/src/libevent/evdns.c

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/* Copyright 2006-2007 Niels Provos
 * Copyright 2007-2012 Nick Mathewson and Niels Provos
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/* Based on software by Adam Langly. Adam's original message:
 *
 * Async DNS Library
 * Adam Langley <agl@imperialviolet.org>
 * http://www.imperialviolet.org/eventdns.html
 * Public Domain code
 *
 * This software is Public Domain. To view a copy of the public domain dedication,
 * visit http://creativecommons.org/licenses/publicdomain/ or send a letter to
 * Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.
 *
 * I ask and expect, but do not require, that all derivative works contain an
 * attribution similar to:
 *  Parts developed by Adam Langley <agl@imperialviolet.org>
 *
 * You may wish to replace the word "Parts" with something else depending on
 * the amount of original code.
 *
 * (Derivative works does not include programs which link against, run or include
 * the source verbatim in their source distributions)
 *
 * Version: 0.1b
 */

#include "event2/event-config.h"
#include "evconfig-private.h"

#include <sys/types.h>

#ifndef _FORTIFY_SOURCE
#define _FORTIFY_SOURCE 3
#endif

#include <string.h>
#include <fcntl.h>
#ifdef EVENT__HAVE_SYS_TIME_H
#include <sys/time.h>
#endif
#ifdef EVENT__HAVE_STDINT_H
#include <stdint.h>
#endif
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#ifdef EVENT__HAVE_UNISTD_H
#include <unistd.h>
#endif
#include <limits.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdarg.h>
#ifdef _WIN32
#include <winsock2.h>
#include <ws2tcpip.h>
#ifndef _WIN32_IE
#define _WIN32_IE 0x400
#endif
#include <shlobj.h>
#endif

#include "event2/dns.h"
#include "event2/dns_struct.h"
#include "event2/dns_compat.h"
#include "event2/util.h"
#include "event2/event.h"
#include "event2/event_struct.h"
#include "event2/thread.h"

#include "defer-internal.h"
#include "log-internal.h"
#include "mm-internal.h"
#include "strlcpy-internal.h"
#include "ipv6-internal.h"
#include "util-internal.h"
#include "evthread-internal.h"
#ifdef _WIN32
#include <ctype.h>
#include <winsock2.h>
#include <windows.h>
#include <iphlpapi.h>
#include <io.h>
#else
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#endif

#ifdef EVENT__HAVE_NETINET_IN6_H
#include <netinet/in6.h>
#endif

#define EVDNS_LOG_DEBUG EVENT_LOG_DEBUG
#define EVDNS_LOG_WARN EVENT_LOG_WARN
#define EVDNS_LOG_MSG EVENT_LOG_MSG

#ifndef HOST_NAME_MAX
#define HOST_NAME_MAX 255
#endif

#include <stdio.h>

#undef MIN
#define MIN(a,b) ((a)<(b)?(a):(b))

#define ASSERT_VALID_REQUEST(req) \
  EVUTIL_ASSERT((req)->handle && (req)->handle->current_req == (req))

#define u64 ev_uint64_t
#define u32 ev_uint32_t
#define u16 ev_uint16_t
#define u8  ev_uint8_t

/* maximum number of addresses from a single packet */
/* that we bother recording */
#define MAX_V4_ADDRS 32
#define MAX_V6_ADDRS 32


#define TYPE_A         EVDNS_TYPE_A
#define TYPE_CNAME     5
#define TYPE_PTR       EVDNS_TYPE_PTR
#define TYPE_SOA       EVDNS_TYPE_SOA
#define TYPE_AAAA      EVDNS_TYPE_AAAA

#define CLASS_INET     EVDNS_CLASS_INET

/* Persistent handle.  We keep this separate from 'struct request' since we
 * need some object to last for as long as an evdns_request is outstanding so
 * that it can be canceled, whereas a search request can lead to multiple
 * 'struct request' instances being created over its lifetime. */
struct evdns_request {
  struct request *current_req;
  struct evdns_base *base;

  int pending_cb; /* Waiting for its callback to be invoked; not
       * owned by event base any more. */

  /* elements used by the searching code */
  int search_index;
  struct search_state *search_state;
  char *search_origname;  /* needs to be free()ed */
  int search_flags;
};

struct request {
  u8 *request;  /* the dns packet data */
  u8 request_type; /* TYPE_PTR or TYPE_A or TYPE_AAAA */
  unsigned int request_len;
  int reissue_count;
  int tx_count;  /* the number of times that this packet has been sent */
  void *user_pointer;  /* the pointer given to us for this request */
  evdns_callback_type user_callback;
  struct nameserver *ns;  /* the server which we last sent it */

  /* these objects are kept in a circular list */
  /* XXX We could turn this into a CIRCLEQ. */
  struct request *next, *prev;

  struct event timeout_event;

  u16 trans_id;  /* the transaction id */
  unsigned request_appended :1; /* true if the request pointer is data which follows this struct */
  unsigned transmit_me :1;  /* needs to be transmitted */

  /* XXXX This is a horrible hack. */
  char **put_cname_in_ptr; /* store the cname here if we get one. */

  struct evdns_base *base;

  struct evdns_request *handle;
};

struct reply {
  unsigned int type;
  unsigned int have_answer : 1;
  union {
    struct {
      u32 addrcount;
      u32 addresses[MAX_V4_ADDRS];
    } a;
    struct {
      u32 addrcount;
      struct in6_addr addresses[MAX_V6_ADDRS];
    } aaaa;
    struct {
      char name[HOST_NAME_MAX];
    } ptr;
  } data;
};

struct nameserver {
  evutil_socket_t socket;  /* a connected UDP socket */
  struct sockaddr_storage address;
  ev_socklen_t addrlen;
  int failed_times;  /* number of times which we have given this server a chance */
  int timedout;  /* number of times in a row a request has timed out */
  struct event event;
  /* these objects are kept in a circular list */
  struct nameserver *next, *prev;
  struct event timeout_event;  /* used to keep the timeout for */
             /* when we next probe this server. */
             /* Valid if state == 0 */
  /* Outstanding probe request for this nameserver, if any */
  struct evdns_request *probe_request;
  char state;  /* zero if we think that this server is down */
  char choked;  /* true if we have an EAGAIN from this server's socket */
  char write_waiting;  /* true if we are waiting for EV_WRITE events */
  struct evdns_base *base;

  /* Number of currently inflight requests: used
   * to track when we should add/del the event. */
  int requests_inflight;
};


/* Represents a local port where we're listening for DNS requests. Right now, */
/* only UDP is supported. */
struct evdns_server_port {
  evutil_socket_t socket; /* socket we use to read queries and write replies. */
  int refcnt; /* reference count. */
  char choked; /* Are we currently blocked from writing? */
  char closing; /* Are we trying to close this port, pending writes? */
  evdns_request_callback_fn_type user_callback; /* Fn to handle requests */
  void *user_data; /* Opaque pointer passed to user_callback */
  struct event event; /* Read/write event */
  /* circular list of replies that we want to write. */
  struct server_request *pending_replies;
  struct event_base *event_base;

#ifndef EVENT__DISABLE_THREAD_SUPPORT
  void *lock;
#endif
};

/* Represents part of a reply being built.  (That is, a single RR.) */
struct server_reply_item {
  struct server_reply_item *next; /* next item in sequence. */
  char *name; /* name part of the RR */
  u16 type; /* The RR type */
  u16 class; /* The RR class (usually CLASS_INET) */
  u32 ttl; /* The RR TTL */
  char is_name; /* True iff data is a label */
  u16 datalen; /* Length of data; -1 if data is a label */
  void *data; /* The contents of the RR */
};

/* Represents a request that we've received as a DNS server, and holds */
/* the components of the reply as we're constructing it. */
struct server_request {
  /* Pointers to the next and previous entries on the list of replies */
  /* that we're waiting to write.  Only set if we have tried to respond */
  /* and gotten EAGAIN. */
  struct server_request *next_pending;
  struct server_request *prev_pending;

  u16 trans_id; /* Transaction id. */
  struct evdns_server_port *port; /* Which port received this request on? */
  struct sockaddr_storage addr; /* Where to send the response */
  ev_socklen_t addrlen; /* length of addr */

  int n_answer; /* how many answer RRs have been set? */
  int n_authority; /* how many authority RRs have been set? */
  int n_additional; /* how many additional RRs have been set? */

  struct server_reply_item *answer; /* linked list of answer RRs */
  struct server_reply_item *authority; /* linked list of authority RRs */
  struct server_reply_item *additional; /* linked list of additional RRs */

  /* Constructed response.  Only set once we're ready to send a reply. */
  /* Once this is set, the RR fields are cleared, and no more should be set. */
  char *response;
  size_t response_len;

  /* Caller-visible fields: flags, questions. */
  struct evdns_server_request base;
};

struct evdns_base {
  /* An array of n_req_heads circular lists for inflight requests.
   * Each inflight request req is in req_heads[req->trans_id % n_req_heads].
   */
  struct request **req_heads;
  /* A circular list of requests that we're waiting to send, but haven't
   * sent yet because there are too many requests inflight */
  struct request *req_waiting_head;
  /* A circular list of nameservers. */
  struct nameserver *server_head;
  int n_req_heads;

  struct event_base *event_base;

  /* The number of good nameservers that we have */
  int global_good_nameservers;

  /* inflight requests are contained in the req_head list */
  /* and are actually going out across the network */
  int global_requests_inflight;
  /* requests which aren't inflight are in the waiting list */
  /* and are counted here */
  int global_requests_waiting;

  int global_max_requests_inflight;

  struct timeval global_timeout;  /* 5 seconds by default */
  int global_max_reissues;  /* a reissue occurs when we get some errors from the server */
  int global_max_retransmits;  /* number of times we'll retransmit a request which timed out */
  /* number of timeouts in a row before we consider this server to be down */
  int global_max_nameserver_timeout;
  /* true iff we will use the 0x20 hack to prevent poisoning attacks. */
  int global_randomize_case;

  /* The first time that a nameserver fails, how long do we wait before
   * probing to see if it has returned?  */
  struct timeval global_nameserver_probe_initial_timeout;

  /** Port to bind to for outgoing DNS packets. */
  struct sockaddr_storage global_outgoing_address;
  /** ev_socklen_t for global_outgoing_address. 0 if it isn't set. */
  ev_socklen_t global_outgoing_addrlen;

  struct timeval global_getaddrinfo_allow_skew;

  int getaddrinfo_ipv4_timeouts;
  int getaddrinfo_ipv6_timeouts;
  int getaddrinfo_ipv4_answered;
  int getaddrinfo_ipv6_answered;

  struct search_state *global_search_state;

  TAILQ_HEAD(hosts_list, hosts_entry) hostsdb;

#ifndef EVENT__DISABLE_THREAD_SUPPORT
  void *lock;
#endif

  int disable_when_inactive;
};

struct hosts_entry {
  TAILQ_ENTRY(hosts_entry) next;
  union {
    struct sockaddr sa;
    struct sockaddr_in sin;
    struct sockaddr_in6 sin6;
  } addr;
  int addrlen;
  char hostname[1];
};

static struct evdns_base *current_base = NULL;

struct evdns_base *
evdns_get_global_base(void)
{
  return current_base;
}

/* Given a pointer to an evdns_server_request, get the corresponding */
/* server_request. */
#define TO_SERVER_REQUEST(base_ptr)         \
  ((struct server_request*)         \
    (((char*)(base_ptr) - evutil_offsetof(struct server_request, base))))

#define REQ_HEAD(base, id) ((base)->req_heads[id % (base)->n_req_heads])

static struct nameserver *nameserver_pick(struct evdns_base *base);
static void evdns_request_insert(struct request *req, struct request **head);
static void evdns_request_remove(struct request *req, struct request **head);
static void nameserver_ready_callback(evutil_socket_t fd, short events, void *arg);
static int evdns_transmit(struct evdns_base *base);
static int evdns_request_transmit(struct request *req);
static void nameserver_send_probe(struct nameserver *const ns);
static void search_request_finished(struct evdns_request *const);
static int search_try_next(struct evdns_request *const req);
static struct request *search_request_new(struct evdns_base *base, struct evdns_request *handle, int type, const char *const name, int flags, evdns_callback_type user_callback, void *user_arg);
static void evdns_requests_pump_waiting_queue(struct evdns_base *base);
static u16 transaction_id_pick(struct evdns_base *base);
static struct request *request_new(struct evdns_base *base, struct evdns_request *handle, int type, const char *name, int flags, evdns_callback_type callback, void *ptr);
static void request_submit(struct request *const req);

static int server_request_free(struct server_request *req);
static void server_request_free_answers(struct server_request *req);
static void server_port_free(struct evdns_server_port *port);
static void server_port_ready_callback(evutil_socket_t fd, short events, void *arg);
static int evdns_base_resolv_conf_parse_impl(struct evdns_base *base, int flags, const char *const filename);
static int evdns_base_set_option_impl(struct evdns_base *base,
    const char *option, const char *val, int flags);
static void evdns_base_free_and_unlock(struct evdns_base *base, int fail_requests);
static void evdns_request_timeout_callback(evutil_socket_t fd, short events, void *arg);

static int strtoint(const char *const str);

#ifdef EVENT__DISABLE_THREAD_SUPPORT
#define EVDNS_LOCK(base)  EVUTIL_NIL_STMT_
#define EVDNS_UNLOCK(base) EVUTIL_NIL_STMT_
#define ASSERT_LOCKED(base) EVUTIL_NIL_STMT_
#else
#define EVDNS_LOCK(base)      \
  EVLOCK_LOCK((base)->lock, 0)
#define EVDNS_UNLOCK(base)      \
  EVLOCK_UNLOCK((base)->lock, 0)
#define ASSERT_LOCKED(base)     \
  EVLOCK_ASSERT_LOCKED((base)->lock)
#endif

static evdns_debug_log_fn_type evdns_log_fn = NULL;

void
evdns_set_log_fn(evdns_debug_log_fn_type fn)
{
  evdns_log_fn = fn;
}

#ifdef __GNUC__
#define EVDNS_LOG_CHECK  __attribute__ ((format(printf, 2, 3)))
#else
#define EVDNS_LOG_CHECK
#endif

static void evdns_log_(int severity, const char *fmt, ...) EVDNS_LOG_CHECK;
static void
evdns_log_(int severity, const char *fmt, ...)
{
  va_list args;
  va_start(args,fmt);
  if (evdns_log_fn) {
    char buf[512];
    int is_warn = (severity == EVDNS_LOG_WARN);
    evutil_vsnprintf(buf, sizeof(buf), fmt, args);
    evdns_log_fn(is_warn, buf);
  } else {
    event_logv_(severity, NULL, fmt, args);
  }
  va_end(args);
}

#define log evdns_log_

/* This walks the list of inflight requests to find the */
/* one with a matching transaction id. Returns NULL on */
/* failure */
static struct request *
request_find_from_trans_id(struct evdns_base *base, u16 trans_id) {
  struct request *req = REQ_HEAD(base, trans_id);
  struct request *const started_at = req;

  ASSERT_LOCKED(base);

  if (req) {
    do {
      if (req->trans_id == trans_id) return req;
      req = req->next;
    } while (req != started_at);
  }

  return NULL;
}

/* a libevent callback function which is called when a nameserver */
/* has gone down and we want to test if it has came back to life yet */
static void
nameserver_prod_callback(evutil_socket_t fd, short events, void *arg) {
  struct nameserver *const ns = (struct nameserver *) arg;
  (void)fd;
  (void)events;

  EVDNS_LOCK(ns->base);
  nameserver_send_probe(ns);
  EVDNS_UNLOCK(ns->base);
}

/* a libevent callback which is called when a nameserver probe (to see if */
/* it has come back to life) times out. We increment the count of failed_times */
/* and wait longer to send the next probe packet. */
static void
nameserver_probe_failed(struct nameserver *const ns) {
  struct timeval timeout;
  int i;

  ASSERT_LOCKED(ns->base);
  (void) evtimer_del(&ns->timeout_event);
  if (ns->state == 1) {
    /* This can happen if the nameserver acts in a way which makes us mark */
    /* it as bad and then starts sending good replies. */
    return;
  }

#define MAX_PROBE_TIMEOUT 3600
#define TIMEOUT_BACKOFF_FACTOR 3

  memcpy(&timeout, &ns->base->global_nameserver_probe_initial_timeout,
      sizeof(struct timeval));
  for (i=ns->failed_times; i > 0 && timeout.tv_sec < MAX_PROBE_TIMEOUT; --i) {
    timeout.tv_sec *= TIMEOUT_BACKOFF_FACTOR;
    timeout.tv_usec *= TIMEOUT_BACKOFF_FACTOR;
    if (timeout.tv_usec > 1000000) {
      timeout.tv_sec += timeout.tv_usec / 1000000;
      timeout.tv_usec %= 1000000;
    }
  }
  if (timeout.tv_sec > MAX_PROBE_TIMEOUT) {
    timeout.tv_sec = MAX_PROBE_TIMEOUT;
    timeout.tv_usec = 0;
  }

  ns->failed_times++;

  if (evtimer_add(&ns->timeout_event, &timeout) < 0) {
    char addrbuf[128];
    log(EVDNS_LOG_WARN,
        "Error from libevent when adding timer event for %s",
        evutil_format_sockaddr_port_(
          (struct sockaddr *)&ns->address,
          addrbuf, sizeof(addrbuf)));
  }
}

static void
request_swap_ns(struct request *req, struct nameserver *ns) {
  if (ns && req->ns != ns) {
    EVUTIL_ASSERT(req->ns->requests_inflight > 0);
    req->ns->requests_inflight--;
    ns->requests_inflight++;

    req->ns = ns;
  }
}

/* called when a nameserver has been deemed to have failed. For example, too */
/* many packets have timed out etc */
static void
nameserver_failed(struct nameserver *const ns, const char *msg) {
  struct request *req, *started_at;
  struct evdns_base *base = ns->base;
  int i;
  char addrbuf[128];

  ASSERT_LOCKED(base);
  /* if this nameserver has already been marked as failed */
  /* then don't do anything */
  if (!ns->state) return;

  log(EVDNS_LOG_MSG, "Nameserver %s has failed: %s",
      evutil_format_sockaddr_port_(
        (struct sockaddr *)&ns->address,
        addrbuf, sizeof(addrbuf)),
      msg);

  base->global_good_nameservers--;
  EVUTIL_ASSERT(base->global_good_nameservers >= 0);
  if (base->global_good_nameservers == 0) {
    log(EVDNS_LOG_MSG, "All nameservers have failed");
  }

  ns->state = 0;
  ns->failed_times = 1;

  if (evtimer_add(&ns->timeout_event,
    &base->global_nameserver_probe_initial_timeout) < 0) {
    log(EVDNS_LOG_WARN,
        "Error from libevent when adding timer event for %s",
        evutil_format_sockaddr_port_(
          (struct sockaddr *)&ns->address,
          addrbuf, sizeof(addrbuf)));
    /* ???? Do more? */
  }

  /* walk the list of inflight requests to see if any can be reassigned to */
  /* a different server. Requests in the waiting queue don't have a */
  /* nameserver assigned yet */

  /* if we don't have *any* good nameservers then there's no point */
  /* trying to reassign requests to one */
  if (!base->global_good_nameservers) return;

  for (i = 0; i < base->n_req_heads; ++i) {
    req = started_at = base->req_heads[i];
    if (req) {
      do {
        if (req->tx_count == 0 && req->ns == ns) {
          /* still waiting to go out, can be moved */
          /* to another server */
          request_swap_ns(req, nameserver_pick(base));
        }
        req = req->next;
      } while (req != started_at);
    }
  }
}

static void
nameserver_up(struct nameserver *const ns)
{
  char addrbuf[128];
  ASSERT_LOCKED(ns->base);
  if (ns->state) return;
  log(EVDNS_LOG_MSG, "Nameserver %s is back up",
      evutil_format_sockaddr_port_(
        (struct sockaddr *)&ns->address,
        addrbuf, sizeof(addrbuf)));
  evtimer_del(&ns->timeout_event);
  if (ns->probe_request) {
    evdns_cancel_request(ns->base, ns->probe_request);
    ns->probe_request = NULL;
  }
  ns->state = 1;
  ns->failed_times = 0;
  ns->timedout = 0;
  ns->base->global_good_nameservers++;
}

static void
request_trans_id_set(struct request *const req, const u16 trans_id) {
  req->trans_id = trans_id;
  *((u16 *) req->request) = htons(trans_id);
}

/* Called to remove a request from a list and dealloc it. */
/* head is a pointer to the head of the list it should be */
/* removed from or NULL if the request isn't in a list. */
/* when free_handle is one, free the handle as well. */
static void
request_finished(struct request *const req, struct request **head, int free_handle) {
  struct evdns_base *base = req->base;
  int was_inflight = (head != &base->req_waiting_head);
  EVDNS_LOCK(base);
  ASSERT_VALID_REQUEST(req);

  if (head)
    evdns_request_remove(req, head);

  log(EVDNS_LOG_DEBUG, "Removing timeout for request %p", req);
  if (was_inflight) {
    evtimer_del(&req->timeout_event);
    base->global_requests_inflight--;
    req->ns->requests_inflight--;
  } else {
    base->global_requests_waiting--;
  }
  /* it was initialized during request_new / evtimer_assign */
  event_debug_unassign(&req->timeout_event);

  if (req->ns &&
      req->ns->requests_inflight == 0 &&
      req->base->disable_when_inactive) {
    event_del(&req->ns->event);
    evtimer_del(&req->ns->timeout_event);
  }

  if (!req->request_appended) {
    /* need to free the request data on it's own */
    mm_free(req->request);
  } else {
    /* the request data is appended onto the header */
    /* so everything gets free()ed when we: */
  }

  if (req->handle) {
    EVUTIL_ASSERT(req->handle->current_req == req);

    if (free_handle) {
      search_request_finished(req->handle);
      req->handle->current_req = NULL;
      if (! req->handle->pending_cb) {
        /* If we're planning to run the callback,
         * don't free the handle until later. */
        mm_free(req->handle);
      }
      req->handle = NULL; /* If we have a bug, let's crash
               * early */
    } else {
      req->handle->current_req = NULL;
    }
  }

  mm_free(req);

  evdns_requests_pump_waiting_queue(base);
  EVDNS_UNLOCK(base);
}

/* This is called when a server returns a funny error code. */
/* We try the request again with another server. */
/* */
/* return: */
/*   0 ok */
/*   1 failed/reissue is pointless */
static int
request_reissue(struct request *req) {
  const struct nameserver *const last_ns = req->ns;
  ASSERT_LOCKED(req->base);
  ASSERT_VALID_REQUEST(req);
  /* the last nameserver should have been marked as failing */
  /* by the caller of this function, therefore pick will try */
  /* not to return it */
  request_swap_ns(req, nameserver_pick(req->base));
  if (req->ns == last_ns) {
    /* ... but pick did return it */
    /* not a lot of point in trying again with the */
    /* same server */
    return 1;
  }

  req->reissue_count++;
  req->tx_count = 0;
  req->transmit_me = 1;

  return 0;
}

/* this function looks for space on the inflight queue and promotes */
/* requests from the waiting queue if it can. */
/* */
/* TODO: */
/* add return code, see at nameserver_pick() and other functions. */
static void
evdns_requests_pump_waiting_queue(struct evdns_base *base) {
  ASSERT_LOCKED(base);
  while (base->global_requests_inflight < base->global_max_requests_inflight &&
       base->global_requests_waiting) {
    struct request *req;

    EVUTIL_ASSERT(base->req_waiting_head);
    req = base->req_waiting_head;

    req->ns = nameserver_pick(base);
    if (!req->ns)
      return;

    /* move a request from the waiting queue to the inflight queue */
    req->ns->requests_inflight++;

    evdns_request_remove(req, &base->req_waiting_head);

    base->global_requests_waiting--;
    base->global_requests_inflight++;

    request_trans_id_set(req, transaction_id_pick(base));

    evdns_request_insert(req, &REQ_HEAD(base, req->trans_id));
    evdns_request_transmit(req);
    evdns_transmit(base);
  }
}

/* TODO(nickm) document */
struct deferred_reply_callback {
  struct event_callback deferred;
  struct evdns_request *handle;
  u8 request_type;
  u8 have_reply;
  u32 ttl;
  u32 err;
  evdns_callback_type user_callback;
  struct reply reply;
};

static void
reply_run_callback(struct event_callback *d, void *user_pointer)
{
  struct deferred_reply_callback *cb =
      EVUTIL_UPCAST(d, struct deferred_reply_callback, deferred);

  switch (cb->request_type) {
  case TYPE_A:
    if (cb->have_reply)
      cb->user_callback(DNS_ERR_NONE, DNS_IPv4_A,
          cb->reply.data.a.addrcount, cb->ttl,
          cb->reply.data.a.addresses,
          user_pointer);
    else
      cb->user_callback(cb->err, 0, 0, cb->ttl, NULL, user_pointer);
    break;
  case TYPE_PTR:
    if (cb->have_reply) {
      char *name = cb->reply.data.ptr.name;
      cb->user_callback(DNS_ERR_NONE, DNS_PTR, 1, cb->ttl,
          &name, user_pointer);
    } else {
      cb->user_callback(cb->err, 0, 0, cb->ttl, NULL, user_pointer);
    }
    break;
  case TYPE_AAAA:
    if (cb->have_reply)
      cb->user_callback(DNS_ERR_NONE, DNS_IPv6_AAAA,
          cb->reply.data.aaaa.addrcount, cb->ttl,
          cb->reply.data.aaaa.addresses,
          user_pointer);
    else
      cb->user_callback(cb->err, 0, 0, cb->ttl, NULL, user_pointer);
    break;
  default:
    EVUTIL_ASSERT(0);
  }

  if (cb->handle && cb->handle->pending_cb) {
    mm_free(cb->handle);
  }

  mm_free(cb);
}

static void
reply_schedule_callback(struct request *const req, u32 ttl, u32 err, struct reply *reply)
{
  struct deferred_reply_callback *d = mm_calloc(1, sizeof(*d));

  if (!d) {
    event_warn("%s: Couldn't allocate space for deferred callback.",
        __func__);
    return;
  }

  ASSERT_LOCKED(req->base);

  d->request_type = req->request_type;
  d->user_callback = req->user_callback;
  d->ttl = ttl;
  d->err = err;
  if (reply) {
    d->have_reply = 1;
    memcpy(&d->reply, reply, sizeof(struct reply));
  }

  if (req->handle) {
    req->handle->pending_cb = 1;
    d->handle = req->handle;
  }

  event_deferred_cb_init_(
      &d->deferred,
      event_get_priority(&req->timeout_event),
      reply_run_callback,
      req->user_pointer);
  event_deferred_cb_schedule_(
    req->base->event_base,
    &d->deferred);
}

/* this processes a parsed reply packet */
static void
reply_handle(struct request *const req, u16 flags, u32 ttl, struct reply *reply) {
  int error;
  char addrbuf[128];
  static const int error_codes[] = {
    DNS_ERR_FORMAT, DNS_ERR_SERVERFAILED, DNS_ERR_NOTEXIST,
    DNS_ERR_NOTIMPL, DNS_ERR_REFUSED
  };

  ASSERT_LOCKED(req->base);
  ASSERT_VALID_REQUEST(req);

  if (flags & 0x020f || !reply || !reply->have_answer) {
    /* there was an error */
    if (flags & 0x0200) {
      error = DNS_ERR_TRUNCATED;
    } else if (flags & 0x000f) {
      u16 error_code = (flags & 0x000f) - 1;
      if (error_code > 4) {
        error = DNS_ERR_UNKNOWN;
      } else {
        error = error_codes[error_code];
      }
    } else if (reply && !reply->have_answer) {
      error = DNS_ERR_NODATA;
    } else {
      error = DNS_ERR_UNKNOWN;
    }

    switch (error) {
    case DNS_ERR_NOTIMPL:
    case DNS_ERR_REFUSED:
      /* we regard these errors as marking a bad nameserver */
      if (req->reissue_count < req->base->global_max_reissues) {
        char msg[64];
        evutil_snprintf(msg, sizeof(msg), "Bad response %d (%s)",
           error, evdns_err_to_string(error));
        nameserver_failed(req->ns, msg);
        if (!request_reissue(req)) return;
      }
      break;
    case DNS_ERR_SERVERFAILED:
      /* rcode 2 (servfailed) sometimes means "we
       * are broken" and sometimes (with some binds)
       * means "that request was very confusing."
       * Treat this as a timeout, not a failure.
       */
      log(EVDNS_LOG_DEBUG, "Got a SERVERFAILED from nameserver"
        "at %s; will allow the request to time out.",
          evutil_format_sockaddr_port_(
            (struct sockaddr *)&req->ns->address,
            addrbuf, sizeof(addrbuf)));
      /* Call the timeout function */
      evdns_request_timeout_callback(0, 0, req);
      return;
    default:
      /* we got a good reply from the nameserver: it is up. */
      if (req->handle == req->ns->probe_request) {
        /* Avoid double-free */
        req->ns->probe_request = NULL;
      }

      nameserver_up(req->ns);
    }

    if (req->handle->search_state &&
        req->request_type != TYPE_PTR) {
      /* if we have a list of domains to search in,
       * try the next one */
      if (!search_try_next(req->handle)) {
        /* a new request was issued so this
         * request is finished and */
        /* the user callback will be made when
         * that request (or a */
        /* child of it) finishes. */
        return;
      }
    }

    /* all else failed. Pass the failure up */
    reply_schedule_callback(req, ttl, error, NULL);
    request_finished(req, &REQ_HEAD(req->base, req->trans_id), 1);
  } else {
    /* all ok, tell the user */
    reply_schedule_callback(req, ttl, 0, reply);
    if (req->handle == req->ns->probe_request)
      req->ns->probe_request = NULL; /* Avoid double-free */
    nameserver_up(req->ns);
    request_finished(req, &REQ_HEAD(req->base, req->trans_id), 1);
  }
}

static int
name_parse(u8 *packet, int length, int *idx, char *name_out, int name_out_len) {
  int name_end = -1;
  int j = *idx;
  int ptr_count = 0;
#define GET32(x) do { if (j + 4 > length) goto err; memcpy(&t32_, packet + j, 4); j += 4; x = ntohl(t32_); } while (0)
#define GET16(x) do { if (j + 2 > length) goto err; memcpy(&t_, packet + j, 2); j += 2; x = ntohs(t_); } while (0)
#define GET8(x) do { if (j >= length) goto err; x = packet[j++]; } while (0)

  char *cp = name_out;
  const char *const end = name_out + name_out_len;

  /* Normally, names are a series of length prefixed strings terminated */
  /* with a length of 0 (the lengths are u8's < 63). */
  /* However, the length can start with a pair of 1 bits and that */
  /* means that the next 14 bits are a pointer within the current */
  /* packet. */

  for (;;) {
    u8 label_len;
    GET8(label_len);
    if (!label_len) break;
    if (label_len & 0xc0) {
      u8 ptr_low;
      GET8(ptr_low);
      if (name_end < 0) name_end = j;
      j = (((int)label_len & 0x3f) << 8) + ptr_low;
      /* Make sure that the target offset is in-bounds. */
      if (j < 0 || j >= length) return -1;
      /* If we've jumped more times than there are characters in the
       * message, we must have a loop. */
      if (++ptr_count > length) return -1;
      continue;
    }
    if (label_len > 63) return -1;
    if (cp != name_out) {
      if (cp + 1 >= end) return -1;
      *cp++ = '.';
    }
    if (cp + label_len >= end) return -1;
    if (j + label_len > length) return -1;
    memcpy(cp, packet + j, label_len);
    cp += label_len;
    j += label_len;
  }
  if (cp >= end) return -1;
  *cp = '\0';
  if (name_end < 0)
    *idx = j;
  else
    *idx = name_end;
  return 0;
 err:
  return -1;
}

/* parses a raw request from a nameserver */
static int
reply_parse(struct evdns_base *base, u8 *packet, int length) {
  int j = 0, k = 0;  /* index into packet */
  u16 t_;   /* used by the macros */
  u32 t32_;  /* used by the macros */
  char tmp_name[256], cmp_name[256]; /* used by the macros */
  int name_matches = 0;

  u16 trans_id, questions, answers, authority, additional, datalength;
  u16 flags = 0;
  u32 ttl, ttl_r = 0xffffffff;
  struct reply reply;
  struct request *req = NULL;
  unsigned int i;

  ASSERT_LOCKED(base);

  GET16(trans_id);
  GET16(flags);
  GET16(questions);
  GET16(answers);
  GET16(authority);
  GET16(additional);
  (void) authority; /* suppress "unused variable" warnings. */
  (void) additional; /* suppress "unused variable" warnings. */

  req = request_find_from_trans_id(base, trans_id);
  if (!req) return -1;
  EVUTIL_ASSERT(req->base == base);

  memset(&reply, 0, sizeof(reply));

  /* If it's not an answer, it doesn't correspond to any request. */
  if (!(flags & 0x8000)) return -1;  /* must be an answer */
  if ((flags & 0x020f) && (flags & 0x020f) != DNS_ERR_NOTEXIST) {
    /* there was an error and it's not NXDOMAIN */
    goto err;
  }
  /* if (!answers) return; */  /* must have an answer of some form */

  /* This macro skips a name in the DNS reply. */
#define SKIP_NAME           \
  do { tmp_name[0] = '\0';       \
    if (name_parse(packet, length, &j, tmp_name,  \
      sizeof(tmp_name))<0)     \
      goto err;       \
  } while (0)

  reply.type = req->request_type;

  /* skip over each question in the reply */
  for (i = 0; i < questions; ++i) {
    /* the question looks like
     *   <label:name><u16:type><u16:class>
     */
    tmp_name[0] = '\0';
    cmp_name[0] = '\0';
    k = j;
    if (name_parse(packet, length, &j, tmp_name, sizeof(tmp_name)) < 0)
      goto err;
    if (name_parse(req->request, req->request_len, &k,
      cmp_name, sizeof(cmp_name))<0)
      goto err;
    if (!base->global_randomize_case) {
      if (strcmp(tmp_name, cmp_name) == 0)
        name_matches = 1;
    } else {
      if (evutil_ascii_strcasecmp(tmp_name, cmp_name) == 0)
        name_matches = 1;
    }

    j += 4;
    if (j > length)
      goto err;
  }

  if (!name_matches)
    goto err;

  /* now we have the answer section which looks like
   * <label:name><u16:type><u16:class><u32:ttl><u16:len><data...>
   */

  for (i = 0; i < answers; ++i) {
    u16 type, class;

    SKIP_NAME;
    GET16(type);
    GET16(class);
    GET32(ttl);
    GET16(datalength);

    if (type == TYPE_A && class == CLASS_INET) {
      int addrcount, addrtocopy;
      if (req->request_type != TYPE_A) {
        j += datalength; continue;
      }
      if ((datalength & 3) != 0) /* not an even number of As. */
          goto err;
      addrcount = datalength >> 2;
      addrtocopy = MIN(MAX_V4_ADDRS - reply.data.a.addrcount, (unsigned)addrcount);

      ttl_r = MIN(ttl_r, ttl);
      /* we only bother with the first four addresses. */
      if (j + 4*addrtocopy > length) goto err;
      memcpy(&reply.data.a.addresses[reply.data.a.addrcount],
           packet + j, 4*addrtocopy);
      j += 4*addrtocopy;
      reply.data.a.addrcount += addrtocopy;
      reply.have_answer = 1;
      if (reply.data.a.addrcount == MAX_V4_ADDRS) break;
    } else if (type == TYPE_PTR && class == CLASS_INET) {
      if (req->request_type != TYPE_PTR) {
        j += datalength; continue;
      }
      if (name_parse(packet, length, &j, reply.data.ptr.name,
               sizeof(reply.data.ptr.name))<0)
        goto err;
      ttl_r = MIN(ttl_r, ttl);
      reply.have_answer = 1;
      break;
    } else if (type == TYPE_CNAME) {
      char cname[HOST_NAME_MAX];
      if (!req->put_cname_in_ptr || *req->put_cname_in_ptr) {
        j += datalength; continue;
      }
      if (name_parse(packet, length, &j, cname,
        sizeof(cname))<0)
        goto err;
      *req->put_cname_in_ptr = mm_strdup(cname);
    } else if (type == TYPE_AAAA && class == CLASS_INET) {
      int addrcount, addrtocopy;
      if (req->request_type != TYPE_AAAA) {
        j += datalength; continue;
      }
      if ((datalength & 15) != 0) /* not an even number of AAAAs. */
        goto err;
      addrcount = datalength >> 4;  /* each address is 16 bytes long */
      addrtocopy = MIN(MAX_V6_ADDRS - reply.data.aaaa.addrcount, (unsigned)addrcount);
      ttl_r = MIN(ttl_r, ttl);

      /* we only bother with the first four addresses. */
      if (j + 16*addrtocopy > length) goto err;
      memcpy(&reply.data.aaaa.addresses[reply.data.aaaa.addrcount],
           packet + j, 16*addrtocopy);
      reply.data.aaaa.addrcount += addrtocopy;
      j += 16*addrtocopy;
      reply.have_answer = 1;
      if (reply.data.aaaa.addrcount == MAX_V6_ADDRS) break;
    } else {
      /* skip over any other type of resource */
      j += datalength;
    }
  }

  if (!reply.have_answer) {
    for (i = 0; i < authority; ++i) {
      u16 type, class;
      SKIP_NAME;
      GET16(type);
      GET16(class);
      GET32(ttl);
      GET16(datalength);
      if (type == TYPE_SOA && class == CLASS_INET) {
        u32 serial, refresh, retry, expire, minimum;
        SKIP_NAME;
        SKIP_NAME;
        GET32(serial);
        GET32(refresh);
        GET32(retry);
        GET32(expire);
        GET32(minimum);
        (void)expire;
        (void)retry;
        (void)refresh;
        (void)serial;
        ttl_r = MIN(ttl_r, ttl);
        ttl_r = MIN(ttl_r, minimum);
      } else {
        /* skip over any other type of resource */
        j += datalength;
      }
    }
  }

  if (ttl_r == 0xffffffff)
    ttl_r = 0;

  reply_handle(req, flags, ttl_r, &reply);
  return 0;
 err:
  if (req)
    reply_handle(req, flags, 0, NULL);
  return -1;
}

/* Parse a raw request (packet,length) sent to a nameserver port (port) from */
/* a DNS client (addr,addrlen), and if it's well-formed, call the corresponding */
/* callback. */
static int
request_parse(u8 *packet, int length, struct evdns_server_port *port, struct sockaddr *addr, ev_socklen_t addrlen)
{
  int j = 0;  /* index into packet */
  u16 t_;   /* used by the macros */
  char tmp_name[256]; /* used by the macros */

  int i;
  u16 trans_id, flags, questions, answers, authority, additional;
  struct server_request *server_req = NULL;

  ASSERT_LOCKED(port);

  /* Get the header fields */
  GET16(trans_id);
  GET16(flags);
  GET16(questions);
  GET16(answers);
  GET16(authority);
  GET16(additional);
  (void)answers;
  (void)additional;
  (void)authority;

  if (flags & 0x8000) return -1; /* Must not be an answer. */
  flags &= 0x0110; /* Only RD and CD get preserved. */

  server_req = mm_malloc(sizeof(struct server_request));
  if (server_req == NULL) return -1;
  memset(server_req, 0, sizeof(struct server_request));

  server_req->trans_id = trans_id;
  memcpy(&server_req->addr, addr, addrlen);
  server_req->addrlen = addrlen;

  server_req->base.flags = flags;
  server_req->base.nquestions = 0;
  server_req->base.questions = mm_calloc(sizeof(struct evdns_server_question *), questions);
  if (server_req->base.questions == NULL)
    goto err;

  for (i = 0; i < questions; ++i) {
    u16 type, class;
    struct evdns_server_question *q;
    int namelen;
    if (name_parse(packet, length, &j, tmp_name, sizeof(tmp_name))<0)
      goto err;
    GET16(type);
    GET16(class);
    namelen = (int)strlen(tmp_name);
    q = mm_malloc(sizeof(struct evdns_server_question) + namelen);
    if (!q)
      goto err;
    q->type = type;
    q->dns_question_class = class;
    memcpy(q->name, tmp_name, namelen+1);
    server_req->base.questions[server_req->base.nquestions++] = q;
  }

  /* Ignore answers, authority, and additional. */

  server_req->port = port;
  port->refcnt++;

  /* Only standard queries are supported. */
  if (flags & 0x7800) {
    evdns_server_request_respond(&(server_req->base), DNS_ERR_NOTIMPL);
    return -1;
  }

  port->user_callback(&(server_req->base), port->user_data);

  return 0;
err:
  if (server_req) {
    if (server_req->base.questions) {
      for (i = 0; i < server_req->base.nquestions; ++i)
        mm_free(server_req->base.questions[i]);
      mm_free(server_req->base.questions);
    }
    mm_free(server_req);
  }
  return -1;

#undef SKIP_NAME
#undef GET32
#undef GET16
#undef GET8
}


void
evdns_set_transaction_id_fn(ev_uint16_t (*fn)(void))
{
}

void
evdns_set_random_bytes_fn(void (*fn)(char *, size_t))
{
}

/* Try to choose a strong transaction id which isn't already in flight */
static u16
transaction_id_pick(struct evdns_base *base) {
  ASSERT_LOCKED(base);
  for (;;) {
    u16 trans_id;
    evutil_secure_rng_get_bytes(&trans_id, sizeof(trans_id));

    if (trans_id == 0xffff) continue;
    /* now check to see if that id is already inflight */
    if (request_find_from_trans_id(base, trans_id) == NULL)
      return trans_id;
  }
}

/* choose a namesever to use. This function will try to ignore */
/* nameservers which we think are down and load balance across the rest */
/* by updating the server_head global each time. */
static struct nameserver *
nameserver_pick(struct evdns_base *base) {
  struct nameserver *started_at = base->server_head, *picked;
  ASSERT_LOCKED(base);
  if (!base->server_head) return NULL;

  /* if we don't have any good nameservers then there's no */
  /* point in trying to find one. */
  if (!base->global_good_nameservers) {
    base->server_head = base->server_head->next;
    return base->server_head;
  }

  /* remember that nameservers are in a circular list */
  for (;;) {
    if (base->server_head->state) {
      /* we think this server is currently good */
      picked = base->server_head;
      base->server_head = base->server_head->next;
      return picked;
    }

    base->server_head = base->server_head->next;
    if (base->server_head == started_at) {
      /* all the nameservers seem to be down */
      /* so we just return this one and hope for the */
      /* best */
      EVUTIL_ASSERT(base->global_good_nameservers == 0);
      picked = base->server_head;
      base->server_head = base->server_head->next;
      return picked;
    }
  }
}

/* this is called when a namesever socket is ready for reading */
static void
nameserver_read(struct nameserver *ns) {
  struct sockaddr_storage ss;
  ev_socklen_t addrlen = sizeof(ss);
  u8 packet[1500];
  char addrbuf[128];
  ASSERT_LOCKED(ns->base);

  for (;;) {
    const int r = recvfrom(ns->socket, (void*)packet,
        sizeof(packet), 0,
        (struct sockaddr*)&ss, &addrlen);
    if (r < 0) {
      int err = evutil_socket_geterror(ns->socket);
      if (EVUTIL_ERR_RW_RETRIABLE(err))
        return;
      nameserver_failed(ns,
          evutil_socket_error_to_string(err));
      return;
    }
    if (evutil_sockaddr_cmp((struct sockaddr*)&ss,
      (struct sockaddr*)&ns->address, 0)) {
      log(EVDNS_LOG_WARN, "Address mismatch on received "
          "DNS packet.  Apparent source was %s",
          evutil_format_sockaddr_port_(
            (struct sockaddr *)&ss,
            addrbuf, sizeof(addrbuf)));
      return;
    }

    ns->timedout = 0;
    reply_parse(ns->base, packet, r);
  }
}

/* Read a packet from a DNS client on a server port s, parse it, and */
/* act accordingly. */
static void
server_port_read(struct evdns_server_port *s) {
  u8 packet[1500];
  struct sockaddr_storage addr;
  ev_socklen_t addrlen;
  int r;
  ASSERT_LOCKED(s);

  for (;;) {
    addrlen = sizeof(struct sockaddr_storage);
    r = recvfrom(s->socket, (void*)packet, sizeof(packet), 0,
           (struct sockaddr*) &addr, &addrlen);
    if (r < 0) {
      int err = evutil_socket_geterror(s->socket);
      if (EVUTIL_ERR_RW_RETRIABLE(err))
        return;
      log(EVDNS_LOG_WARN,
          "Error %s (%d) while reading request.",
          evutil_socket_error_to_string(err), err);
      return;
    }
    request_parse(packet, r, s, (struct sockaddr*) &addr, addrlen);
  }
}

/* Try to write all pending replies on a given DNS server port. */
static void
server_port_flush(struct evdns_server_port *port)
{
  struct server_request *req = port->pending_replies;
  ASSERT_LOCKED(port);
  while (req) {
    int r = sendto(port->socket, req->response, (int)req->response_len, 0,
         (struct sockaddr*) &req->addr, (ev_socklen_t)req->addrlen);
    if (r < 0) {
      int err = evutil_socket_geterror(port->socket);
      if (EVUTIL_ERR_RW_RETRIABLE(err))
        return;
      log(EVDNS_LOG_WARN, "Error %s (%d) while writing response to port; dropping", evutil_socket_error_to_string(err), err);
    }
    if (server_request_free(req)) {
      /* we released the last reference to req->port. */
      return;
    } else {
      EVUTIL_ASSERT(req != port->pending_replies);
      req = port->pending_replies;
    }
  }

  /* We have no more pending requests; stop listening for 'writeable' events. */
  (void) event_del(&port->event);
  event_assign(&port->event, port->event_base,
         port->socket, EV_READ | EV_PERSIST,
         server_port_ready_callback, port);

  if (event_add(&port->event, NULL) < 0) {
    log(EVDNS_LOG_WARN, "Error from libevent when adding event for DNS server.");
    /* ???? Do more? */
  }
}

/* set if we are waiting for the ability to write to this server. */
/* if waiting is true then we ask libevent for EV_WRITE events, otherwise */
/* we stop these events. */
static void
nameserver_write_waiting(struct nameserver *ns, char waiting) {
  ASSERT_LOCKED(ns->base);
  if (ns->write_waiting == waiting) return;

  ns->write_waiting = waiting;
  (void) event_del(&ns->event);
  event_assign(&ns->event, ns->base->event_base,
      ns->socket, EV_READ | (waiting ? EV_WRITE : 0) | EV_PERSIST,
      nameserver_ready_callback, ns);
  if (event_add(&ns->event, NULL) < 0) {
    char addrbuf[128];
    log(EVDNS_LOG_WARN, "Error from libevent when adding event for %s",
        evutil_format_sockaddr_port_(
          (struct sockaddr *)&ns->address,
          addrbuf, sizeof(addrbuf)));
    /* ???? Do more? */
  }
}

/* a callback function. Called by libevent when the kernel says that */
/* a nameserver socket is ready for writing or reading */
static void
nameserver_ready_callback(evutil_socket_t fd, short events, void *arg) {
  struct nameserver *ns = (struct nameserver *) arg;
  (void)fd;

  EVDNS_LOCK(ns->base);
  if (events & EV_WRITE) {
    ns->choked = 0;
    if (!evdns_transmit(ns->base)) {
      nameserver_write_waiting(ns, 0);
    }
  }
  if (events & EV_READ) {
    nameserver_read(ns);
  }
  EVDNS_UNLOCK(ns->base);
}

/* a callback function. Called by libevent when the kernel says that */
/* a server socket is ready for writing or reading. */
static void
server_port_ready_callback(evutil_socket_t fd, short events, void *arg) {
  struct evdns_server_port *port = (struct evdns_server_port *) arg;
  (void) fd;

  EVDNS_LOCK(port);
  if (events & EV_WRITE) {
    port->choked = 0;
    server_port_flush(port);
  }
  if (events & EV_READ) {
    server_port_read(port);
  }
  EVDNS_UNLOCK(port);
}

/* This is an inefficient representation; only use it via the dnslabel_table_*
 * functions, so that is can be safely replaced with something smarter later. */
#define MAX_LABELS 128
/* Structures used to implement name compression */
struct dnslabel_entry { char *v; off_t pos; };
struct dnslabel_table {
  int n_labels; /* number of current entries */
  /* map from name to position in message */
  struct dnslabel_entry labels[MAX_LABELS];
};

/* Initialize dnslabel_table. */
static void
dnslabel_table_init(struct dnslabel_table *table)
{
  table->n_labels = 0;
}

/* Free all storage held by table, but not the table itself. */
static void
dnslabel_clear(struct dnslabel_table *table)
{
  int i;
  for (i = 0; i < table->n_labels; ++i)
    mm_free(table->labels[i].v);
  table->n_labels = 0;
}

/* return the position of the label in the current message, or -1 if the label */
/* hasn't been used yet. */
static int
dnslabel_table_get_pos(const struct dnslabel_table *table, const char *label)
{
  int i;
  for (i = 0; i < table->n_labels; ++i) {
    if (!strcmp(label, table->labels[i].v))
      return table->labels[i].pos;
  }
  return -1;
}

/* remember that we've used the label at position pos */
static int
dnslabel_table_add(struct dnslabel_table *table, const char *label, off_t pos)
{
  char *v;
  int p;
  if (table->n_labels == MAX_LABELS)
    return (-1);
  v = mm_strdup(label);
  if (v == NULL)
    return (-1);
  p = table->n_labels++;
  table->labels[p].v = v;
  table->labels[p].pos = pos;

  return (0);
}

/* Converts a string to a length-prefixed set of DNS labels, starting */
/* at buf[j]. name and buf must not overlap. name_len should be the length */
/* of name.  table is optional, and is used for compression. */
/* */
/* Input: abc.def */
/* Output: <3>abc<3>def<0> */
/* */
/* Returns the first index after the encoded name, or negative on error. */
/*   -1  label was > 63 bytes */
/*   -2  name too long to fit in buffer. */
/* */
static off_t
dnsname_to_labels(u8 *const buf, size_t buf_len, off_t j,
          const char *name, const size_t name_len,
          struct dnslabel_table *table) {
  const char *end = name + name_len;
  int ref = 0;
  u16 t_;

#define APPEND16(x) do {           \
    if (j + 2 > (off_t)buf_len)       \
      goto overflow;         \
    t_ = htons(x);            \
    memcpy(buf + j, &t_, 2);        \
    j += 2;             \
  } while (0)
#define APPEND32(x) do {           \
    if (j + 4 > (off_t)buf_len)       \
      goto overflow;         \
    t32_ = htonl(x);          \
    memcpy(buf + j, &t32_, 4);        \
    j += 4;             \
  } while (0)

  if (name_len > 255) return -2;

  for (;;) {
    const char *const start = name;
    if (table && (ref = dnslabel_table_get_pos(table, name)) >= 0) {
      APPEND16(ref | 0xc000);
      return j;
    }
    name = strchr(name, '.');
    if (!name) {
      const size_t label_len = end - start;
      if (label_len > 63) return -1;
      if ((size_t)(j+label_len+1) > buf_len) return -2;
      if (table) dnslabel_table_add(table, start, j);
      buf[j++] = (ev_uint8_t)label_len;

      memcpy(buf + j, start, label_len);
      j += (int) label_len;
      break;
    } else {
      /* append length of the label. */
      const size_t label_len = name - start;
      if (label_len > 63) return -1;
      if ((size_t)(j+label_len+1) > buf_len) return -2;
      if (table) dnslabel_table_add(table, start, j);
      buf[j++] = (ev_uint8_t)label_len;

      memcpy(buf + j, start, label_len);
      j += (int) label_len;
      /* hop over the '.' */
      name++;
    }
  }

  /* the labels must be terminated by a 0. */
  /* It's possible that the name ended in a . */
  /* in which case the zero is already there */
  if (!j || buf[j-1]) buf[j++] = 0;
  return j;
 overflow:
  return (-2);
}

/* Finds the length of a dns request for a DNS name of the given */
/* length. The actual request may be smaller than the value returned */
/* here */
static size_t
evdns_request_len(const size_t name_len) {
  return 96 + /* length of the DNS standard header */
    name_len + 2 +
    4;  /* space for the resource type */
}

/* build a dns request packet into buf. buf should be at least as long */
/* as evdns_request_len told you it should be. */
/* */
/* Returns the amount of space used. Negative on error. */
static int
evdns_request_data_build(const char *const name, const size_t name_len,
    const u16 trans_id, const u16 type, const u16 class,
    u8 *const buf, size_t buf_len) {
  off_t j = 0;  /* current offset into buf */
  u16 t_;   /* used by the macros */

  APPEND16(trans_id);
  APPEND16(0x0100);  /* standard query, recusion needed */
  APPEND16(1);  /* one question */
  APPEND16(0);  /* no answers */
  APPEND16(0);  /* no authority */
  APPEND16(0);  /* no additional */

  j = dnsname_to_labels(buf, buf_len, j, name, name_len, NULL);
  if (j < 0) {
    return (int)j;
  }

  APPEND16(type);
  APPEND16(class);

  return (int)j;
 overflow:
  return (-1);
}

/* exported function */
struct evdns_server_port *
evdns_add_server_port_with_base(struct event_base *base, evutil_socket_t socket, int flags, evdns_request_callback_fn_type cb, void *user_data)
{
  struct evdns_server_port *port;
  if (flags)
    return NULL; /* flags not yet implemented */
  if (!(port = mm_malloc(sizeof(struct evdns_server_port))))
    return NULL;
  memset(port, 0, sizeof(struct evdns_server_port));


  port->socket = socket;
  port->refcnt = 1;
  port->choked = 0;
  port->closing = 0;
  port->user_callback = cb;
  port->user_data = user_data;
  port->pending_replies = NULL;
  port->event_base = base;

  event_assign(&port->event, port->event_base,
         port->socket, EV_READ | EV_PERSIST,
         server_port_ready_callback, port);
  if (event_add(&port->event, NULL) < 0) {
    mm_free(port);
    return NULL;
  }
  EVTHREAD_ALLOC_LOCK(port->lock, EVTHREAD_LOCKTYPE_RECURSIVE);
  return port;
}

struct evdns_server_port *
evdns_add_server_port(evutil_socket_t socket, int flags, evdns_request_callback_fn_type cb, void *user_data)
{
  return evdns_add_server_port_with_base(NULL, socket, flags, cb, user_data);
}

/* exported function */
void
evdns_close_server_port(struct evdns_server_port *port)
{
  EVDNS_LOCK(port);
  if (--port->refcnt == 0) {
    EVDNS_UNLOCK(port);
    server_port_free(port);
  } else {
    port->closing = 1;
  }
}

/* exported function */
int
evdns_server_request_add_reply(struct evdns_server_request *req_, int section, const char *name, int type, int class, int ttl, int datalen, int is_name, const char *data)
{
  struct server_request *req = TO_SERVER_REQUEST(req_);
  struct server_reply_item **itemp, *item;
  int *countp;
  int result = -1;

  EVDNS_LOCK(req->port);
  if (req->response) /* have we already answered? */
    goto done;

  switch (section) {
  case EVDNS_ANSWER_SECTION:
    itemp = &req->answer;
    countp = &req->n_answer;
    break;
  case EVDNS_AUTHORITY_SECTION:
    itemp = &req->authority;
    countp = &req->n_authority;
    break;
  case EVDNS_ADDITIONAL_SECTION:
    itemp = &req->additional;
    countp = &req->n_additional;
    break;
  default:
    goto done;
  }
  while (*itemp) {
    itemp = &((*itemp)->next);
  }
  item = mm_malloc(sizeof(struct server_reply_item));
  if (!item)
    goto done;
  item->next = NULL;
  if (!(item->name = mm_strdup(name))) {
    mm_free(item);
    goto done;
  }
  item->type = type;
  item->dns_question_class = class;
  item->ttl = ttl;
  item->is_name = is_name != 0;
  item->datalen = 0;
  item->data = NULL;
  if (data) {
    if (item->is_name) {
      if (!(item->data = mm_strdup(data))) {
        mm_free(item->name);
        mm_free(item);
        goto done;
      }
      item->datalen = (u16)-1;
    } else {
      if (!(item->data = mm_malloc(datalen))) {
        mm_free(item->name);
        mm_free(item);
        goto done;
      }
      item->datalen = datalen;
      memcpy(item->data, data, datalen);
    }
  }

  *itemp = item;
  ++(*countp);
  result = 0;
done:
  EVDNS_UNLOCK(req->port);
  return result;
}

/* exported function */
int
evdns_server_request_add_a_reply(struct evdns_server_request *req, const char *name, int n, const void *addrs, int ttl)
{
  return evdns_server_request_add_reply(
      req, EVDNS_ANSWER_SECTION, name, TYPE_A, CLASS_INET,
      ttl, n*4, 0, addrs);
}

/* exported function */
int
evdns_server_request_add_aaaa_reply(struct evdns_server_request *req, const char *name, int n, const void *addrs, int ttl)
{
  return evdns_server_request_add_reply(
      req, EVDNS_ANSWER_SECTION, name, TYPE_AAAA, CLASS_INET,
      ttl, n*16, 0, addrs);
}

/* exported function */
int
evdns_server_request_add_ptr_reply(struct evdns_server_request *req, struct in_addr *in, const char *inaddr_name, const char *hostname, int ttl)
{
  u32 a;
  char buf[32];
  if (in && inaddr_name)
    return -1;
  else if (!in && !inaddr_name)
    return -1;
  if (in) {
    a = ntohl(in->s_addr);
    evutil_snprintf(buf, sizeof(buf), "%d.%d.%d.%d.in-addr.arpa",
        (int)(u8)((a  )&0xff),
        (int)(u8)((a>>8 )&0xff),
        (int)(u8)((a>>16)&0xff),
        (int)(u8)((a>>24)&0xff));
    inaddr_name = buf;
  }
  return evdns_server_request_add_reply(
      req, EVDNS_ANSWER_SECTION, inaddr_name, TYPE_PTR, CLASS_INET,
      ttl, -1, 1, hostname);
}

/* exported function */
int
evdns_server_request_add_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl)
{
  return evdns_server_request_add_reply(
      req, EVDNS_ANSWER_SECTION, name, TYPE_CNAME, CLASS_INET,
      ttl, -1, 1, cname);
}

/* exported function */
void
evdns_server_request_set_flags(struct evdns_server_request *exreq, int flags)
{
  struct server_request *req = TO_SERVER_REQUEST(exreq);
  req->base.flags &= ~(EVDNS_FLAGS_AA|EVDNS_FLAGS_RD);
  req->base.flags |= flags;
}

static int
evdns_server_request_format_response(struct server_request *req, int err)
{
  unsigned char buf[1500];
  size_t buf_len = sizeof(buf);
  off_t j = 0, r;
  u16 t_;
  u32 t32_;
  int i;
  u16 flags;
  struct dnslabel_table table;

  if (err < 0 || err > 15) return -1;

  /* Set response bit and error code; copy OPCODE and RD fields from
   * question; copy RA and AA if set by caller. */
  flags = req->base.flags;
  flags |= (0x8000 | err);

  dnslabel_table_init(&table);
  APPEND16(req->trans_id);
  APPEND16(flags);
  APPEND16(req->base.nquestions);
  APPEND16(req->n_answer);
  APPEND16(req->n_authority);
  APPEND16(req->n_additional);

  /* Add questions. */
  for (i=0; i < req->base.nquestions; ++i) {
    const char *s = req->base.questions[i]->name;
    j = dnsname_to_labels(buf, buf_len, j, s, strlen(s), &table);
    if (j < 0) {
      dnslabel_clear(&table);
      return (int) j;
    }
    APPEND16(req->base.questions[i]->type);
    APPEND16(req->base.questions[i]->dns_question_class);
  }

  /* Add answer, authority, and additional sections. */
  for (i=0; i<3; ++i) {
    struct server_reply_item *item;
    if (i==0)
      item = req->answer;
    else if (i==1)
      item = req->authority;
    else
      item = req->additional;
    while (item) {
      r = dnsname_to_labels(buf, buf_len, j, item->name, strlen(item->name), &table);
      if (r < 0)
        goto overflow;
      j = r;

      APPEND16(item->type);
      APPEND16(item->dns_question_class);
      APPEND32(item->ttl);
      if (item->is_name) {
        off_t len_idx = j, name_start;
        j += 2;
        name_start = j;
        r = dnsname_to_labels(buf, buf_len, j, item->data, strlen(item->data), &table);
        if (r < 0)
          goto overflow;
        j = r;
        t_ = htons( (short) (j-name_start) );
        memcpy(buf+len_idx, &t_, 2);
      } else {
        APPEND16(item->datalen);
        if (j+item->datalen > (off_t)buf_len)
          goto overflow;
        memcpy(buf+j, item->data, item->datalen);
        j += item->datalen;
      }
      item = item->next;
    }
  }

  if (j > 512) {
overflow:
    j = 512;
    buf[2] |= 0x02; /* set the truncated bit. */
  }

  req->response_len = j;

  if (!(req->response = mm_malloc(req->response_len))) {
    server_request_free_answers(req);
    dnslabel_clear(&table);
    return (-1);
  }
  memcpy(req->response, buf, req->response_len);
  server_request_free_answers(req);
  dnslabel_clear(&table);
  return (0);
}

/* exported function */
int
evdns_server_request_respond(struct evdns_server_request *req_, int err)
{
  struct server_request *req = TO_SERVER_REQUEST(req_);
  struct evdns_server_port *port = req->port;
  int r = -1;

  EVDNS_LOCK(port);
  if (!req->response) {
    if ((r = evdns_server_request_format_response(req, err))<0)
      goto done;
  }

  r = sendto(port->socket, req->response, (int)req->response_len, 0,
         (struct sockaddr*) &req->addr, (ev_socklen_t)req->addrlen);
  if (r<0) {
    int sock_err = evutil_socket_geterror(port->socket);
    if (EVUTIL_ERR_RW_RETRIABLE(sock_err))
      goto done;

    if (port->pending_replies) {
      req->prev_pending = port->pending_replies->prev_pending;
      req->next_pending = port->pending_replies;
      req->prev_pending->next_pending =
        req->next_pending->prev_pending = req;
    } else {
      req->prev_pending = req->next_pending = req;
      port->pending_replies = req;
      port->choked = 1;

      (void) event_del(&port->event);
      event_assign(&port->event, port->event_base, port->socket, (port->closing?0:EV_READ) | EV_WRITE | EV_PERSIST, server_port_ready_callback, port);

      if (event_add(&port->event, NULL) < 0) {
        log(EVDNS_LOG_WARN, "Error from libevent when adding event for DNS server");
      }

    }

    r = 1;
    goto done;
  }
  if (server_request_free(req)) {
    r = 0;
    goto done;
  }

  if (port->pending_replies)
    server_port_flush(port);

  r = 0;
done:
  EVDNS_UNLOCK(port);
  return r;
}

/* Free all storage held by RRs in req. */
static void
server_request_free_answers(struct server_request *req)
{
  struct server_reply_item *victim, *next, **list;
  int i;
  for (i = 0; i < 3; ++i) {
    if (i==0)
      list = &req->answer;
    else if (i==1)
      list = &req->authority;
    else
      list = &req->additional;

    victim = *list;
    while (victim) {
      next = victim->next;
      mm_free(victim->name);
      if (victim->data)
        mm_free(victim->data);
      mm_free(victim);
      victim = next;
    }
    *list = NULL;
  }
}

/* Free all storage held by req, and remove links to it. */
/* return true iff we just wound up freeing the server_port. */
static int
server_request_free(struct server_request *req)
{
  int i, rc=1, lock=0;
  if (req->base.questions) {
    for (i = 0; i < req->base.nquestions; ++i)
      mm_free(req->base.questions[i]);
    mm_free(req->base.questions);
  }

  if (req->port) {
    EVDNS_LOCK(req->port);
    lock=1;
    if (req->port->pending_replies == req) {
      if (req->next_pending && req->next_pending != req)
        req->port->pending_replies = req->next_pending;
      else
        req->port->pending_replies = NULL;
    }
    rc = --req->port->refcnt;
  }

  if (req->response) {
    mm_free(req->response);
  }

  server_request_free_answers(req);

  if (req->next_pending && req->next_pending != req) {
    req->next_pending->prev_pending = req->prev_pending;
    req->prev_pending->next_pending = req->next_pending;
  }

  if (rc == 0) {
    EVDNS_UNLOCK(req->port); /* ????? nickm */
    server_port_free(req->port);
    mm_free(req);
    return (1);
  }
  if (lock)
    EVDNS_UNLOCK(req->port);
  mm_free(req);
  return (0);
}

/* Free all storage held by an evdns_server_port.  Only called when  */
static void
server_port_free(struct evdns_server_port *port)
{
  EVUTIL_ASSERT(port);
  EVUTIL_ASSERT(!port->refcnt);
  EVUTIL_ASSERT(!port->pending_replies);
  if (port->socket > 0) {
    evutil_closesocket(port->socket);
    port->socket = -1;
  }
  (void) event_del(&port->event);
  event_debug_unassign(&port->event);
  EVTHREAD_FREE_LOCK(port->lock, EVTHREAD_LOCKTYPE_RECURSIVE);
  mm_free(port);
}

/* exported function */
int
evdns_server_request_drop(struct evdns_server_request *req_)
{
  struct server_request *req = TO_SERVER_REQUEST(req_);
  server_request_free(req);
  return 0;
}

/* exported function */
int
evdns_server_request_get_requesting_addr(struct evdns_server_request *req_, struct sockaddr *sa, int addr_len)
{
  struct server_request *req = TO_SERVER_REQUEST(req_);
  if (addr_len < (int)req->addrlen)
    return -1;
  memcpy(sa, &(req->addr), req->addrlen);
  return req->addrlen;
}

#undef APPEND16
#undef APPEND32

/* this is a libevent callback function which is called when a request */
/* has timed out. */
static void
evdns_request_timeout_callback(evutil_socket_t fd, short events, void *arg) {
  struct request *const req = (struct request *) arg;
  struct evdns_base *base = req->base;

  (void) fd;
  (void) events;

  log(EVDNS_LOG_DEBUG, "Request %p timed out", arg);
  EVDNS_LOCK(base);

  if (req->tx_count >= req->base->global_max_retransmits) {
    struct nameserver *ns = req->ns;
    /* this request has failed */
    log(EVDNS_LOG_DEBUG, "Giving up on request %p; tx_count==%d",
        arg, req->tx_count);
    reply_schedule_callback(req, 0, DNS_ERR_TIMEOUT, NULL);

    request_finished(req, &REQ_HEAD(req->base, req->trans_id), 1);
    nameserver_failed(ns, "request timed out.");
  } else {
    /* retransmit it */
    log(EVDNS_LOG_DEBUG, "Retransmitting request %p; tx_count==%d",
        arg, req->tx_count);
    (void) evtimer_del(&req->timeout_event);
    request_swap_ns(req, nameserver_pick(base));
    evdns_request_transmit(req);

    req->ns->timedout++;
    if (req->ns->timedout > req->base->global_max_nameserver_timeout) {
      req->ns->timedout = 0;
      nameserver_failed(req->ns, "request timed out.");
    }
  }

  EVDNS_UNLOCK(base);
}

/* try to send a request to a given server. */
/* */
/* return: */
/*   0 ok */
/*   1 temporary failure */
/*   2 other failure */
static int
evdns_request_transmit_to(struct request *req, struct nameserver *server) {
  int r;
  ASSERT_LOCKED(req->base);
  ASSERT_VALID_REQUEST(req);

  if (server->requests_inflight == 1 &&
    req->base->disable_when_inactive &&
    event_add(&server->event, NULL) < 0) {
    return 1;
  }

  r = sendto(server->socket, (void*)req->request, req->request_len, 0,
      (struct sockaddr *)&server->address, server->addrlen);
  if (r < 0) {
    int err = evutil_socket_geterror(server->socket);
    if (EVUTIL_ERR_RW_RETRIABLE(err))
      return 1;
    nameserver_failed(req->ns, evutil_socket_error_to_string(err));
    return 2;
  } else if (r != (int)req->request_len) {
    return 1;  /* short write */
  } else {
    return 0;
  }
}

/* try to send a request, updating the fields of the request */
/* as needed */
/* */
/* return: */
/*   0 ok */
/*   1 failed */
static int
evdns_request_transmit(struct request *req) {
  int retcode = 0, r;

  ASSERT_LOCKED(req->base);
  ASSERT_VALID_REQUEST(req);
  /* if we fail to send this packet then this flag marks it */
  /* for evdns_transmit */
  req->transmit_me = 1;
  EVUTIL_ASSERT(req->trans_id != 0xffff);

  if (!req->ns)
  {
    /* unable to transmit request if no nameservers */
    return 1;
  }

  if (req->ns->choked) {
    /* don't bother trying to write to a socket */
    /* which we have had EAGAIN from */
    return 1;
  }

  r = evdns_request_transmit_to(req, req->ns);
  switch (r) {
  case 1:
    /* temp failure */
    req->ns->choked = 1;
    nameserver_write_waiting(req->ns, 1);
    return 1;
  case 2:
    /* failed to transmit the request entirely. we can fallthrough since
     * we'll set a timeout, which will time out, and make us retransmit the
     * request anyway. */
    retcode = 1;
    EVUTIL_FALLTHROUGH;
  default:
    /* all ok */
    log(EVDNS_LOG_DEBUG,
        "Setting timeout for request %p, sent to nameserver %p", req, req->ns);
    if (evtimer_add(&req->timeout_event, &req->base->global_timeout) < 0) {
      log(EVDNS_LOG_WARN,
          "Error from libevent when adding timer for request %p",
          req);
      /* ???? Do more? */
    }
    req->tx_count++;
    req->transmit_me = 0;
    return retcode;
  }
}

static void
nameserver_probe_callback(int result, char type, int count, int ttl, void *addresses, void *arg) {
  struct nameserver *const ns = (struct nameserver *) arg;
  (void) type;
  (void) count;
  (void) ttl;
  (void) addresses;

  if (result == DNS_ERR_CANCEL) {
    /* We canceled this request because the nameserver came up
     * for some other reason.  Do not change our opinion about
     * the nameserver. */
    return;
  }

  EVDNS_LOCK(ns->base);
  ns->probe_request = NULL;
  if (result == DNS_ERR_NONE || result == DNS_ERR_NOTEXIST) {
    /* this is a good reply */
    nameserver_up(ns);
  } else {
    nameserver_probe_failed(ns);
  }
  EVDNS_UNLOCK(ns->base);
}

static void
nameserver_send_probe(struct nameserver *const ns) {
  struct evdns_request *handle;
  struct request *req;
  char addrbuf[128];
  /* here we need to send a probe to a given nameserver */
  /* in the hope that it is up now. */

  ASSERT_LOCKED(ns->base);
  log(EVDNS_LOG_DEBUG, "Sending probe to %s",
      evutil_format_sockaddr_port_(
        (struct sockaddr *)&ns->address,
        addrbuf, sizeof(addrbuf)));
  handle = mm_calloc(1, sizeof(*handle));
  if (!handle) return;
  req = request_new(ns->base, handle, TYPE_A, "google.com", DNS_QUERY_NO_SEARCH, nameserver_probe_callback, ns);
  if (!req) {
    mm_free(handle);
    return;
  }
  ns->probe_request = handle;
  /* we force this into the inflight queue no matter what */
  request_trans_id_set(req, transaction_id_pick(ns->base));
  req->ns = ns;
  request_submit(req);
}

/* returns: */
/*   0 didn't try to transmit anything */
/*   1 tried to transmit something */
static int
evdns_transmit(struct evdns_base *base) {
  char did_try_to_transmit = 0;
  int i;

  ASSERT_LOCKED(base);
  for (i = 0; i < base->n_req_heads; ++i) {
    if (base->req_heads[i]) {
      struct request *const started_at = base->req_heads[i], *req = started_at;
      /* first transmit all the requests which are currently waiting */
      do {
        if (req->transmit_me) {
          did_try_to_transmit = 1;
          evdns_request_transmit(req);
        }

        req = req->next;
      } while (req != started_at);
    }
  }

  return did_try_to_transmit;
}

/* exported function */
int
evdns_base_count_nameservers(struct evdns_base *base)
{
  const struct nameserver *server;
  int n = 0;

  EVDNS_LOCK(base);
  server = base->server_head;
  if (!server)
    goto done;
  do {
    ++n;
    server = server->next;
  } while (server != base->server_head);
done:
  EVDNS_UNLOCK(base);
  return n;
}

int
evdns_count_nameservers(void)
{
  return evdns_base_count_nameservers(current_base);
}

/* exported function */
int
evdns_base_clear_nameservers_and_suspend(struct evdns_base *base)
{
  struct nameserver *server, *started_at;
  int i;

  EVDNS_LOCK(base);
  server = base->server_head;
  started_at = base->server_head;
  if (!server) {
    EVDNS_UNLOCK(base);
    return 0;
  }
  while (1) {
    struct nameserver *next = server->next;
    (void) event_del(&server->event);
    if (evtimer_initialized(&server->timeout_event))
      (void) evtimer_del(&server->timeout_event);
    if (server->probe_request) {
      evdns_cancel_request(server->base, server->probe_request);
      server->probe_request = NULL;
    }
    if (server->socket >= 0)
      evutil_closesocket(server->socket);
    mm_free(server);
    if (next == started_at)
      break;
    server = next;
  }
  base->server_head = NULL;
  base->global_good_nameservers = 0;

  for (i = 0; i < base->n_req_heads; ++i) {
    struct request *req, *req_started_at;
    req = req_started_at = base->req_heads[i];
    while (req) {
      struct request *next = req->next;
      req->tx_count = req->reissue_count = 0;
      req->ns = NULL;
      /* ???? What to do about searches? */
      (void) evtimer_del(&req->timeout_event);
      req->trans_id = 0;
      req->transmit_me = 0;

      base->global_requests_waiting++;
      evdns_request_insert(req, &base->req_waiting_head);
      /* We want to insert these suspended elements at the front of
       * the waiting queue, since they were pending before any of
       * the waiting entries were added.  This is a circular list,
       * so we can just shift the start back by one.*/
      base->req_waiting_head = base->req_waiting_head->prev;

      if (next == req_started_at)
        break;
      req = next;
    }
    base->req_heads[i] = NULL;
  }

  base->global_requests_inflight = 0;

  EVDNS_UNLOCK(base);
  return 0;
}

int
evdns_clear_nameservers_and_suspend(void)
{
  return evdns_base_clear_nameservers_and_suspend(current_base);
}


/* exported function */
int
evdns_base_resume(struct evdns_base *base)
{
  EVDNS_LOCK(base);
  evdns_requests_pump_waiting_queue(base);
  EVDNS_UNLOCK(base);

  return 0;
}

int
evdns_resume(void)
{
  return evdns_base_resume(current_base);
}

static int
evdns_nameserver_add_impl_(struct evdns_base *base, const struct sockaddr *address, int addrlen) {
  /* first check to see if we already have this nameserver */

  const struct nameserver *server = base->server_head, *const started_at = base->server_head;
  struct nameserver *ns;
  int err = 0;
  char addrbuf[128];

  ASSERT_LOCKED(base);
  if (server) {
    do {
      if (!evutil_sockaddr_cmp((struct sockaddr*)&server->address, address, 1)) return 3;
      server = server->next;
    } while (server != started_at);
  }
  if (addrlen > (int)sizeof(ns->address)) {
    log(EVDNS_LOG_DEBUG, "Addrlen %d too long.", (int)addrlen);
    return 2;
  }

  ns = (struct nameserver *) mm_malloc(sizeof(struct nameserver));
  if (!ns) return -1;

  memset(ns, 0, sizeof(struct nameserver));
  ns->base = base;

  evtimer_assign(&ns->timeout_event, ns->base->event_base, nameserver_prod_callback, ns);

  ns->socket = evutil_socket_(address->sa_family,
      SOCK_DGRAM|EVUTIL_SOCK_NONBLOCK|EVUTIL_SOCK_CLOEXEC, 0);
  if (ns->socket < 0) { err = 1; goto out1; }

  if (base->global_outgoing_addrlen &&
      !evutil_sockaddr_is_loopback_(address)) {
    if (bind(ns->socket,
      (struct sockaddr*)&base->global_outgoing_address,
      base->global_outgoing_addrlen) < 0) {
      log(EVDNS_LOG_WARN,"Couldn't bind to outgoing address");
      err = 2;
      goto out2;
    }
  }

  memcpy(&ns->address, address, addrlen);
  ns->addrlen = addrlen;
  ns->state = 1;
  event_assign(&ns->event, ns->base->event_base, ns->socket,
         EV_READ | EV_PERSIST, nameserver_ready_callback, ns);
  if (!base->disable_when_inactive && event_add(&ns->event, NULL) < 0) {
    err = 2;
    goto out2;
  }

  log(EVDNS_LOG_DEBUG, "Added nameserver %s as %p",
      evutil_format_sockaddr_port_(address, addrbuf, sizeof(addrbuf)), ns);

  /* insert this nameserver into the list of them */
  if (!base->server_head) {
    ns->next = ns->prev = ns;
    base->server_head = ns;
  } else {
    ns->next = base->server_head->next;
    ns->prev = base->server_head;
    base->server_head->next = ns;
    ns->next->prev = ns;
  }

  base->global_good_nameservers++;

  return 0;

out2:
  evutil_closesocket(ns->socket);
out1:
  event_debug_unassign(&ns->event);
  mm_free(ns);
  log(EVDNS_LOG_WARN, "Unable to add nameserver %s: error %d",
      evutil_format_sockaddr_port_(address, addrbuf, sizeof(addrbuf)), err);
  return err;
}

/* exported function */
int
evdns_base_nameserver_add(struct evdns_base *base, unsigned long int address)
{
  struct sockaddr_in sin;
  int res;
  memset(&sin, 0, sizeof(sin));
  sin.sin_addr.s_addr = address;
  sin.sin_port = htons(53);
  sin.sin_family = AF_INET;
  EVDNS_LOCK(base);
  res = evdns_nameserver_add_impl_(base, (struct sockaddr*)&sin, sizeof(sin));
  EVDNS_UNLOCK(base);
  return res;
}

int
evdns_nameserver_add(unsigned long int address) {
  if (!current_base)
    current_base = evdns_base_new(NULL, 0);
  return evdns_base_nameserver_add(current_base, address);
}

static void
sockaddr_setport(struct sockaddr *sa, ev_uint16_t port)
{
  if (sa->sa_family == AF_INET) {
    ((struct sockaddr_in *)sa)->sin_port = htons(port);
  } else if (sa->sa_family == AF_INET6) {
    ((struct sockaddr_in6 *)sa)->sin6_port = htons(port);
  }
}

static ev_uint16_t
sockaddr_getport(struct sockaddr *sa)
{
  if (sa->sa_family == AF_INET) {
    return ntohs(((struct sockaddr_in *)sa)->sin_port);
  } else if (sa->sa_family == AF_INET6) {
    return ntohs(((struct sockaddr_in6 *)sa)->sin6_port);
  } else {
    return 0;
  }
}

/* exported function */
int
evdns_base_nameserver_ip_add(struct evdns_base *base, const char *ip_as_string) {
  struct sockaddr_storage ss;
  struct sockaddr *sa;
  int len = sizeof(ss);
  int res;
  if (evutil_parse_sockaddr_port(ip_as_string, (struct sockaddr *)&ss,
    &len)) {
    log(EVDNS_LOG_WARN, "Unable to parse nameserver address %s",
      ip_as_string);
    return 4;
  }
  sa = (struct sockaddr *) &ss;
  if (sockaddr_getport(sa) == 0)
    sockaddr_setport(sa, 53);

  EVDNS_LOCK(base);
  res = evdns_nameserver_add_impl_(base, sa, len);
  EVDNS_UNLOCK(base);
  return res;
}

int
evdns_nameserver_ip_add(const char *ip_as_string) {
  if (!current_base)
    current_base = evdns_base_new(NULL, 0);
  return evdns_base_nameserver_ip_add(current_base, ip_as_string);
}

int
evdns_base_nameserver_sockaddr_add(struct evdns_base *base,
    const struct sockaddr *sa, ev_socklen_t len, unsigned flags)
{
  int res;
  EVUTIL_ASSERT(base);
  EVDNS_LOCK(base);
  res = evdns_nameserver_add_impl_(base, sa, len);
  EVDNS_UNLOCK(base);
  return res;
}

int
evdns_base_get_nameserver_addr(struct evdns_base *base, int idx,
    struct sockaddr *sa, ev_socklen_t len)
{
  int result = -1;
  int i;
  struct nameserver *server;
  EVDNS_LOCK(base);
  server = base->server_head;
  for (i = 0; i < idx && server; ++i, server = server->next) {
    if (server->next == base->server_head)
      goto done;
  }
  if (! server)
    goto done;

  if (server->addrlen > len) {
    result = (int) server->addrlen;
    goto done;
  }

  memcpy(sa, &server->address, server->addrlen);
  result = (int) server->addrlen;
done:
  EVDNS_UNLOCK(base);
  return result;
}

/* remove from the queue */
static void
evdns_request_remove(struct request *req, struct request **head)
{
  ASSERT_LOCKED(req->base);
  ASSERT_VALID_REQUEST(req);

#if 0
  {
    struct request *ptr;
    int found = 0;
    EVUTIL_ASSERT(*head != NULL);

    ptr = *head;
    do {
      if (ptr == req) {
        found = 1;
        break;
      }
      ptr = ptr->next;
    } while (ptr != *head);
    EVUTIL_ASSERT(found);

    EVUTIL_ASSERT(req->next);
  }
#endif

  if (req->next == req) {
    /* only item in the list */
    *head = NULL;
  } else {
    req->next->prev = req->prev;
    req->prev->next = req->next;
    if (*head == req) *head = req->next;
  }
  req->next = req->prev = NULL;
}

/* insert into the tail of the queue */
static void
evdns_request_insert(struct request *req, struct request **head) {
  ASSERT_LOCKED(req->base);
  ASSERT_VALID_REQUEST(req);
  if (!*head) {
    *head = req;
    req->next = req->prev = req;
    return;
  }

  req->prev = (*head)->prev;
  req->prev->next = req;
  req->next = *head;
  (*head)->prev = req;
}

static int
string_num_dots(const char *s) {
  int count = 0;
  while ((s = strchr(s, '.'))) {
    s++;
    count++;
  }
  return count;
}

static struct request *
request_new(struct evdns_base *base, struct evdns_request *handle, int type,
      const char *name, int flags, evdns_callback_type callback,
      void *user_ptr) {

  const char issuing_now =
      (base->global_requests_inflight < base->global_max_requests_inflight) ? 1 : 0;

  const size_t name_len = strlen(name);
  const size_t request_max_len = evdns_request_len(name_len);
  const u16 trans_id = issuing_now ? transaction_id_pick(base) : 0xffff;
  /* the request data is alloced in a single block with the header */
  struct request *const req =
      mm_malloc(sizeof(struct request) + request_max_len);
  int rlen;
  char namebuf[256];
  (void) flags;

  ASSERT_LOCKED(base);

  if (!req) return NULL;

  if (name_len >= sizeof(namebuf)) {
    mm_free(req);
    return NULL;
  }

  memset(req, 0, sizeof(struct request));
  req->base = base;

  evtimer_assign(&req->timeout_event, req->base->event_base, evdns_request_timeout_callback, req);

  if (base->global_randomize_case) {
    unsigned i;
    char randbits[(sizeof(namebuf)+7)/8];
    strlcpy(namebuf, name, sizeof(namebuf));
    evutil_secure_rng_get_bytes(randbits, (name_len+7)/8);
    for (i = 0; i < name_len; ++i) {
      if (EVUTIL_ISALPHA_(namebuf[i])) {
        if ((randbits[i >> 3] & (1<<(i & 7))))
          namebuf[i] |= 0x20;
        else
          namebuf[i] &= ~0x20;
      }
    }
    name = namebuf;
  }

  /* request data lives just after the header */
  req->request = ((u8 *) req) + sizeof(struct request);
  /* denotes that the request data shouldn't be free()ed */
  req->request_appended = 1;
  rlen = evdns_request_data_build(name, name_len, trans_id,
      type, CLASS_INET, req->request, request_max_len);
  if (rlen < 0)
    goto err1;

  req->request_len = rlen;
  req->trans_id = trans_id;
  req->tx_count = 0;
  req->request_type = type;
  req->user_pointer = user_ptr;
  req->user_callback = callback;
  req->ns = issuing_now ? nameserver_pick(base) : NULL;
  req->next = req->prev = NULL;
  req->handle = handle;
  if (handle) {
    handle->current_req = req;
    handle->base = base;
  }

  return req;
err1:
  mm_free(req);
  return NULL;
}

static void
request_submit(struct request *const req) {
  struct evdns_base *base = req->base;
  ASSERT_LOCKED(base);
  ASSERT_VALID_REQUEST(req);
  if (req->ns) {
    /* if it has a nameserver assigned then this is going */
    /* straight into the inflight queue */
    evdns_request_insert(req, &REQ_HEAD(base, req->trans_id));

    base->global_requests_inflight++;
    req->ns->requests_inflight++;

    evdns_request_transmit(req);
  } else {
    evdns_request_insert(req, &base->req_waiting_head);
    base->global_requests_waiting++;
  }
}

/* exported function */
void
evdns_cancel_request(struct evdns_base *base, struct evdns_request *handle)
{
  struct request *req;

  if (!handle->current_req)
    return;

  if (!base) {
    /* This redundancy is silly; can we fix it? (Not for 2.0) XXXX */
    base = handle->base;
    if (!base)
      base = handle->current_req->base;
  }

  EVDNS_LOCK(base);
  if (handle->pending_cb) {
    EVDNS_UNLOCK(base);
    return;
  }

  req = handle->current_req;
  ASSERT_VALID_REQUEST(req);

  reply_schedule_callback(req, 0, DNS_ERR_CANCEL, NULL);
  if (req->ns) {
    /* remove from inflight queue */
    request_finished(req, &REQ_HEAD(base, req->trans_id), 1);
  } else {
    /* remove from global_waiting head */
    request_finished(req, &base->req_waiting_head, 1);
  }
  EVDNS_UNLOCK(base);
}

/* exported function */
struct evdns_request *
evdns_base_resolve_ipv4(struct evdns_base *base, const char *name, int flags,
    evdns_callback_type callback, void *ptr) {
  struct evdns_request *handle;
  struct request *req;
  log(EVDNS_LOG_DEBUG, "Resolve requested for %s", name);
  handle = mm_calloc(1, sizeof(*handle));
  if (handle == NULL)
    return NULL;
  EVDNS_LOCK(base);
  if (flags & DNS_QUERY_NO_SEARCH) {
    req =
      request_new(base, handle, TYPE_A, name, flags,
            callback, ptr);
    if (req)
      request_submit(req);
  } else {
    search_request_new(base, handle, TYPE_A, name, flags,
        callback, ptr);
  }
  if (handle->current_req == NULL) {
    mm_free(handle);
    handle = NULL;
  }
  EVDNS_UNLOCK(base);
  return handle;
}

int evdns_resolve_ipv4(const char *name, int flags,
             evdns_callback_type callback, void *ptr)
{
  return evdns_base_resolve_ipv4(current_base, name, flags, callback, ptr)
    ? 0 : -1;
}


/* exported function */
struct evdns_request *
evdns_base_resolve_ipv6(struct evdns_base *base,
    const char *name, int flags,
    evdns_callback_type callback, void *ptr)
{
  struct evdns_request *handle;
  struct request *req;
  log(EVDNS_LOG_DEBUG, "Resolve requested for %s", name);
  handle = mm_calloc(1, sizeof(*handle));
  if (handle == NULL)
    return NULL;
  EVDNS_LOCK(base);
  if (flags & DNS_QUERY_NO_SEARCH) {
    req = request_new(base, handle, TYPE_AAAA, name, flags,
          callback, ptr);
    if (req)
      request_submit(req);
  } else {
    search_request_new(base, handle, TYPE_AAAA, name, flags,
        callback, ptr);
  }
  if (handle->current_req == NULL) {
    mm_free(handle);
    handle = NULL;
  }
  EVDNS_UNLOCK(base);
  return handle;
}

int evdns_resolve_ipv6(const char *name, int flags,
    evdns_callback_type callback, void *ptr) {
  return evdns_base_resolve_ipv6(current_base, name, flags, callback, ptr)
    ? 0 : -1;
}

struct evdns_request *
evdns_base_resolve_reverse(struct evdns_base *base, const struct in_addr *in, int flags, evdns_callback_type callback, void *ptr) {
  char buf[32];
  struct evdns_request *handle;
  struct request *req;
  u32 a;
  EVUTIL_ASSERT(in);
  a = ntohl(in->s_addr);
  evutil_snprintf(buf, sizeof(buf), "%d.%d.%d.%d.in-addr.arpa",
      (int)(u8)((a  )&0xff),
      (int)(u8)((a>>8 )&0xff),
      (int)(u8)((a>>16)&0xff),
      (int)(u8)((a>>24)&0xff));
  handle = mm_calloc(1, sizeof(*handle));
  if (handle == NULL)
    return NULL;
  log(EVDNS_LOG_DEBUG, "Resolve requested for %s (reverse)", buf);
  EVDNS_LOCK(base);
  req = request_new(base, handle, TYPE_PTR, buf, flags, callback, ptr);
  if (req)
    request_submit(req);
  if (handle->current_req == NULL) {
    mm_free(handle);
    handle = NULL;
  }
  EVDNS_UNLOCK(base);
  return (handle);
}

int evdns_resolve_reverse(const struct in_addr *in, int flags, evdns_callback_type callback, void *ptr) {
  return evdns_base_resolve_reverse(current_base, in, flags, callback, ptr)
    ? 0 : -1;
}

struct evdns_request *
evdns_base_resolve_reverse_ipv6(struct evdns_base *base, const struct in6_addr *in, int flags, evdns_callback_type callback, void *ptr) {
  /* 32 nybbles, 32 periods, "ip6.arpa", NUL. */
  char buf[73];
  char *cp;
  struct evdns_request *handle;
  struct request *req;
  int i;
  EVUTIL_ASSERT(in);
  cp = buf;
  for (i=15; i >= 0; --i) {
    u8 byte = in->s6_addr[i];
    *cp++ = "0123456789abcdef"[byte & 0x0f];
    *cp++ = '.';
    *cp++ = "0123456789abcdef"[byte >> 4];
    *cp++ = '.';
  }
  EVUTIL_ASSERT(cp + strlen("ip6.arpa") < buf+sizeof(buf));
  memcpy(cp, "ip6.arpa", strlen("ip6.arpa")+1);
  handle = mm_calloc(1, sizeof(*handle));
  if (handle == NULL)
    return NULL;
  log(EVDNS_LOG_DEBUG, "Resolve requested for %s (reverse)", buf);
  EVDNS_LOCK(base);
  req = request_new(base, handle, TYPE_PTR, buf, flags, callback, ptr);
  if (req)
    request_submit(req);
  if (handle->current_req == NULL) {
    mm_free(handle);
    handle = NULL;
  }
  EVDNS_UNLOCK(base);
  return (handle);
}

int evdns_resolve_reverse_ipv6(const struct in6_addr *in, int flags, evdns_callback_type callback, void *ptr) {
  return evdns_base_resolve_reverse_ipv6(current_base, in, flags, callback, ptr)
    ? 0 : -1;
}

/* ================================================================= */
/* Search support */
/* */
/* the libc resolver has support for searching a number of domains */
/* to find a name. If nothing else then it takes the single domain */
/* from the gethostname() call. */
/* */
/* It can also be configured via the domain and search options in a */
/* resolv.conf. */
/* */
/* The ndots option controls how many dots it takes for the resolver */
/* to decide that a name is non-local and so try a raw lookup first. */

struct search_domain {
  int len;
  struct search_domain *next;
  /* the text string is appended to this structure */
};

struct search_state {
  int refcount;
  int ndots;
  int num_domains;
  struct search_domain *head;
};

static void
search_state_decref(struct search_state *const state) {
  if (!state) return;
  state->refcount--;
  if (!state->refcount) {
    struct search_domain *next, *dom;
    for (dom = state->head; dom; dom = next) {
      next = dom->next;
      mm_free(dom);
    }
    mm_free(state);
  }
}

static struct search_state *
search_state_new(void) {
  struct search_state *state = (struct search_state *) mm_malloc(sizeof(struct search_state));
  if (!state) return NULL;
  memset(state, 0, sizeof(struct search_state));
  state->refcount = 1;
  state->ndots = 1;

  return state;
}

static void
search_postfix_clear(struct evdns_base *base) {
  search_state_decref(base->global_search_state);

  base->global_search_state = search_state_new();
}

/* exported function */
void
evdns_base_search_clear(struct evdns_base *base)
{
  EVDNS_LOCK(base);
  search_postfix_clear(base);
  EVDNS_UNLOCK(base);
}

void
evdns_search_clear(void) {
  evdns_base_search_clear(current_base);
}

static void
search_postfix_add(struct evdns_base *base, const char *domain) {
  size_t domain_len;
  struct search_domain *sdomain;
  while (domain[0] == '.') domain++;
  domain_len = strlen(domain);

  ASSERT_LOCKED(base);
  if (!base->global_search_state) base->global_search_state = search_state_new();
  if (!base->global_search_state) return;
  base->global_search_state->num_domains++;

  sdomain = (struct search_domain *) mm_malloc(sizeof(struct search_domain) + domain_len);
  if (!sdomain) return;
  memcpy( ((u8 *) sdomain) + sizeof(struct search_domain), domain, domain_len);
  sdomain->next = base->global_search_state->head;
  sdomain->len = (int) domain_len;

  base->global_search_state->head = sdomain;
}

/* reverse the order of members in the postfix list. This is needed because, */
/* when parsing resolv.conf we push elements in the wrong order */
static void
search_reverse(struct evdns_base *base) {
  struct search_domain *cur, *prev = NULL, *next;
  ASSERT_LOCKED(base);
  cur = base->global_search_state->head;
  while (cur) {
    next = cur->next;
    cur->next = prev;
    prev = cur;
    cur = next;
  }

  base->global_search_state->head = prev;
}

/* exported function */
void
evdns_base_search_add(struct evdns_base *base, const char *domain) {
  EVDNS_LOCK(base);
  search_postfix_add(base, domain);
  EVDNS_UNLOCK(base);
}
void
evdns_search_add(const char *domain) {
  evdns_base_search_add(current_base, domain);
}

/* exported function */
void
evdns_base_search_ndots_set(struct evdns_base *base, const int ndots) {
  EVDNS_LOCK(base);
  if (!base->global_search_state) base->global_search_state = search_state_new();
  if (base->global_search_state)
    base->global_search_state->ndots = ndots;
  EVDNS_UNLOCK(base);
}
void
evdns_search_ndots_set(const int ndots) {
  evdns_base_search_ndots_set(current_base, ndots);
}

static void
search_set_from_hostname(struct evdns_base *base) {
  char hostname[HOST_NAME_MAX + 1], *domainname;

  ASSERT_LOCKED(base);
  search_postfix_clear(base);
  if (gethostname(hostname, sizeof(hostname))) return;
  domainname = strchr(hostname, '.');
  if (!domainname) return;
  search_postfix_add(base, domainname);
}

/* warning: returns malloced string */
static char *
search_make_new(const struct search_state *const state, int n, const char *const base_name) {
  const size_t base_len = strlen(base_name);
  char need_to_append_dot;
  struct search_domain *dom;

  if (!base_len) return NULL;
  need_to_append_dot = base_name[base_len - 1] == '.' ? 0 : 1;

  for (dom = state->head; dom; dom = dom->next) {
    if (!n--) {
      /* this is the postfix we want */
      /* the actual postfix string is kept at the end of the structure */
      const u8 *const postfix = ((u8 *) dom) + sizeof(struct search_domain);
      const int postfix_len = dom->len;
      char *const newname = (char *) mm_malloc(base_len + need_to_append_dot + postfix_len + 1);
      if (!newname) return NULL;
      memcpy(newname, base_name, base_len);
      if (need_to_append_dot) newname[base_len] = '.';
      memcpy(newname + base_len + need_to_append_dot, postfix, postfix_len);
      newname[base_len + need_to_append_dot + postfix_len] = 0;
      return newname;
    }
  }

  /* we ran off the end of the list and still didn't find the requested string */
  EVUTIL_ASSERT(0);
  return NULL; /* unreachable; stops warnings in some compilers. */
}

static struct request *
search_request_new(struct evdns_base *base, struct evdns_request *handle,
       int type, const char *const name, int flags,
       evdns_callback_type user_callback, void *user_arg) {
  ASSERT_LOCKED(base);
  EVUTIL_ASSERT(type == TYPE_A || type == TYPE_AAAA);
  EVUTIL_ASSERT(handle->current_req == NULL);
  if ( ((flags & DNS_QUERY_NO_SEARCH) == 0) &&
       base->global_search_state &&
     base->global_search_state->num_domains) {
    /* we have some domains to search */
    struct request *req;
    if (string_num_dots(name) >= base->global_search_state->ndots) {
      req = request_new(base, handle, type, name, flags, user_callback, user_arg);
      if (!req) return NULL;
      handle->search_index = -1;
    } else {
      char *const new_name = search_make_new(base->global_search_state, 0, name);
      if (!new_name) return NULL;
      req = request_new(base, handle, type, new_name, flags, user_callback, user_arg);
      mm_free(new_name);
      if (!req) return NULL;
      handle->search_index = 0;
    }
    EVUTIL_ASSERT(handle->search_origname == NULL);
    handle->search_origname = mm_strdup(name);
    if (handle->search_origname == NULL) {
      /* XXX Should we dealloc req? If yes, how? */
      if (req)
        mm_free(req);
      return NULL;
    }
    handle->search_state = base->global_search_state;
    handle->search_flags = flags;
    base->global_search_state->refcount++;
    request_submit(req);
    return req;
  } else {
    struct request *const req = request_new(base, handle, type, name, flags, user_callback, user_arg);
    if (!req) return NULL;
    request_submit(req);
    return req;
  }
}

/* this is called when a request has failed to find a name. We need to check */
/* if it is part of a search and, if so, try the next name in the list */
/* returns: */
/*   0 another request has been submitted */
/*   1 no more requests needed */
static int
search_try_next(struct evdns_request *const handle) {
  struct request *req = handle->current_req;
  struct evdns_base *base = req->base;
  struct request *newreq;
  ASSERT_LOCKED(base);
  if (handle->search_state) {
    /* it is part of a search */
    char *new_name;
    handle->search_index++;
    if (handle->search_index >= handle->search_state->num_domains) {
      /* no more postfixes to try, however we may need to try */
      /* this name without a postfix */
      if (string_num_dots(handle->search_origname) < handle->search_state->ndots) {
        /* yep, we need to try it raw */
        newreq = request_new(base, NULL, req->request_type, handle->search_origname, handle->search_flags, req->user_callback, req->user_pointer);
        log(EVDNS_LOG_DEBUG, "Search: trying raw query %s", handle->search_origname);
        if (newreq) {
          search_request_finished(handle);
          goto submit_next;
        }
      }
      return 1;
    }

    new_name = search_make_new(handle->search_state, handle->search_index, handle->search_origname);
    if (!new_name) return 1;
    log(EVDNS_LOG_DEBUG, "Search: now trying %s (%d)", new_name, handle->search_index);
    newreq = request_new(base, NULL, req->request_type, new_name, handle->search_flags, req->user_callback, req->user_pointer);
    mm_free(new_name);
    if (!newreq) return 1;
    goto submit_next;
  }
  return 1;

submit_next:
  request_finished(req, &REQ_HEAD(req->base, req->trans_id), 0);
  handle->current_req = newreq;
  newreq->handle = handle;
  request_submit(newreq);
  return 0;
}

static void
search_request_finished(struct evdns_request *const handle) {
  ASSERT_LOCKED(handle->current_req->base);
  if (handle->search_state) {
    search_state_decref(handle->search_state);
    handle->search_state = NULL;
  }
  if (handle->search_origname) {
    mm_free(handle->search_origname);
    handle->search_origname = NULL;
  }
}

/* ================================================================= */
/* Parsing resolv.conf files */

static void
evdns_resolv_set_defaults(struct evdns_base *base, int flags) {
  /* if the file isn't found then we assume a local resolver */
  ASSERT_LOCKED(base);
  if (flags & DNS_OPTION_SEARCH) search_set_from_hostname(base);
  if (flags & DNS_OPTION_NAMESERVERS) evdns_base_nameserver_ip_add(base,"127.0.0.1");
}

#ifndef EVENT__HAVE_STRTOK_R
static char *
strtok_r(char *s, const char *delim, char **state) {
  char *cp, *start;
  start = cp = s ? s : *state;
  if (!cp)
    return NULL;
  while (*cp && !strchr(delim, *cp))
    ++cp;
  if (!*cp) {
    if (cp == start)
      return NULL;
    *state = NULL;
    return start;
  } else {
    *cp++ = '\0';
    *state = cp;
    return start;
  }
}
#endif

/* helper version of atoi which returns -1 on error */
static int
strtoint(const char *const str)
{
  char *endptr;
  const int r = strtol(str, &endptr, 10);
  if (*endptr) return -1;
  return r;
}

/* Parse a number of seconds into a timeval; return -1 on error. */
static int
evdns_strtotimeval(const char *const str, struct timeval *out)
{
  double d;
  char *endptr;
  d = strtod(str, &endptr);
  if (*endptr) return -1;
  if (d < 0) return -1;
  out->tv_sec = (int) d;
  out->tv_usec = (int) ((d - (int) d)*1000000);
  if (out->tv_sec == 0 && out->tv_usec < 1000) /* less than 1 msec */
    return -1;
  return 0;
}

/* helper version of atoi that returns -1 on error and clips to bounds. */
static int
strtoint_clipped(const char *const str, int min, int max)
{
  int r = strtoint(str);
  if (r == -1)
    return r;
  else if (r<min)
    return min;
  else if (r>max)
    return max;
  else
    return r;
}

static int
evdns_base_set_max_requests_inflight(struct evdns_base *base, int maxinflight)
{
  int old_n_heads = base->n_req_heads, n_heads;
  struct request **old_heads = base->req_heads, **new_heads, *req;
  int i;

  ASSERT_LOCKED(base);
  if (maxinflight < 1)
    maxinflight = 1;
  n_heads = (maxinflight+4) / 5;
  EVUTIL_ASSERT(n_heads > 0);
  new_heads = mm_calloc(n_heads, sizeof(struct request*));
  if (!new_heads)
    return (-1);
  if (old_heads) {
    for (i = 0; i < old_n_heads; ++i) {
      while (old_heads[i]) {
        req = old_heads[i];
        evdns_request_remove(req, &old_heads[i]);
        evdns_request_insert(req, &new_heads[req->trans_id % n_heads]);
      }
    }
    mm_free(old_heads);
  }
  base->req_heads = new_heads;
  base->n_req_heads = n_heads;
  base->global_max_requests_inflight = maxinflight;
  return (0);
}

/* exported function */
int
evdns_base_set_option(struct evdns_base *base,
    const char *option, const char *val)
{
  int res;
  EVDNS_LOCK(base);
  res = evdns_base_set_option_impl(base, option, val, DNS_OPTIONS_ALL);
  EVDNS_UNLOCK(base);
  return res;
}

static inline int
str_matches_option(const char *s1, const char *optionname)
{
  /* Option names are given as "option:" We accept either 'option' in
   * s1, or 'option:randomjunk'.  The latter form is to implement the
   * resolv.conf parser. */
  size_t optlen = strlen(optionname);
  size_t slen = strlen(s1);
  if (slen == optlen || slen == optlen - 1)
    return !strncmp(s1, optionname, slen);
  else if (slen > optlen)
    return !strncmp(s1, optionname, optlen);
  else
    return 0;
}

static int
evdns_base_set_option_impl(struct evdns_base *base,
    const char *option, const char *val, int flags)
{
  ASSERT_LOCKED(base);
  if (str_matches_option(option, "ndots:")) {
    const int ndots = strtoint(val);
    if (ndots == -1) return -1;
    if (!(flags & DNS_OPTION_SEARCH)) return 0;
    log(EVDNS_LOG_DEBUG, "Setting ndots to %d", ndots);
    if (!base->global_search_state) base->global_search_state = search_state_new();
    if (!base->global_search_state) return -1;
    base->global_search_state->ndots = ndots;
  } else if (str_matches_option(option, "timeout:")) {
    struct timeval tv;
    if (evdns_strtotimeval(val, &tv) == -1) return -1;
    if (!(flags & DNS_OPTION_MISC)) return 0;
    log(EVDNS_LOG_DEBUG, "Setting timeout to %s", val);
    memcpy(&base->global_timeout, &tv, sizeof(struct timeval));
  } else if (str_matches_option(option, "getaddrinfo-allow-skew:")) {
    struct timeval tv;
    if (evdns_strtotimeval(val, &tv) == -1) return -1;
    if (!(flags & DNS_OPTION_MISC)) return 0;
    log(EVDNS_LOG_DEBUG, "Setting getaddrinfo-allow-skew to %s",
        val);
    memcpy(&base->global_getaddrinfo_allow_skew, &tv,
        sizeof(struct timeval));
  } else if (str_matches_option(option, "max-timeouts:")) {
    const int maxtimeout = strtoint_clipped(val, 1, 255);
    if (maxtimeout == -1) return -1;
    if (!(flags & DNS_OPTION_MISC)) return 0;
    log(EVDNS_LOG_DEBUG, "Setting maximum allowed timeouts to %d",
      maxtimeout);
    base->global_max_nameserver_timeout = maxtimeout;
  } else if (str_matches_option(option, "max-inflight:")) {
    const int maxinflight = strtoint_clipped(val, 1, 65000);
    if (maxinflight == -1) return -1;
    if (!(flags & DNS_OPTION_MISC)) return 0;
    log(EVDNS_LOG_DEBUG, "Setting maximum inflight requests to %d",
      maxinflight);
    evdns_base_set_max_requests_inflight(base, maxinflight);
  } else if (str_matches_option(option, "attempts:")) {
    int retries = strtoint(val);
    if (retries == -1) return -1;
    if (retries > 255) retries = 255;
    if (!(flags & DNS_OPTION_MISC)) return 0;
    log(EVDNS_LOG_DEBUG, "Setting retries to %d", retries);
    base->global_max_retransmits = retries;
  } else if (str_matches_option(option, "randomize-case:")) {
    int randcase = strtoint(val);
    if (!(flags & DNS_OPTION_MISC)) return 0;
    base->global_randomize_case = randcase;
  } else if (str_matches_option(option, "bind-to:")) {
    /* XXX This only applies to successive nameservers, not
     * to already-configured ones.  We might want to fix that. */
    int len = sizeof(base->global_outgoing_address);
    if (!(flags & DNS_OPTION_NAMESERVERS)) return 0;
    if (evutil_parse_sockaddr_port(val,
      (struct sockaddr*)&base->global_outgoing_address, &len))
      return -1;
    base->global_outgoing_addrlen = len;
  } else if (str_matches_option(option, "initial-probe-timeout:")) {
    struct timeval tv;
    if (evdns_strtotimeval(val, &tv) == -1) return -1;
    if (tv.tv_sec > 3600)
      tv.tv_sec = 3600;
    if (!(flags & DNS_OPTION_MISC)) return 0;
    log(EVDNS_LOG_DEBUG, "Setting initial probe timeout to %s",
        val);
    memcpy(&base->global_nameserver_probe_initial_timeout, &tv,
        sizeof(tv));
  }
  return 0;
}

int
evdns_set_option(const char *option, const char *val, int flags)
{
  if (!current_base)
    current_base = evdns_base_new(NULL, 0);
  return evdns_base_set_option(current_base, option, val);
}

static void
resolv_conf_parse_line(struct evdns_base *base, char *const start, int flags) {
  char *strtok_state;
  static const char *const delims = " \t";
#define NEXT_TOKEN strtok_r(NULL, delims, &strtok_state)


  char *const first_token = strtok_r(start, delims, &strtok_state);
  ASSERT_LOCKED(base);
  if (!first_token) return;

  if (!strcmp(first_token, "nameserver") && (flags & DNS_OPTION_NAMESERVERS)) {
    const char *const nameserver = NEXT_TOKEN;

    if (nameserver)
      evdns_base_nameserver_ip_add(base, nameserver);
  } else if (!strcmp(first_token, "domain") && (flags & DNS_OPTION_SEARCH)) {
    const char *const domain = NEXT_TOKEN;
    if (domain) {
      search_postfix_clear(base);
      search_postfix_add(base, domain);
    }
  } else if (!strcmp(first_token, "search") && (flags & DNS_OPTION_SEARCH)) {
    const char *domain;
    search_postfix_clear(base);

    while ((domain = NEXT_TOKEN)) {
      search_postfix_add(base, domain);
    }
    search_reverse(base);
  } else if (!strcmp(first_token, "options")) {
    const char *option;
    while ((option = NEXT_TOKEN)) {
      const char *val = strchr(option, ':');
      evdns_base_set_option_impl(base, option, val ? val+1 : "", flags);
    }
  }
#undef NEXT_TOKEN
}

/* exported function */
/* returns: */
/*   0 no errors */
/*   1 failed to open file */
/*   2 failed to stat file */
/*   3 file too large */
/*   4 out of memory */
/*   5 short read from file */
int
evdns_base_resolv_conf_parse(struct evdns_base *base, int flags, const char *const filename) {
  int res;
  EVDNS_LOCK(base);
  res = evdns_base_resolv_conf_parse_impl(base, flags, filename);
  EVDNS_UNLOCK(base);
  return res;
}

static char *
evdns_get_default_hosts_filename(void)
{
#ifdef _WIN32
  /* Windows is a little coy about where it puts its configuration
   * files.  Sure, they're _usually_ in C:\windows\system32, but
   * there's no reason in principle they couldn't be in
   * W:\hoboken chicken emergency\
   */
  char path[MAX_PATH+1];
  static const char hostfile[] = "\\drivers\\etc\\hosts";
  char *path_out;
  size_t len_out;

  if (! SHGetSpecialFolderPathA(NULL, path, CSIDL_SYSTEM, 0))
    return NULL;
  len_out = strlen(path)+strlen(hostfile)+1;
  path_out = mm_malloc(len_out);
  evutil_snprintf(path_out, len_out, "%s%s", path, hostfile);
  return path_out;
#else
  return mm_strdup("/etc/hosts");
#endif
}

static int
evdns_base_resolv_conf_parse_impl(struct evdns_base *base, int flags, const char *const filename) {
  size_t n;
  char *resolv;
  char *start;
  int err = 0;

  log(EVDNS_LOG_DEBUG, "Parsing resolv.conf file %s", filename);

  if (flags & DNS_OPTION_HOSTSFILE) {
    char *fname = evdns_get_default_hosts_filename();
    evdns_base_load_hosts(base, fname);
    if (fname)
      mm_free(fname);
  }

  if ((err = evutil_read_file_(filename, &resolv, &n, 0)) < 0) {
    if (err == -1) {
      /* No file. */
      evdns_resolv_set_defaults(base, flags);
      return 1;
    } else {
      return 2;
    }
  }

  start = resolv;
  for (;;) {
    char *const newline = strchr(start, '\n');
    if (!newline) {
      resolv_conf_parse_line(base, start, flags);
      break;
    } else {
      *newline = 0;
      resolv_conf_parse_line(base, start, flags);
      start = newline + 1;
    }
  }

  if (!base->server_head && (flags & DNS_OPTION_NAMESERVERS)) {
    /* no nameservers were configured. */
    evdns_base_nameserver_ip_add(base, "127.0.0.1");
    err = 6;
  }
  if (flags & DNS_OPTION_SEARCH && (!base->global_search_state || base->global_search_state->num_domains == 0)) {
    search_set_from_hostname(base);
  }

  mm_free(resolv);
  return err;
}

int
evdns_resolv_conf_parse(int flags, const char *const filename) {
  if (!current_base)
    current_base = evdns_base_new(NULL, 0);
  return evdns_base_resolv_conf_parse(current_base, flags, filename);
}


#ifdef _WIN32
/* Add multiple nameservers from a space-or-comma-separated list. */
static int
evdns_nameserver_ip_add_line(struct evdns_base *base, const char *ips) {
  const char *addr;
  char *buf;
  int r;
  ASSERT_LOCKED(base);
  while (*ips) {
    while (isspace(*ips) || *ips == ',' || *ips == '\t')
      ++ips;
    addr = ips;
    while (isdigit(*ips) || *ips == '.' || *ips == ':' ||
        *ips=='[' || *ips==']')
      ++ips;
    buf = mm_malloc(ips-addr+1);
    if (!buf) return 4;
    memcpy(buf, addr, ips-addr);
    buf[ips-addr] = '\0';
    r = evdns_base_nameserver_ip_add(base, buf);
    mm_free(buf);
    if (r) return r;
  }
  return 0;
}

typedef DWORD(WINAPI *GetNetworkParams_fn_t)(FIXED_INFO *, DWORD*);

/* Use the windows GetNetworkParams interface in iphlpapi.dll to */
/* figure out what our nameservers are. */
static int
load_nameservers_with_getnetworkparams(struct evdns_base *base)
{
  /* Based on MSDN examples and inspection of  c-ares code. */
  FIXED_INFO *fixed;
  HMODULE handle = 0;
  ULONG size = sizeof(FIXED_INFO);
  void *buf = NULL;
  int status = 0, r, added_any;
  IP_ADDR_STRING *ns;
  GetNetworkParams_fn_t fn;

  ASSERT_LOCKED(base);
  if (!(handle = evutil_load_windows_system_library_(
      TEXT("iphlpapi.dll")))) {
    log(EVDNS_LOG_WARN, "Could not open iphlpapi.dll");
    status = -1;
    goto done;
  }
  if (!(fn = (GetNetworkParams_fn_t) GetProcAddress(handle, "GetNetworkParams"))) {
    log(EVDNS_LOG_WARN, "Could not get address of function.");
    status = -1;
    goto done;
  }

  buf = mm_malloc(size);
  if (!buf) { status = 4; goto done; }
  fixed = buf;
  r = fn(fixed, &size);
  if (r != ERROR_SUCCESS && r != ERROR_BUFFER_OVERFLOW) {
    status = -1;
    goto done;
  }
  if (r != ERROR_SUCCESS) {
    mm_free(buf);
    buf = mm_malloc(size);
    if (!buf) { status = 4; goto done; }
    fixed = buf;
    r = fn(fixed, &size);
    if (r != ERROR_SUCCESS) {
      log(EVDNS_LOG_DEBUG, "fn() failed.");
      status = -1;
      goto done;
    }
  }

  EVUTIL_ASSERT(fixed);
  added_any = 0;
  ns = &(fixed->DnsServerList);
  while (ns) {
    r = evdns_nameserver_ip_add_line(base, ns->IpAddress.String);
    if (r) {
      log(EVDNS_LOG_DEBUG,"Could not add nameserver %s to list,error: %d",
        (ns->IpAddress.String),(int)GetLastError());
      status = r;
    } else {
      ++added_any;
      log(EVDNS_LOG_DEBUG,"Successfully added %s as nameserver",ns->IpAddress.String);
    }

    ns = ns->Next;
  }

  if (!added_any) {
    log(EVDNS_LOG_DEBUG, "No nameservers added.");
    if (status == 0)
      status = -1;
  } else {
    status = 0;
  }

 done:
  if (buf)
    mm_free(buf);
  if (handle)
    FreeLibrary(handle);
  return status;
}

static int
config_nameserver_from_reg_key(struct evdns_base *base, HKEY key, const TCHAR *subkey)
{
  char *buf;
  DWORD bufsz = 0, type = 0;
  int status = 0;

  ASSERT_LOCKED(base);
  if (RegQueryValueEx(key, subkey, 0, &type, NULL, &bufsz)
      != ERROR_MORE_DATA)
    return -1;
  if (!(buf = mm_malloc(bufsz)))
    return -1;

  if (RegQueryValueEx(key, subkey, 0, &type, (LPBYTE)buf, &bufsz)
      == ERROR_SUCCESS && bufsz > 1) {
    status = evdns_nameserver_ip_add_line(base,buf);
  }

  mm_free(buf);
  return status;
}

#define SERVICES_KEY TEXT("System\\CurrentControlSet\\Services\\")
#define WIN_NS_9X_KEY  SERVICES_KEY TEXT("VxD\\MSTCP")
#define WIN_NS_NT_KEY  SERVICES_KEY TEXT("Tcpip\\Parameters")

static int
load_nameservers_from_registry(struct evdns_base *base)
{
  int found = 0;
  int r;
#define TRY(k, name) \
  if (!found && config_nameserver_from_reg_key(base,k,TEXT(name)) == 0) { \
    log(EVDNS_LOG_DEBUG,"Found nameservers in %s/%s",#k,name); \
    found = 1;            \
  } else if (!found) {            \
    log(EVDNS_LOG_DEBUG,"Didn't find nameservers in %s/%s", \
        #k,#name);            \
  }

  ASSERT_LOCKED(base);

  if (((int)GetVersion()) > 0) { /* NT */
    HKEY nt_key = 0, interfaces_key = 0;

    if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, WIN_NS_NT_KEY, 0,
         KEY_READ, &nt_key) != ERROR_SUCCESS) {
      log(EVDNS_LOG_DEBUG,"Couldn't open nt key, %d",(int)GetLastError());
      return -1;
    }
    r = RegOpenKeyEx(nt_key, TEXT("Interfaces"), 0,
           KEY_QUERY_VALUE|KEY_ENUMERATE_SUB_KEYS,
           &interfaces_key);
    if (r != ERROR_SUCCESS) {
      log(EVDNS_LOG_DEBUG,"Couldn't open interfaces key, %d",(int)GetLastError());
      return -1;
    }
    TRY(nt_key, "NameServer");
    TRY(nt_key, "DhcpNameServer");
    TRY(interfaces_key, "NameServer");
    TRY(interfaces_key, "DhcpNameServer");
    RegCloseKey(interfaces_key);
    RegCloseKey(nt_key);
  } else {
    HKEY win_key = 0;
    if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, WIN_NS_9X_KEY, 0,
         KEY_READ, &win_key) != ERROR_SUCCESS) {
      log(EVDNS_LOG_DEBUG, "Couldn't open registry key, %d", (int)GetLastError());
      return -1;
    }
    TRY(win_key, "NameServer");
    RegCloseKey(win_key);
  }

  if (found == 0) {
    log(EVDNS_LOG_WARN,"Didn't find any nameservers.");
  }

  return found ? 0 : -1;
#undef TRY
}

int
evdns_base_config_windows_nameservers(struct evdns_base *base)
{
  int r;
  char *fname;
  if (base == NULL)
    base = current_base;
  if (base == NULL)
    return -1;
  EVDNS_LOCK(base);
  fname = evdns_get_default_hosts_filename();
  log(EVDNS_LOG_DEBUG, "Loading hosts entries from %s", fname);
  evdns_base_load_hosts(base, fname);
  if (fname)
    mm_free(fname);

  if (load_nameservers_with_getnetworkparams(base) == 0) {
    EVDNS_UNLOCK(base);
    return 0;
  }
  r = load_nameservers_from_registry(base);

  EVDNS_UNLOCK(base);
  return r;
}

int
evdns_config_windows_nameservers(void)
{
  if (!current_base) {
    current_base = evdns_base_new(NULL, 1);
    return current_base == NULL ? -1 : 0;
  } else {
    return evdns_base_config_windows_nameservers(current_base);
  }
}
#endif

struct evdns_base *
evdns_base_new(struct event_base *event_base, int flags)
{
  struct evdns_base *base;

  if (evutil_secure_rng_init() < 0) {
    log(EVDNS_LOG_WARN, "Unable to seed random number generator; "
        "DNS can't run.");
    return NULL;
  }

  /* Give the evutil library a hook into its evdns-enabled
   * functionality.  We can't just call evdns_getaddrinfo directly or
   * else libevent-core will depend on libevent-extras. */
  evutil_set_evdns_getaddrinfo_fn_(evdns_getaddrinfo);
  evutil_set_evdns_getaddrinfo_cancel_fn_(evdns_getaddrinfo_cancel);

  base = mm_malloc(sizeof(struct evdns_base));
  if (base == NULL)
    return (NULL);
  memset(base, 0, sizeof(struct evdns_base));
  base->req_waiting_head = NULL;

  EVTHREAD_ALLOC_LOCK(base->lock, EVTHREAD_LOCKTYPE_RECURSIVE);
  EVDNS_LOCK(base);

  /* Set max requests inflight and allocate req_heads. */
  base->req_heads = NULL;

  evdns_base_set_max_requests_inflight(base, 64);

  base->server_head = NULL;
  base->event_base = event_base;
  base->global_good_nameservers = base->global_requests_inflight =
    base->global_requests_waiting = 0;

  base->global_timeout.tv_sec = 5;
  base->global_timeout.tv_usec = 0;
  base->global_max_reissues = 1;
  base->global_max_retransmits = 3;
  base->global_max_nameserver_timeout = 3;
  base->global_search_state = NULL;
  base->global_randomize_case = 1;
  base->global_getaddrinfo_allow_skew.tv_sec = 3;
  base->global_getaddrinfo_allow_skew.tv_usec = 0;
  base->global_nameserver_probe_initial_timeout.tv_sec = 10;
  base->global_nameserver_probe_initial_timeout.tv_usec = 0;

  TAILQ_INIT(&base->hostsdb);

#define EVDNS_BASE_ALL_FLAGS (0x8001)
  if (flags & ~EVDNS_BASE_ALL_FLAGS) {
    flags = EVDNS_BASE_INITIALIZE_NAMESERVERS;
    log(EVDNS_LOG_WARN,
        "Unrecognized flag passed to evdns_base_new(). Assuming "
        "you meant EVDNS_BASE_INITIALIZE_NAMESERVERS.");
  }
#undef EVDNS_BASE_ALL_FLAGS

  if (flags & EVDNS_BASE_INITIALIZE_NAMESERVERS) {
    int r;
#ifdef _WIN32
    r = evdns_base_config_windows_nameservers(base);
#else
    r = evdns_base_resolv_conf_parse(base, DNS_OPTIONS_ALL, "/etc/resolv.conf");
#endif
    if (r == -1) {
      evdns_base_free_and_unlock(base, 0);
      return NULL;
    }
  }
  if (flags & EVDNS_BASE_DISABLE_WHEN_INACTIVE) {
    base->disable_when_inactive = 1;
  }

  EVDNS_UNLOCK(base);
  return base;
}

int
evdns_init(void)
{
  struct evdns_base *base = evdns_base_new(NULL, 1);
  if (base) {
    current_base = base;
    return 0;
  } else {
    return -1;
  }
}

const char *
evdns_err_to_string(int err)
{
    switch (err) {
  case DNS_ERR_NONE: return "no error";
  case DNS_ERR_FORMAT: return "misformatted query";
  case DNS_ERR_SERVERFAILED: return "server failed";
  case DNS_ERR_NOTEXIST: return "name does not exist";
  case DNS_ERR_NOTIMPL: return "query not implemented";
  case DNS_ERR_REFUSED: return "refused";

  case DNS_ERR_TRUNCATED: return "reply truncated or ill-formed";
  case DNS_ERR_UNKNOWN: return "unknown";
  case DNS_ERR_TIMEOUT: return "request timed out";
  case DNS_ERR_SHUTDOWN: return "dns subsystem shut down";
  case DNS_ERR_CANCEL: return "dns request canceled";
  case DNS_ERR_NODATA: return "no records in the reply";
  default: return "[Unknown error code]";
    }
}

static void
evdns_nameserver_free(struct nameserver *server)
{
  if (server->socket >= 0)
    evutil_closesocket(server->socket);
  (void) event_del(&server->event);
  event_debug_unassign(&server->event);
  if (server->state == 0)
    (void) event_del(&server->timeout_event);
  if (server->probe_request) {
    evdns_cancel_request(server->base, server->probe_request);
    server->probe_request = NULL;
  }
  event_debug_unassign(&server->timeout_event);
  mm_free(server);
}

static void
evdns_base_free_and_unlock(struct evdns_base *base, int fail_requests)
{
  struct nameserver *server, *server_next;
  struct search_domain *dom, *dom_next;
  int i;

  /* Requires that we hold the lock. */

  /* TODO(nickm) we might need to refcount here. */

  for (i = 0; i < base->n_req_heads; ++i) {
    while (base->req_heads[i]) {
      if (fail_requests)
        reply_schedule_callback(base->req_heads[i], 0, DNS_ERR_SHUTDOWN, NULL);
      request_finished(base->req_heads[i], &REQ_HEAD(base, base->req_heads[i]->trans_id), 1);
    }
  }
  while (base->req_waiting_head) {
    if (fail_requests)
      reply_schedule_callback(base->req_waiting_head, 0, DNS_ERR_SHUTDOWN, NULL);
    request_finished(base->req_waiting_head, &base->req_waiting_head, 1);
  }
  base->global_requests_inflight = base->global_requests_waiting = 0;

  for (server = base->server_head; server; server = server_next) {
    server_next = server->next;
    /** already done something before */
    server->probe_request = NULL;
    evdns_nameserver_free(server);
    if (server_next == base->server_head)
      break;
  }
  base->server_head = NULL;
  base->global_good_nameservers = 0;

  if (base->global_search_state) {
    for (dom = base->global_search_state->head; dom; dom = dom_next) {
      dom_next = dom->next;
      mm_free(dom);
    }
    mm_free(base->global_search_state);
    base->global_search_state = NULL;
  }

  {
    struct hosts_entry *victim;
    while ((victim = TAILQ_FIRST(&base->hostsdb))) {
      TAILQ_REMOVE(&base->hostsdb, victim, next);
      mm_free(victim);
    }
  }

  mm_free(base->req_heads);

  EVDNS_UNLOCK(base);
  EVTHREAD_FREE_LOCK(base->lock, EVTHREAD_LOCKTYPE_RECURSIVE);

  mm_free(base);
}

void
evdns_base_free(struct evdns_base *base, int fail_requests)
{
  EVDNS_LOCK(base);
  evdns_base_free_and_unlock(base, fail_requests);
}

void
evdns_base_clear_host_addresses(struct evdns_base *base)
{
  struct hosts_entry *victim;
  EVDNS_LOCK(base);
  while ((victim = TAILQ_FIRST(&base->hostsdb))) {
    TAILQ_REMOVE(&base->hostsdb, victim, next);
    mm_free(victim);
  }
  EVDNS_UNLOCK(base);
}

void
evdns_shutdown(int fail_requests)
{
  if (current_base) {
    struct evdns_base *b = current_base;
    current_base = NULL;
    evdns_base_free(b, fail_requests);
  }
  evdns_log_fn = NULL;
}

static int
evdns_base_parse_hosts_line(struct evdns_base *base, char *line)
{
  char *strtok_state;
  static const char *const delims = " \t";
  char *const addr = strtok_r(line, delims, &strtok_state);
  char *hostname, *hash;
  struct sockaddr_storage ss;
  int socklen = sizeof(ss);
  ASSERT_LOCKED(base);

#define NEXT_TOKEN strtok_r(NULL, delims, &strtok_state)

  if (!addr || *addr == '#')
    return 0;

  memset(&ss, 0, sizeof(ss));
  if (evutil_parse_sockaddr_port(addr, (struct sockaddr*)&ss, &socklen)<0)
    return -1;
  if (socklen > (int)sizeof(struct sockaddr_in6))
    return -1;

  if (sockaddr_getport((struct sockaddr*)&ss))
    return -1;

  while ((hostname = NEXT_TOKEN)) {
    struct hosts_entry *he;
    size_t namelen;
    if ((hash = strchr(hostname, '#'))) {
      if (hash == hostname)
        return 0;
      *hash = '\0';
    }

    namelen = strlen(hostname);

    he = mm_calloc(1, sizeof(struct hosts_entry)+namelen);
    if (!he)
      return -1;
    EVUTIL_ASSERT(socklen <= (int)sizeof(he->addr));
    memcpy(&he->addr, &ss, socklen);
    memcpy(he->hostname, hostname, namelen+1);
    he->addrlen = socklen;

    TAILQ_INSERT_TAIL(&base->hostsdb, he, next);

    if (hash)
      return 0;
  }

  return 0;
#undef NEXT_TOKEN
}

static int
evdns_base_load_hosts_impl(struct evdns_base *base, const char *hosts_fname)
{
  char *str=NULL, *cp, *eol;
  size_t len;
  int err=0;

  ASSERT_LOCKED(base);

  if (hosts_fname == NULL ||
      (err = evutil_read_file_(hosts_fname, &str, &len, 0)) < 0) {
    char tmp[64];
    strlcpy(tmp, "127.0.0.1   localhost", sizeof(tmp));
    evdns_base_parse_hosts_line(base, tmp);
    strlcpy(tmp, "::1   localhost", sizeof(tmp));
    evdns_base_parse_hosts_line(base, tmp);
    return err ? -1 : 0;
  }

  /* This will break early if there is a NUL in the hosts file.
   * Probably not a problem.*/
  cp = str;
  for (;;) {
    eol = strchr(cp, '\n');

    if (eol) {
      *eol = '\0';
      evdns_base_parse_hosts_line(base, cp);
      cp = eol+1;
    } else {
      evdns_base_parse_hosts_line(base, cp);
      break;
    }
  }

  mm_free(str);
  return 0;
}

int
evdns_base_load_hosts(struct evdns_base *base, const char *hosts_fname)
{
  int res;
  if (!base)
    base = current_base;
  EVDNS_LOCK(base);
  res = evdns_base_load_hosts_impl(base, hosts_fname);
  EVDNS_UNLOCK(base);
  return res;
}

/* A single request for a getaddrinfo, either v4 or v6. */
struct getaddrinfo_subrequest {
  struct evdns_request *r;
  ev_uint32_t type;
};

/* State data used to implement an in-progress getaddrinfo. */
struct evdns_getaddrinfo_request {
  struct evdns_base *evdns_base;
  /* Copy of the modified 'hints' data that we'll use to build
   * answers. */
  struct evutil_addrinfo hints;
  /* The callback to invoke when we're done */
  evdns_getaddrinfo_cb user_cb;
  /* User-supplied data to give to the callback. */
  void *user_data;
  /* The port to use when building sockaddrs. */
  ev_uint16_t port;
  /* The sub_request for an A record (if any) */
  struct getaddrinfo_subrequest ipv4_request;
  /* The sub_request for an AAAA record (if any) */
  struct getaddrinfo_subrequest ipv6_request;

  /* The cname result that we were told (if any) */
  char *cname_result;

  /* If we have one request answered and one request still inflight,
   * then this field holds the answer from the first request... */
  struct evutil_addrinfo *pending_result;
  /* And this event is a timeout that will tell us to cancel the second
   * request if it's taking a long time. */
  struct event timeout;

  /* And this field holds the error code from the first request... */
  int pending_error;
  /* If this is set, the user canceled this request. */
  unsigned user_canceled : 1;
  /* If this is set, the user can no longer cancel this request; we're
   * just waiting for the free. */
  unsigned request_done : 1;
};

/* Convert an evdns errors to the equivalent getaddrinfo error. */
static int
evdns_err_to_getaddrinfo_err(int e1)
{
  /* XXX Do this better! */
  if (e1 == DNS_ERR_NONE)
    return 0;
  else if (e1 == DNS_ERR_NOTEXIST)
    return EVUTIL_EAI_NONAME;
  else
    return EVUTIL_EAI_FAIL;
}

/* Return the more informative of two getaddrinfo errors. */
static int
getaddrinfo_merge_err(int e1, int e2)
{
  /* XXXX be cleverer here. */
  if (e1 == 0)
    return e2;
  else
    return e1;
}

static void
free_getaddrinfo_request(struct evdns_getaddrinfo_request *data)
{
  /* DO NOT CALL this if either of the requests is pending.  Only once
   * both callbacks have been invoked is it safe to free the request */
  if (data->pending_result)
    evutil_freeaddrinfo(data->pending_result);
  if (data->cname_result)
    mm_free(data->cname_result);
  event_del(&data->timeout);
  mm_free(data);
  return;
}

static void
add_cname_to_reply(struct evdns_getaddrinfo_request *data,
    struct evutil_addrinfo *ai)
{
  if (data->cname_result && ai) {
    ai->ai_canonname = data->cname_result;
    data->cname_result = NULL;
  }
}

/* Callback: invoked when one request in a mixed-format A/AAAA getaddrinfo
 * request has finished, but the other one took too long to answer. Pass
 * along the answer we got, and cancel the other request.
 */
static void
evdns_getaddrinfo_timeout_cb(evutil_socket_t fd, short what, void *ptr)
{
  int v4_timedout = 0, v6_timedout = 0;
  struct evdns_getaddrinfo_request *data = ptr;

  /* Cancel any pending requests, and note which one */
  if (data->ipv4_request.r) {
    /* XXXX This does nothing if the request's callback is already
     * running (pending_cb is set). */
    evdns_cancel_request(NULL, data->ipv4_request.r);
    v4_timedout = 1;
    EVDNS_LOCK(data->evdns_base);
    ++data->evdns_base->getaddrinfo_ipv4_timeouts;
    EVDNS_UNLOCK(data->evdns_base);
  }
  if (data->ipv6_request.r) {
    /* XXXX This does nothing if the request's callback is already
     * running (pending_cb is set). */
    evdns_cancel_request(NULL, data->ipv6_request.r);
    v6_timedout = 1;
    EVDNS_LOCK(data->evdns_base);
    ++data->evdns_base->getaddrinfo_ipv6_timeouts;
    EVDNS_UNLOCK(data->evdns_base);
  }

  /* We only use this timeout callback when we have an answer for
   * one address. */
  EVUTIL_ASSERT(!v4_timedout || !v6_timedout);

  /* Report the outcome of the other request that didn't time out. */
  if (data->pending_result) {
    add_cname_to_reply(data, data->pending_result);
    data->user_cb(0, data->pending_result, data->user_data);
    data->pending_result = NULL;
  } else {
    int e = data->pending_error;
    if (!e)
      e = EVUTIL_EAI_AGAIN;
    data->user_cb(e, NULL, data->user_data);
  }

  data->user_cb = NULL; /* prevent double-call if evdns callbacks are
             * in-progress. XXXX It would be better if this
             * weren't necessary. */

  if (!v4_timedout && !v6_timedout) {
    /* should be impossible? XXXX */
    free_getaddrinfo_request(data);
  }
}

static int
evdns_getaddrinfo_set_timeout(struct evdns_base *evdns_base,
    struct evdns_getaddrinfo_request *data)
{
  return event_add(&data->timeout, &evdns_base->global_getaddrinfo_allow_skew);
}

static inline int
evdns_result_is_answer(int result)
{
  return (result != DNS_ERR_NOTIMPL && result != DNS_ERR_REFUSED &&
      result != DNS_ERR_SERVERFAILED && result != DNS_ERR_CANCEL);
}

static void
evdns_getaddrinfo_gotresolve(int result, char type, int count,
    int ttl, void *addresses, void *arg)
{
  int i;
  struct getaddrinfo_subrequest *req = arg;
  struct getaddrinfo_subrequest *other_req;
  struct evdns_getaddrinfo_request *data;

  struct evutil_addrinfo *res;

  struct sockaddr_in sin;
  struct sockaddr_in6 sin6;
  struct sockaddr *sa;
  int socklen, addrlen;
  void *addrp;
  int err;
  int user_canceled;

  EVUTIL_ASSERT(req->type == DNS_IPv4_A || req->type == DNS_IPv6_AAAA);
  if (req->type == DNS_IPv4_A) {
    data = EVUTIL_UPCAST(req, struct evdns_getaddrinfo_request, ipv4_request);
    other_req = &data->ipv6_request;
  } else {
    data = EVUTIL_UPCAST(req, struct evdns_getaddrinfo_request, ipv6_request);
    other_req = &data->ipv4_request;
  }

  /** Called from evdns_base_free() with @fail_requests == 1 */
  if (result != DNS_ERR_SHUTDOWN) {
    EVDNS_LOCK(data->evdns_base);
    if (evdns_result_is_answer(result)) {
      if (req->type == DNS_IPv4_A)
        ++data->evdns_base->getaddrinfo_ipv4_answered;
      else
        ++data->evdns_base->getaddrinfo_ipv6_answered;
    }
    user_canceled = data->user_canceled;
    if (other_req->r == NULL)
      data->request_done = 1;
    EVDNS_UNLOCK(data->evdns_base);
  } else {
    data->evdns_base = NULL;
    user_canceled = data->user_canceled;
  }

  req->r = NULL;

  if (result == DNS_ERR_CANCEL && ! user_canceled) {
    /* Internal cancel request from timeout or internal error.
     * we already answered the user. */
    if (other_req->r == NULL)
      free_getaddrinfo_request(data);
    return;
  }

  if (data->user_cb == NULL) {
    /* We already answered.  XXXX This shouldn't be needed; see
     * comments in evdns_getaddrinfo_timeout_cb */
    free_getaddrinfo_request(data);
    return;
  }

  if (result == DNS_ERR_NONE) {
    if (count == 0)
      err = EVUTIL_EAI_NODATA;
    else
      err = 0;
  } else {
    err = evdns_err_to_getaddrinfo_err(result);
  }

  if (err) {
    /* Looks like we got an error. */
    if (other_req->r) {
      /* The other request is still working; maybe it will
       * succeed. */
      /* XXXX handle failure from set_timeout */
      if (result != DNS_ERR_SHUTDOWN) {
        evdns_getaddrinfo_set_timeout(data->evdns_base, data);
      }
      data->pending_error = err;
      return;
    }

    if (user_canceled) {
      data->user_cb(EVUTIL_EAI_CANCEL, NULL, data->user_data);
    } else if (data->pending_result) {
      /* If we have an answer waiting, and we weren't
       * canceled, ignore this error. */
      add_cname_to_reply(data, data->pending_result);
      data->user_cb(0, data->pending_result, data->user_data);
      data->pending_result = NULL;
    } else {
      if (data->pending_error)
        err = getaddrinfo_merge_err(err,
            data->pending_error);
      data->user_cb(err, NULL, data->user_data);
    }
    free_getaddrinfo_request(data);
    return;
  } else if (user_canceled) {
    if (other_req->r) {
      /* The other request is still working; let it hit this
       * callback with EVUTIL_EAI_CANCEL callback and report
       * the failure. */
      return;
    }
    data->user_cb(EVUTIL_EAI_CANCEL, NULL, data->user_data);
    free_getaddrinfo_request(data);
    return;
  }

  /* Looks like we got some answers. We should turn them into addrinfos
   * and then either queue those or return them all. */
  EVUTIL_ASSERT(type == DNS_IPv4_A || type == DNS_IPv6_AAAA);

  if (type == DNS_IPv4_A) {
    memset(&sin, 0, sizeof(sin));
    sin.sin_family = AF_INET;
    sin.sin_port = htons(data->port);

    sa = (struct sockaddr *)&sin;
    socklen = sizeof(sin);
    addrlen = 4;
    addrp = &sin.sin_addr.s_addr;
  } else {
    memset(&sin6, 0, sizeof(sin6));
    sin6.sin6_family = AF_INET6;
    sin6.sin6_port = htons(data->port);

    sa = (struct sockaddr *)&sin6;
    socklen = sizeof(sin6);
    addrlen = 16;
    addrp = &sin6.sin6_addr.s6_addr;
  }

  res = NULL;
  for (i=0; i < count; ++i) {
    struct evutil_addrinfo *ai;
    memcpy(addrp, ((char*)addresses)+i*addrlen, addrlen);
    ai = evutil_new_addrinfo_(sa, socklen, &data->hints);
    if (!ai) {
      if (other_req->r) {
        evdns_cancel_request(NULL, other_req->r);
      }
      data->user_cb(EVUTIL_EAI_MEMORY, NULL, data->user_data);
      if (res)
        evutil_freeaddrinfo(res);

      if (other_req->r == NULL)
        free_getaddrinfo_request(data);
      return;
    }
    res = evutil_addrinfo_append_(res, ai);
  }

  if (other_req->r) {
    /* The other request is still in progress; wait for it */
    /* XXXX handle failure from set_timeout */
    evdns_getaddrinfo_set_timeout(data->evdns_base, data);
    data->pending_result = res;
    return;
  } else {
    /* The other request is done or never started; append its
     * results (if any) and return them. */
    if (data->pending_result) {
      if (req->type == DNS_IPv4_A)
        res = evutil_addrinfo_append_(res,
            data->pending_result);
      else
        res = evutil_addrinfo_append_(
            data->pending_result, res);
      data->pending_result = NULL;
    }

    /* Call the user callback. */
    add_cname_to_reply(data, res);
    data->user_cb(0, res, data->user_data);

    /* Free data. */
    free_getaddrinfo_request(data);
  }
}

static struct hosts_entry *
find_hosts_entry(struct evdns_base *base, const char *hostname,
    struct hosts_entry *find_after)
{
  struct hosts_entry *e;

  if (find_after)
    e = TAILQ_NEXT(find_after, next);
  else
    e = TAILQ_FIRST(&base->hostsdb);

  for (; e; e = TAILQ_NEXT(e, next)) {
    if (!evutil_ascii_strcasecmp(e->hostname, hostname))
      return e;
  }
  return NULL;
}

static int
evdns_getaddrinfo_fromhosts(struct evdns_base *base,
    const char *nodename, struct evutil_addrinfo *hints, ev_uint16_t port,
    struct evutil_addrinfo **res)
{
  int n_found = 0;
  struct hosts_entry *e;
  struct evutil_addrinfo *ai=NULL;
  int f = hints->ai_family;

  EVDNS_LOCK(base);
  for (e = find_hosts_entry(base, nodename, NULL); e;
      e = find_hosts_entry(base, nodename, e)) {
    struct evutil_addrinfo *ai_new;
    ++n_found;
    if ((e->addr.sa.sa_family == AF_INET && f == PF_INET6) ||
        (e->addr.sa.sa_family == AF_INET6 && f == PF_INET))
      continue;
    ai_new = evutil_new_addrinfo_(&e->addr.sa, e->addrlen, hints);
    if (!ai_new) {
      n_found = 0;
      goto out;
    }
    sockaddr_setport(ai_new->ai_addr, port);
    ai = evutil_addrinfo_append_(ai, ai_new);
  }
  EVDNS_UNLOCK(base);
out:
  if (n_found) {
    /* Note that we return an empty answer if we found entries for
     * this hostname but none were of the right address type. */
    *res = ai;
    return 0;
  } else {
    if (ai)
      evutil_freeaddrinfo(ai);
    return -1;
  }
}

struct evdns_getaddrinfo_request *
evdns_getaddrinfo(struct evdns_base *dns_base,
    const char *nodename, const char *servname,
    const struct evutil_addrinfo *hints_in,
    evdns_getaddrinfo_cb cb, void *arg)
{
  struct evdns_getaddrinfo_request *data;
  struct evutil_addrinfo hints;
  struct evutil_addrinfo *res = NULL;
  int err;
  int port = 0;
  int want_cname = 0;
  int started = 0;

  if (!dns_base) {
    dns_base = current_base;
    if (!dns_base) {
      log(EVDNS_LOG_WARN,
          "Call to getaddrinfo_async with no "
          "evdns_base configured.");
      cb(EVUTIL_EAI_FAIL, NULL, arg); /* ??? better error? */
      return NULL;
    }
  }

  /* If we _must_ answer this immediately, do so. */
  if ((hints_in && (hints_in->ai_flags & EVUTIL_AI_NUMERICHOST))) {
    res = NULL;
    err = evutil_getaddrinfo(nodename, servname, hints_in, &res);
    cb(err, res, arg);
    return NULL;
  }

  if (hints_in) {
    memcpy(&hints, hints_in, sizeof(hints));
  } else {
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = PF_UNSPEC;
  }

  evutil_adjust_hints_for_addrconfig_(&hints);

  /* Now try to see if we _can_ answer immediately. */
  /* (It would be nice to do this by calling getaddrinfo directly, with
   * AI_NUMERICHOST, on plaforms that have it, but we can't: there isn't
   * a reliable way to distinguish the "that wasn't a numeric host!" case
   * from any other EAI_NONAME cases.) */
  err = evutil_getaddrinfo_common_(nodename, servname, &hints, &res, &port);
  if (err != EVUTIL_EAI_NEED_RESOLVE) {
    cb(err, res, arg);
    return NULL;
  }

  /* If there is an entry in the hosts file, we should give it now. */
  if (!evdns_getaddrinfo_fromhosts(dns_base, nodename, &hints, port, &res)) {
    cb(0, res, arg);
    return NULL;
  }

  /* Okay, things are serious now. We're going to need to actually
   * launch a request.
   */
  data = mm_calloc(1,sizeof(struct evdns_getaddrinfo_request));
  if (!data) {
    cb(EVUTIL_EAI_MEMORY, NULL, arg);
    return NULL;
  }

  memcpy(&data->hints, &hints, sizeof(data->hints));
  data->port = (ev_uint16_t)port;
  data->ipv4_request.type = DNS_IPv4_A;
  data->ipv6_request.type = DNS_IPv6_AAAA;
  data->user_cb = cb;
  data->user_data = arg;
  data->evdns_base = dns_base;

  want_cname = (hints.ai_flags & EVUTIL_AI_CANONNAME);

  /* If we are asked for a PF_UNSPEC address, we launch two requests in
   * parallel: one for an A address and one for an AAAA address.  We
   * can't send just one request, since many servers only answer one
   * question per DNS request.
   *
   * Once we have the answer to one request, we allow for a short
   * timeout before we report it, to see if the other one arrives.  If
   * they both show up in time, then we report both the answers.
   *
   * If too many addresses of one type time out or fail, we should stop
   * launching those requests. (XXX we don't do that yet.)
   */

  EVDNS_LOCK(dns_base);

  if (hints.ai_family != PF_INET6) {
    log(EVDNS_LOG_DEBUG, "Sending request for %s on ipv4 as %p",
        nodename, &data->ipv4_request);

    data->ipv4_request.r = evdns_base_resolve_ipv4(dns_base,
        nodename, 0, evdns_getaddrinfo_gotresolve,
        &data->ipv4_request);
    if (want_cname && data->ipv4_request.r)
      data->ipv4_request.r->current_req->put_cname_in_ptr =
          &data->cname_result;
  }
  if (hints.ai_family != PF_INET) {
    log(EVDNS_LOG_DEBUG, "Sending request for %s on ipv6 as %p",
        nodename, &data->ipv6_request);

    data->ipv6_request.r = evdns_base_resolve_ipv6(dns_base,
        nodename, 0, evdns_getaddrinfo_gotresolve,
        &data->ipv6_request);
    if (want_cname && data->ipv6_request.r)
      data->ipv6_request.r->current_req->put_cname_in_ptr =
          &data->cname_result;
  }

  evtimer_assign(&data->timeout, dns_base->event_base,
      evdns_getaddrinfo_timeout_cb, data);

  started = (data->ipv4_request.r || data->ipv6_request.r);

  EVDNS_UNLOCK(dns_base);

  if (started) {
    return data;
  } else {
    mm_free(data);
    cb(EVUTIL_EAI_FAIL, NULL, arg);
    return NULL;
  }
}

void
evdns_getaddrinfo_cancel(struct evdns_getaddrinfo_request *data)
{
  EVDNS_LOCK(data->evdns_base);
  if (data->request_done) {
    EVDNS_UNLOCK(data->evdns_base);
    return;
  }
  event_del(&data->timeout);
  data->user_canceled = 1;
  if (data->ipv4_request.r)
    evdns_cancel_request(data->evdns_base, data->ipv4_request.r);
  if (data->ipv6_request.r)
    evdns_cancel_request(data->evdns_base, data->ipv6_request.r);
  EVDNS_UNLOCK(data->evdns_base);
}

Coverage Report

Created: 2018-08-29 13:53