/* Copyright (c) 2021, The Tor Project, Inc. */
/* See LICENSE for licensing information */

/**
 * @file relay_metrics.c
 * @brief Relay metrics exposed through the MetricsPort
 **/

#define RELAY_METRICS_ENTRY_PRIVATE

#include "orconfig.h"

#include "core/or/or.h"
#include "core/or/relay.h"

#include "lib/malloc/malloc.h"
#include "lib/container/smartlist.h"
#include "lib/metrics/metrics_store.h"
#include "lib/log/util_bug.h"

#include "feature/relay/relay_metrics.h"
#include "feature/stats/rephist.h"

#include <event2/dns.h>

/** Declarations of each fill function for metrics defined in base_metrics. */
static void fill_dns_error_values(void);
static void fill_dns_query_values(void);
static void fill_global_bw_limit_values(void);
static void fill_socket_values(void);
static void fill_onionskins_values(void);
static void fill_oom_values(void);
static void fill_tcp_exhaustion_values(void);

/** The base metrics that is a static array of metrics added to the metrics
 * store.
 *
 * The key member MUST be also the index of the entry in the array. */
static const relay_metrics_entry_t base_metrics[] =
{
  {
    .key = RELAY_METRICS_NUM_OOM_BYTES,
    .type = METRICS_TYPE_COUNTER,
    .name = METRICS_NAME(relay_load_oom_bytes_total),
    .help = "Total number of bytes the OOM has freed by subsystem",
    .fill_fn = fill_oom_values,
  },
  {
    .key = RELAY_METRICS_NUM_ONIONSKINS,
    .type = METRICS_TYPE_COUNTER,
    .name = METRICS_NAME(relay_load_onionskins_total),
    .help = "Total number of onionskins handled",
    .fill_fn = fill_onionskins_values,
  },
  {
    .key = RELAY_METRICS_NUM_SOCKETS,
    .type = METRICS_TYPE_GAUGE,
    .name = METRICS_NAME(relay_load_socket_total),
    .help = "Total number of sockets",
    .fill_fn = fill_socket_values,
  },
  {
    .key = RELAY_METRICS_NUM_GLOBAL_RW_LIMIT,
    .type = METRICS_TYPE_COUNTER,
    .name = METRICS_NAME(relay_load_global_rate_limit_reached_total),
    .help = "Total number of global connection bucket limit reached",
    .fill_fn = fill_global_bw_limit_values,
  },
  {
    .key = RELAY_METRICS_NUM_DNS,
    .type = METRICS_TYPE_COUNTER,
    .name = METRICS_NAME(relay_exit_dns_query_total),
    .help = "Total number of DNS queries done by this relay",
    .fill_fn = fill_dns_query_values,
  },
  {
    .key = RELAY_METRICS_NUM_DNS_ERRORS,
    .type = METRICS_TYPE_COUNTER,
    .name = METRICS_NAME(relay_exit_dns_error_total),
    .help = "Total number of DNS errors encountered by this relay",
    .fill_fn = fill_dns_error_values,
  },
  {
    .key = RELAY_METRICS_NUM_TCP_EXHAUSTION,
    .type = METRICS_TYPE_COUNTER,
    .name = METRICS_NAME(relay_load_tcp_exhaustion_total),
    .help = "Total number of times we ran out of TCP ports",
    .fill_fn = fill_tcp_exhaustion_values,
  },
};
static const size_t num_base_metrics = ARRAY_LENGTH(base_metrics);

/** The only and single store of all the relay metrics. */
static metrics_store_t *the_store;

/** Helper function to convert an handshake type into a string. */
static inline const char *
handshake_type_to_str(const uint16_t type)
{
  switch (type) {
    case ONION_HANDSHAKE_TYPE_TAP:
      return "tap";
    case ONION_HANDSHAKE_TYPE_FAST:
      return "fast";
    case ONION_HANDSHAKE_TYPE_NTOR:
      return "ntor";
    default:
      // LCOV_EXCL_START
      tor_assert_unreached();
      // LCOV_EXCL_STOP
  }
}

/** Fill function for the RELAY_METRICS_NUM_DNS metrics. */
static void
fill_tcp_exhaustion_values(void)
{
  metrics_store_entry_t *sentry;
  const relay_metrics_entry_t *rentry =
    &base_metrics[RELAY_METRICS_NUM_TCP_EXHAUSTION];

  sentry = metrics_store_add(the_store, rentry->type, rentry->name,
                             rentry->help);
  metrics_store_entry_update(sentry, rep_hist_get_n_tcp_exhaustion());
}

/** Helper array containing mapping for the name of the different DNS records
 * and their corresponding libevent values. */
static struct dns_type {
  const char *name;
  uint8_t type;
} dns_types[] = {
  { .name = "A",    .type = DNS_IPv4_A     },
  { .name = "PTR",  .type = DNS_PTR        },
  { .name = "AAAA", .type = DNS_IPv6_AAAA  },
};
static const size_t num_dns_types = ARRAY_LENGTH(dns_types);

/** Fill function for the RELAY_METRICS_NUM_DNS_ERRORS metrics. */
static void
fill_dns_error_values(void)
{
  metrics_store_entry_t *sentry;
  const relay_metrics_entry_t *rentry =
    &base_metrics[RELAY_METRICS_NUM_DNS_ERRORS];

  /* Helper array to map libeven DNS errors to their names and so we can
   * iterate over this array to add all metrics. */
  static struct dns_error {
    const char *name;
    uint8_t key;
  } errors[] = {
    { .name = "success",      .key = DNS_ERR_NONE         },
    { .name = "format",       .key = DNS_ERR_FORMAT       },
    { .name = "serverfailed", .key = DNS_ERR_SERVERFAILED },
    { .name = "notexist",     .key = DNS_ERR_NOTEXIST     },
    { .name = "notimpl",      .key = DNS_ERR_NOTIMPL      },
    { .name = "refused",      .key = DNS_ERR_REFUSED      },
    { .name = "truncated",    .key = DNS_ERR_TRUNCATED    },
    { .name = "unknown",      .key = DNS_ERR_UNKNOWN      },
    { .name = "timeout",      .key = DNS_ERR_TIMEOUT      },
    { .name = "shutdown",     .key = DNS_ERR_SHUTDOWN     },
    { .name = "cancel",       .key = DNS_ERR_CANCEL       },
    { .name = "nodata",       .key = DNS_ERR_NODATA       },
  };
  static const size_t num_errors = ARRAY_LENGTH(errors);

  for (size_t i = 0; i < num_dns_types; i++) {
    /* Dup the label because metrics_format_label() returns a pointer to a
     * string on the stack and we need that label for all metrics. */
    char *record_label =
      tor_strdup(metrics_format_label("record", dns_types[i].name));

    for (size_t j = 0; j < num_errors; j++) {
      sentry = metrics_store_add(the_store, rentry->type, rentry->name,
                                 rentry->help);
      metrics_store_entry_add_label(sentry, record_label);
      metrics_store_entry_add_label(sentry,
              metrics_format_label("reason", errors[j].name));
      metrics_store_entry_update(sentry,
              rep_hist_get_n_dns_error(dns_types[i].type, errors[j].key));
    }
    tor_free(record_label);
  }
}

/** Fill function for the RELAY_METRICS_NUM_DNS metrics. */
static void
fill_dns_query_values(void)
{
  metrics_store_entry_t *sentry;
  const relay_metrics_entry_t *rentry =
    &base_metrics[RELAY_METRICS_NUM_DNS];

  for (size_t i = 0; i < num_dns_types; i++) {
    /* Dup the label because metrics_format_label() returns a pointer to a
     * string on the stack and we need that label for all metrics. */
    char *record_label =
      tor_strdup(metrics_format_label("record", dns_types[i].name));
    sentry = metrics_store_add(the_store, rentry->type, rentry->name,
                               rentry->help);
    metrics_store_entry_add_label(sentry, record_label);
    metrics_store_entry_update(sentry,
                               rep_hist_get_n_dns_request(dns_types[i].type));
    tor_free(record_label);
  }
}

/** Fill function for the RELAY_METRICS_NUM_GLOBAL_RW_LIMIT metrics. */
static void
fill_global_bw_limit_values(void)
{
  metrics_store_entry_t *sentry;
  const relay_metrics_entry_t *rentry =
    &base_metrics[RELAY_METRICS_NUM_GLOBAL_RW_LIMIT];

  sentry = metrics_store_add(the_store, rentry->type, rentry->name,
                             rentry->help);
  metrics_store_entry_add_label(sentry,
                                metrics_format_label("side", "read"));
  metrics_store_entry_update(sentry, rep_hist_get_n_read_limit_reached());

  sentry = metrics_store_add(the_store, rentry->type, rentry->name,
                             rentry->help);
  metrics_store_entry_add_label(sentry,
                                metrics_format_label("side", "write"));
  metrics_store_entry_update(sentry, rep_hist_get_n_write_limit_reached());
}

/** Fill function for the RELAY_METRICS_NUM_SOCKETS metrics. */
static void
fill_socket_values(void)
{
  metrics_store_entry_t *sentry;
  const relay_metrics_entry_t *rentry =
    &base_metrics[RELAY_METRICS_NUM_SOCKETS];

  sentry = metrics_store_add(the_store, rentry->type, rentry->name,
                             rentry->help);
  metrics_store_entry_add_label(sentry,
                                metrics_format_label("state", "opened"));
  metrics_store_entry_update(sentry, get_n_open_sockets());

  sentry = metrics_store_add(the_store, rentry->type, rentry->name,
                             rentry->help);
  metrics_store_entry_update(sentry, get_max_sockets());
}

/** Fill function for the RELAY_METRICS_NUM_ONIONSKINS metrics. */
static void
fill_onionskins_values(void)
{
  metrics_store_entry_t *sentry;
  const relay_metrics_entry_t *rentry =
    &base_metrics[RELAY_METRICS_NUM_ONIONSKINS];

  for (uint16_t t = 0; t <= MAX_ONION_HANDSHAKE_TYPE; t++) {
    /* Dup the label because metrics_format_label() returns a pointer to a
     * string on the stack and we need that label for all metrics. */
    char *type_label =
      tor_strdup(metrics_format_label("type", handshake_type_to_str(t)));
    sentry = metrics_store_add(the_store, rentry->type, rentry->name,
                               rentry->help);
    metrics_store_entry_add_label(sentry, type_label);
    metrics_store_entry_add_label(sentry,
                        metrics_format_label("action", "processed"));
    metrics_store_entry_update(sentry,
                               rep_hist_get_circuit_handshake_assigned(t));

    sentry = metrics_store_add(the_store, rentry->type, rentry->name,
                               rentry->help);
    metrics_store_entry_add_label(sentry, type_label);
    metrics_store_entry_add_label(sentry,
                        metrics_format_label("action", "dropped"));
    metrics_store_entry_update(sentry,
                               rep_hist_get_circuit_handshake_dropped(t));
    tor_free(type_label);
  }
}

/** Fill function for the RELAY_METRICS_NUM_OOM_BYTES metrics. */
static void
fill_oom_values(void)
{
  metrics_store_entry_t *sentry;
  const relay_metrics_entry_t *rentry =
    &base_metrics[RELAY_METRICS_NUM_OOM_BYTES];

  sentry = metrics_store_add(the_store, rentry->type, rentry->name,
                             rentry->help);
  metrics_store_entry_add_label(sentry, "subsys=cell");
  metrics_store_entry_update(sentry, oom_stats_n_bytes_removed_cell);

  sentry = metrics_store_add(the_store, rentry->type, rentry->name,
                             rentry->help);
  metrics_store_entry_add_label(sentry, "subsys=dns");
  metrics_store_entry_update(sentry, oom_stats_n_bytes_removed_dns);

  sentry = metrics_store_add(the_store, rentry->type, rentry->name,
                             rentry->help);
  metrics_store_entry_add_label(sentry, "subsys=geoip");
  metrics_store_entry_update(sentry, oom_stats_n_bytes_removed_geoip);

  sentry = metrics_store_add(the_store, rentry->type, rentry->name,
                             rentry->help);
  metrics_store_entry_add_label(sentry, "subsys=hsdir");
  metrics_store_entry_update(sentry, oom_stats_n_bytes_removed_hsdir);
}

/** Reset the global store and fill it with all the metrics from base_metrics
 * and their associated values.
 *
 * To pull this off, every metrics has a "fill" function that is called and in
 * charge of adding the metrics to the store, appropriate labels and finally
 * updating the value to report. */
static void
fill_store(void)
{
  /* Reset the current store, we are about to fill it with all the things. */
  metrics_store_reset(the_store);

  /* Call the fill function for each metrics. */
  for (size_t i = 0; i < num_base_metrics; i++) {
    if (BUG(!base_metrics[i].fill_fn)) {
      continue;
    }
    base_metrics[i].fill_fn();
  }
}

/** Return a list of all the relay metrics stores. This is the
 * function attached to the .get_metrics() member of the subsys_t. */
const smartlist_t *
relay_metrics_get_stores(void)
{
  /* We can't have the caller to free the returned list so keep it static,
   * simply update it. */
  static smartlist_t *stores_list = NULL;

  /* We dynamically fill the store with all the metrics upon a request. The
   * reason for this is because the exposed metrics of a relay are often
   * internal counters in the fast path and thus we fetch the value when a
   * metrics port request arrives instead of keeping a local metrics store of
   * those values. */
  fill_store();

  if (!stores_list) {
    stores_list = smartlist_new();
    smartlist_add(stores_list, the_store);
  }

  return stores_list;
}

/** Initialize the relay metrics. */
void
relay_metrics_init(void)
{
  if (BUG(the_store)) {
    return;
  }
  the_store = metrics_store_new();
}

/** Free the relay metrics. */
void
relay_metrics_free(void)
{
  if (!the_store) {
    return;
  }
  /* NULL is set with this call. */
  metrics_store_free(the_store);
}