lib/dns/ncache.c

	ncache.c revision b335299322e50f045f10e4636262cd2f8d407a8b
/*
 * Copyright (C) 2004, 2005, 2007, 2008, 2010  Internet Systems Consortium, Inc. ("ISC")
 * Copyright (C) 1999-2003  Internet Software Consortium.
 *
 * Permission to use, copy, modify, and/or 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 ISC DISCLAIMS ALL WARRANTIES WITH
 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS.  IN NO EVENT SHALL ISC 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.
 */

/* $Id: ncache.c,v 1.46 2010/05/14 00:13:43 marka Exp $ */

/*! \file */

#include <config.h>

#include <isc/buffer.h>
#include <isc/util.h>

#include <dns/db.h>
#include <dns/message.h>
#include <dns/ncache.h>
#include <dns/rdata.h>
#include <dns/rdatalist.h>
#include <dns/rdataset.h>
#include <dns/rdatastruct.h>

#define DNS_NCACHE_RDATA 20U

/*
 * The format of an ncache rdata is a sequence of one or more records of
 * the following format:
 *
 *  owner name
 *  type
 *  trust
 *  rdata count
 *      rdata length            These two occur 'rdata count'
 *      rdata               times.
 *
 */

static inline isc_result_t
copy_rdataset(dns_rdataset_t *rdataset, isc_buffer_t *buffer) {
    isc_result_t result;
    unsigned int count;
    isc_region_t ar, r;
    dns_rdata_t rdata = DNS_RDATA_INIT;

    /*
     * Copy the rdataset count to the buffer.
     */
    isc_buffer_availableregion(buffer, &ar);
    if (ar.length < 2)
        return (ISC_R_NOSPACE);
    count = dns_rdataset_count(rdataset);
    INSIST(count <= 65535);
    isc_buffer_putuint16(buffer, (isc_uint16_t)count);

    result = dns_rdataset_first(rdataset);
    while (result == ISC_R_SUCCESS) {
        dns_rdataset_current(rdataset, &rdata);
        dns_rdata_toregion(&rdata, &r);
        INSIST(r.length <= 65535);
        isc_buffer_availableregion(buffer, &ar);
        if (ar.length < 2)
            return (ISC_R_NOSPACE);
        /*
         * Copy the rdata length to the buffer.
         */
        isc_buffer_putuint16(buffer, (isc_uint16_t)r.length);
        /*
         * Copy the rdata to the buffer.
         */
        result = isc_buffer_copyregion(buffer, &r);
        if (result != ISC_R_SUCCESS)
            return (result);
        dns_rdata_reset(&rdata);
        result = dns_rdataset_next(rdataset);
    }
    if (result != ISC_R_NOMORE)
        return (result);

    return (ISC_R_SUCCESS);
}

isc_result_t
dns_ncache_add(dns_message_t *message, dns_db_t *cache, dns_dbnode_t *node,
           dns_rdatatype_t covers, isc_stdtime_t now, dns_ttl_t maxttl,
           dns_rdataset_t *addedrdataset)
{
    return (dns_ncache_addoptout(message, cache, node, covers, now, maxttl,
                    ISC_FALSE, addedrdataset));
}

isc_result_t
dns_ncache_addoptout(dns_message_t *message, dns_db_t *cache,
             dns_dbnode_t *node, dns_rdatatype_t covers,
             isc_stdtime_t now, dns_ttl_t maxttl,
             isc_boolean_t optout, dns_rdataset_t *addedrdataset)
{
    isc_result_t result;
    isc_buffer_t buffer;
    isc_region_t r;
    dns_rdataset_t *rdataset;
    dns_rdatatype_t type;
    dns_name_t *name;
    dns_ttl_t ttl;
    dns_trust_t trust;
    dns_rdata_t rdata[DNS_NCACHE_RDATA];
    dns_rdataset_t ncrdataset;
    dns_rdatalist_t ncrdatalist;
    unsigned char data[4096];
    unsigned int next = 0;

    /*
     * Convert the authority data from 'message' into a negative cache
     * rdataset, and store it in 'cache' at 'node'.
     */

    REQUIRE(message != NULL);

    /*
     * We assume that all data in the authority section has been
     * validated by the caller.
     */

    /*
     * Initialize the list.
     */
    ncrdatalist.rdclass = dns_db_class(cache);
    ncrdatalist.type = 0;
    ncrdatalist.covers = covers;
    ncrdatalist.ttl = maxttl;
    ISC_LIST_INIT(ncrdatalist.rdata);
    ISC_LINK_INIT(&ncrdatalist, link);

    /*
     * Build an ncache rdatas into buffer.
     */
    ttl = maxttl;
    trust = 0xffff;
    isc_buffer_init(&buffer, data, sizeof(data));
    if (message->counts[DNS_SECTION_AUTHORITY])
        result = dns_message_firstname(message, DNS_SECTION_AUTHORITY);
    else
        result = ISC_R_NOMORE;
    while (result == ISC_R_SUCCESS) {
        name = NULL;
        dns_message_currentname(message, DNS_SECTION_AUTHORITY,
                    &name);
        if ((name->attributes & DNS_NAMEATTR_NCACHE) != 0) {
            for (rdataset = ISC_LIST_HEAD(name->list);
                 rdataset != NULL;
                 rdataset = ISC_LIST_NEXT(rdataset, link)) {
                if ((rdataset->attributes &
                     DNS_RDATASETATTR_NCACHE) == 0)
                    continue;
                type = rdataset->type;
                if (type == dns_rdatatype_rrsig)
                    type = rdataset->covers;
                if (type == dns_rdatatype_soa ||
                    type == dns_rdatatype_nsec ||
                    type == dns_rdatatype_nsec3) {
                    if (ttl > rdataset->ttl)
                        ttl = rdataset->ttl;
                    if (trust > rdataset->trust)
                        trust = rdataset->trust;
                    /*
                     * Copy the owner name to the buffer.
                     */
                    dns_name_toregion(name, &r);
                    result = isc_buffer_copyregion(&buffer,
                                       &r);
                    if (result != ISC_R_SUCCESS)
                        return (result);
                    /*
                     * Copy the type to the buffer.
                     */
                    isc_buffer_availableregion(&buffer,
                                   &r);
                    if (r.length < 2)
                        return (ISC_R_NOSPACE);
                    isc_buffer_putuint16(&buffer,
                                 rdataset->type);
                    isc_buffer_putuint8(&buffer,
                                 rdataset->trust);
                    /*
                     * Copy the rdataset into the buffer.
                     */
                    result = copy_rdataset(rdataset,
                                   &buffer);
                    if (result != ISC_R_SUCCESS)
                        return (result);

                    if (next >= DNS_NCACHE_RDATA)
                        return (ISC_R_NOSPACE);
                    dns_rdata_init(&rdata[next]);
                    isc_buffer_remainingregion(&buffer, &r);
                    rdata[next].data = r.base;
                    rdata[next].length = r.length;
                    rdata[next].rdclass =
                        ncrdatalist.rdclass;
                    rdata[next].type = 0;
                    rdata[next].flags = 0;
                    ISC_LIST_APPEND(ncrdatalist.rdata,
                            &rdata[next], link);
                    isc_buffer_forward(&buffer, r.length);
                    next++;
                }
            }
        }
        result = dns_message_nextname(message, DNS_SECTION_AUTHORITY);
    }
    if (result != ISC_R_NOMORE)
        return (result);

    if (trust == 0xffff) {
        /*
         * We didn't find any authority data from which to create a
         * negative cache rdataset.  In particular, we have no SOA.
         *
         * We trust that the caller wants negative caching, so this
         * means we have a "type 3 nxdomain" or "type 3 nodata"
         * response (see RFC2308 for details).
         *
         * We will now build a suitable negative cache rdataset that
         * will cause zero bytes to be emitted when converted to
         * wire format.
         */

        /*
         * The ownername must exist, but it doesn't matter what value
         * it has.  We use the root name.
         */
        dns_name_toregion(dns_rootname, &r);
        result = isc_buffer_copyregion(&buffer, &r);
        if (result != ISC_R_SUCCESS)
            return (result);
        /*
         * Copy the type and a zero rdata count to the buffer.
         */
        isc_buffer_availableregion(&buffer, &r);
        if (r.length < 4)
            return (ISC_R_NOSPACE);
        isc_buffer_putuint16(&buffer, 0);
        isc_buffer_putuint16(&buffer, 0);
        /*
         * RFC2308, section 5, says that negative answers without
         * SOAs should not be cached.
         */
        ttl = 0;
        /*
         * Set trust.
         */
        if ((message->flags & DNS_MESSAGEFLAG_AA) != 0 &&
            message->counts[DNS_SECTION_ANSWER] == 0) {
            /*
             * The response has aa set and we haven't followed
             * any CNAME or DNAME chains.
             */
            trust = dns_trust_authauthority;
        } else
            trust = dns_trust_additional;
        /*
         * Now add it to the cache.
         */
        if (next >= DNS_NCACHE_RDATA)
            return (ISC_R_NOSPACE);
        dns_rdata_init(&rdata[next]);
        isc_buffer_remainingregion(&buffer, &r);
        rdata[next].data = r.base;
        rdata[next].length = r.length;
        rdata[next].rdclass = ncrdatalist.rdclass;
        rdata[next].type = 0;
        rdata[next].flags = 0;
        ISC_LIST_APPEND(ncrdatalist.rdata, &rdata[next], link);
    }

    INSIST(trust != 0xffff);

    ncrdatalist.ttl = ttl;

    dns_rdataset_init(&ncrdataset);
    RUNTIME_CHECK(dns_rdatalist_tordataset(&ncrdatalist, &ncrdataset)
              == ISC_R_SUCCESS);
    ncrdataset.trust = trust;
    if (message->rcode == dns_rcode_nxdomain)
        ncrdataset.attributes |= DNS_RDATASETATTR_NXDOMAIN;
    if (optout)
        ncrdataset.attributes |= DNS_RDATASETATTR_OPTOUT;

    return (dns_db_addrdataset(cache, node, NULL, now, &ncrdataset,
                   0, addedrdataset));
}

isc_result_t
dns_ncache_towire(dns_rdataset_t *rdataset, dns_compress_t *cctx,
          isc_buffer_t *target, unsigned int options,
          unsigned int *countp)
{
    dns_rdata_t rdata = DNS_RDATA_INIT;
    isc_result_t result;
    isc_region_t remaining, tavailable;
    isc_buffer_t source, savedbuffer, rdlen;
    dns_name_t name;
    dns_rdatatype_t type;
    unsigned int i, rcount, count;

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

    REQUIRE(rdataset != NULL);
    REQUIRE(rdataset->type == 0);

    savedbuffer = *target;
    count = 0;

    result = dns_rdataset_first(rdataset);
    while (result == ISC_R_SUCCESS) {
        dns_rdataset_current(rdataset, &rdata);
        isc_buffer_init(&source, rdata.data, rdata.length);
        isc_buffer_add(&source, rdata.length);
        dns_name_init(&name, NULL);
        isc_buffer_remainingregion(&source, &remaining);
        dns_name_fromregion(&name, &remaining);
        INSIST(remaining.length >= name.length);
        isc_buffer_forward(&source, name.length);
        remaining.length -= name.length;

        INSIST(remaining.length >= 5);
        type = isc_buffer_getuint16(&source);
        isc_buffer_forward(&source, 1);
        rcount = isc_buffer_getuint16(&source);

        for (i = 0; i < rcount; i++) {
            /*
             * Get the length of this rdata and set up an
             * rdata structure for it.
             */
            isc_buffer_remainingregion(&source, &remaining);
            INSIST(remaining.length >= 2);
            dns_rdata_reset(&rdata);
            rdata.length = isc_buffer_getuint16(&source);
            isc_buffer_remainingregion(&source, &remaining);
            rdata.data = remaining.base;
            rdata.type = type;
            rdata.rdclass = rdataset->rdclass;
            INSIST(remaining.length >= rdata.length);
            isc_buffer_forward(&source, rdata.length);

            if ((options & DNS_NCACHETOWIRE_OMITDNSSEC) != 0 &&
                dns_rdatatype_isdnssec(type))
                continue;

            /*
             * Write the name.
             */
            dns_compress_setmethods(cctx, DNS_COMPRESS_GLOBAL14);
            result = dns_name_towire(&name, cctx, target);
            if (result != ISC_R_SUCCESS)
                goto rollback;

            /*
             * See if we have space for type, class, ttl, and
             * rdata length.  Write the type, class, and ttl.
             */
            isc_buffer_availableregion(target, &tavailable);
            if (tavailable.length < 10) {
                result = ISC_R_NOSPACE;
                goto rollback;
            }
            isc_buffer_putuint16(target, type);
            isc_buffer_putuint16(target, rdataset->rdclass);
            isc_buffer_putuint32(target, rdataset->ttl);

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

            /*
             * Write the rdata.
             */
            result = dns_rdata_towire(&rdata, cctx, target);
            if (result != ISC_R_SUCCESS)
                goto rollback;

            /*
             * Set the rdata length field to the compressed
             * length.
             */
            INSIST((target->used >= rdlen.used + 2) &&
                   (target->used - rdlen.used - 2 < 65536));
            isc_buffer_putuint16(&rdlen,
                         (isc_uint16_t)(target->used -
                                rdlen.used - 2));

            count++;
        }
        INSIST(isc_buffer_remaininglength(&source) == 0);
        result = dns_rdataset_next(rdataset);
        dns_rdata_reset(&rdata);
    }
    if (result != ISC_R_NOMORE)
        goto rollback;

    *countp = count;

    return (ISC_R_SUCCESS);

 rollback:
    INSIST(savedbuffer.used < 65536);
    dns_compress_rollback(cctx, (isc_uint16_t)savedbuffer.used);
    *countp = 0;
    *target = savedbuffer;

    return (result);
}

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

static isc_result_t
rdataset_first(dns_rdataset_t *rdataset) {
    unsigned char *raw = rdataset->private3;
    unsigned int count;

    count = raw[0] * 256 + raw[1];
    if (count == 0) {
        rdataset->private5 = NULL;
        return (ISC_R_NOMORE);
    }
    raw += 2;
    /*
     * The privateuint4 field is the number of rdata beyond the cursor
     * position, so we decrement the total count by one before storing
     * it.
     */
    count--;
    rdataset->privateuint4 = count;
    rdataset->private5 = raw;

    return (ISC_R_SUCCESS);
}

static isc_result_t
rdataset_next(dns_rdataset_t *rdataset) {
    unsigned int count;
    unsigned int length;
    unsigned char *raw;

    count = rdataset->privateuint4;
    if (count == 0)
        return (ISC_R_NOMORE);
    count--;
    rdataset->privateuint4 = count;
    raw = rdataset->private5;
    length = raw[0] * 256 + raw[1];
    raw += length + 2;
    rdataset->private5 = raw;

    return (ISC_R_SUCCESS);
}

static void
rdataset_current(dns_rdataset_t *rdataset, dns_rdata_t *rdata) {
    unsigned char *raw = rdataset->private5;
    isc_region_t r;

    REQUIRE(raw != NULL);

    r.length = raw[0] * 256 + raw[1];
    raw += 2;
    r.base = raw;
    dns_rdata_fromregion(rdata, rdataset->rdclass, rdataset->type, &r);
}

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

    /*
     * Reset iterator state.
     */
    target->privateuint4 = 0;
    target->private5 = NULL;
}

static unsigned int
rdataset_count(dns_rdataset_t *rdataset) {
    unsigned char *raw = rdataset->private3;
    unsigned int count;

    count = raw[0] * 256 + raw[1];

    return (count);
}

static void
rdataset_settrust(dns_rdataset_t *rdataset, dns_trust_t trust) {
    unsigned char *raw = rdataset->private3;

    raw[-1] = trust;
}

static dns_rdatasetmethods_t rdataset_methods = {
    rdataset_disassociate,
    rdataset_first,
    rdataset_next,
    rdataset_current,
    rdataset_clone,
    rdataset_count,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    rdataset_settrust,
    NULL
};

isc_result_t
dns_ncache_getrdataset(dns_rdataset_t *ncacherdataset, dns_name_t *name,
               dns_rdatatype_t type, dns_rdataset_t *rdataset)
{
    isc_result_t result;
    dns_rdata_t rdata = DNS_RDATA_INIT;
    isc_region_t remaining;
    isc_buffer_t source;
    dns_name_t tname;
    dns_rdatatype_t ttype;
    dns_trust_t trust = dns_trust_none;
    dns_rdataset_t clone;

    REQUIRE(ncacherdataset != NULL);
    REQUIRE(ncacherdataset->type == 0);
    REQUIRE(name != NULL);
    REQUIRE(!dns_rdataset_isassociated(rdataset));
    REQUIRE(type != dns_rdatatype_rrsig);

    dns_rdataset_init(&clone);
    dns_rdataset_clone(ncacherdataset, &clone);
    result = dns_rdataset_first(&clone);
    while (result == ISC_R_SUCCESS) {
        dns_rdataset_current(&clone, &rdata);
        isc_buffer_init(&source, rdata.data, rdata.length);
        isc_buffer_add(&source, rdata.length);
        dns_name_init(&tname, NULL);
        isc_buffer_remainingregion(&source, &remaining);
        dns_name_fromregion(&tname, &remaining);
        INSIST(remaining.length >= tname.length);
        isc_buffer_forward(&source, tname.length);
        remaining.length -= tname.length;

        INSIST(remaining.length >= 3);
        ttype = isc_buffer_getuint16(&source);

        if (ttype == type && dns_name_equal(&tname, name)) {
            trust = isc_buffer_getuint8(&source);
            INSIST(trust <= dns_trust_ultimate);
            isc_buffer_remainingregion(&source, &remaining);
            break;
        }
        result = dns_rdataset_next(&clone);
        dns_rdata_reset(&rdata);
    }
    dns_rdataset_disassociate(&clone);
    if (result == ISC_R_NOMORE)
        return (ISC_R_NOTFOUND);
    if (result != ISC_R_SUCCESS)
        return (result);

    INSIST(remaining.length != 0);

    rdataset->methods = &rdataset_methods;
    rdataset->rdclass = ncacherdataset->rdclass;
    rdataset->type = type;
    rdataset->covers = 0;
    rdataset->ttl = ncacherdataset->ttl;
    rdataset->trust = trust;
    rdataset->private1 = NULL;
    rdataset->private2 = NULL;

    rdataset->private3 = remaining.base;

    /*
     * Reset iterator state.
     */
    rdataset->privateuint4 = 0;
    rdataset->private5 = NULL;
    rdataset->private6 = NULL;
    return (ISC_R_SUCCESS);
}

isc_result_t
dns_ncache_getsigrdataset(dns_rdataset_t *ncacherdataset, dns_name_t *name,
                  dns_rdatatype_t covers, dns_rdataset_t *rdataset)
{
    dns_name_t tname;
    dns_rdata_rrsig_t rrsig;
    dns_rdata_t rdata = DNS_RDATA_INIT;
    dns_rdataset_t clone;
    dns_rdatatype_t type;
    dns_trust_t trust = dns_trust_none;
    isc_buffer_t source;
    isc_region_t remaining, sigregion;
    isc_result_t result;
    unsigned char *raw;
    unsigned int count;

    REQUIRE(ncacherdataset != NULL);
    REQUIRE(ncacherdataset->type == 0);
    REQUIRE(name != NULL);
    REQUIRE(!dns_rdataset_isassociated(rdataset));

    dns_rdataset_init(&clone);
    dns_rdataset_clone(ncacherdataset, &clone);
    result = dns_rdataset_first(&clone);
    while (result == ISC_R_SUCCESS) {
        dns_rdataset_current(&clone, &rdata);
        isc_buffer_init(&source, rdata.data, rdata.length);
        isc_buffer_add(&source, rdata.length);
        dns_name_init(&tname, NULL);
        isc_buffer_remainingregion(&source, &remaining);
        dns_name_fromregion(&tname, &remaining);
        INSIST(remaining.length >= tname.length);
        isc_buffer_forward(&source, tname.length);
        remaining.length -= tname.length;
        remaining.base += tname.length;

        INSIST(remaining.length >= 2);
        type = isc_buffer_getuint16(&source);
        remaining.length -= 2;
        remaining.base += 2;

        if (type != dns_rdatatype_rrsig ||
            !dns_name_equal(&tname, name)) {
            result = dns_rdataset_next(&clone);
            dns_rdata_reset(&rdata);
            continue;
        }

        INSIST(remaining.length >= 1);
        trust = isc_buffer_getuint8(&source);
        INSIST(trust <= dns_trust_ultimate);
        remaining.length -= 1;
        remaining.base += 1;

        raw = remaining.base;
        count = raw[0] * 256 + raw[1];
        INSIST(count > 0);
        raw += 2;
        sigregion.length = raw[0] * 256 + raw[1];
        raw += 2;
        sigregion.base = raw;
        dns_rdata_reset(&rdata);
        dns_rdata_fromregion(&rdata, rdataset->rdclass,
                     dns_rdatatype_rrsig, &sigregion);
        (void)dns_rdata_tostruct(&rdata, &rrsig, NULL);
        if (rrsig.covered == covers) {
            isc_buffer_remainingregion(&source, &remaining);
            break;
        }

        result = dns_rdataset_next(&clone);
        dns_rdata_reset(&rdata);
    }
    dns_rdataset_disassociate(&clone);
    if (result == ISC_R_NOMORE)
        return (ISC_R_NOTFOUND);
    if (result != ISC_R_SUCCESS)
        return (result);

    INSIST(remaining.length != 0);

    rdataset->methods = &rdataset_methods;
    rdataset->rdclass = ncacherdataset->rdclass;
    rdataset->type = dns_rdatatype_rrsig;
    rdataset->covers = covers;
    rdataset->ttl = ncacherdataset->ttl;
    rdataset->trust = trust;
    rdataset->private1 = NULL;
    rdataset->private2 = NULL;

    rdataset->private3 = remaining.base;

    /*
     * Reset iterator state.
     */
    rdataset->privateuint4 = 0;
    rdataset->private5 = NULL;
    rdataset->private6 = NULL;
    return (ISC_R_SUCCESS);
}

void
dns_ncache_current(dns_rdataset_t *ncacherdataset, dns_name_t *found,
           dns_rdataset_t *rdataset)
{
    dns_rdata_t rdata = DNS_RDATA_INIT;
    dns_trust_t trust;
    isc_region_t remaining, sigregion;
    isc_buffer_t source;
    dns_name_t tname;
    dns_rdatatype_t type;
    unsigned int count;
    dns_rdata_rrsig_t rrsig;
    unsigned char *raw;

    REQUIRE(ncacherdataset != NULL);
    REQUIRE(ncacherdataset->type == 0);
    REQUIRE(found != NULL);
    REQUIRE(!dns_rdataset_isassociated(rdataset));

    dns_rdataset_current(ncacherdataset, &rdata);
    isc_buffer_init(&source, rdata.data, rdata.length);
    isc_buffer_add(&source, rdata.length);

    dns_name_init(&tname, NULL);
    isc_buffer_remainingregion(&source, &remaining);
    dns_name_fromregion(found, &remaining);
    INSIST(remaining.length >= found->length);
    isc_buffer_forward(&source, found->length);
    remaining.length -= found->length;

    INSIST(remaining.length >= 5);
    type = isc_buffer_getuint16(&source);
    trust = isc_buffer_getuint8(&source);
    INSIST(trust <= dns_trust_ultimate);
    isc_buffer_remainingregion(&source, &remaining);

    rdataset->methods = &rdataset_methods;
    rdataset->rdclass = ncacherdataset->rdclass;
    rdataset->type = type;
    if (type == dns_rdatatype_rrsig) {
        /*
         * Extract covers from RRSIG.
         */
        raw = remaining.base;
        count = raw[0] * 256 + raw[1];
        INSIST(count > 0);
        raw += 2;
        sigregion.length = raw[0] * 256 + raw[1];
        raw += 2;
        sigregion.base = raw;
        dns_rdata_reset(&rdata);
        dns_rdata_fromregion(&rdata, rdataset->rdclass,
                     rdataset->type, &sigregion);
        (void)dns_rdata_tostruct(&rdata, &rrsig, NULL);
        rdataset->covers = rrsig.covered;
    } else
        rdataset->covers = 0;
    rdataset->ttl = ncacherdataset->ttl;
    rdataset->trust = trust;
    rdataset->private1 = NULL;
    rdataset->private2 = NULL;

    rdataset->private3 = remaining.base;

    /*
     * Reset iterator state.
     */
    rdataset->privateuint4 = 0;
    rdataset->private5 = NULL;
    rdataset->private6 = NULL;
}