tor/src/or/dirserv.c

/* Copyright 2001-2004 Roger Dingledine.
 * Copyright 2004-2007 Roger Dingledine, Nick Mathewson. */
/* See LICENSE for licensing information */
/* $Id$ */
const char dirserv_c_id[] =
  "$Id$";

#include "or.h"

/**
 * \file dirserv.c
 * \brief Directory server core implementation. Manages directory
 * contents and generates directories.
 **/

/** How far in the future do we allow a router to get? (seconds) */
#define ROUTER_ALLOW_SKEW (60*60*12)
/** How many seconds do we wait before regenerating the directory? */
#define DIR_REGEN_SLACK_TIME 30
/** If we're a cache, keep this many networkstatuses around from non-trusted
 * directory authorities. */
#define MAX_UNTRUSTED_NETWORKSTATUSES 16

/** If a v1 directory is older than this, discard it. */
#define MAX_V1_DIRECTORY_AGE (30*24*60*60)
/** If a v1 running-routers is older than this, discard it. */
#define MAX_V1_RR_AGE (7*24*60*60)

/** Do we need to regenerate the directory when someone asks for it? */
static int the_directory_is_dirty = 1;
static int runningrouters_is_dirty = 1;
static int the_v2_networkstatus_is_dirty = 1;

static void directory_remove_invalid(void);
static cached_dir_t *dirserv_regenerate_directory(void);
static char *format_versions_list(config_line_t *ln);
/* Should be static; exposed for testing */
struct authdir_config_t;
int add_fingerprint_to_dir(const char *nickname, const char *fp,
                           struct authdir_config_t *list);
static uint32_t dirserv_router_get_status(const routerinfo_t *router,
                                          const char **msg);
static uint32_t
dirserv_get_status_impl(const char *fp, const char *nickname,
                        const char *address,
                        uint32_t addr, uint16_t or_port,
                        const char *platform, const char *contact,
                        const char **msg, int should_log);
static int dirserv_thinks_router_is_reachable(routerinfo_t *router,
                                              time_t now);
static void clear_cached_dir(cached_dir_t *d);

/************** Fingerprint handling code ************/

#define FP_NAMED   1  /**< Listed in fingerprint file. */
#define FP_INVALID 2  /**< Believed invalid. */
#define FP_REJECT  4  /**< We will not publish this router. */
#define FP_BADEXIT 8 /**< We'll tell clients not to use this as an exit. */

/** Encapsulate a nickname and an FP_* status; target of status_by_digest
 * map. */
typedef struct router_status_t {
  char nickname[MAX_NICKNAME_LEN+1];
  uint32_t status;
} router_status_t;

/** List of nickname-\>identity fingerprint mappings for all the routers
 * that we name.  Used to prevent router impersonation. */
typedef struct authdir_config_t {
  strmap_t *fp_by_name; /**< Map from lc nickname to fingerprint. */
  digestmap_t *status_by_digest; /**< Map from digest to router_status_t. */
} authdir_config_t;

/** Should be static; exposed for testing. */
authdir_config_t *fingerprint_list = NULL;

/** Allocate and return a new, empty, authdir_config_t. */
static authdir_config_t *
authdir_config_new(void)
{
  authdir_config_t *list = tor_malloc_zero(sizeof(authdir_config_t));
  list->fp_by_name = strmap_new();
  list->status_by_digest = digestmap_new();
  return list;
}

/** Add the fingerprint <b>fp</b> for the nickname <b>nickname</b> to
 * the smartlist of fingerprint_entry_t's <b>list</b>. Return 0 if it's
 * new, or 1 if we replaced the old value.
 */
int /* Should be static; exposed for testing */
add_fingerprint_to_dir(const char *nickname, const char *fp,
                       authdir_config_t *list)
{
  char *fingerprint;
  char d[DIGEST_LEN];
  router_status_t *status;
  tor_assert(nickname);
  tor_assert(fp);
  tor_assert(list);

  fingerprint = tor_strdup(fp);
  tor_strstrip(fingerprint, " ");
  if (base16_decode(d, DIGEST_LEN, fingerprint, strlen(fingerprint))) {
    log_warn(LD_DIRSERV, "Couldn't decode fingerprint \"%s\"",
             escaped(fp));
    tor_free(fingerprint);
    return 0;
  }

  if (!strcasecmp(nickname, UNNAMED_ROUTER_NICKNAME)) {
    log_warn(LD_DIRSERV, "Tried to add a mapping for reserved nickname %s",
             UNNAMED_ROUTER_NICKNAME);
    tor_free(fingerprint);
    return 0;
  }

  status = digestmap_get(list->status_by_digest, d);
  if (!status) {
    status = tor_malloc_zero(sizeof(router_status_t));
    digestmap_set(list->status_by_digest, d, status);
  }

  if (nickname[0] != '!') {
    char *old_fp = strmap_get_lc(list->fp_by_name, nickname);
    if (old_fp && !strcasecmp(fingerprint, old_fp)) {
      tor_free(fingerprint);
    } else {
      tor_free(old_fp);
      strmap_set_lc(list->fp_by_name, nickname, fingerprint);
    }
    status->status |= FP_NAMED;
    strlcpy(status->nickname, nickname, sizeof(status->nickname));
  } else {
    tor_free(fingerprint);
    if (!strcasecmp(nickname, "!reject")) {
      status->status |= FP_REJECT;
    } else if (!strcasecmp(nickname, "!invalid")) {
      status->status |= FP_INVALID;
    } else if (!strcasecmp(nickname, "!badexit")) {
      status->status |= FP_BADEXIT;
    }
  }
  return 0;
}

/** Add the nickname and fingerprint for this OR to the
 * global list of recognized identity key fingerprints. */
int
dirserv_add_own_fingerprint(const char *nickname, crypto_pk_env_t *pk)
{
  char fp[FINGERPRINT_LEN+1];
  if (crypto_pk_get_fingerprint(pk, fp, 0)<0) {
    log_err(LD_BUG, "Error computing fingerprint");
    return -1;
  }
  if (!fingerprint_list)
    fingerprint_list = authdir_config_new();
  add_fingerprint_to_dir(nickname, fp, fingerprint_list);
  return 0;
}

/** Load the nickname-\>fingerprint mappings stored in the approved-routers
 * file.  The file format is line-based, with each non-blank holding one
 * nickname, some space, and a fingerprint for that nickname.  On success,
 * replace the current fingerprint list with the new list and return 0.  On
 * failure, leave the current fingerprint list untouched, and
 * return -1. */
int
dirserv_load_fingerprint_file(void)
{
  char fname[512];
  char *cf;
  char *nickname, *fingerprint;
  authdir_config_t *fingerprint_list_new;
  int result;
  config_line_t *front=NULL, *list;
  or_options_t *options = get_options();

  tor_snprintf(fname, sizeof(fname),
               "%s/approved-routers", options->DataDirectory);
  log_info(LD_GENERAL,
           "Reloading approved fingerprints from \"%s\"...", fname);

  cf = read_file_to_str(fname, 0, NULL);
  if (!cf) {
    if (options->NamingAuthoritativeDir) {
      log_warn(LD_FS, "Cannot open fingerprint file '%s'. Failing.", fname);
      return -1;
    } else {
      log_info(LD_FS, "Cannot open fingerprint file '%s'. Returning.", fname);
      return 0;
    }
  }
  result = config_get_lines(cf, &front);
  tor_free(cf);
  if (result < 0) {
    log_warn(LD_CONFIG, "Error reading from fingerprint file");
    return -1;
  }

  fingerprint_list_new = authdir_config_new();

  for (list=front; list; list=list->next) {
    nickname = list->key; fingerprint = list->value;
    if (strlen(nickname) > MAX_NICKNAME_LEN) {
      log_notice(LD_CONFIG,
                 "Nickname '%s' too long in fingerprint file. Skipping.",
                 nickname);
      continue;
    }
    if (!is_legal_nickname(nickname) &&
        strcasecmp(nickname, "!reject") &&
        strcasecmp(nickname, "!invalid") &&
        strcasecmp(nickname, "!badexit")) {
      log_notice(LD_CONFIG,
                 "Invalid nickname '%s' in fingerprint file. Skipping.",
                 nickname);
      continue;
    }
    if (strlen(fingerprint) != FINGERPRINT_LEN ||
        !crypto_pk_check_fingerprint_syntax(fingerprint)) {
      log_notice(LD_CONFIG,
                 "Invalid fingerprint (nickname '%s', "
                 "fingerprint %s). Skipping.",
                 nickname, fingerprint);
      continue;
    }
    if (0==strcasecmp(nickname, DEFAULT_CLIENT_NICKNAME)) {
      /* If you approved an OR called "client", then clients who use
       * the default nickname could all be rejected.  That's no good. */
      log_notice(LD_CONFIG,
                 "Authorizing a nickname '%s' would break "
                 "many clients; skipping.",
                 DEFAULT_CLIENT_NICKNAME);
      continue;
    }
    if (0==strcasecmp(nickname, DEFAULT_CLIENT_NICKNAME)) {
      /* If you approved an OR called "client", then clients who use
       * the default nickname could all be rejected.  That's no good. */
      log_notice(LD_CONFIG,
                 "Authorizing a nickname '%s' would break "
                 "many clients; skipping.",
                 DEFAULT_CLIENT_NICKNAME);
      continue;
    }
    if (0==strcasecmp(nickname, UNNAMED_ROUTER_NICKNAME)) {
      /* If you approved an OR called "unnamed", then clients will be
       * confused. */
      log_notice(LD_CONFIG,
                 "Authorizing a nickname '%s' is not allowed; skipping.",
                 UNNAMED_ROUTER_NICKNAME);
      continue;
    }
    if (add_fingerprint_to_dir(nickname, fingerprint, fingerprint_list_new)
        != 0)
      log_notice(LD_CONFIG, "Duplicate nickname '%s'.", nickname);
  }

  config_free_lines(front);
  dirserv_free_fingerprint_list();
  fingerprint_list = fingerprint_list_new;
  /* Delete any routers whose fingerprints we no longer recognize */
  directory_remove_invalid();
  return 0;
}

/** Check whether <b>router</b> has a nickname/identity key combination that
 * we recognize from the fingerprint list, or an IP we automatically act on
 * according to our configuration.  Return the appropriate router status.
 *
 * If the status is 'FP_REJECT' and <b>msg</b> is provided, set
 * *<b>msg</b> to an explanation of why. */
static uint32_t
dirserv_router_get_status(const routerinfo_t *router, const char **msg)
{
  char d[DIGEST_LEN];

  if (crypto_pk_get_digest(router->identity_pkey, d)) {
    log_warn(LD_BUG,"Error computing fingerprint");
    if (msg)
      *msg = "Bug: Error computing fingerprint";
    return FP_REJECT;
  }

  return dirserv_get_status_impl(d, router->nickname,
                                 router->address,
                                 router->addr, router->or_port,
                                 router->platform, router->contact_info,
                                 msg, 1);
}

/** Return true if there is no point in downloading the router described by
 * <b>rs</b> because this directory would reject it. */
int
dirserv_would_reject_router(routerstatus_t *rs)
{
  uint32_t res;

  res = dirserv_get_status_impl(rs->identity_digest, rs->nickname,
                                "", /* address is only used in logs */
                                rs->addr, rs->or_port,
                                NULL, NULL,
                                NULL, 0);

  return (res & FP_REJECT) != 0;
}

/** Helper: As dirserv_get_router_status, but takes the router fingerprint
 * (hex, no spaces), nickname, address (used for logging only), IP address, OR
 * port, platform (logging only) and contact info (logging only) as arguments.
 *
 * If should_log is false, do not log messages.  (There's not much point in
 * logging that we're rejecting servers we'll not download.)
 */
static uint32_t
dirserv_get_status_impl(const char *id_digest, const char *nickname,
                        const char *address,
                        uint32_t addr, uint16_t or_port,
                        const char *platform, const char *contact,
                        const char **msg, int should_log)
{
  char fp[HEX_DIGEST_LEN+1];
  int reject_unlisted = get_options()->AuthDirRejectUnlisted;
  uint32_t result = 0;
  router_status_t *status_by_digest;
  char *fp_by_name;
  if (!fingerprint_list)
    fingerprint_list = authdir_config_new();

  base16_encode(fp, sizeof(fp), id_digest, DIGEST_LEN);

  if (should_log)
    log_debug(LD_DIRSERV, "%d fingerprints, %d digests known.",
              strmap_size(fingerprint_list->fp_by_name),
              digestmap_size(fingerprint_list->status_by_digest));

  if ((fp_by_name =
       strmap_get_lc(fingerprint_list->fp_by_name, nickname))) {
    if (!strcasecmp(fp, fp_by_name)) {
      result |= FP_NAMED;
      if (should_log)
        log_debug(LD_DIRSERV,"Good fingerprint for '%s'",nickname);
    } else {
      if (should_log) {
        char *esc_contact = esc_for_log(contact);
        log_warn(LD_DIRSERV,
                 "Mismatched fingerprint for '%s': expected '%s' got '%s'. "
                 "ContactInfo '%s', platform '%s'.)",
                 nickname, fp_by_name, fp,
                 esc_contact,
                 platform ? escaped(platform) : "");
        tor_free(esc_contact);
      }
      if (msg)
        *msg = "Rejected: There is already a named server with this nickname "
          "and a different fingerprint.";
      return FP_REJECT; /* Wrong fingerprint. */
    }
  }
  status_by_digest = digestmap_get(fingerprint_list->status_by_digest,
                                   id_digest);
  if (status_by_digest)
    result |= (status_by_digest->status & ~FP_NAMED);

  if (result & FP_REJECT) {
    if (msg)
      *msg = "Fingerprint is marked rejected";
    return FP_REJECT;
  } else if (result & FP_INVALID) {
    if (msg)
      *msg = "Fingerprint is marked invalid";
  }

  if (authdir_policy_badexit_address(addr, or_port)) {
    if (should_log)
      log_info(LD_DIRSERV, "Marking '%s' as bad exit because of address '%s'",
               nickname, address);
    result |= FP_BADEXIT;
  }

  if (!(result & FP_NAMED)) {
    if (!authdir_policy_permits_address(addr, or_port)) {
      if (should_log)
        log_info(LD_DIRSERV, "Rejecting '%s' because of address '%s'",
                 nickname, address);
      if (msg)
        *msg = "Authdir is rejecting routers in this range.";
      return FP_REJECT;
    }
    if (!authdir_policy_valid_address(addr, or_port)) {
      if (should_log)
        log_info(LD_DIRSERV, "Not marking '%s' valid because of address '%s'",
                 nickname, address);
      result |= FP_INVALID;
    }
    if (reject_unlisted) {
      if (msg)
        *msg = "Authdir rejects unknown routers.";
      return FP_REJECT;
    }
    /* 0.1.0.2-rc was the first version that did enough self-testing that
     * we're willing to take its word about whether it's running. */
    if (platform && !tor_version_as_new_as(platform,"0.1.0.2-rc"))
      result |= FP_INVALID;
  }

  return result;
}

/** If we are an authoritative dirserver, and the list of approved
 * servers contains one whose identity key digest is <b>digest</b>,
 * return that router's nickname.  Otherwise return NULL. */
const char *
dirserv_get_nickname_by_digest(const char *digest)
{
  router_status_t *status;
  if (!fingerprint_list)
    return NULL;
  tor_assert(digest);

  status = digestmap_get(fingerprint_list->status_by_digest, digest);
  return status ? status->nickname : NULL;
}

/** Clear the current fingerprint list. */
void
dirserv_free_fingerprint_list(void)
{
  if (!fingerprint_list)
    return;

  strmap_free(fingerprint_list->fp_by_name, _tor_free);
  digestmap_free(fingerprint_list->status_by_digest, _tor_free);
  tor_free(fingerprint_list);
}

/*
 *    Descriptor list
 */

/** Return -1 if <b>ri</b> has a private or otherwise bad address,
 * unless we're configured to not care. Return 0 if all ok. */
static int
dirserv_router_has_valid_address(routerinfo_t *ri)
{
  struct in_addr iaddr;
  if (get_options()->DirAllowPrivateAddresses)
    return 0; /* whatever it is, we're fine with it */
  if (!tor_inet_aton(ri->address, &iaddr)) {
    log_info(LD_DIRSERV,"Router '%s' published non-IP address '%s'. Refusing.",
             ri->nickname, ri->address);
    return -1;
  }
  if (is_internal_IP(ntohl(iaddr.s_addr), 0)) {
    log_info(LD_DIRSERV,
             "Router '%s' published internal IP address '%s'. Refusing.",
             ri->nickname, ri->address);
    return -1; /* it's a private IP, we should reject it */
  }
  return 0;
}

/** Check whether we, as a directory server, want to accept <b>ri</b>.  If so,
 * set its is_valid,named,running fields and return 0.  Otherwise, return -1.
 *
 * If the router is rejected, set *<b>msg</b> to an explanation of why.
 *
 * If <b>complain</b> then explain at log-level 'notice' why we refused
 * a descriptor; else explain at log-level 'info'.
 */
int
authdir_wants_to_reject_router(routerinfo_t *ri, const char **msg,
                               int complain)
{
  /* Okay.  Now check whether the fingerprint is recognized. */
  uint32_t status = dirserv_router_get_status(ri, msg);
  time_t now;
  int severity = complain ? LOG_NOTICE : LOG_INFO;
  tor_assert(msg);
  if (status & FP_REJECT)
    return -1; /* msg is already set. */

  /* Is there too much clock skew? */
  now = time(NULL);
  if (ri->cache_info.published_on > now+ROUTER_ALLOW_SKEW) {
    log_fn(severity, LD_DIRSERV, "Publication time for nickname '%s' is too "
           "far (%d minutes) in the future; possible clock skew. Not adding "
           "(%s)",
           ri->nickname, (int)((ri->cache_info.published_on-now)/60),
           esc_router_info(ri));
    *msg = "Rejected: Your clock is set too far in the future, or your "
      "timezone is not correct.";
    return -1;
  }
  if (ri->cache_info.published_on < now-ROUTER_MAX_AGE_TO_PUBLISH) {
    log_fn(severity, LD_DIRSERV,
           "Publication time for router with nickname '%s' is too far "
           "(%d minutes) in the past. Not adding (%s)",
           ri->nickname, (int)((now-ri->cache_info.published_on)/60),
           esc_router_info(ri));
    *msg = "Rejected: Server is expired, or your clock is too far in the past,"
      " or your timezone is not correct.";
    return -1;
  }
  if (dirserv_router_has_valid_address(ri) < 0) {
    log_fn(severity, LD_DIRSERV,
           "Router with nickname '%s' has invalid address '%s'. "
           "Not adding (%s).",
           ri->nickname, ri->address,
           esc_router_info(ri));
    *msg = "Rejected: Address is not an IP, or IP is a private address.";
    return -1;
  }
  /* Okay, looks like we're willing to accept this one. */
  ri->is_named = (status & FP_NAMED) ? 1 : 0;
  ri->is_valid = (status & FP_INVALID) ? 0 : 1;
  ri->is_bad_exit = (status & FP_BADEXIT) ? 1 : 0;

  return 0;
}

/** Parse the server descriptor at <b>desc</b> and maybe insert it into
 * the list of server descriptors. Set *<b>msg</b> to a message that
 * should be passed back to the origin of this descriptor.
 *
 * Return 2 if descriptor is well-formed and accepted;
 *  1 if well-formed and accepted but origin should hear *msg;
 *  0 if well-formed but redundant with one we already have;
 * -1 if it looks vaguely like a router descriptor but rejected;
 * -2 if we can't find a router descriptor in <b>desc</b>.
 */
int
dirserv_add_descriptor(const char *desc, const char **msg)
{
  int r;
  routerinfo_t *ri = NULL, *ri_old = NULL;
  tor_assert(msg);
  *msg = NULL;

  /* Check: is the descriptor syntactically valid? */
  ri = router_parse_entry_from_string(desc, NULL, 1);
  if (!ri) {
    log_warn(LD_DIRSERV, "Couldn't parse uploaded server descriptor");
    *msg = "Rejected: Couldn't parse server descriptor.";
    return -2;
  }
  /* Check whether this descriptor is semantically identical to the last one
   * from this server.  (We do this here and not in router_add_to_routerlist
   * because we want to be able to accept the newest router descriptor that
   * another authority has, so we all converge on the same one.) */
  ri_old = router_get_by_digest(ri->cache_info.identity_digest);
  if (ri_old && ri_old->cache_info.published_on < ri->cache_info.published_on
      && router_differences_are_cosmetic(ri_old, ri)
      && !router_is_me(ri)) {
    log_info(LD_DIRSERV,
             "Not replacing descriptor from '%s'; differences are cosmetic.",
             ri->nickname);
    *msg = "Not replacing router descriptor; no information has changed since "
      "the last one with this identity.";
    routerinfo_free(ri);
    control_event_or_authdir_new_descriptor("DROPPED", desc, *msg);
    return 0;
  }
  if ((r = router_add_to_routerlist(ri, msg, 0, 0))<0) {
    if (r < -1) /* unless the routerinfo was fine, just out-of-date */
      control_event_or_authdir_new_descriptor("REJECTED", desc, *msg);
    return r == -1 ? 0 : -1;
  } else {
    smartlist_t *changed;
    control_event_or_authdir_new_descriptor("ACCEPTED", desc, *msg);

    changed = smartlist_create();
    smartlist_add(changed, ri);
    control_event_descriptors_changed(changed);
    smartlist_free(changed);
    if (!*msg) {
      *msg =  ri->is_valid ? "Descriptor for valid server accepted" :
        "Descriptor for invalid server accepted";
    }
    return r == 0 ? 2 : 1;
  }
}

/** Remove all descriptors whose nicknames or fingerprints no longer
 * are allowed by our fingerprint list. (Descriptors that used to be
 * good can become bad when we reload the fingerprint list.)
 */
static void
directory_remove_invalid(void)
{
  int i;
  int changed = 0;
  routerlist_t *rl = router_get_routerlist();

  for (i = 0; i < smartlist_len(rl->routers); ++i) {
    const char *msg;
    routerinfo_t *ent = smartlist_get(rl->routers, i);
    uint32_t r = dirserv_router_get_status(ent, &msg);
    if (r & FP_REJECT) {
      log_info(LD_DIRSERV, "Router '%s' is now rejected: %s",
               ent->nickname, msg?msg:"");
      routerlist_remove(rl, ent, i--, 0);
      changed = 1;
    }
    if (bool_neq((r & FP_NAMED), ent->is_named)) {
      log_info(LD_DIRSERV,
               "Router '%s' is now %snamed.", ent->nickname,
               (r&FP_NAMED)?"":"un");
      ent->is_named = (r&FP_NAMED)?1:0;
      changed = 1;
    }
    if (bool_neq((r & FP_INVALID), !ent->is_valid)) {
      log_info(LD_DIRSERV, "Router '%s' is now %svalid.", ent->nickname,
               (r&FP_INVALID) ? "in" : "");
      ent->is_valid = (r&FP_INVALID)?0:1;
      changed = 1;
    }
    if (bool_neq((r & FP_BADEXIT), ent->is_bad_exit)) {
      log_info(LD_DIRSERV, "Router '%s' is now a %s exit", ent->nickname,
               (r & FP_BADEXIT) ? "bad" : "good");
      ent->is_bad_exit = (r&FP_BADEXIT) ? 1: 0;
      changed = 1;
    }
  }
  if (changed)
    directory_set_dirty();
}

/** Write a list of unregistered descriptors into a newly allocated
 * string and return it. Used by dirserv operators to keep track of
 * fast nodes that haven't registered.
 */
int
getinfo_helper_dirserv_unregistered(control_connection_t *control_conn,
                                    const char *question, char **answer_out)
{
  smartlist_t *answerlist;
  char buf[1024];
  char *answer;
  int min_bw = atoi(question);
  routerlist_t *rl = router_get_routerlist();

  (void) control_conn;

  if (strcmpstart(question, "unregistered-servers-"))
    return 0;
  question += strlen("unregistered-servers-");

  answerlist = smartlist_create();
  SMARTLIST_FOREACH(rl->routers, routerinfo_t *, ent, {
    uint32_t r = dirserv_router_get_status(ent, NULL);
    if (router_get_advertised_bandwidth(ent) >= (size_t)min_bw &&
        !(r & FP_NAMED)) {
      /* then log this one */
      tor_snprintf(buf, sizeof(buf),
                   "%s: BW %d on '%s'.",
                   ent->nickname, router_get_advertised_bandwidth(ent),
                   ent->platform ? ent->platform : "");
      smartlist_add(answerlist, tor_strdup(buf));
    }
  });
  answer = smartlist_join_strings(answerlist, "\r\n", 0, NULL);
  SMARTLIST_FOREACH(answerlist, char *, cp, tor_free(cp));
  smartlist_free(answerlist);
  *answer_out = answer;
  return 0;
}

/** Mark the directory as <b>dirty</b> -- when we're next asked for a
 * directory, we will rebuild it instead of reusing the most recently
 * generated one.
 */
void
directory_set_dirty(void)
{
  time_t now = time(NULL);

  if (!the_directory_is_dirty)
    the_directory_is_dirty = now;
  if (!runningrouters_is_dirty)
    runningrouters_is_dirty = now;
  if (!the_v2_networkstatus_is_dirty)
    the_v2_networkstatus_is_dirty = now;
}

/**
 * Allocate and return a description of the status of the server <b>desc</b>,
 * for use in a router-status line.  The server is listed
 * as running iff <b>is_live</b> is true.
 */
static char *
list_single_server_status(routerinfo_t *desc, int is_live)
{
  char buf[MAX_NICKNAME_LEN+HEX_DIGEST_LEN+4]; /* !nickname=$hexdigest\0 */
  char *cp;

  tor_assert(desc);

  cp = buf;
  if (!is_live) {
    *cp++ = '!';
  }
  if (desc->is_valid) {
    strlcpy(cp, desc->nickname, sizeof(buf)-(cp-buf));
    cp += strlen(cp);
    *cp++ = '=';
  }
  *cp++ = '$';
  base16_encode(cp, HEX_DIGEST_LEN+1, desc->cache_info.identity_digest,
                DIGEST_LEN);
  return tor_strdup(buf);
}

/** Each server needs to have passed a reachability test no more
 * than this number of seconds ago, or he is listed as down in
 * the directory. */
#define REACHABLE_TIMEOUT (45*60)

/** Treat a router as alive if
 *    - It's me, and I'm not hibernating.
 * or - We've found it reachable recently. */
static int
dirserv_thinks_router_is_reachable(routerinfo_t *router, time_t now)
{
  if (router_is_me(router) && !we_are_hibernating())
    return 1;
  return get_options()->AssumeReachable ||
         now < router->last_reachable + REACHABLE_TIMEOUT;
}

/** Return 1 if we're confident that there's a problem with
 * <b>router</b>'s reachability and its operator should be notified.
 */
int
dirserv_thinks_router_is_blatantly_unreachable(routerinfo_t *router,
                                               time_t now)
{
  if (router->is_hibernating)
    return 0;
  if (now >= router->last_reachable + 5*REACHABLE_TIMEOUT &&
      router->testing_since &&
      now >= router->testing_since + 5*REACHABLE_TIMEOUT)
    return 1;
  return 0;
}

/** Based on the routerinfo_ts in <b>routers</b>, allocate the
 * contents of a router-status line, and store it in
 * *<b>router_status_out</b>.  Return 0 on success, -1 on failure.
 *
 * If for_controller is true, include the routers with very old descriptors.
 * If for_controller is &gt;1, use the verbose nickname format.
 */
int
list_server_status(smartlist_t *routers, char **router_status_out,
                   int for_controller)
{
  /* List of entries in a router-status style: An optional !, then an optional
   * equals-suffixed nickname, then a dollar-prefixed hexdigest. */
  smartlist_t *rs_entries;
  time_t now = time(NULL);
  time_t cutoff = now - ROUTER_MAX_AGE_TO_PUBLISH;
  int authdir_mode = get_options()->AuthoritativeDir;
  tor_assert(router_status_out);

  rs_entries = smartlist_create();

  SMARTLIST_FOREACH(routers, routerinfo_t *, ri,
  {
    if (authdir_mode) {
      /* Update router status in routerinfo_t. */
      ri->is_running = dirserv_thinks_router_is_reachable(ri, now);
    }
    if (for_controller == 1 || ri->cache_info.published_on >= cutoff)
      smartlist_add(rs_entries, list_single_server_status(ri, ri->is_running));
    else if (for_controller > 2) {
      char name_buf[MAX_VERBOSE_NICKNAME_LEN+2];
      char *cp = name_buf;
      if (!ri->is_running)
        *cp++ = '!';
      router_get_verbose_nickname(cp, ri);
      smartlist_add(rs_entries, tor_strdup(name_buf));
    }
  });

  *router_status_out = smartlist_join_strings(rs_entries, " ", 0, NULL);

  SMARTLIST_FOREACH(rs_entries, char *, cp, tor_free(cp));
  smartlist_free(rs_entries);

  return 0;
}

/** Given a (possibly empty) list of config_line_t, each line of which contains
 * a list of comma-separated version numbers surrounded by optional space,
 * allocate and return a new string containing the version numbers, in order,
 * separated by commas.  Used to generate Recommended(Client|Server)?Versions
 */
static char *
format_versions_list(config_line_t *ln)
{
  smartlist_t *versions;
  char *result;
  versions = smartlist_create();
  for ( ; ln; ln = ln->next) {
    smartlist_split_string(versions, ln->value, ",",
                           SPLIT_SKIP_SPACE|SPLIT_IGNORE_BLANK, 0);
  }
  sort_version_list(versions, 1);
  result = smartlist_join_strings(versions,",",0,NULL);
  SMARTLIST_FOREACH(versions,char *,s,tor_free(s));
  smartlist_free(versions);
  return result;
}

/** Return 1 if <b>ri</b>'s descriptor is "active" -- running, valid,
 * not hibernating, and not too old. Else return 0.
 */
static int
router_is_active(routerinfo_t *ri, time_t now)
{
  time_t cutoff = now - ROUTER_MAX_AGE_TO_PUBLISH;
  if (ri->cache_info.published_on < cutoff)
    return 0;
  if (!ri->is_running || !ri->is_valid || ri->is_hibernating)
    return 0;
  return 1;
}

/** Generate a new v1 directory and write it into a newly allocated string.
 * Point *<b>dir_out</b> to the allocated string.  Sign the
 * directory with <b>private_key</b>.  Return 0 on success, -1 on
 * failure. If <b>complete</b> is set, give us all the descriptors;
 * otherwise leave out non-running and non-valid ones.
 */
int
dirserv_dump_directory_to_string(char **dir_out,
                                 crypto_pk_env_t *private_key, int complete)
{
  char *cp;
  char *router_status;
  char *identity_pkey; /* Identity key, DER64-encoded. */
  char *recommended_versions;
  char digest[DIGEST_LEN];
  char published[ISO_TIME_LEN+1];
  char *buf = NULL;
  size_t buf_len;
  size_t identity_pkey_len;
  routerlist_t *rl = router_get_routerlist();
  time_t now = time(NULL);

  tor_assert(dir_out);
  *dir_out = NULL;

  if (list_server_status(rl->routers, &router_status, 0))
    return -1;

  if (crypto_pk_write_public_key_to_string(private_key,&identity_pkey,
                                           &identity_pkey_len)<0) {
    log_warn(LD_BUG,"write identity_pkey to string failed!");
    return -1;
  }

  recommended_versions =
    format_versions_list(get_options()->RecommendedVersions);

  format_iso_time(published, now);

  buf_len = 2048+strlen(recommended_versions)+
    strlen(router_status);
  SMARTLIST_FOREACH(rl->routers, routerinfo_t *, ri,
                    if (complete || router_is_active(ri, now))
                      buf_len += ri->cache_info.signed_descriptor_len+1);
  buf = tor_malloc(buf_len);
  /* We'll be comparing against buf_len throughout the rest of the
     function, though strictly speaking we shouldn't be able to exceed
     it.  This is C, after all, so we may as well check for buffer
     overruns.*/

  tor_snprintf(buf, buf_len,
               "signed-directory\n"
               "published %s\n"
               "recommended-software %s\n"
               "router-status %s\n"
               "dir-signing-key\n%s\n",
               published, recommended_versions, router_status,
               identity_pkey);

  tor_free(recommended_versions);
  tor_free(router_status);
  tor_free(identity_pkey);

  cp = buf + strlen(buf);
  SMARTLIST_FOREACH(rl->routers, routerinfo_t *, ri,
    {
      size_t len = ri->cache_info.signed_descriptor_len;
      const char *body;
      if (!complete && !router_is_active(ri, now))
        continue;
      if (cp+len+1 >= buf+buf_len)
        goto truncated;
      body = signed_descriptor_get_body(&ri->cache_info);
      memcpy(cp, body, len);
      cp += len;
      *cp++ = '\n'; /* add an extra newline in case somebody was depending on
                     * it. */
    });
  *cp = '\0';

  /* These multiple strlcat calls are inefficient, but dwarfed by the RSA
     signature. */
  if (strlcat(buf, "directory-signature ", buf_len) >= buf_len)
    goto truncated;
  if (strlcat(buf, get_options()->Nickname, buf_len) >= buf_len)
    goto truncated;
  if (strlcat(buf, "\n", buf_len) >= buf_len)
    goto truncated;

  if (router_get_dir_hash(buf,digest)) {
    log_warn(LD_BUG,"couldn't compute digest");
    tor_free(buf);
    return -1;
  }
  note_crypto_pk_op(SIGN_DIR);
  if (router_append_dirobj_signature(buf,buf_len,digest,private_key)<0) {
    tor_free(buf);
    return -1;
  }

  *dir_out = buf;
  return 0;
 truncated:
  log_warn(LD_BUG,"tried to exceed string length.");
  tor_free(buf);
  return -1;
}

/** Most recently generated encoded signed v1 directory. (auth dirservers
 * only.)*/
static cached_dir_t *the_directory = NULL;

/* Used only by non-auth dirservers: The v1 directory and runningrouters we'll
 * serve when requested. */
static cached_dir_t *cached_directory = NULL;
static cached_dir_t cached_runningrouters = { NULL, NULL, 0, 0, 0, -1 };

/** Used for other dirservers' v2 network statuses.  Map from hexdigest to
 * cached_dir_t. */
static digestmap_t *cached_v2_networkstatus = NULL;

/** Possibly replace the contents of <b>d</b> with the value of
 * <b>directory</b> published on <b>when</b>, unless <b>when</b> is older than
 * the last value, or too far in the future.
 *
 * Does not copy <b>directory</b>; frees it if it isn't used.
 */
static void
set_cached_dir(cached_dir_t *d, char *directory, time_t when)
{
  time_t now = time(NULL);
  if (when<=d->published) {
    log_info(LD_DIRSERV, "Ignoring old directory; not caching.");
    tor_free(directory);
  } else if (when>=now+ROUTER_MAX_AGE_TO_PUBLISH) {
    log_info(LD_DIRSERV, "Ignoring future directory; not caching.");
    tor_free(directory);
  } else {
    /* if (when>d->published && when<now+ROUTER_MAX_AGE) */
    log_debug(LD_DIRSERV, "Caching directory.");
    tor_free(d->dir);
    d->dir = directory;
    d->dir_len = strlen(directory);
    tor_free(d->dir_z);
    if (tor_gzip_compress(&(d->dir_z), &(d->dir_z_len), d->dir, d->dir_len,
                          ZLIB_METHOD)) {
      log_warn(LD_BUG,"Error compressing cached directory");
    }
    d->published = when;
  }
}

/** Decrement the reference count on <b>d</b>, and free it if it no longer has
 * any references. */
void
cached_dir_decref(cached_dir_t *d)
{
  if (!d || --d->refcnt > 0)
    return;
  clear_cached_dir(d);
  tor_free(d);
}

/** Allocate and return a new cached_dir_t containing the string <b>s</b>,
 * published at <b>published</b>. */
static cached_dir_t *
new_cached_dir(char *s, time_t published)
{
  cached_dir_t *d = tor_malloc_zero(sizeof(cached_dir_t));
  d->refcnt = 1;
  d->dir = s;
  d->dir_len = strlen(s);
  d->published = published;
  if (tor_gzip_compress(&(d->dir_z), &(d->dir_z_len), d->dir, d->dir_len,
                        ZLIB_METHOD)) {
    log_warn(LD_BUG, "Error compressing directory");
  }
  return d;
}

/** Remove all storage held in <b>d</b>, but do not free <b>d</b> itself. */
static void
clear_cached_dir(cached_dir_t *d)
{
  tor_free(d->dir);
  tor_free(d->dir_z);
  memset(d, 0, sizeof(cached_dir_t));
}

/** Free all storage held by the cached_dir_t in <b>d</b>. */
static void
_free_cached_dir(void *_d)
{
  cached_dir_t *d = (cached_dir_t *)_d;
  cached_dir_decref(d);
}

/** If we have no cached directory, or it is older than <b>published</b>,
 * then replace it with <b>directory</b>, published at <b>published</b>.
 *
 * If <b>published</b> is too old, do nothing.
 *
 * If <b>is_running_routers</b>, this is really a running_routers document
 * rather than a v1 directory.
 */
void
dirserv_set_cached_directory(const char *directory, time_t published,
                             int is_running_routers)
{
  time_t now = time(NULL);

  if (is_running_routers) {
    if (published >= now - MAX_V1_RR_AGE)
      set_cached_dir(&cached_runningrouters, tor_strdup(directory), published);
  } else {
    if (published >= now - MAX_V1_DIRECTORY_AGE) {
      cached_dir_decref(cached_directory);
      cached_directory = new_cached_dir(tor_strdup(directory), published);
    }
  }
}

/** We've just received a v2 network-status for an authoritative directory
 * with identity digest <b>identity</b> published at
 * <b>published</b>.  Store it so we can serve it to others.  If
 * <b>directory</b> is NULL, remove the entry with the given fingerprint from
 * the cache.
 */
void
dirserv_set_cached_networkstatus_v2(const char *networkstatus,
                                    const char *identity,
                                    time_t published)
{
  cached_dir_t *d, *old_d;
  smartlist_t *trusted_dirs;
  if (!cached_v2_networkstatus)
    cached_v2_networkstatus = digestmap_new();

  old_d = digestmap_get(cached_v2_networkstatus, identity);
  if (!old_d && !networkstatus)
    return;

  if (networkstatus) {
    if (!old_d || published > old_d->published) {
      d = new_cached_dir(tor_strdup(networkstatus), published);
      digestmap_set(cached_v2_networkstatus, identity, d);
      if (old_d)
        cached_dir_decref(old_d);
    }
  } else {
    if (old_d) {
      digestmap_remove(cached_v2_networkstatus, identity);
      cached_dir_decref(old_d);
    }
  }

  /* Now purge old entries. */
  trusted_dirs = router_get_trusted_dir_servers();
  if (digestmap_size(cached_v2_networkstatus) >
      smartlist_len(trusted_dirs) + MAX_UNTRUSTED_NETWORKSTATUSES) {
    /* We need to remove the oldest untrusted networkstatus. */
    const char *oldest = NULL;
    time_t oldest_published = TIME_MAX;
    digestmap_iter_t *iter;

    for (iter = digestmap_iter_init(cached_v2_networkstatus);
         !digestmap_iter_done(iter);
         iter = digestmap_iter_next(cached_v2_networkstatus, iter)) {
      const char *ident;
      void *val;
      digestmap_iter_get(iter, &ident, &val);
      d = val;
      if (d->published < oldest_published &&
          !router_digest_is_trusted_dir(ident)) {
        oldest = ident;
        oldest_published = d->published;
      }
    }
    tor_assert(oldest);
    d = digestmap_remove(cached_v2_networkstatus, oldest);
    if (d)
      cached_dir_decref(d);
  }
}

/** Remove any networkstatus from the directory cache that was published
 * before <b>cutoff</b>. */
void
dirserv_clear_old_networkstatuses(time_t cutoff)
{
  digestmap_iter_t *iter;

  if (!cached_v2_networkstatus)
    return;

  for (iter = digestmap_iter_init(cached_v2_networkstatus);
       !digestmap_iter_done(iter); ) {
    const char *ident;
    void *val;
    cached_dir_t *dir;
    digestmap_iter_get(iter, &ident, &val);
    dir = val;
    if (dir->published < cutoff) {
      char *fname;
      iter = digestmap_iter_next_rmv(cached_v2_networkstatus, iter);
      fname = networkstatus_get_cache_filename(ident);
      if (file_status(fname) == FN_FILE) {
        log_info(LD_DIR, "Removing too-old untrusted networkstatus in %s",
                 fname);
        unlink(fname);
      }
      tor_free(fname);
      cached_dir_decref(dir);
    } else {
      iter = digestmap_iter_next(cached_v2_networkstatus, iter);
    }
  }
}

/** Remove any v1 info from the directory cache that was published
 * too long ago. */
void
dirserv_clear_old_v1_info(time_t now)
{
  if (cached_directory &&
      cached_directory->published < (now - MAX_V1_DIRECTORY_AGE)) {
    cached_dir_decref(cached_directory);
    cached_directory = NULL;
  }
  if (cached_runningrouters.published < (now - MAX_V1_RR_AGE)) {
    clear_cached_dir(&cached_runningrouters);
  }
}

/** Helper: If we're an authority for the right directory version (the
 * directory version is determined by <b>is_v1_object</b>), try to regenerate
 * auth_src as appropriate and return it, falling back to cache_src on
 * failure.  If we're a cache, return cache_src.
 */
static cached_dir_t *
dirserv_pick_cached_dir_obj(cached_dir_t *cache_src,
                            cached_dir_t *auth_src,
                            time_t dirty, cached_dir_t *(*regenerate)(void),
                            const char *name,
                            int is_v1_object)
{
  int authority = get_options()->AuthoritativeDir &&
    (!is_v1_object || get_options()->V1AuthoritativeDir);

  if (!authority) {
    return cache_src;
  } else {
    /* We're authoritative. */
    if (regenerate != NULL) {
      if (dirty && dirty + DIR_REGEN_SLACK_TIME < time(NULL)) {
        if (!(auth_src = regenerate())) {
          log_err(LD_BUG, "Couldn't generate %s?", name);
          exit(1);
        }
      } else {
        log_info(LD_DIRSERV, "The %s is still clean; reusing.", name);
      }
    }
    return auth_src ? auth_src : cache_src;
  }
}

/** Helper: If we're authoritative and <b>auth_src</b> is set, use
 * <b>auth_src</b>, otherwise use <b>cache_src</b>.  If we're using
 * <b>auth_src</b> and it's been <b>dirty</b> for at least
 * DIR_REGEN_SLACK_TIME seconds, call <b>regenerate</b>() to make a fresh one.
 * Yields the compressed version of the directory object if <b>compress</b> is
 * set; otherwise return the uncompressed version.  (In either case, sets
 * *<b>out</b> and returns the size of the buffer in *<b>out</b>.)
 *
 * Use <b>is_v1_object</b> to help determine whether we're authoritative for
 * this kind of object.
 **/
static size_t
dirserv_get_obj(const char **out,
                int compress,
                cached_dir_t *cache_src,
                cached_dir_t *auth_src,
                time_t dirty, cached_dir_t *(*regenerate)(void),
                const char *name,
                int is_v1_object)
{
  cached_dir_t *d = dirserv_pick_cached_dir_obj(
      cache_src, auth_src,
      dirty, regenerate, name, is_v1_object);

  if (!d)
    return 0;
  *out = compress ? d->dir_z : d->dir;
  if (*out) {
    return compress ? d->dir_z_len : d->dir_len;
  } else {
    /* not yet available. */
    return 0;
  }
}

/** Return the most recently generated encoded signed directory, generating a
 * new one as necessary.  If not an authoritative directory may return NULL if
 * no directory is yet cached. */
cached_dir_t *
dirserv_get_directory(void)
{
  return dirserv_pick_cached_dir_obj(cached_directory, the_directory,
                                     the_directory_is_dirty,
                                     dirserv_regenerate_directory,
                                     "server directory", 1);
}

/**
 * Generate a fresh v1 directory (authdirservers only); set the_directory
 * and return a pointer to the new value.
 */
static cached_dir_t *
dirserv_regenerate_directory(void)
{
  char *new_directory=NULL;

  if (dirserv_dump_directory_to_string(&new_directory,
                                       get_identity_key(), 0)) {
    log_warn(LD_BUG, "Error creating directory.");
    tor_free(new_directory);
    return NULL;
  }
  cached_dir_decref(the_directory);
  the_directory = new_cached_dir(new_directory, time(NULL));
  log_info(LD_DIRSERV,"New directory (size %d) has been built.",
           (int)the_directory->dir_len);
  log_debug(LD_DIRSERV,"New directory (size %d):\n%s",
            (int)the_directory->dir_len, the_directory->dir);

  the_directory_is_dirty = 0;

  /* Save the directory to disk so we re-load it quickly on startup.
   */
  dirserv_set_cached_directory(the_directory->dir, time(NULL), 0);

  return the_directory;
}

/** For authoritative directories: the current (v1) network status. */
static cached_dir_t the_runningrouters = { NULL, NULL, 0, 0, 0, -1 };

/** Replace the current running-routers list with a newly generated one. */
static cached_dir_t *
generate_runningrouters(void)
{
  char *s=NULL;
  char *router_status=NULL;
  char digest[DIGEST_LEN];
  char published[ISO_TIME_LEN+1];
  size_t len;
  crypto_pk_env_t *private_key = get_identity_key();
  char *identity_pkey; /* Identity key, DER64-encoded. */
  size_t identity_pkey_len;
  routerlist_t *rl = router_get_routerlist();

  if (list_server_status(rl->routers, &router_status, 0)) {
    goto err;
  }
  if (crypto_pk_write_public_key_to_string(private_key,&identity_pkey,
                                           &identity_pkey_len)<0) {
    log_warn(LD_BUG,"write identity_pkey to string failed!");
    goto err;
  }
  format_iso_time(published, time(NULL));

  len = 2048+strlen(router_status);
  s = tor_malloc_zero(len);
  tor_snprintf(s, len,
               "network-status\n"
               "published %s\n"
               "router-status %s\n"
               "dir-signing-key\n%s"
               "directory-signature %s\n",
               published, router_status, identity_pkey,
               get_options()->Nickname);
  tor_free(router_status);
  tor_free(identity_pkey);
  if (router_get_runningrouters_hash(s,digest)) {
    log_warn(LD_BUG,"couldn't compute digest");
    goto err;
  }
  note_crypto_pk_op(SIGN_DIR);
  if (router_append_dirobj_signature(s, len, digest, private_key)<0)
    goto err;

  set_cached_dir(&the_runningrouters, s, time(NULL));
  runningrouters_is_dirty = 0;

  return &the_runningrouters;
 err:
  tor_free(s);
  tor_free(router_status);
  return NULL;
}

/** Set *<b>rr</b> to the most recently generated encoded signed
 * running-routers list, generating a new one as necessary.  Return the
 * size of the directory on success, and 0 on failure. */
size_t
dirserv_get_runningrouters(const char **rr, int compress)
{
  return dirserv_get_obj(rr, compress,
                         &cached_runningrouters, &the_runningrouters,
                         runningrouters_is_dirty,
                         generate_runningrouters,
                         "v1 network status list", 1);
}

/** For authoritative directories: the current (v2) network status. */
static cached_dir_t *the_v2_networkstatus = NULL;

/** Return true iff our opinion of the routers has been stale for long
 * enough that we should generate a new network status doc. */
static int
should_generate_v2_networkstatus(void)
{
  return get_options()->AuthoritativeDir &&
    the_v2_networkstatus_is_dirty &&
    the_v2_networkstatus_is_dirty + DIR_REGEN_SLACK_TIME < time(NULL);
}

/** If a router's uptime is at least this value, then it is always
 * considered stable, regardless of the rest of the network. This
 * way we resist attacks where an attacker doubles the size of the
 * network using allegedly high-uptime nodes, displacing all the
 * current guards. */
#define UPTIME_TO_GUARANTEE_STABLE (3600*24*30)

/* Thresholds for server performance: set by
 * dirserv_compute_performance_thresholds, and used by
 * generate_v2_networkstatus */
static uint32_t stable_uptime = 0; /* start at a safe value */
static uint32_t fast_bandwidth = 0;
static uint32_t guard_bandwidth_including_exits = 0;
static uint32_t guard_bandwidth_excluding_exits = 0;
static uint64_t total_bandwidth = 0;
static uint64_t total_exit_bandwidth = 0;

/** Helper: estimate the uptime of a router given its stated uptime and the
 * amount of time since it last stated its stated uptime. */
static INLINE int
real_uptime(routerinfo_t *router, time_t now)
{
  if (now < router->cache_info.published_on)
    return router->uptime;
  else
    return router->uptime + (now - router->cache_info.published_on);
}

/** Return 1 if <b>router</b> is not suitable for these parameters, else 0.
 * If <b>need_uptime</b> is non-zero, we require a minimum uptime.
 * If <b>need_capacity</b> is non-zero, we require a minimum advertised
 * bandwidth.
 */
static int
dirserv_thinks_router_is_unreliable(time_t now,
                                    routerinfo_t *router,
                                    int need_uptime, int need_capacity)
{
  if (need_uptime) {
    int uptime = real_uptime(router, now);
    if ((unsigned)uptime < stable_uptime &&
        (unsigned)uptime < UPTIME_TO_GUARANTEE_STABLE)
      return 1;
  }
  if (need_capacity &&
      router_get_advertised_bandwidth(router) < fast_bandwidth)
    return 1;
  return 0;
}

/** Helper: returns a tristate based on comparing **(uint32_t**)<b>a</b>
 * to **(uint32_t**)<b>b</b>. */
static int
_compare_uint32(const void **a, const void **b)
{
  uint32_t first = **(uint32_t **)a, second = **(uint32_t **)b;
  if (first < second) return -1;
  if (first > second) return 1;
  return 0;
}

/** Look through the routerlist, and assign the median uptime of running valid
 * servers to stable_uptime, and the relative bandwidth capacities to
 * fast_bandwidth and guard_bandwidth.  Set total_bandwidth to the total
 * capacity of all running valid servers and total_exit_bandwidth to the
 * capacity of all running valid exits.  Set the is_exit flag of each router
 * appropriately. */
static void
dirserv_compute_performance_thresholds(routerlist_t *rl)
{
  smartlist_t *uptimes, *bandwidths, *bandwidths_excluding_exits;
  time_t now = time(NULL);

  /* initialize these all here, in case there are no routers */
  stable_uptime = 0;
  fast_bandwidth = 0;
  guard_bandwidth_including_exits = 0;
  guard_bandwidth_excluding_exits = 0;

  total_bandwidth = 0;
  total_exit_bandwidth = 0;

  uptimes = smartlist_create();
  bandwidths = smartlist_create();
  bandwidths_excluding_exits = smartlist_create();

  SMARTLIST_FOREACH(rl->routers, routerinfo_t *, ri, {
    if (router_is_active(ri, now)) {
      uint32_t *up = tor_malloc(sizeof(uint32_t));
      uint32_t *bw = tor_malloc(sizeof(uint32_t));
      ri->is_exit = exit_policy_is_general_exit(ri->exit_policy);
      *up = (uint32_t) real_uptime(ri, now);
      smartlist_add(uptimes, up);
      *bw = router_get_advertised_bandwidth(ri);
      total_bandwidth += *bw;
      if (ri->is_exit && !ri->is_bad_exit) {
        total_exit_bandwidth += *bw;
      } else {
        uint32_t *bw_not_exit = tor_malloc(sizeof(uint32_t));
        *bw_not_exit = *bw;
        smartlist_add(bandwidths_excluding_exits, bw_not_exit);
      }
      smartlist_add(bandwidths, bw);
    }
  });

  smartlist_sort(uptimes, _compare_uint32);
  smartlist_sort(bandwidths, _compare_uint32);
  smartlist_sort(bandwidths_excluding_exits, _compare_uint32);

  if (smartlist_len(uptimes))
    stable_uptime = *(uint32_t*)smartlist_get(uptimes,
                                              smartlist_len(uptimes)/2);

  if (smartlist_len(bandwidths)) {
    fast_bandwidth = *(uint32_t*)smartlist_get(bandwidths,
                                               smartlist_len(bandwidths)/8);
    if (fast_bandwidth < ROUTER_REQUIRED_MIN_BANDWIDTH)
      fast_bandwidth = *(uint32_t*)smartlist_get(bandwidths,
                                                 smartlist_len(bandwidths)/4);
    guard_bandwidth_including_exits =
      *(uint32_t*)smartlist_get(bandwidths, smartlist_len(bandwidths)/2);
  }

  if (smartlist_len(bandwidths_excluding_exits)) {
    guard_bandwidth_excluding_exits =
      *(uint32_t*)smartlist_get(bandwidths_excluding_exits,
                                smartlist_len(bandwidths_excluding_exits)/2);
  }

  log(LOG_INFO, LD_DIRSERV,
      "Cutoffs: %lus uptime, %lu b/s fast, %lu or %lu b/s guard.",
      (unsigned long)stable_uptime,
      (unsigned long)fast_bandwidth,
      (unsigned long)guard_bandwidth_including_exits,
      (unsigned long)guard_bandwidth_excluding_exits);

  SMARTLIST_FOREACH(uptimes, uint32_t *, up, tor_free(up));
  SMARTLIST_FOREACH(bandwidths, uint32_t *, bw, tor_free(bw));
  SMARTLIST_FOREACH(bandwidths_excluding_exits, uint32_t *, bw, tor_free(bw));
  smartlist_free(uptimes);
  smartlist_free(bandwidths);
  smartlist_free(bandwidths_excluding_exits);
}

/** For authoritative directories only: replace the contents of
 * <b>the_v2_networkstatus</b> with a newly generated network status
 * object. */
static cached_dir_t *
generate_v2_networkstatus(void)
{
/** Longest status flag name that we generate. */
#define LONGEST_STATUS_FLAG_NAME_LEN 9
/** Maximum number of status flags we'll apply to one router. */
#define N_STATUS_FLAGS 10
/** Amount of space to allocate for each entry. (r line and s line.) */
#define RS_ENTRY_LEN                                                    \
  ( /* first line */                                                    \
   MAX_NICKNAME_LEN+BASE64_DIGEST_LEN*2+ISO_TIME_LEN+INET_NTOA_BUF_LEN+ \
   5*2 /* ports */ + 10 /* punctuation */ +                             \
   /* second line */                                                    \
   (LONGEST_STATUS_FLAG_NAME_LEN+1)*N_STATUS_FLAGS + 2)

  cached_dir_t *r = NULL;
  size_t len, identity_pkey_len;
  char *status = NULL, *client_versions = NULL, *server_versions = NULL,
    *identity_pkey = NULL, *hostname = NULL;
  char *outp, *endp;
  or_options_t *options = get_options();
  char fingerprint[FINGERPRINT_LEN+1];
  char ipaddr[INET_NTOA_BUF_LEN];
  char published[ISO_TIME_LEN+1];
  char digest[DIGEST_LEN];
  struct in_addr in;
  uint32_t addr;
  crypto_pk_env_t *private_key = get_identity_key();
  routerlist_t *rl = router_get_routerlist();
  time_t now = time(NULL);
  time_t cutoff = now - ROUTER_MAX_AGE_TO_PUBLISH;
  int naming = options->NamingAuthoritativeDir;
  int versioning = options->VersioningAuthoritativeDir;
  int listbadexits = options->AuthDirListBadExits;
  int exits_can_be_guards;
  const char *contact;

  if (resolve_my_address(LOG_WARN, options, &addr, &hostname)<0) {
    log_warn(LD_NET, "Couldn't resolve my hostname");
    goto done;
  }
  in.s_addr = htonl(addr);
  tor_inet_ntoa(&in, ipaddr, sizeof(ipaddr));

  format_iso_time(published, time(NULL));

  client_versions = format_versions_list(options->RecommendedClientVersions);
  server_versions = format_versions_list(options->RecommendedServerVersions);

  if (crypto_pk_write_public_key_to_string(private_key, &identity_pkey,
                                           &identity_pkey_len)<0) {
    log_warn(LD_BUG,"Writing public key to string failed.");
    goto done;
  }

  if (crypto_pk_get_fingerprint(private_key, fingerprint, 0)<0) {
    log_err(LD_BUG, "Error computing fingerprint");
    goto done;
  }

  contact = get_options()->ContactInfo;
  if (!contact)
    contact = "(none)";

  len = 2048+strlen(client_versions)+strlen(server_versions);
  len += identity_pkey_len*2;
  len += (RS_ENTRY_LEN)*smartlist_len(rl->routers);

  status = tor_malloc(len);
  tor_snprintf(status, len,
               "network-status-version 2\n"
               "dir-source %s %s %d\n"
               "fingerprint %s\n"
               "contact %s\n"
               "published %s\n"
               "dir-options%s%s%s\n"
               "%s%s" /* client versions %s */
               "%s%s%s" /* \nserver versions %s \n */
               "dir-signing-key\n%s\n",
               hostname, ipaddr, (int)options->DirPort,
               fingerprint,
               contact,
               published,
               naming ? " Names" : "",
               listbadexits ? " BadExits" : "",
               versioning ? " Versions" : "",
               versioning ? "client-versions " : "",
               versioning ? client_versions : "",
               versioning ? "\nserver-versions " : "",
               versioning ? server_versions : "",
               versioning ? "\n" : "",
               identity_pkey);
  outp = status + strlen(status);
  endp = status + len;

  /* precompute this part, since we need it to decide what "stable"
   * means. */
  SMARTLIST_FOREACH(rl->routers, routerinfo_t *, ri, {
    ri->is_running = dirserv_thinks_router_is_reachable(ri, now);
  });

  dirserv_compute_performance_thresholds(rl);

  /* XXXX We should take steps to keep this from oscillating if
   * total_exit_bandwidth is close to total_bandwidth/3. */
  exits_can_be_guards = total_exit_bandwidth >= (total_bandwidth / 3);

  SMARTLIST_FOREACH(rl->routers, routerinfo_t *, ri, {
    if (ri->cache_info.published_on >= cutoff) {
      /* Already set by compute_performance_thresholds. */
      int f_exit = ri->is_exit;
      /* These versions dump connections with idle live circuits
         sometimes. D'oh!*/
      int unstable_version =
        tor_version_as_new_as(ri->platform,"0.1.1.10-alpha") &&
        !tor_version_as_new_as(ri->platform,"0.1.1.16-rc-cvs");
      int f_stable = ri->is_stable =
        router_is_active(ri, now) &&
        !dirserv_thinks_router_is_unreliable(now, ri, 1, 0) &&
        !unstable_version;
      int f_fast = ri->is_fast =
        router_is_active(ri, now) &&
        !dirserv_thinks_router_is_unreliable(now, ri, 0, 1);
      int f_running = ri->is_running; /* computed above */
      int f_authority = router_digest_is_trusted_dir(
                                      ri->cache_info.identity_digest);
      int f_named = naming && ri->is_named;
      int f_valid = ri->is_valid;
      int f_guard = f_fast && f_stable &&
        (!f_exit || exits_can_be_guards) &&
        router_get_advertised_bandwidth(ri) >=
          (exits_can_be_guards ? guard_bandwidth_including_exits :
                                 guard_bandwidth_excluding_exits);
      int f_bad_exit = listbadexits && ri->is_bad_exit;
      /* 0.1.1.9-alpha is the first version to support fetch by descriptor
       * hash. */
      int f_v2_dir = ri->dir_port &&
        tor_version_as_new_as(ri->platform,"0.1.1.9-alpha");
      char identity64[BASE64_DIGEST_LEN+1];
      char digest64[BASE64_DIGEST_LEN+1];

      if (!strcasecmp(ri->nickname, UNNAMED_ROUTER_NICKNAME))
        f_named = 0;

      format_iso_time(published, ri->cache_info.published_on);

      digest_to_base64(identity64, ri->cache_info.identity_digest);
      digest_to_base64(digest64, ri->cache_info.signed_descriptor_digest);

      in.s_addr = htonl(ri->addr);
      tor_inet_ntoa(&in, ipaddr, sizeof(ipaddr));

      if (tor_snprintf(outp, endp-outp,
                       "r %s %s %s %s %s %d %d\n"
                       "s%s%s%s%s%s%s%s%s%s%s\n",
                       ri->nickname,
                       identity64,
                       digest64,
                       published,
                       ipaddr,
                       ri->or_port,
                       ri->dir_port,
                       f_authority?" Authority":"",
                       f_bad_exit?" BadExit":"",
                       f_exit?" Exit":"",
                       f_fast?" Fast":"",
                       f_guard?" Guard":"",
                       f_named?" Named":"",
                       f_stable?" Stable":"",
                       f_running?" Running":"",
                       f_valid?" Valid":"",
                       f_v2_dir?" V2Dir":"")<0) {
        log_warn(LD_BUG, "Unable to print router status.");
        goto done;
      }
      outp += strlen(outp);
      if (ri->platform && !strcmpstart(ri->platform, "Tor ")) {
        const char *eos = find_whitespace(ri->platform+4);
        if (eos) {
          char *platform = tor_strndup(ri->platform, eos-(ri->platform));
          if (tor_snprintf(outp, endp-outp,
                           "opt v %s\n", platform)<0) {
            log_warn(LD_BUG, "Unable to print router version.");
            goto done;
          }
          tor_free(platform);
          outp += strlen(outp);
        }
      }
    }
  });

  if (tor_snprintf(outp, endp-outp, "directory-signature %s\n",
                   get_options()->Nickname)<0) {
    log_warn(LD_BUG, "Unable to write signature line.");
    goto done;
  }

  if (router_get_networkstatus_v2_hash(status, digest)<0) {
    log_warn(LD_BUG, "Unable to hash network status");
    goto done;
  }

  note_crypto_pk_op(SIGN_DIR);
  if (router_append_dirobj_signature(outp,endp-outp,digest,private_key)<0) {
    log_warn(LD_BUG, "Unable to sign router status.");
    goto done;
  }

  if (the_v2_networkstatus)
    cached_dir_decref(the_v2_networkstatus);
  the_v2_networkstatus = new_cached_dir(status, time(NULL));
  status = NULL; /* So it doesn't get double-freed. */
  the_v2_networkstatus_is_dirty = 0;
  router_set_networkstatus(the_v2_networkstatus->dir,
                           time(NULL), NS_GENERATED, NULL);
  r = the_v2_networkstatus;
 done:
  tor_free(client_versions);
  tor_free(server_versions);
  tor_free(status);
  tor_free(hostname);
  tor_free(identity_pkey);
  return r;
}

/** Given the portion of a networkstatus request URL after "tor/status/" in
 * <b>key</b>, append to <b>result</b> the digests of the identity keys of the
 * networkstatus objects that the client has requested. */
void
dirserv_get_networkstatus_v2_fingerprints(smartlist_t *result,
                                          const char *key)
{
  tor_assert(result);

  if (!cached_v2_networkstatus)
    cached_v2_networkstatus = digestmap_new();

  if (should_generate_v2_networkstatus())
    generate_v2_networkstatus();

  if (!strcmp(key,"authority")) {
    if (get_options()->AuthoritativeDir) {
      routerinfo_t *me = router_get_my_routerinfo();
      if (me)
        smartlist_add(result,
                      tor_memdup(me->cache_info.identity_digest, DIGEST_LEN));
    }
  } else if (!strcmp(key, "all")) {
    if (digestmap_size(cached_v2_networkstatus)) {
      digestmap_iter_t *iter;
      iter = digestmap_iter_init(cached_v2_networkstatus);
      while (!digestmap_iter_done(iter)) {
        const char *ident;
        void *val;
        digestmap_iter_get(iter, &ident, &val);
        smartlist_add(result, tor_memdup(ident, DIGEST_LEN));
        iter = digestmap_iter_next(cached_v2_networkstatus, iter);
      }
    } else {
      SMARTLIST_FOREACH(router_get_trusted_dir_servers(),
                  trusted_dir_server_t *, ds,
                  smartlist_add(result, tor_memdup(ds->digest, DIGEST_LEN)));
    }
    smartlist_sort_digests(result);
    if (smartlist_len(result) == 0)
      log_warn(LD_DIRSERV,
               "Client requested 'all' network status objects; we have none.");
  } else if (!strcmpstart(key, "fp/")) {
    dir_split_resource_into_fingerprints(key+3, result, NULL, 1, 1);
  }
}

/** Look for a network status object as specified by <b>key</b>, which should
 * be either "authority" (to find a network status generated by us), a hex
 * identity digest (to find a network status generated by given directory), or
 * "all" (to return all the v2 network status objects we have).
 */
void
dirserv_get_networkstatus_v2(smartlist_t *result,
                             const char *key)
{
  cached_dir_t *cached;
  smartlist_t *fingerprints = smartlist_create();
  tor_assert(result);

  if (!cached_v2_networkstatus)
    cached_v2_networkstatus = digestmap_new();

  dirserv_get_networkstatus_v2_fingerprints(fingerprints, key);
  SMARTLIST_FOREACH(fingerprints, const char *, fp,
    {
      if (router_digest_is_me(fp) && should_generate_v2_networkstatus())
        generate_v2_networkstatus();
      cached = digestmap_get(cached_v2_networkstatus, fp);
      if (cached) {
        smartlist_add(result, cached);
      } else {
        char hexbuf[HEX_DIGEST_LEN+1];
        base16_encode(hexbuf, sizeof(hexbuf), fp, DIGEST_LEN);
        log_info(LD_DIRSERV, "Don't know about any network status with "
                 "fingerprint '%s'", hexbuf);
      }
    });
  SMARTLIST_FOREACH(fingerprints, char *, cp, tor_free(cp));
  smartlist_free(fingerprints);
}

/** As dirserv_get_routerdescs(), but instead of getting signed_descriptor_t
 * pointers, adds copies of digests to fps_out.  For a /tor/server/d/ request,
 * adds descriptor digests; for other requests, adds identity digests.
 */
int
dirserv_get_routerdesc_fingerprints(smartlist_t *fps_out, const char *key,
                                    const char **msg)
{
  *msg = NULL;

  if (!strcmp(key, "/tor/server/all")) {
    routerlist_t *rl = router_get_routerlist();
    SMARTLIST_FOREACH(rl->routers, routerinfo_t *, r,
                      smartlist_add(fps_out,
                      tor_memdup(r->cache_info.identity_digest, DIGEST_LEN)));
  } else if (!strcmp(key, "/tor/server/authority")) {
    routerinfo_t *ri = router_get_my_routerinfo();
    if (ri)
      smartlist_add(fps_out,
                    tor_memdup(ri->cache_info.identity_digest, DIGEST_LEN));
  } else if (!strcmpstart(key, "/tor/server/d/")) {
    key += strlen("/tor/server/d/");
    dir_split_resource_into_fingerprints(key, fps_out, NULL, 1, 1);
  } else if (!strcmpstart(key, "/tor/server/fp/")) {
    key += strlen("/tor/server/fp/");
    dir_split_resource_into_fingerprints(key, fps_out, NULL, 1, 1);
  } else {
    *msg = "Key not recognized";
    return -1;
  }

  if (!smartlist_len(fps_out)) {
    *msg = "Servers unavailable";
    return -1;
  }
  return 0;
}

/** Add a signed_descriptor_t to <b>descs_out</b> for each router matching
 * <b>key</b>.  The key should be either
 *   - "/tor/server/authority" for our own routerinfo;
 *   - "/tor/server/all" for all the routerinfos we have, concatenated;
 *   - "/tor/server/fp/FP" where FP is a plus-separated sequence of
 *     hex identity digests; or
 *   - "/tor/server/d/D" where D is a plus-separated sequence
 *     of server descriptor digests, in hex.
 *
 * Return 0 if we found some matching descriptors, or -1 if we do not
 * have any descriptors, no matching descriptors, or if we did not
 * recognize the key (URL).
 * If -1 is returned *<b>msg</b> will be set to an appropriate error
 * message.
 *
 * (Despite its name, this function is also called from the controller, which
 * exposes a similar means to fetch descriptors.)
 */
int
dirserv_get_routerdescs(smartlist_t *descs_out, const char *key,
  const char **msg)
{
  *msg = NULL;

  if (!strcmp(key, "/tor/server/all")) {
    routerlist_t *rl = router_get_routerlist();
    SMARTLIST_FOREACH(rl->routers, routerinfo_t *, r,
                      smartlist_add(descs_out, &(r->cache_info)));
  } else if (!strcmp(key, "/tor/server/authority")) {
    routerinfo_t *ri = router_get_my_routerinfo();
    if (ri)
      smartlist_add(descs_out, &(ri->cache_info));
  } else if (!strcmpstart(key, "/tor/server/d/")) {
    smartlist_t *digests = smartlist_create();
    key += strlen("/tor/server/d/");
    dir_split_resource_into_fingerprints(key, digests, NULL, 1, 1);
    SMARTLIST_FOREACH(digests, const char *, d,
       {
         signed_descriptor_t *sd = router_get_by_descriptor_digest(d);
         if (sd)
           smartlist_add(descs_out,sd);
       });
    SMARTLIST_FOREACH(digests, char *, d, tor_free(d));
    smartlist_free(digests);
  } else if (!strcmpstart(key, "/tor/server/fp/")) {
    smartlist_t *digests = smartlist_create();
    time_t cutoff = time(NULL) - ROUTER_MAX_AGE_TO_PUBLISH;
    key += strlen("/tor/server/fp/");
    dir_split_resource_into_fingerprints(key, digests, NULL, 1, 1);
    SMARTLIST_FOREACH(digests, const char *, d,
       {
         if (router_digest_is_me(d)) {
           smartlist_add(descs_out, &(router_get_my_routerinfo()->cache_info));
         } else {
           routerinfo_t *ri = router_get_by_digest(d);
           /* Don't actually serve a descriptor that everyone will think is
            * expired.  This is an (ugly) workaround to keep buggy 0.1.1.10
            * Tors from downloading descriptors that they will throw away.
            */
           if (ri && ri->cache_info.published_on > cutoff)
             smartlist_add(descs_out, &(ri->cache_info));
         }
       });
    SMARTLIST_FOREACH(digests, char *, d, tor_free(d));
    smartlist_free(digests);
  } else {
    *msg = "Key not recognized";
    return -1;
  }

  if (!smartlist_len(descs_out)) {
    *msg = "Servers unavailable";
    return -1;
  }
  return 0;
}

/** Called when a TLS handshake has completed successfully with a
 * router listening at <b>address</b>:<b>or_port</b>, and has yielded
 * a certificate with digest <b>digest_rcvd</b>.
 *
 * Also, if as_advertised is 1, then inform the reachability checker
 * that we could get to this guy.
 */
void
dirserv_orconn_tls_done(const char *address,
                        uint16_t or_port,
                        const char *digest_rcvd,
                        int as_advertised)
{
  routerlist_t *rl = router_get_routerlist();
  tor_assert(address);
  tor_assert(digest_rcvd);

  SMARTLIST_FOREACH(rl->routers, routerinfo_t *, ri, {
    if (!strcasecmp(address, ri->address) && or_port == ri->or_port &&
        as_advertised &&
        !memcmp(ri->cache_info.identity_digest, digest_rcvd, DIGEST_LEN)) {
      /* correct digest. mark this router reachable! */
      log_info(LD_DIRSERV, "Found router %s to be reachable. Yay.",
               ri->nickname);
      ri->last_reachable = time(NULL);
      ri->num_unreachable_notifications = 0;
    }
  });
  /* FFFF Maybe we should reinstate the code that dumps routers with the same
   * addr/port but with nonmatching keys, but instead of dumping, we should
   * skip testing. */
}

/** Auth dir server only: if <b>try_all</b> is 1, launch connections to
 * all known routers; else we want to load balance such that we only
 * try a few connections per call.
 *
 * The load balancing is such that if we get called once every ten
 * seconds, we will cycle through all the tests in 1280 seconds (a
 * bit over 20 minutes).
 */
void
dirserv_test_reachability(int try_all)
{
  time_t now = time(NULL);
  /* XXX decide what to do here; see or-talk thread "purging old router
   * information, revocation." -NM
   * We can't afford to mess with this in 0.1.2.x. The reason is that
   * if we stop doing reachability tests on some of routerlist, then
   * we'll for-sure think they're down, which may have unexpected
   * effects in other parts of the code. It doesn't hurt much to do
   * the testing, and directory authorities are easy to upgrade. Let's
   * wait til 0.2.0. -RD */
//  time_t cutoff = now - ROUTER_MAX_AGE_TO_PUBLISH;
  routerlist_t *rl = router_get_routerlist();
  static char ctr = 0;

  SMARTLIST_FOREACH(rl->routers, routerinfo_t *, router, {
    const char *id_digest = router->cache_info.identity_digest;
    if (router_is_me(router))
      continue;
//    if (router->cache_info.published_on > cutoff)
//      continue;
    if (try_all || (((uint8_t)id_digest[0]) % 128) == ctr) {
      log_debug(LD_OR,"Testing reachability of %s at %s:%u.",
                router->nickname, router->address, router->or_port);
      /* Remember when we started trying to determine reachability */
      if (!router->testing_since)
        router->testing_since = now;
      connection_or_connect(router->addr, router->or_port,
                            id_digest);
    }
  });
  if (!try_all) /* increment ctr */
    ctr = (ctr + 1) % 128;
}

/** Return an approximate estimate of the number of bytes that will
 * be needed to transmit the server descriptors (if is_serverdescs --
 * they can be either d/ or fp/ queries) or networkstatus objects (if
 * !is_serverdescs) listed in <b>fps</b>.  If <b>compressed</b> is set,
 * we guess how large the data will be after compression.
 *
 * The return value is an estimate; it might be larger or smaller.
 **/
size_t
dirserv_estimate_data_size(smartlist_t *fps, int is_serverdescs,
                           int compressed)
{
  size_t result;
  tor_assert(fps);
  if (is_serverdescs) {
    int n = smartlist_len(fps);
    routerinfo_t *me = router_get_my_routerinfo();
    result = (me?me->cache_info.signed_descriptor_len:2048) * n;
    if (compressed)
      result /= 2; /* observed compressability is between 35 and 55%. */
  } else {
    result = 0;
    SMARTLIST_FOREACH(fps, const char *, d, {
        cached_dir_t *dir = digestmap_get(cached_v2_networkstatus, d);
        if (dir)
          result += compressed ? dir->dir_z_len : dir->dir_len;
      });
  }
  return result;
}

/** When we're spooling data onto our outbuf, add more whenever we dip
 * below this threshold. */
#define DIRSERV_BUFFER_MIN 16384

/** Spooling helper: called when we have no more data to spool to <b>conn</b>.
 * Flushes any remaining data to be (un)compressed, and changes the spool
 * source to NONE.  Returns 0 on success, negative on failure. */
static int
connection_dirserv_finish_spooling(dir_connection_t *conn)
{
  if (conn->zlib_state) {
    connection_write_to_buf_zlib("", 0, conn, 1);
    tor_zlib_free(conn->zlib_state);
    conn->zlib_state = NULL;
  }
  conn->dir_spool_src = DIR_SPOOL_NONE;
  return 0;
}

/** Spooling helper: called when we're sending a bunch of server descriptors,
 * and the outbuf has become too empty. Pulls some entries from
 * fingerprint_stack, and writes the corresponding servers onto outbuf.  If we
 * run out of entries, flushes the zlib state and sets the spool source to
 * NONE.  Returns 0 on success, negative on failure.
 */
static int
connection_dirserv_add_servers_to_outbuf(dir_connection_t *conn)
{
  int by_fp = conn->dir_spool_src == DIR_SPOOL_SERVER_BY_FP;

  while (smartlist_len(conn->fingerprint_stack) &&
         buf_datalen(conn->_base.outbuf) < DIRSERV_BUFFER_MIN) {
    const char *body;
    char *fp = smartlist_pop_last(conn->fingerprint_stack);
    signed_descriptor_t *sd = NULL;
    if (by_fp) {
      if (router_digest_is_me(fp)) {
        sd = &(router_get_my_routerinfo()->cache_info);
      } else {
        routerinfo_t *ri = router_get_by_digest(fp);
        if (ri &&
            ri->cache_info.published_on > time(NULL)-ROUTER_MAX_AGE_TO_PUBLISH)
          sd = &ri->cache_info;
      }
    } else
      sd = router_get_by_descriptor_digest(fp);
    tor_free(fp);
    if (!sd)
      continue;
    body = signed_descriptor_get_body(sd);
    if (conn->zlib_state) {
      int last = ! smartlist_len(conn->fingerprint_stack);
      connection_write_to_buf_zlib(body, sd->signed_descriptor_len, conn,
                                   last);
      if (last) {
        tor_zlib_free(conn->zlib_state);
        conn->zlib_state = NULL;
      }
    } else {
      connection_write_to_buf(body,
                              sd->signed_descriptor_len,
                              TO_CONN(conn));
    }
  }

  if (!smartlist_len(conn->fingerprint_stack)) {
    /* We just wrote the last one; finish up. */
    conn->dir_spool_src = DIR_SPOOL_NONE;
    smartlist_free(conn->fingerprint_stack);
    conn->fingerprint_stack = NULL;
  }
  return 0;
}

/** Spooling helper: Called when we're sending a directory or networkstatus,
 * and the outbuf has become too empty.  Pulls some bytes from
 * <b>conn</b>-\>cached_dir-\>dir_z, uncompresses them if appropriate, and
 * puts them on the outbuf.  If we run out of entries, flushes the zlib state
 * and sets the spool source to NONE.  Returns 0 on success, negative on
 * failure. */
static int
connection_dirserv_add_dir_bytes_to_outbuf(dir_connection_t *conn)
{
  ssize_t bytes;
  int64_t remaining;

  bytes = DIRSERV_BUFFER_MIN - buf_datalen(conn->_base.outbuf);
  tor_assert(bytes > 0);
  tor_assert(conn->cached_dir);
  if (bytes < 8192)
    bytes = 8192;
  remaining = conn->cached_dir->dir_z_len - conn->cached_dir_offset;
  if (bytes > remaining)
    bytes = (ssize_t) remaining;

  if (conn->zlib_state) {
    connection_write_to_buf_zlib(
                             conn->cached_dir->dir_z + conn->cached_dir_offset,
                             bytes, conn, bytes == remaining);
  } else {
    connection_write_to_buf(conn->cached_dir->dir_z + conn->cached_dir_offset,
                            bytes, TO_CONN(conn));
  }
  conn->cached_dir_offset += bytes;
  if (conn->cached_dir_offset == (int)conn->cached_dir->dir_z_len) {
    /* We just wrote the last one; finish up. */
    connection_dirserv_finish_spooling(conn);
    cached_dir_decref(conn->cached_dir);
    conn->cached_dir = NULL;
  }
  return 0;
}

/** Spooling helper: Called when we're spooling networkstatus objects on
 * <b>conn</b>, and the outbuf has become too empty.  If the current
 * networkstatus object (in <b>conn</b>-\>cached_dir) has more data, pull data
 * from there.  Otherwise, pop the next fingerprint from fingerprint_stack,
 * and start spooling the next networkstatus.  If we run out of entries,
 * flushes the zlib state and sets the spool source to NONE.  Returns 0 on
 * success, negative on failure. */
static int
connection_dirserv_add_networkstatus_bytes_to_outbuf(dir_connection_t *conn)
{

  while (buf_datalen(conn->_base.outbuf) < DIRSERV_BUFFER_MIN) {
    if (conn->cached_dir) {
      int uncompressing = (conn->zlib_state != NULL);
      int r = connection_dirserv_add_dir_bytes_to_outbuf(conn);
      if (conn->dir_spool_src == DIR_SPOOL_NONE) {
        /* add_dir_bytes thinks we're done with the cached_dir.  But we
         * may have more cached_dirs! */
        conn->dir_spool_src = DIR_SPOOL_NETWORKSTATUS;
        /* This bit is tricky.  If we were uncompressing the last
         * networkstatus, we may need to make a new zlib object to
         * uncompress the next one. */
        if (uncompressing && ! conn->zlib_state &&
            conn->fingerprint_stack &&
            smartlist_len(conn->fingerprint_stack)) {
          conn->zlib_state = tor_zlib_new(0, ZLIB_METHOD);
        }
      }
      if (r) return r;
    } else if (conn->fingerprint_stack &&
               smartlist_len(conn->fingerprint_stack)) {
      /* Add another networkstatus; start serving it. */
      char *fp = smartlist_pop_last(conn->fingerprint_stack);
      cached_dir_t *d;
      if (router_digest_is_me(fp))
        d = the_v2_networkstatus;
      else
        d = digestmap_get(cached_v2_networkstatus, fp);
      tor_free(fp);
      if (d) {
        ++d->refcnt;
        conn->cached_dir = d;
        conn->cached_dir_offset = 0;
      }
    } else {
      connection_dirserv_finish_spooling(conn);
      if (conn->fingerprint_stack)
        smartlist_free(conn->fingerprint_stack);
      conn->fingerprint_stack = NULL;
      return 0;
    }
  }
  return 0;
}

/** Called whenever we have flushed some directory data in state
 * SERVER_WRITING. */
int
connection_dirserv_flushed_some(dir_connection_t *conn)
{
  tor_assert(conn->_base.state == DIR_CONN_STATE_SERVER_WRITING);

  if (buf_datalen(conn->_base.outbuf) >= DIRSERV_BUFFER_MIN)
    return 0;

  switch (conn->dir_spool_src) {
    case DIR_SPOOL_SERVER_BY_DIGEST:
    case DIR_SPOOL_SERVER_BY_FP:
      return connection_dirserv_add_servers_to_outbuf(conn);
    case DIR_SPOOL_CACHED_DIR:
      return connection_dirserv_add_dir_bytes_to_outbuf(conn);
    case DIR_SPOOL_NETWORKSTATUS:
      return connection_dirserv_add_networkstatus_bytes_to_outbuf(conn);
    case DIR_SPOOL_NONE:
    default:
      return 0;
  }
}

/** Release all storage used by the directory server. */
void
dirserv_free_all(void)
{
  dirserv_free_fingerprint_list();

  cached_dir_decref(the_directory);
  clear_cached_dir(&the_runningrouters);
  cached_dir_decref(the_v2_networkstatus);
  cached_dir_decref(cached_directory);
  clear_cached_dir(&cached_runningrouters);
  if (cached_v2_networkstatus) {
    digestmap_free(cached_v2_networkstatus, _free_cached_dir);
    cached_v2_networkstatus = NULL;
  }
}