hs: Collect rendezvous circuit metrics

The total number of rendezvous circuit created and the number of established
ones which is a gauge that decreases to keep an updated counter.

Related to #40063
Signed-off-by: David Goulet <dgoulet@torproject.org>

src/feature/hs/hs_circuit.c

@@ -24,6 +24,7 @@
 #include "feature/hs/hs_circuitmap.h"
 #include "feature/hs/hs_client.h"
 #include "feature/hs/hs_ident.h"
+#include "feature/hs/hs_metrics.h"
 #include "feature/hs/hs_service.h"
 #include "feature/nodelist/describe.h"
 #include "feature/nodelist/nodelist.h"
@@ -429,6 +430,9 @@ launch_rendezvous_point_circuit,(const hs_service_t *service,
              safe_str_client(service->onion_address));
     goto end;
   }
+  /* Update metrics with this new rendezvous circuit launched. */
+  hs_metrics_new_rdv(&service->keys.identity_pk);
+
   log_info(LD_REND, "Rendezvous circuit launched to %s with cookie %s "
                     "for %s service %s",
            safe_str_client(extend_info_describe(info)),
@@ -1312,6 +1316,12 @@ hs_circ_cleanup_on_close(circuit_t *circ)
     cleanup_on_close_client_circ(circ);
   }
 
+  if (circuit_purpose_is_hs_service(circ->purpose)) {
+    if (circuit_is_hs_v3(circ)) {
+      hs_service_circuit_cleanup_on_close(circ);
+    }
+  }
+
   /* On close, we simply remove it from the circuit map. It can not be used
    * anymore. We keep this code path fast and lean. */
 

src/feature/hs/hs_metrics.h

@@ -43,4 +43,18 @@ void hs_metrics_update_by_service(const hs_metrics_key_t key,
 #define hs_metrics_app_read_bytes(i, port, n) \
   hs_metrics_update_by_ident(HS_METRICS_APP_READ_BYTES, (i), (port), (n))
 
+/** Newly established rendezvous. This is called as soon as the circuit purpose
+ * is REND_JOINED which is when the RENDEZVOUS2 cell is sent. */
+#define hs_metrics_new_established_rdv(s) \
+  hs_metrics_update_by_service(HS_METRICS_NUM_ESTABLISHED_RDV, (s), 0, 1)
+
+/** Established rendezvous closed. This is called when the circuit in
+ * REND_JOINED state is marked for close. */
+#define hs_metrics_close_established_rdv(i) \
+  hs_metrics_update_by_ident(HS_METRICS_NUM_ESTABLISHED_RDV, (i), 0, -1)
+
+/** New rendezvous circuit being launched. */
+#define hs_metrics_new_rdv(i) \
+  hs_metrics_update_by_ident(HS_METRICS_NUM_RDV, (i), 0, 1)
+
 #endif /* !defined(TOR_FEATURE_HS_HS_METRICS_H) */

src/feature/hs/hs_metrics_entry.c

@@ -41,6 +41,18 @@ const hs_metrics_entry_t base_metrics[] =
     .help = "Total number of bytes read from the application",
     .port_as_label = true,
   },
+  {
+    .key = HS_METRICS_NUM_ESTABLISHED_RDV,
+    .type = METRICS_TYPE_GAUGE,
+    .name = "hs_rdv_established_count",
+    .help = "Total number of established rendezvous circuit",
+  },
+  {
+    .key = HS_METRICS_NUM_RDV,
+    .type = METRICS_TYPE_COUNTER,
+    .name = "hs_rdv_num_total",
+    .help = "Total number of rendezvous circuit created",
+  },
 };
 
 /** Size of base_metrics array that is number of entries. */

src/feature/hs/hs_metrics_entry.h

@@ -21,6 +21,10 @@ typedef enum {
   HS_METRICS_APP_WRITE_BYTES = 1,
   /** Number of bytes read from application to onion service. */
   HS_METRICS_APP_READ_BYTES = 2,
+  /** Number of established rendezsvous. */
+  HS_METRICS_NUM_ESTABLISHED_RDV = 3,
+  /** Number of rendezsvous circuits created. */
+  HS_METRICS_NUM_RDV = 4,
 } hs_metrics_key_t;
 
 /** The metadata of an HS metrics. */

src/feature/hs/hs_service.c

@@ -3391,6 +3391,15 @@ service_rendezvous_circ_has_opened(origin_circuit_t *circ)
   /* If the cell can't be sent, the circuit will be closed within this
    * function. */
   hs_circ_service_rp_has_opened(service, circ);
+
+  /* Update metrics that we have an established rendezvous circuit. It is not
+   * entirely true until the client receives the RENDEZVOUS2 cell and starts
+   * sending but if that circuit collapes, we'll decrement the counter thus it
+   * will even out the metric. */
+  if (TO_CIRCUIT(circ)->purpose == CIRCUIT_PURPOSE_S_REND_JOINED) {
+    hs_metrics_new_established_rdv(service);
+  }
+
   goto done;
 
  err:
@@ -3579,6 +3588,26 @@ service_encode_descriptor(const hs_service_t *service,
 /* Public API */
 /* ========== */
 
+/** Called when a circuit was just cleaned up. This is done right before the
+ * circuit is marked for close. */
+void
+hs_service_circuit_cleanup_on_close(const circuit_t *circ)
+{
+  tor_assert(circ);
+  tor_assert(CIRCUIT_IS_ORIGIN(circ));
+
+  switch (circ->purpose) {
+  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. */
+    hs_metrics_close_established_rdv(
+      &CONST_TO_ORIGIN_CIRCUIT(circ)->hs_ident->identity_pk);
+    break;
+  default:
+    break;
+  }
+}
+
 /** This is called everytime the service map (v2 or v3) changes that is if an
  * element is added or removed. */
 void

src/feature/hs/hs_service.h

@@ -386,6 +386,7 @@ hs_circuit_id_protocol_t
 hs_service_exports_circuit_id(const ed25519_public_key_t *pk);
 
 void hs_service_dump_stats(int severity);
+void hs_service_circuit_cleanup_on_close(const circuit_t *circ);
 
 #ifdef HS_SERVICE_PRIVATE