hs: Collect introduction circuit metrics

Tracks the total number of established introduction circuit.

Related to #40063

Signed-off-by: David Goulet <dgoulet@torproject.org>

src/feature/hs/hs_metrics.h

@@ -57,4 +57,14 @@ void hs_metrics_update_by_service(const hs_metrics_key_t key,
 #define hs_metrics_new_rdv(i) \
   hs_metrics_update_by_ident(HS_METRICS_NUM_RDV, (i), 0, 1)
 
+/** New introduction circuit has been established. This is called when the
+ * INTRO_ESTABLISHED has been received by the service. */
+#define hs_metrics_new_established_intro(s) \
+  hs_metrics_update_by_service(HS_METRICS_NUM_ESTABLISHED_INTRO, (s), 0, 1)
+
+/** Established introduction circuit closes. This is called when
+ * INTRO_ESTABLISHED circuit is marked for close. */
+#define hs_metrics_close_established_intro(i) \
+  hs_metrics_update_by_ident(HS_METRICS_NUM_ESTABLISHED_INTRO, (i), 0, 1)
+
 #endif /* !defined(TOR_FEATURE_HS_HS_METRICS_H) */

src/feature/hs/hs_metrics_entry.c

@@ -53,6 +53,12 @@ const hs_metrics_entry_t base_metrics[] =
     .name = "hs_rdv_num_total",
     .help = "Total number of rendezvous circuit created",
   },
+  {
+    .key = HS_METRICS_NUM_ESTABLISHED_INTRO,
+    .type = METRICS_TYPE_GAUGE,
+    .name = "hs_intro_established_count",
+    .help = "Total number of established introduction circuit",
+  },
 };
 
 /** Size of base_metrics array that is number of entries. */

src/feature/hs/hs_metrics_entry.h

@@ -25,6 +25,8 @@ typedef enum {
   HS_METRICS_NUM_ESTABLISHED_RDV = 3,
   /** Number of rendezsvous circuits created. */
   HS_METRICS_NUM_RDV = 4,
+  /** Number of established introducton points. */
+  HS_METRICS_NUM_ESTABLISHED_INTRO = 5,
 } hs_metrics_key_t;
 
 /** The metadata of an HS metrics. */

src/feature/hs/hs_service.c

@@ -3451,6 +3451,9 @@ service_handle_intro_established(origin_circuit_t *circ,
     goto err;
   }
 
+  /* Update metrics. */
+  hs_metrics_new_established_intro(service);
+
   log_info(LD_REND, "Successfully received an INTRO_ESTABLISHED cell "
                     "on circuit %u for service %s",
            TO_CIRCUIT(circ)->n_circ_id,
@@ -3597,6 +3600,12 @@ hs_service_circuit_cleanup_on_close(const circuit_t *circ)
   tor_assert(CIRCUIT_IS_ORIGIN(circ));
 
   switch (circ->purpose) {
+  case CIRCUIT_PURPOSE_S_INTRO:
+    /* About to close an established introduction circuit. Update the metrics
+     * to reflect how many we have at the moment. */
+    hs_metrics_close_established_intro(
+      &CONST_TO_ORIGIN_CIRCUIT(circ)->hs_ident->identity_pk);
+    break;
   case CIRCUIT_PURPOSE_S_REND_JOINED:
     /* About to close an established rendezvous circuit. Update the metrics to
      * reflect how many we have at the moment. */