2006-03-02 Roland McGrath <roland@redhat.com>

[glibc.git] / resolv / res_send.c

/*
 * Copyright (c) 1985, 1989, 1993
 *    The Regents of the University of California.  All rights reserved.
 *
 * 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.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``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 REGENTS OR CONTRIBUTORS 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.
 */

/*
 * Portions Copyright (c) 1993 by Digital Equipment Corporation.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies, and that
 * the name of Digital Equipment Corporation not be used in advertising or
 * publicity pertaining to distribution of the document or software without
 * specific, written prior permission.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND DIGITAL EQUIPMENT CORP. DISCLAIMS ALL
 * WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS.   IN NO EVENT SHALL DIGITAL EQUIPMENT
 * CORPORATION BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 */

/*
 * Portions Copyright (c) 1996-1999 by Internet Software Consortium.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
 * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
 * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 */

#if defined(LIBC_SCCS) && !defined(lint)
static const char sccsid[] = "@(#)res_send.c    8.1 (Berkeley) 6/4/93";
static const char rcsid[] = "$BINDId: res_send.c,v 8.38 2000/03/30 20:16:51 vixie Exp $";
#endif /* LIBC_SCCS and not lint */

/*
 * Send query to name server and wait for reply.
 */

#include <assert.h>
#include <sys/types.h>
#include <sys/param.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <sys/uio.h>
#include <sys/poll.h>

#include <netinet/in.h>
#include <arpa/nameser.h>
#include <arpa/inet.h>
#include <sys/ioctl.h>

#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#include <resolv.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#if PACKETSZ > 65536
#define MAXPACKET       PACKETSZ
#else
#define MAXPACKET       65536
#endif


/* From ev_streams.c.  */

static inline void
__attribute ((always_inline))
evConsIovec(void *buf, size_t cnt, struct iovec *vec) {
        memset(vec, 0xf5, sizeof (*vec));
        vec->iov_base = buf;
        vec->iov_len = cnt;
}

/* From ev_timers.c.  */

#define BILLION 1000000000

static inline void
evConsTime(struct timespec *res, time_t sec, long nsec) {
        res->tv_sec = sec;
        res->tv_nsec = nsec;
}

static inline void
evAddTime(struct timespec *res, const struct timespec *addend1,
          const struct timespec *addend2) {
        res->tv_sec = addend1->tv_sec + addend2->tv_sec;
        res->tv_nsec = addend1->tv_nsec + addend2->tv_nsec;
        if (res->tv_nsec >= BILLION) {
                res->tv_sec++;
                res->tv_nsec -= BILLION;
        }
}

static inline void
evSubTime(struct timespec *res, const struct timespec *minuend,
          const struct timespec *subtrahend) {
       res->tv_sec = minuend->tv_sec - subtrahend->tv_sec;
        if (minuend->tv_nsec >= subtrahend->tv_nsec)
                res->tv_nsec = minuend->tv_nsec - subtrahend->tv_nsec;
        else {
                res->tv_nsec = (BILLION
                                - subtrahend->tv_nsec + minuend->tv_nsec);
                res->tv_sec--;
        }
}

static inline int
evCmpTime(struct timespec a, struct timespec b) {
        long x = a.tv_sec - b.tv_sec;

        if (x == 0L)
                x = a.tv_nsec - b.tv_nsec;
        return (x < 0L ? (-1) : x > 0L ? (1) : (0));
}

static inline void
evNowTime(struct timespec *res) {
        struct timeval now;

        if (gettimeofday(&now, NULL) < 0)
                evConsTime(res, 0, 0);
        else
                TIMEVAL_TO_TIMESPEC (&now, res);
}


/* Options.  Leave them on. */
/* #undef DEBUG */
#include "res_debug.h"

#define EXT(res) ((res)->_u._ext)

/* Forward. */

static int              send_vc(res_state, const u_char *, int,
                                u_char **, int *, int *, int, u_char **);
static int              send_dg(res_state, const u_char *, int,
                                u_char **, int *, int *, int,
                                int *, int *, u_char **);
#ifdef DEBUG
static void             Aerror(const res_state, FILE *, const char *, int,
                               const struct sockaddr *);
static void             Perror(const res_state, FILE *, const char *, int);
#endif
static int              sock_eq(struct sockaddr_in6 *, struct sockaddr_in6 *);

/* Reachover. */

static void convaddr4to6(struct sockaddr_in6 *sa);
void res_pquery(const res_state, const u_char *, int, FILE *);

/* Public. */

/* int
 * res_isourserver(ina)
 *      looks up "ina" in _res.ns_addr_list[]
 * returns:
 *      0  : not found
 *      >0 : found
 * author:
 *      paul vixie, 29may94
 */
int
res_ourserver_p(const res_state statp, const struct sockaddr_in6 *inp)
{
        int ns;

        if (inp->sin6_family == AF_INET) {
            struct sockaddr_in *in4p = (struct sockaddr_in *) inp;
            in_port_t port = in4p->sin_port;
            in_addr_t addr = in4p->sin_addr.s_addr;

            for (ns = 0;  ns < MAXNS;  ns++) {
                const struct sockaddr_in *srv =
                    (struct sockaddr_in *)EXT(statp).nsaddrs[ns];

                if ((srv != NULL) && (srv->sin_family == AF_INET) &&
                    (srv->sin_port == port) &&
                    (srv->sin_addr.s_addr == INADDR_ANY ||
                     srv->sin_addr.s_addr == addr))
                    return (1);
            }
        } else if (inp->sin6_family == AF_INET6) {
            for (ns = 0;  ns < MAXNS;  ns++) {
                const struct sockaddr_in6 *srv = EXT(statp).nsaddrs[ns];
                if ((srv != NULL) && (srv->sin6_family == AF_INET6) &&
                    (srv->sin6_port == inp->sin6_port) &&
                    !(memcmp(&srv->sin6_addr, &in6addr_any,
                             sizeof (struct in6_addr)) &&
                      memcmp(&srv->sin6_addr, &inp->sin6_addr,
                             sizeof (struct in6_addr))))
                    return (1);
            }
        }
        return (0);
}

/* int
 * res_nameinquery(name, type, class, buf, eom)
 *      look for (name,type,class) in the query section of packet (buf,eom)
 * requires:
 *      buf + HFIXEDSZ <= eom
 * returns:
 *      -1 : format error
 *      0  : not found
 *      >0 : found
 * author:
 *      paul vixie, 29may94
 */
int
res_nameinquery(const char *name, int type, int class,
                const u_char *buf, const u_char *eom)
{
        const u_char *cp = buf + HFIXEDSZ;
        int qdcount = ntohs(((HEADER*)buf)->qdcount);

        while (qdcount-- > 0) {
                char tname[MAXDNAME+1];
                int n, ttype, tclass;

                n = dn_expand(buf, eom, cp, tname, sizeof tname);
                if (n < 0)
                        return (-1);
                cp += n;
                if (cp + 2 * INT16SZ > eom)
                        return (-1);
                ttype = ns_get16(cp); cp += INT16SZ;
                tclass = ns_get16(cp); cp += INT16SZ;
                if (ttype == type && tclass == class &&
                    ns_samename(tname, name) == 1)
                        return (1);
        }
        return (0);
}
libresolv_hidden_def (res_nameinquery)

/* int
 * res_queriesmatch(buf1, eom1, buf2, eom2)
 *      is there a 1:1 mapping of (name,type,class)
 *      in (buf1,eom1) and (buf2,eom2)?
 * returns:
 *      -1 : format error
 *      0  : not a 1:1 mapping
 *      >0 : is a 1:1 mapping
 * author:
 *      paul vixie, 29may94
 */
int
res_queriesmatch(const u_char *buf1, const u_char *eom1,
                 const u_char *buf2, const u_char *eom2)
{
        const u_char *cp = buf1 + HFIXEDSZ;
        int qdcount = ntohs(((HEADER*)buf1)->qdcount);

        if (buf1 + HFIXEDSZ > eom1 || buf2 + HFIXEDSZ > eom2)
                return (-1);

        /*
         * Only header section present in replies to
         * dynamic update packets.
         */
        if ((((HEADER *)buf1)->opcode == ns_o_update) &&
            (((HEADER *)buf2)->opcode == ns_o_update))
                return (1);

        if (qdcount != ntohs(((HEADER*)buf2)->qdcount))
                return (0);
        while (qdcount-- > 0) {
                char tname[MAXDNAME+1];
                int n, ttype, tclass;

                n = dn_expand(buf1, eom1, cp, tname, sizeof tname);
                if (n < 0)
                        return (-1);
                cp += n;
                if (cp + 2 * INT16SZ > eom1)
                        return (-1);
                ttype = ns_get16(cp);   cp += INT16SZ;
                tclass = ns_get16(cp); cp += INT16SZ;
                if (!res_nameinquery(tname, ttype, tclass, buf2, eom2))
                        return (0);
        }
        return (1);
}
libresolv_hidden_def (res_queriesmatch)

int
__libc_res_nsend(res_state statp, const u_char *buf, int buflen,
                 u_char *ans, int anssiz, u_char **ansp)
{
        int gotsomewhere, terrno, try, v_circuit, resplen, ns, n;

        if (statp->nscount == 0) {
                __set_errno (ESRCH);
                return (-1);
        }

        if (anssiz < HFIXEDSZ) {
                __set_errno (EINVAL);
                return (-1);
        }

        if ((statp->qhook || statp->rhook) && anssiz < MAXPACKET && ansp) {
                u_char *buf = malloc (MAXPACKET);
                if (buf == NULL)
                        return (-1);
                memcpy (buf, ans, HFIXEDSZ);
                *ansp = buf;
                ans = buf;
                anssiz = MAXPACKET;
        }

        DprintQ((statp->options & RES_DEBUG) || (statp->pfcode & RES_PRF_QUERY),
                (stdout, ";; res_send()\n"), buf, buflen);
        v_circuit = (statp->options & RES_USEVC) || buflen > PACKETSZ;
        gotsomewhere = 0;
        terrno = ETIMEDOUT;

        /*
         * If the ns_addr_list in the resolver context has changed, then
         * invalidate our cached copy and the associated timing data.
         */
        if (EXT(statp).nsinit) {
                int needclose = 0;

                if (EXT(statp).nscount != statp->nscount)
                        needclose++;
                else
                        for (ns = 0; ns < MAXNS; ns++) {
                                unsigned int map = EXT(statp).nsmap[ns];
                                if (map < MAXNS
                                    && !sock_eq((struct sockaddr_in6 *)
                                                &statp->nsaddr_list[map],
                                                EXT(statp).nsaddrs[ns]))
                                {
                                        needclose++;
                                        break;
                                }
                        }
                if (needclose)
                        __res_iclose(statp, false);
        }

        /*
         * Maybe initialize our private copy of the ns_addr_list.
         */
        if (EXT(statp).nsinit == 0) {
                unsigned char map[MAXNS];

                memset (map, MAXNS, sizeof (map));
                for (n = 0; n < MAXNS; n++) {
                        ns = EXT(statp).nsmap[n];
                        if (ns < statp->nscount)
                                map[ns] = n;
                        else if (ns < MAXNS) {
                                free(EXT(statp).nsaddrs[n]);
                                EXT(statp).nsaddrs[n] = NULL;
                                EXT(statp).nsmap[n] = MAXNS;
                        }
                }
                n = statp->nscount;
                if (statp->nscount > EXT(statp).nscount)
                        for (n = EXT(statp).nscount, ns = 0;
                             n < statp->nscount; n++) {
                                while (ns < MAXNS
                                       && EXT(statp).nsmap[ns] != MAXNS)
                                        ns++;
                                if (ns == MAXNS)
                                        break;
                                EXT(statp).nsmap[ns] = n;
                                map[n] = ns++;
                        }
                EXT(statp).nscount = n;
                for (ns = 0; ns < EXT(statp).nscount; ns++) {
                        n = map[ns];
                        if (EXT(statp).nsaddrs[n] == NULL)
                                EXT(statp).nsaddrs[n] =
                                    malloc(sizeof (struct sockaddr_in6));
                        if (EXT(statp).nsaddrs[n] != NULL) {
                                memcpy(EXT(statp).nsaddrs[n],
                                       &statp->nsaddr_list[ns],
                                       sizeof (struct sockaddr_in));
                                EXT(statp).nssocks[n] = -1;
                                n++;
                        }
                }
                EXT(statp).nsinit = 1;
        }

        /*
         * Some resolvers want to even out the load on their nameservers.
         * Note that RES_BLAST overrides RES_ROTATE.
         */
        if ((statp->options & RES_ROTATE) != 0 &&
            (statp->options & RES_BLAST) == 0) {
                struct sockaddr_in6 *ina;
                unsigned int map;

                n = 0;
                while (n < MAXNS && EXT(statp).nsmap[n] == MAXNS)
                        n++;
                if (n < MAXNS) {
                        ina = EXT(statp).nsaddrs[n];
                        map = EXT(statp).nsmap[n];
                        for (;;) {
                                ns = n + 1;
                                while (ns < MAXNS
                                       && EXT(statp).nsmap[ns] == MAXNS)
                                        ns++;
                                if (ns == MAXNS)
                                        break;
                                EXT(statp).nsaddrs[n] = EXT(statp).nsaddrs[ns];
                                EXT(statp).nsmap[n] = EXT(statp).nsmap[ns];
                                n = ns;
                        }
                        EXT(statp).nsaddrs[n] = ina;
                        EXT(statp).nsmap[n] = map;
                }
        }

        /*
         * Send request, RETRY times, or until successful.
         */
        for (try = 0; try < statp->retry; try++) {
            for (ns = 0; ns < MAXNS; ns++)
            {
                struct sockaddr_in6 *nsap = EXT(statp).nsaddrs[ns];

                if (nsap == NULL)
                        goto next_ns;
 same_ns:
                if (statp->qhook) {
                        int done = 0, loops = 0;

                        do {
                                res_sendhookact act;

                                struct sockaddr_in *nsap4;
                                nsap4 = (struct sockaddr_in *) nsap;
                                act = (*statp->qhook)(&nsap4, &buf, &buflen,
                                                      ans, anssiz, &resplen);
                                nsap = (struct sockaddr_in6 *) nsap4;
                                switch (act) {
                                case res_goahead:
                                        done = 1;
                                        break;
                                case res_nextns:
                                        __res_iclose(statp, false);
                                        goto next_ns;
                                case res_done:
                                        return (resplen);
                                case res_modified:
                                        /* give the hook another try */
                                        if (++loops < 42) /*doug adams*/
                                                break;
                                        /*FALLTHROUGH*/
                                case res_error:
                                        /*FALLTHROUGH*/
                                default:
                                        return (-1);
                                }
                        } while (!done);
                }

#ifdef DEBUG
                char tmpbuf[40];
#endif
                Dprint(statp->options & RES_DEBUG,
                       (stdout, ";; Querying server (# %d) address = %s\n",
                        ns + 1, inet_ntop(AF_INET6, &nsap->sin6_addr,
                                          tmpbuf, sizeof (tmpbuf))));

                if (v_circuit) {
                        /* Use VC; at most one attempt per server. */
                        try = statp->retry;
                        n = send_vc(statp, buf, buflen, &ans, &anssiz, &terrno,
                                    ns, ansp);
                        if (n < 0)
                                return (-1);
                        if (n == 0)
                                goto next_ns;
                        resplen = n;
                } else {
                        /* Use datagrams. */
                        n = send_dg(statp, buf, buflen, &ans, &anssiz, &terrno,
                                    ns, &v_circuit, &gotsomewhere, ansp);
                        if (n < 0)
                                return (-1);
                        if (n == 0)
                                goto next_ns;
                        if (v_circuit)
                                goto same_ns;
                        resplen = n;
                }

                Dprint((statp->options & RES_DEBUG) ||
                       ((statp->pfcode & RES_PRF_REPLY) &&
                        (statp->pfcode & RES_PRF_HEAD1)),
                       (stdout, ";; got answer:\n"));

                DprintQ((statp->options & RES_DEBUG) ||
                        (statp->pfcode & RES_PRF_REPLY),
                        (stdout, "%s", ""),
                        ans, (resplen > anssiz) ? anssiz : resplen);

                /*
                 * If we have temporarily opened a virtual circuit,
                 * or if we haven't been asked to keep a socket open,
                 * close the socket.
                 */
                if ((v_circuit && (statp->options & RES_USEVC) == 0) ||
                    (statp->options & RES_STAYOPEN) == 0) {
                        __res_iclose(statp, false);
                }
                if (statp->rhook) {
                        int done = 0, loops = 0;

                        do {
                                res_sendhookact act;

                                act = (*statp->rhook)((struct sockaddr_in *)
                                                      nsap, buf, buflen,
                                                      ans, anssiz, &resplen);
                                switch (act) {
                                case res_goahead:
                                case res_done:
                                        done = 1;
                                        break;
                                case res_nextns:
                                        __res_iclose(statp, false);
                                        goto next_ns;
                                case res_modified:
                                        /* give the hook another try */
                                        if (++loops < 42) /*doug adams*/
                                                break;
                                        /*FALLTHROUGH*/
                                case res_error:
                                        /*FALLTHROUGH*/
                                default:
                                        return (-1);
                                }
                        } while (!done);

                }
                return (resplen);
 next_ns: ;
           } /*foreach ns*/
        } /*foreach retry*/
        __res_iclose(statp, false);
        if (!v_circuit) {
                if (!gotsomewhere)
                        __set_errno (ECONNREFUSED);     /* no nameservers found */
                else
                        __set_errno (ETIMEDOUT);        /* no answer obtained */
        } else
                __set_errno (terrno);
        return (-1);
}

int
res_nsend(res_state statp,
          const u_char *buf, int buflen, u_char *ans, int anssiz)
{
        return __libc_res_nsend(statp, buf, buflen, ans, anssiz, NULL);
}
libresolv_hidden_def (res_nsend)

/* Private */

static int
send_vc(res_state statp,
        const u_char *buf, int buflen, u_char **ansp, int *anssizp,
        int *terrno, int ns, u_char **anscp)
{
        const HEADER *hp = (HEADER *) buf;
        u_char *ans = *ansp;
        int anssiz = *anssizp;
        HEADER *anhp = (HEADER *) ans;
        struct sockaddr_in6 *nsap = EXT(statp).nsaddrs[ns];
        int truncating, connreset, resplen, n;
        struct iovec iov[2];
        u_short len;
        u_char *cp;

        connreset = 0;
 same_ns:
        truncating = 0;

        /* Are we still talking to whom we want to talk to? */
        if (statp->_vcsock >= 0 && (statp->_flags & RES_F_VC) != 0) {
                struct sockaddr_in6 peer;
                socklen_t size = sizeof peer;

                if (getpeername(statp->_vcsock,
                                (struct sockaddr *)&peer, &size) < 0 ||
                    !sock_eq(&peer, nsap)) {
                  __res_iclose(statp, false);
                        statp->_flags &= ~RES_F_VC;
                }
        }

        if (statp->_vcsock < 0 || (statp->_flags & RES_F_VC) == 0) {
                if (statp->_vcsock >= 0)
                  __res_iclose(statp, false);

                statp->_vcsock = socket(nsap->sin6_family, SOCK_STREAM, 0);
                if (statp->_vcsock < 0) {
                        *terrno = errno;
                        Perror(statp, stderr, "socket(vc)", errno);
                        return (-1);
                }
                __set_errno (0);
                if (connect(statp->_vcsock, (struct sockaddr *)nsap,
                            nsap->sin6_family == AF_INET
                            ? sizeof (struct sockaddr_in)
                            : sizeof (struct sockaddr_in6)) < 0) {
                        *terrno = errno;
                        Aerror(statp, stderr, "connect/vc", errno,
                               (struct sockaddr *) nsap);
                        __res_iclose(statp, false);
                        return (0);
                }
                statp->_flags |= RES_F_VC;
        }

        /*
         * Send length & message
         */
        putshort((u_short)buflen, (u_char*)&len);
        evConsIovec(&len, INT16SZ, &iov[0]);
        evConsIovec((void*)buf, buflen, &iov[1]);
        if (TEMP_FAILURE_RETRY (writev(statp->_vcsock, iov, 2))
            != (INT16SZ + buflen)) {
                *terrno = errno;
                Perror(statp, stderr, "write failed", errno);
                __res_iclose(statp, false);
                return (0);
        }
        /*
         * Receive length & response
         */
 read_len:
        cp = ans;
        len = INT16SZ;
        while ((n = TEMP_FAILURE_RETRY (read(statp->_vcsock, (char *)cp,
                                             (int)len))) > 0) {
                cp += n;
                if ((len -= n) <= 0)
                        break;
        }
        if (n <= 0) {
                *terrno = errno;
                Perror(statp, stderr, "read failed", errno);
                __res_iclose(statp, false);
                /*
                 * A long running process might get its TCP
                 * connection reset if the remote server was
                 * restarted.  Requery the server instead of
                 * trying a new one.  When there is only one
                 * server, this means that a query might work
                 * instead of failing.  We only allow one reset
                 * per query to prevent looping.
                 */
                if (*terrno == ECONNRESET && !connreset) {
                        connreset = 1;
                        goto same_ns;
                }
                return (0);
        }
        resplen = ns_get16(ans);
        if (resplen > anssiz) {
                if (anscp) {
                        ans = malloc (MAXPACKET);
                        if (ans == NULL) {
                                *terrno = ENOMEM;
                                __res_iclose(statp, false);
                                return (0);
                        }
                        anssiz = MAXPACKET;
                        *anssizp = MAXPACKET;
                        *ansp = ans;
                        *anscp = ans;
                        anhp = (HEADER *) ans;
                        len = resplen;
                } else {
                        Dprint(statp->options & RES_DEBUG,
                                (stdout, ";; response truncated\n")
                        );
                        truncating = 1;
                        len = anssiz;
                }
        } else
                len = resplen;
        if (len < HFIXEDSZ) {
                /*
                 * Undersized message.
                 */
                Dprint(statp->options & RES_DEBUG,
                       (stdout, ";; undersized: %d\n", len));
                *terrno = EMSGSIZE;
                __res_iclose(statp, false);
                return (0);
        }
        cp = ans;
        while (len != 0 && (n = read(statp->_vcsock, (char *)cp, (int)len)) > 0){
                cp += n;
                len -= n;
        }
        if (n <= 0) {
                *terrno = errno;
                Perror(statp, stderr, "read(vc)", errno);
                __res_iclose(statp, false);
                return (0);
        }
        if (truncating) {
                /*
                 * Flush rest of answer so connection stays in synch.
                 */
                anhp->tc = 1;
                len = resplen - anssiz;
                while (len != 0) {
                        char junk[PACKETSZ];

                        n = read(statp->_vcsock, junk,
                                 (len > sizeof junk) ? sizeof junk : len);
                        if (n > 0)
                                len -= n;
                        else
                                break;
                }
        }
        /*
         * If the calling applicating has bailed out of
         * a previous call and failed to arrange to have
         * the circuit closed or the server has got
         * itself confused, then drop the packet and
         * wait for the correct one.
         */
        if (hp->id != anhp->id) {
                DprintQ((statp->options & RES_DEBUG) ||
                        (statp->pfcode & RES_PRF_REPLY),
                        (stdout, ";; old answer (unexpected):\n"),
                        ans, (resplen > anssiz) ? anssiz: resplen);
                goto read_len;
        }

        /*
         * All is well, or the error is fatal.  Signal that the
         * next nameserver ought not be tried.
         */
        return (resplen);
}

static int
send_dg(res_state statp,
        const u_char *buf, int buflen, u_char **ansp, int *anssizp,
        int *terrno, int ns, int *v_circuit, int *gotsomewhere, u_char **anscp)
{
        const HEADER *hp = (HEADER *) buf;
        u_char *ans = *ansp;
        int anssiz = *anssizp;
        HEADER *anhp = (HEADER *) ans;
        struct sockaddr_in6 *nsap = EXT(statp).nsaddrs[ns];
        struct timespec now, timeout, finish;
        struct pollfd pfd[1];
        int ptimeout;
        struct sockaddr_in6 from;
        static int socket_pf = 0;
        socklen_t fromlen;
        int resplen, seconds, n;

        if (EXT(statp).nssocks[ns] == -1) {
                /* only try IPv6 if IPv6 NS and if not failed before */
                if ((EXT(statp).nscount6 > 0) && (socket_pf != PF_INET)) {
                        EXT(statp).nssocks[ns] =
                            socket(PF_INET6, SOCK_DGRAM, 0);
                        socket_pf = EXT(statp).nssocks[ns] < 0 ? PF_INET
                                                               : PF_INET6;
                }
                if (EXT(statp).nssocks[ns] < 0)
                        EXT(statp).nssocks[ns] = socket(PF_INET, SOCK_DGRAM, 0);
                if (EXT(statp).nssocks[ns] < 0) {
                        *terrno = errno;
                        Perror(statp, stderr, "socket(dg)", errno);
                        return (-1);
                }
                /* If IPv6 socket and nsap is IPv4, make it IPv4-mapped */
                if ((socket_pf == PF_INET6) && (nsap->sin6_family == AF_INET))
                        convaddr4to6(nsap);
                /*
                 * On a 4.3BSD+ machine (client and server,
                 * actually), sending to a nameserver datagram
                 * port with no nameserver will cause an
                 * ICMP port unreachable message to be returned.
                 * If our datagram socket is "connected" to the
                 * server, we get an ECONNREFUSED error on the next
                 * socket operation, and select returns if the
                 * error message is received.  We can thus detect
                 * the absence of a nameserver without timing out.
                 */
                if (connect(EXT(statp).nssocks[ns], (struct sockaddr *)nsap,
                            sizeof *nsap) < 0) {
                        Aerror(statp, stderr, "connect(dg)", errno,
                               (struct sockaddr *) nsap);
                        __res_iclose(statp, false);
                        return (0);
                }
                /* Make socket non-blocking.  */
                int fl = __fcntl (EXT(statp).nssocks[ns], F_GETFL);
                if  (fl != -1)
                        __fcntl (EXT(statp).nssocks[ns], F_SETFL,
                                 fl | O_NONBLOCK);
                Dprint(statp->options & RES_DEBUG,
                       (stdout, ";; new DG socket\n"))
        }

        /*
         * Compute time for the total operation.
         */
        seconds = (statp->retrans << ns);
        if (ns > 0)
                seconds /= statp->nscount;
        if (seconds <= 0)
                seconds = 1;
        evNowTime(&now);
        evConsTime(&timeout, seconds, 0);
        evAddTime(&finish, &now, &timeout);
        int need_recompute = 0;
        int nwritten = 0;
        pfd[0].fd = EXT(statp).nssocks[ns];
        pfd[0].events = POLLOUT;
 wait:
        if (need_recompute) {
                evNowTime(&now);
                if (evCmpTime(finish, now) <= 0) {
                        Perror(statp, stderr, "select", errno);
                        __res_iclose(statp, false);
                        return (0);
                }
                evSubTime(&timeout, &finish, &now);
        }
        /* Convert struct timespec in milliseconds.  */
        ptimeout = timeout.tv_sec * 1000 + timeout.tv_nsec / 1000000;

        n = 0;
        if (nwritten == 0)
          n = __poll (pfd, 1, 0);
        if (__builtin_expect (n == 0, 0)) {
                n = __poll (pfd, 1, ptimeout);
                need_recompute = 1;
        }
        if (n == 0) {
                Dprint(statp->options & RES_DEBUG, (stdout,
                                                    ";; timeout sending\n"));
                *gotsomewhere = 1;
                return (0);
        }
        if (n < 0) {
                if (errno == EINTR) {
                recompute_resend:
                        evNowTime(&now);
                        if (evCmpTime(finish, now) > 0) {
                                evSubTime(&timeout, &finish, &now);
                                goto wait;
                        }
                }
                Perror(statp, stderr, "poll", errno);
                __res_iclose(statp, false);
                return (0);
        }
        __set_errno (0);
        if (pfd[0].revents & POLLOUT) {
                if (send(pfd[0].fd, (char*)buf, buflen, 0) != buflen) {
                        if (errno == EINTR || errno == EAGAIN)
                                goto recompute_resend;
                        Perror(statp, stderr, "send", errno);
                        __res_iclose(statp, false);
                        return (0);
                }
                pfd[0].events = POLLIN;
                ++nwritten;
                goto wait;
        } else if (pfd[0].revents & POLLIN) {
                fromlen = sizeof(struct sockaddr_in6);
                if (anssiz < MAXPACKET
                    && anscp
                    && (ioctl (pfd[0].fd, FIONREAD, &resplen) < 0
                || anssiz < resplen)) {
                        ans = malloc (MAXPACKET);
                        if (ans == NULL)
                                ans = *ansp;
                        else {
                                anssiz = MAXPACKET;
                                *anssizp = MAXPACKET;
                                *ansp = ans;
                                *anscp = ans;
                                anhp = (HEADER *) ans;
                        }
                }
                resplen = recvfrom(pfd[0].fd, (char*)ans, anssiz,0,
                                   (struct sockaddr *)&from, &fromlen);
                if (resplen <= 0) {
                        if (errno == EINTR || errno == EAGAIN) {
                                need_recompute = 1;
                                goto wait;
                        }
                        Perror(statp, stderr, "recvfrom", errno);
                        __res_iclose(statp, false);
                        return (0);
                }
                *gotsomewhere = 1;
                if (resplen < HFIXEDSZ) {
                        /*
                         * Undersized message.
                         */
                        Dprint(statp->options & RES_DEBUG,
                               (stdout, ";; undersized: %d\n",
                                resplen));
                        *terrno = EMSGSIZE;
                        __res_iclose(statp, false);
                        return (0);
                }
                if (hp->id != anhp->id) {
                        /*
                         * response from old query, ignore it.
                         * XXX - potential security hazard could
                         *       be detected here.
                         */
                        DprintQ((statp->options & RES_DEBUG) ||
                                (statp->pfcode & RES_PRF_REPLY),
                                (stdout, ";; old answer:\n"),
                                ans, (resplen > anssiz) ? anssiz : resplen);
                        goto wait;
                }
                if (!(statp->options & RES_INSECURE1) &&
                    !res_ourserver_p(statp, &from)) {
                        /*
                         * response from wrong server? ignore it.
                         * XXX - potential security hazard could
                         *       be detected here.
                         */
                        DprintQ((statp->options & RES_DEBUG) ||
                                (statp->pfcode & RES_PRF_REPLY),
                                (stdout, ";; not our server:\n"),
                                ans, (resplen > anssiz) ? anssiz : resplen);
                        goto wait;
                }
                if (!(statp->options & RES_INSECURE2) &&
                    !res_queriesmatch(buf, buf + buflen,
                                      ans, ans + anssiz)) {
                        /*
                         * response contains wrong query? ignore it.
                         * XXX - potential security hazard could
                         *       be detected here.
                         */
                        DprintQ((statp->options & RES_DEBUG) ||
                                (statp->pfcode & RES_PRF_REPLY),
                                (stdout, ";; wrong query name:\n"),
                                ans, (resplen > anssiz) ? anssiz : resplen);
                        goto wait;
                }
                if (anhp->rcode == SERVFAIL ||
                    anhp->rcode == NOTIMP ||
                    anhp->rcode == REFUSED) {
                        DprintQ(statp->options & RES_DEBUG,
                                (stdout, "server rejected query:\n"),
                                ans, (resplen > anssiz) ? anssiz : resplen);
                next_ns:
                        __res_iclose(statp, false);
                        /* don't retry if called from dig */
                        if (!statp->pfcode)
                                return (0);
                }
                if (anhp->rcode == NOERROR && anhp->ancount == 0
                    && anhp->aa == 0 && anhp->ra == 0 && anhp->arcount == 0) {
                        DprintQ(statp->options & RES_DEBUG,
                                (stdout, "referred query:\n"),
                                ans, (resplen > anssiz) ? anssiz : resplen);
                        goto next_ns;
                }
                if (!(statp->options & RES_IGNTC) && anhp->tc) {
                        /*
                         * To get the rest of answer,
                         * use TCP with same server.
                         */
                        Dprint(statp->options & RES_DEBUG,
                               (stdout, ";; truncated answer\n"));
                        *v_circuit = 1;
                        __res_iclose(statp, false);
                        return (1);
                }
                /*
                 * All is well, or the error is fatal.  Signal that the
                 * next nameserver ought not be tried.
                 */
                return (resplen);
        } else if (pfd[0].revents & (POLLERR | POLLHUP | POLLNVAL)) {
                /* Something went wrong.  We can stop trying.  */
          __res_iclose(statp, false);
                return (0);
        }
        else {
                /* poll should not have returned > 0 in this case.  */
                abort ();
        }
}

#ifdef DEBUG
static void
Aerror(const res_state statp, FILE *file, const char *string, int error,
       const struct sockaddr *address)
{
        int save = errno;

        if ((statp->options & RES_DEBUG) != 0) {
                char tmp[sizeof "xxxx.xxxx.xxxx.255.255.255.255"];

                fprintf(file, "res_send: %s ([%s].%u): %s\n",
                        string,
                        (address->sa_family == AF_INET
                         ? inet_ntop(address->sa_family,
                                     &((const struct sockaddr_in *) address)->sin_addr,
                                     tmp, sizeof tmp)
                         : inet_ntop(address->sa_family,
                                     &((const struct sockaddr_in6 *) address)->sin6_addr,
                                     tmp, sizeof tmp)),
                        (address->sa_family == AF_INET
                         ? ntohs(((struct sockaddr_in *) address)->sin_port)
                         : address->sa_family == AF_INET6
                         ? ntohs(((struct sockaddr_in6 *) address)->sin6_port)
                         : 0),
                        strerror(error));
        }
        __set_errno (save);
}

static void
Perror(const res_state statp, FILE *file, const char *string, int error) {
        int save = errno;

        if ((statp->options & RES_DEBUG) != 0)
                fprintf(file, "res_send: %s: %s\n",
                        string, strerror(error));
        __set_errno (save);
}
#endif

static int
sock_eq(struct sockaddr_in6 *a1, struct sockaddr_in6 *a2) {
        if (a1->sin6_family == a2->sin6_family) {
                if (a1->sin6_family == AF_INET)
                        return ((((struct sockaddr_in *)a1)->sin_port ==
                                 ((struct sockaddr_in *)a2)->sin_port) &&
                                (((struct sockaddr_in *)a1)->sin_addr.s_addr ==
                                 ((struct sockaddr_in *)a2)->sin_addr.s_addr));
                else
                        return ((a1->sin6_port == a2->sin6_port) &&
                                !memcmp(&a1->sin6_addr, &a2->sin6_addr,
                                        sizeof (struct in6_addr)));
        }
        if (a1->sin6_family == AF_INET) {
                struct sockaddr_in6 *sap = a1;
                a1 = a2;
                a2 = sap;
        } /* assumes that AF_INET and AF_INET6 are the only possibilities */
        return ((a1->sin6_port == ((struct sockaddr_in *)a2)->sin_port) &&
                IN6_IS_ADDR_V4MAPPED(&a1->sin6_addr) &&
                (a1->sin6_addr.s6_addr32[3] ==
                 ((struct sockaddr_in *)a2)->sin_addr.s_addr));
}

/*
 * Converts IPv4 family, address and port to
 * IPv6 family, IPv4-mapped IPv6 address and port.
 */
static void
convaddr4to6(struct sockaddr_in6 *sa)
{
    struct sockaddr_in *sa4p = (struct sockaddr_in *) sa;
    in_port_t port = sa4p->sin_port;
    in_addr_t addr = sa4p->sin_addr.s_addr;

    sa->sin6_family = AF_INET6;
    sa->sin6_port = port;
    sa->sin6_addr.s6_addr32[0] = 0;
    sa->sin6_addr.s6_addr32[1] = 0;
    sa->sin6_addr.s6_addr32[2] = htonl(0xFFFF);
    sa->sin6_addr.s6_addr32[3] = addr;
}