDPort,                    LINELIST, NULL),
   V(Nickname,                    STRING,   NULL),
+  V(PredictedCircsRelevanceTime,  INTERVAL, "1 hour"),
   V(WarnUnsafeSocks,              BOOL,     "1"),
   OBSOLETE("NoPublish"),
   VAR("NodeFamily",              LINELIST, NodeFamilies,         NULL),
diff --git a/src/or/or.h b/src/or/or.h
index bd038f783c..5ca63e605b 100644
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -3673,6 +3673,9 @@ typedef struct {
                          * a new one? */
   int MaxCircuitDirtiness; /**< Never use circs that were first used more than
                                 this interval ago. */
+  int PredictedCircsRelevanceTime; /** How long after we've seen a request for
+                                    * a given port, do we want to continue
+                                    * to make connections to the same port?  */
   uint64_t BandwidthRate; /**< How much bandwidth, on average, are we willing
                            * to use in a second? */
   uint64_t BandwidthBurst; /**< How much bandwidth, at maximum, are we willing
diff --git a/src/or/rephist.c b/src/or/rephist.c
index 13404badf4..309e597551 100644
--- a/src/or/rephist.c
+++ b/src/or/rephist.c
@@ -1862,22 +1862,20 @@ rep_hist_note_used_port(time_t now, uint16_t port)
   add_predicted_port(now, port);
 }
 
-/** For this long after we've seen a request for a given port, assume that
- * we'll want to make connections to the same port in the future.  */
-#define PREDICTED_CIRCS_RELEVANCE_TIME (60*60)
-
 /** Return a newly allocated pointer to a list of uint16_t * for ports that
  * are likely to be asked for in the near future.
  */
 smartlist_t *
 rep_hist_get_predicted_ports(time_t now)
 {
+  int predicted_circs_relevance_time;
   smartlist_t *out = smartlist_new();
   tor_assert(predicted_ports_list);
+  predicted_circs_relevance_time = get_options()->PredictedCircsRelevanceTime;
 
   /* clean out obsolete entries */
   SMARTLIST_FOREACH_BEGIN(predicted_ports_list, predicted_port_t *, pp) {
-    if (pp->time + PREDICTED_CIRCS_RELEVANCE_TIME < now) {
+    if (pp->time + predicted_circs_relevance_time < now) {
       log_debug(LD_CIRC, "Expiring predicted port %d", pp->port);
 
       rephist_total_alloc -= sizeof(predicted_port_t);
@@ -1944,14 +1942,17 @@ int
 rep_hist_get_predicted_internal(time_t now, int *need_uptime,
                                 int *need_capacity)
 {
+  int predicted_circs_relevance_time;
+  predicted_circs_relevance_time = get_options()->PredictedCircsRelevanceTime;
+
   if (!predicted_internal_time) { /* initialize it */
     predicted_internal_time = now;
     predicted_internal_uptime_time = now;
     predicted_internal_capacity_time = now;
   }
-  if (predicted_internal_time + PREDICTED_CIRCS_RELEVANCE_TIME < now)
+  if (predicted_internal_time + predicted_circs_relevance_time < now)
     return 0; /* too long ago */
-  if (predicted_internal_uptime_time + PREDICTED_CIRCS_RELEVANCE_TIME >= now)
+  if (predicted_internal_uptime_time + predicted_circs_relevance_time >= now)
     *need_uptime = 1;
   // Always predict that we need capacity.
   *need_capacity = 1;
@@ -1963,8 +1964,11 @@ rep_hist_get_predicted_internal(time_t now, int *need_uptime,
 int
 any_predicted_circuits(time_t now)
 {
+  int predicted_circs_relevance_time;
+  predicted_circs_relevance_time = get_options()->PredictedCircsRelevanceTime;
+
   return smartlist_len(predicted_ports_list) ||
-         predicted_internal_time + PREDICTED_CIRCS_RELEVANCE_TIME >= now;
+         predicted_internal_time + predicted_circs_relevance_time >= now;
 }
 
 /** Return 1 if we have no need for circuits currently, else return 0. */