text: /* 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 "event2/bufferevent.h"
  #include "event2/bufferevent_struct.h"
  #include "bufferevent-internal.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 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)));
  	}
  }
  
  /* 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 */
  					req->ns = 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);
  	}
  
  	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 */
  	req->ns = 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)));
  			break;
  		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;
  		if (j >= length) return -1;
  		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;
  		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)
  #define TEST_NAME							\
  	do { 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;			\
  		}							\
  	} 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>
  		 */
  		TEST_NAME;
  		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);
  
  	req->ns->timedout++;
  	if (req->ns->timedout > req->base->global_max_nameserver_timeout) {
  		req->ns->timedout = 0;
  		nameserver_failed(req->ns, "request timed out.");
  	}
  
  	if (req->tx_count >= req->base->global_max_retransmits) {
  		/* 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);
  	} else {
  		/* retransmit it */
  		struct nameserver *new_ns;
  		log(EVDNS_LOG_DEBUG, "Retransmitting request %p; tx_count==%d",
  		    arg, req->tx_count);
  		(void) evtimer_del(&req->timeout_event);
  		new_ns = nameserver_pick(base);
  		if (new_ns)
  			req->ns = new_ns;
  		evdns_request_transmit(req);
  	}
  	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. */
  		retcode = 1;
  		/* fall through: we'll set a timeout, which will time out,
  		 * and make us retransmit the request anyway. */
  	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;
  }
  
  /* 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);
  	const char need_to_append_dot = base_name[base_len - 1] == '.' ? 0 : 1;
  	struct search_domain *dom;
  
  	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
  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 (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 (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 (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);
  	path_out = mm_malloc(len_out+1);
  	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);
  	if (load_nameservers_with_getnetworkparams(base) == 0) {
  		EVDNS_UNLOCK(base);
  		return 0;
  	}
  	r = load_nameservers_from_registry(base);
  
  	fname = evdns_get_default_hosts_filename();
  	evdns_base_load_hosts(base, fname);
  	if (fname)
  		mm_free(fname);
  
  	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);
  
  	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);
  	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;
  		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_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;
  	}
  
  	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);
  
  	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 */
  			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;
  
  	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.)
  	 */
  
  	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->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->current_req->put_cname_in_ptr =
  			    &data->cname_result;
  	}
  
  	evtimer_assign(&data->timeout, dns_base->event_base,
  	    evdns_getaddrinfo_timeout_cb, data);
  
  	if (data->ipv4_request.r || data->ipv6_request.r) {
  		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);
  }
  