Introduce v3 stat formatting functions.

They will be merged with the v2 ones in later commits.

src/feature/stats/rephist.c

@@ -2048,6 +2048,82 @@ rep_hist_hs_v2_stats_write(time_t now)
   return start_of_hs_v2_stats_interval + WRITE_STATS_INTERVAL;
 }
 
+/** Allocate and return a string containing hidden service stats that
+ *  are meant to be placed in the extra-info descriptor. */
+STATIC char *
+rep_hist_format_hs_v3_stats(time_t now)
+{
+  char t[ISO_TIME_LEN+1];
+  char *hs_v3_stats_string;
+  int64_t obfuscated_onions_seen, obfuscated_cells_seen;
+
+  uint64_t rounded_cells_seen
+    = round_uint64_to_next_multiple_of(hs_v3_stats->rp_v3_relay_cells_seen,
+                                       REND_CELLS_BIN_SIZE);
+  rounded_cells_seen = MIN(rounded_cells_seen, INT64_MAX);
+  obfuscated_cells_seen = add_laplace_noise((int64_t)rounded_cells_seen,
+                          crypto_rand_double(),
+                          REND_CELLS_DELTA_F, REND_CELLS_EPSILON);
+
+  uint64_t rounded_onions_seen =
+    round_uint64_to_next_multiple_of((size_t)digestmap_size(
+                                        hs_v3_stats->v3_onions_seen_this_period),
+                                     ONIONS_SEEN_BIN_SIZE);
+  rounded_onions_seen = MIN(rounded_onions_seen, INT64_MAX);
+  obfuscated_onions_seen = add_laplace_noise((int64_t)rounded_onions_seen,
+                           crypto_rand_double(), ONIONS_SEEN_DELTA_F,
+                           ONIONS_SEEN_EPSILON);
+
+  format_iso_time(t, now);
+  tor_asprintf(&hs_v3_stats_string, "hidserv-v3-stats-end %s (%d s)\n"
+               "hidserv-rend-v3-relayed-cells %"PRId64" delta_f=%d "
+                                           "epsilon=%.2f bin_size=%d\n"
+               "hidserv-dir-v3-onions-seen %"PRId64" delta_f=%d "
+                                           "epsilon=%.2f bin_size=%d\n",
+               t, (unsigned) (now - start_of_hs_v3_stats_interval),
+               (obfuscated_cells_seen), REND_CELLS_DELTA_F,
+               REND_CELLS_EPSILON, REND_CELLS_BIN_SIZE,
+               (obfuscated_onions_seen), ONIONS_SEEN_DELTA_F,
+               ONIONS_SEEN_EPSILON, ONIONS_SEEN_BIN_SIZE);
+
+  return hs_v3_stats_string;
+}
+
+/** If 24 hours have passed since the beginning of the current HS
+ * stats period, write buffer stats to $DATADIR/stats/hidserv-v3-stats
+ * (possibly overwriting an existing file) and reset counters.  Return
+ * when we would next want to write buffer stats or 0 if we never want to
+ * write. */
+time_t
+rep_hist_hs_v3_stats_write(time_t now)
+{
+  char *str = NULL;
+
+  if (!start_of_hs_v3_stats_interval) {
+    return 0; /* Not initialized. */
+  }
+
+  if (start_of_hs_v3_stats_interval + WRITE_STATS_INTERVAL > now) {
+    goto done; /* Not ready to write */
+  }
+
+  /* Generate history string. */
+  str = rep_hist_format_hs_v3_stats(now);
+
+  /* Reset HS history. */
+  rep_hist_reset_hs_v3_stats(now);
+
+  /* Try to write to disk. */
+  if (!check_or_create_data_subdir("stats")) {
+    write_to_data_subdir("stats", "hidserv-v3-stats", str,
+                         "hidden service stats");
+  }
+
+ done:
+  tor_free(str);
+  return start_of_hs_v3_stats_interval + WRITE_STATS_INTERVAL;
+}
+
 static uint64_t link_proto_count[MAX_LINK_PROTO+1][2];
 
 /** Note that we negotiated link protocol version <b>link_proto</b>, on