lib/dns/rdataset.c

	rdataset.c revision 0c27b3fe77ac1d5094ba3521e8142d9e7973133f
/*
 * Copyright (C) 1999-2012, 2014-2016  Internet Systems Consortium, Inc. ("ISC")
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

/* $Id$ */

/*! \file */

#include <config.h>

#include <stdlib.h>

#include <isc/buffer.h>
#include <isc/mem.h>
#include <isc/random.h>
#include <isc/serial.h>
#include <isc/util.h>

#include <dns/compress.h>
#include <dns/fixedname.h>
#include <dns/name.h>
#include <dns/ncache.h>
#include <dns/rdata.h>
#include <dns/rdataset.h>

static const char *trustnames[] = {
    "none",
    "pending-additional",
    "pending-answer",
    "additional",
    "glue",
    "answer",
    "authauthority",
    "authanswer",
    "secure",
    "local" /* aka ultimate */
};

const char *
dns_trust_totext(dns_trust_t trust) {
    if (trust >= sizeof(trustnames)/sizeof(*trustnames))
        return ("bad");
    return (trustnames[trust]);
}

void
dns_rdataset_init(dns_rdataset_t *rdataset) {

    /*
     * Make 'rdataset' a valid, disassociated rdataset.
     */

    REQUIRE(rdataset != NULL);

    rdataset->magic = DNS_RDATASET_MAGIC;
    rdataset->methods = NULL;
    ISC_LINK_INIT(rdataset, link);
    rdataset->rdclass = 0;
    rdataset->type = 0;
    rdataset->ttl = 0;
    rdataset->trust = 0;
    rdataset->covers = 0;
    rdataset->attributes = 0;
    rdataset->count = ISC_UINT32_MAX;
    rdataset->private1 = NULL;
    rdataset->private2 = NULL;
    rdataset->private3 = NULL;
    rdataset->privateuint4 = 0;
    rdataset->private5 = NULL;
    rdataset->private6 = NULL;
    rdataset->private7 = NULL;
    rdataset->resign = 0;
}

void
dns_rdataset_invalidate(dns_rdataset_t *rdataset) {

    /*
     * Invalidate 'rdataset'.
     */

    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods == NULL);

    rdataset->magic = 0;
    ISC_LINK_INIT(rdataset, link);
    rdataset->rdclass = 0;
    rdataset->type = 0;
    rdataset->ttl = 0;
    rdataset->trust = 0;
    rdataset->covers = 0;
    rdataset->attributes = 0;
    rdataset->count = ISC_UINT32_MAX;
    rdataset->private1 = NULL;
    rdataset->private2 = NULL;
    rdataset->private3 = NULL;
    rdataset->privateuint4 = 0;
    rdataset->private5 = NULL;
}

void
dns_rdataset_disassociate(dns_rdataset_t *rdataset) {

    /*
     * Disassociate 'rdataset' from its rdata, allowing it to be reused.
     */

    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);

    (rdataset->methods->disassociate)(rdataset);
    rdataset->methods = NULL;
    ISC_LINK_INIT(rdataset, link);
    rdataset->rdclass = 0;
    rdataset->type = 0;
    rdataset->ttl = 0;
    rdataset->trust = 0;
    rdataset->covers = 0;
    rdataset->attributes = 0;
    rdataset->count = ISC_UINT32_MAX;
    rdataset->private1 = NULL;
    rdataset->private2 = NULL;
    rdataset->private3 = NULL;
    rdataset->privateuint4 = 0;
    rdataset->private5 = NULL;
    rdataset->private6 = NULL;
}

isc_boolean_t
dns_rdataset_isassociated(dns_rdataset_t *rdataset) {
    /*
     * Is 'rdataset' associated?
     */

    REQUIRE(DNS_RDATASET_VALID(rdataset));

    if (rdataset->methods != NULL)
        return (ISC_TRUE);

    return (ISC_FALSE);
}

static void
question_disassociate(dns_rdataset_t *rdataset) {
    UNUSED(rdataset);
}

static isc_result_t
question_cursor(dns_rdataset_t *rdataset) {
    UNUSED(rdataset);

    return (ISC_R_NOMORE);
}

static void
question_current(dns_rdataset_t *rdataset, dns_rdata_t *rdata) {
    /*
     * This routine should never be called.
     */
    UNUSED(rdataset);
    UNUSED(rdata);

    REQUIRE(0);
}

static void
question_clone(dns_rdataset_t *source, dns_rdataset_t *target) {
    *target = *source;
}

static unsigned int
question_count(dns_rdataset_t *rdataset) {
    /*
     * This routine should never be called.
     */
    UNUSED(rdataset);
    REQUIRE(0);

    return (0);
}

static dns_rdatasetmethods_t question_methods = {
    question_disassociate,
    question_cursor,
    question_cursor,
    question_current,
    question_clone,
    question_count,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL
};

void
dns_rdataset_makequestion(dns_rdataset_t *rdataset, dns_rdataclass_t rdclass,
              dns_rdatatype_t type)
{

    /*
     * Make 'rdataset' a valid, associated, question rdataset, with a
     * question class of 'rdclass' and type 'type'.
     */

    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods == NULL);

    rdataset->methods = &question_methods;
    rdataset->rdclass = rdclass;
    rdataset->type = type;
    rdataset->attributes |= DNS_RDATASETATTR_QUESTION;
}

unsigned int
dns_rdataset_count(dns_rdataset_t *rdataset) {

    /*
     * Return the number of records in 'rdataset'.
     */

    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);

    return ((rdataset->methods->count)(rdataset));
}

void
dns_rdataset_clone(dns_rdataset_t *source, dns_rdataset_t *target) {

    /*
     * Make 'target' refer to the same rdataset as 'source'.
     */

    REQUIRE(DNS_RDATASET_VALID(source));
    REQUIRE(source->methods != NULL);
    REQUIRE(DNS_RDATASET_VALID(target));
    REQUIRE(target->methods == NULL);

    (source->methods->clone)(source, target);
}

isc_result_t
dns_rdataset_first(dns_rdataset_t *rdataset) {

    /*
     * Move the rdata cursor to the first rdata in the rdataset (if any).
     */

    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);

    return ((rdataset->methods->first)(rdataset));
}

isc_result_t
dns_rdataset_next(dns_rdataset_t *rdataset) {

    /*
     * Move the rdata cursor to the next rdata in the rdataset (if any).
     */

    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);

    return ((rdataset->methods->next)(rdataset));
}

void
dns_rdataset_current(dns_rdataset_t *rdataset, dns_rdata_t *rdata) {

    /*
     * Make 'rdata' refer to the current rdata.
     */

    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);

    (rdataset->methods->current)(rdataset, rdata);
}

#define MAX_SHUFFLE 32
#define WANT_FIXED(r)   (((r)->attributes & DNS_RDATASETATTR_FIXEDORDER) != 0)
#define WANT_RANDOM(r)  (((r)->attributes & DNS_RDATASETATTR_RANDOMIZE) != 0)

struct towire_sort {
    int key;
    dns_rdata_t *rdata;
};

static int
towire_compare(const void *av, const void *bv) {
    const struct towire_sort *a = (const struct towire_sort *) av;
    const struct towire_sort *b = (const struct towire_sort *) bv;
    return (a->key - b->key);
}

static isc_result_t
towiresorted(dns_rdataset_t *rdataset, const dns_name_t *owner_name,
         dns_compress_t *cctx, isc_buffer_t *target,
         dns_rdatasetorderfunc_t order, const void *order_arg,
         isc_boolean_t partial, unsigned int options,
         unsigned int *countp, void **state)
{
    dns_rdata_t rdata = DNS_RDATA_INIT;
    isc_region_t r;
    isc_result_t result;
    unsigned int i, count = 0, added, choice;
    isc_buffer_t savedbuffer, rdlen, rrbuffer;
    unsigned int headlen;
    isc_boolean_t question = ISC_FALSE;
    isc_boolean_t shuffle = ISC_FALSE;
    dns_rdata_t *shuffled = NULL, shuffled_fixed[MAX_SHUFFLE];
    struct towire_sort *sorted = NULL, sorted_fixed[MAX_SHUFFLE];
    dns_fixedname_t fixed;
    dns_name_t *name;

    UNUSED(state);

    /*
     * Convert 'rdataset' to wire format, compressing names as specified
     * in cctx, and storing the result in 'target'.
     */

    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(countp != NULL);
    REQUIRE((order == NULL) == (order_arg == NULL));
    REQUIRE(cctx != NULL && cctx->mctx != NULL);

    if ((rdataset->attributes & DNS_RDATASETATTR_QUESTION) != 0) {
        question = ISC_TRUE;
        count = 1;
        result = dns_rdataset_first(rdataset);
        INSIST(result == ISC_R_NOMORE);
    } else if ((rdataset->attributes & DNS_RDATASETATTR_NEGATIVE) != 0) {
        /*
         * This is a negative caching rdataset.
         */
        unsigned int ncache_opts = 0;
        if ((options & DNS_RDATASETTOWIRE_OMITDNSSEC) != 0)
            ncache_opts |= DNS_NCACHETOWIRE_OMITDNSSEC;
        return (dns_ncache_towire(rdataset, cctx, target, ncache_opts,
                      countp));
    } else {
        count = (rdataset->methods->count)(rdataset);
        result = dns_rdataset_first(rdataset);
        if (result == ISC_R_NOMORE)
            return (ISC_R_SUCCESS);
        if (result != ISC_R_SUCCESS)
            return (result);
    }

    /*
     * Do we want to shuffle this answer?
     */
    if (!question && count > 1 &&
        (!WANT_FIXED(rdataset) || order != NULL) &&
        rdataset->type != dns_rdatatype_rrsig)
        shuffle = ISC_TRUE;

    if (shuffle && count > MAX_SHUFFLE) {
        shuffled = isc_mem_get(cctx->mctx, count * sizeof(*shuffled));
        sorted = isc_mem_get(cctx->mctx, count * sizeof(*sorted));
        if (shuffled == NULL || sorted == NULL)
            shuffle = ISC_FALSE;
    } else {
        shuffled = shuffled_fixed;
        sorted = sorted_fixed;
    }

    if (shuffle) {
        /*
         * First we get handles to all of the rdata.
         */
        i = 0;
        do {
            INSIST(i < count);
            dns_rdata_init(&shuffled[i]);
            dns_rdataset_current(rdataset, &shuffled[i]);
            i++;
            result = dns_rdataset_next(rdataset);
        } while (result == ISC_R_SUCCESS);
        if (result != ISC_R_NOMORE)
            goto cleanup;
        INSIST(i == count);

        /*
         * Now we shuffle.
         */
        if (WANT_FIXED(rdataset)) {
            /*
             * 'Fixed' order.
             */
            INSIST(order != NULL);
            for (i = 0; i < count; i++) {
                sorted[i].key = (*order)(&shuffled[i],
                             order_arg);
                sorted[i].rdata = &shuffled[i];
            }
        } else if (WANT_RANDOM(rdataset)) {
            /*
             * 'Random' order.
             */
            for (i = 0; i < count; i++) {
                isc_uint32_t val;

                isc_random_get(&val);
                choice = i + (val % (count - i));
                rdata = shuffled[i];
                shuffled[i] = shuffled[choice];
                shuffled[choice] = rdata;
                if (order != NULL)
                    sorted[i].key = (*order)(&shuffled[i],
                                 order_arg);
                else
                    sorted[i].key = 0; /* Unused */
                sorted[i].rdata = &shuffled[i];
            }
        } else {
            /*
             * "Cyclic" order.
             */
            isc_uint32_t val;
            unsigned int j;

            val = rdataset->count;
            if (val == ISC_UINT32_MAX)
                isc_random_get(&val);
            j = val % count;
            for (i = 0; i < count; i++) {
                if (order != NULL)
                    sorted[i].key = (*order)(&shuffled[j],
                                 order_arg);
                else
                    sorted[i].key = 0; /* Unused */
                sorted[i].rdata = &shuffled[j];
                j++;
                if (j == count)
                    j = 0; /* Wrap around. */
            }
        }

        /*
         * Sorted order.
         */
        if (order != NULL)
            qsort(sorted, count, sizeof(sorted[0]),
                  towire_compare);
    }

    savedbuffer = *target;
    i = 0;
    added = 0;

    dns_fixedname_init(&fixed);
    name = dns_fixedname_name(&fixed);
    dns_name_copy(owner_name, name, NULL);
    dns_rdataset_getownercase(rdataset, name);

    do {
        /*
         * Copy out the name, type, class, ttl.
         */

        rrbuffer = *target;
        dns_compress_setmethods(cctx, DNS_COMPRESS_GLOBAL14);
        result = dns_name_towire(name, cctx, target);
        if (result != ISC_R_SUCCESS)
            goto rollback;
        headlen = sizeof(dns_rdataclass_t) + sizeof(dns_rdatatype_t);
        if (!question)
            headlen += sizeof(dns_ttl_t)
                + 2;  /* XXX 2 for rdata len */
        isc_buffer_availableregion(target, &r);
        if (r.length < headlen) {
            result = ISC_R_NOSPACE;
            goto rollback;
        }
        isc_buffer_putuint16(target, rdataset->type);
        isc_buffer_putuint16(target, rdataset->rdclass);
        if (!question) {
            isc_buffer_putuint32(target, rdataset->ttl);

            /*
             * Save space for rdlen.
             */
            rdlen = *target;
            isc_buffer_add(target, 2);

            /*
             * Copy out the rdata
             */
            if (shuffle)
                rdata = *(sorted[i].rdata);
            else {
                dns_rdata_reset(&rdata);
                dns_rdataset_current(rdataset, &rdata);
            }
            result = dns_rdata_towire(&rdata, cctx, target);
            if (result != ISC_R_SUCCESS)
                goto rollback;
            INSIST((target->used >= rdlen.used + 2) &&
                   (target->used - rdlen.used - 2 < 65536));
            isc_buffer_putuint16(&rdlen,
                         (isc_uint16_t)(target->used -
                                rdlen.used - 2));
            added++;
        }

        if (shuffle) {
            i++;
            if (i == count)
                result = ISC_R_NOMORE;
            else
                result = ISC_R_SUCCESS;
        } else {
            result = dns_rdataset_next(rdataset);
        }
    } while (result == ISC_R_SUCCESS);

    if (result != ISC_R_NOMORE)
        goto rollback;

    *countp += count;

    result = ISC_R_SUCCESS;
    goto cleanup;

 rollback:
    if (partial && result == ISC_R_NOSPACE) {
        INSIST(rrbuffer.used < 65536);
        dns_compress_rollback(cctx, (isc_uint16_t)rrbuffer.used);
        *countp += added;
        *target = rrbuffer;
        goto cleanup;
    }
    INSIST(savedbuffer.used < 65536);
    dns_compress_rollback(cctx, (isc_uint16_t)savedbuffer.used);
    *countp = 0;
    *target = savedbuffer;

 cleanup:
    if (sorted != NULL && sorted != sorted_fixed)
        isc_mem_put(cctx->mctx, sorted, count * sizeof(*sorted));
    if (shuffled != NULL && shuffled != shuffled_fixed)
        isc_mem_put(cctx->mctx, shuffled, count * sizeof(*shuffled));
    return (result);
}

isc_result_t
dns_rdataset_towiresorted(dns_rdataset_t *rdataset,
              const dns_name_t *owner_name,
              dns_compress_t *cctx,
              isc_buffer_t *target,
              dns_rdatasetorderfunc_t order,
              const void *order_arg,
              unsigned int options,
              unsigned int *countp)
{
    return (towiresorted(rdataset, owner_name, cctx, target,
                 order, order_arg, ISC_FALSE, options,
                 countp, NULL));
}

isc_result_t
dns_rdataset_towirepartial(dns_rdataset_t *rdataset,
               const dns_name_t *owner_name,
               dns_compress_t *cctx,
               isc_buffer_t *target,
               dns_rdatasetorderfunc_t order,
               const void *order_arg,
               unsigned int options,
               unsigned int *countp,
               void **state)
{
    REQUIRE(state == NULL); /* XXX remove when implemented */
    return (towiresorted(rdataset, owner_name, cctx, target,
                 order, order_arg, ISC_TRUE, options,
                 countp, state));
}

isc_result_t
dns_rdataset_towire(dns_rdataset_t *rdataset,
            dns_name_t *owner_name,
            dns_compress_t *cctx,
            isc_buffer_t *target,
            unsigned int options,
            unsigned int *countp)
{
    return (towiresorted(rdataset, owner_name, cctx, target,
                 NULL, NULL, ISC_FALSE, options, countp, NULL));
}

isc_result_t
dns_rdataset_additionaldata(dns_rdataset_t *rdataset,
                dns_additionaldatafunc_t add, void *arg)
{
    dns_rdata_t rdata = DNS_RDATA_INIT;
    isc_result_t result;

    /*
     * For each rdata in rdataset, call 'add' for each name and type in the
     * rdata which is subject to additional section processing.
     */

    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE((rdataset->attributes & DNS_RDATASETATTR_QUESTION) == 0);

    result = dns_rdataset_first(rdataset);
    if (result != ISC_R_SUCCESS)
        return (result);

    do {
        dns_rdataset_current(rdataset, &rdata);
        result = dns_rdata_additionaldata(&rdata, add, arg);
        if (result == ISC_R_SUCCESS)
            result = dns_rdataset_next(rdataset);
        dns_rdata_reset(&rdata);
    } while (result == ISC_R_SUCCESS);

    if (result != ISC_R_NOMORE)
        return (result);

    return (ISC_R_SUCCESS);
}

isc_result_t
dns_rdataset_addnoqname(dns_rdataset_t *rdataset, dns_name_t *name) {

    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);
    if (rdataset->methods->addnoqname == NULL)
        return (ISC_R_NOTIMPLEMENTED);
    return((rdataset->methods->addnoqname)(rdataset, name));
}

isc_result_t
dns_rdataset_getnoqname(dns_rdataset_t *rdataset, dns_name_t *name,
            dns_rdataset_t *neg, dns_rdataset_t *negsig)
{
    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);

    if (rdataset->methods->getnoqname == NULL)
        return (ISC_R_NOTIMPLEMENTED);
    return((rdataset->methods->getnoqname)(rdataset, name, neg, negsig));
}

isc_result_t
dns_rdataset_addclosest(dns_rdataset_t *rdataset, dns_name_t *name) {

    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);
    if (rdataset->methods->addclosest == NULL)
        return (ISC_R_NOTIMPLEMENTED);
    return((rdataset->methods->addclosest)(rdataset, name));
}

isc_result_t
dns_rdataset_getclosest(dns_rdataset_t *rdataset, dns_name_t *name,
            dns_rdataset_t *neg, dns_rdataset_t *negsig)
{
    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);

    if (rdataset->methods->getclosest == NULL)
        return (ISC_R_NOTIMPLEMENTED);
    return((rdataset->methods->getclosest)(rdataset, name, neg, negsig));
}

/*
 * Additional cache stuff
 */
isc_result_t
dns_rdataset_getadditional(dns_rdataset_t *rdataset,
               dns_rdatasetadditional_t type,
               dns_rdatatype_t qtype,
               dns_acache_t *acache,
               dns_zone_t **zonep,
               dns_db_t **dbp,
               dns_dbversion_t **versionp,
               dns_dbnode_t **nodep,
               dns_name_t *fname,
               dns_message_t *msg,
               isc_stdtime_t now)
{
    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);
    REQUIRE(zonep == NULL || *zonep == NULL);
    REQUIRE(dbp != NULL && *dbp == NULL);
    REQUIRE(versionp != NULL && *versionp == NULL);
    REQUIRE(nodep != NULL && *nodep == NULL);
    REQUIRE(fname != NULL);
    REQUIRE(msg != NULL);

    if (acache != NULL && rdataset->methods->getadditional != NULL) {
        return ((rdataset->methods->getadditional)(rdataset, type,
                               qtype, acache,
                               zonep, dbp,
                               versionp, nodep,
                               fname, msg, now));
    }

    return (ISC_R_FAILURE);
}

isc_result_t
dns_rdataset_setadditional(dns_rdataset_t *rdataset,
               dns_rdatasetadditional_t type,
               dns_rdatatype_t qtype,
               dns_acache_t *acache,
               dns_zone_t *zone,
               dns_db_t *db,
               dns_dbversion_t *version,
               dns_dbnode_t *node,
               dns_name_t *fname)
{
    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);

    if (acache != NULL && rdataset->methods->setadditional != NULL) {
        return ((rdataset->methods->setadditional)(rdataset, type,
                               qtype, acache, zone,
                               db, version,
                               node, fname));
    }

    return (ISC_R_FAILURE);
}

isc_result_t
dns_rdataset_putadditional(dns_acache_t *acache,
               dns_rdataset_t *rdataset,
               dns_rdatasetadditional_t type,
               dns_rdatatype_t qtype)
{
    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);

    if (acache != NULL && rdataset->methods->putadditional != NULL) {
        return ((rdataset->methods->putadditional)(acache, rdataset,
                               type, qtype));
    }

    return (ISC_R_FAILURE);
}

void
dns_rdataset_settrust(dns_rdataset_t *rdataset, dns_trust_t trust) {
    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);

    if (rdataset->methods->settrust != NULL)
        (rdataset->methods->settrust)(rdataset, trust);
    else
        rdataset->trust = trust;
}

void
dns_rdataset_expire(dns_rdataset_t *rdataset) {
    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);

    if (rdataset->methods->expire != NULL)
        (rdataset->methods->expire)(rdataset);
}

void
dns_rdataset_clearprefetch(dns_rdataset_t *rdataset) {
    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);

    if (rdataset->methods->clearprefetch != NULL)
        (rdataset->methods->clearprefetch)(rdataset);
}

void
dns_rdataset_setownercase(dns_rdataset_t *rdataset, const dns_name_t *name) {
    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);

    if (rdataset->methods->setownercase != NULL)
        (rdataset->methods->setownercase)(rdataset, name);
}

void
dns_rdataset_getownercase(const dns_rdataset_t *rdataset, dns_name_t *name) {
    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(rdataset->methods != NULL);

    if (rdataset->methods->getownercase != NULL)
        (rdataset->methods->getownercase)(rdataset, name);
}

void
dns_rdataset_trimttl(dns_rdataset_t *rdataset, dns_rdataset_t *sigrdataset,
             dns_rdata_rrsig_t *rrsig, isc_stdtime_t now,
             isc_boolean_t acceptexpired)
{
    isc_uint32_t ttl = 0;

    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(DNS_RDATASET_VALID(sigrdataset));
    REQUIRE(rrsig != NULL);

    /*
     * If we accept expired RRsets keep them for no more than 120 seconds.
     */
    if (acceptexpired &&
        (isc_serial_le(rrsig->timeexpire, ((now + 120) & 0xffffffff)) ||
         isc_serial_le(rrsig->timeexpire, now)))
        ttl = 120;
    else if (isc_serial_ge(rrsig->timeexpire, now))
        ttl = rrsig->timeexpire - now;

    ttl = ISC_MIN(ISC_MIN(rdataset->ttl, sigrdataset->ttl),
              ISC_MIN(rrsig->originalttl, ttl));
    rdataset->ttl = ttl;
    sigrdataset->ttl = ttl;
}