lib/dns/message.c

	message.c revision 1db717f2f36d45f0f545083a72189c68add162d0
/*
 * Copyright (C) 1999  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.
 */

/***
 *** Imports
 ***/

#include <config.h>

#include <stddef.h>
#include <string.h>

#include <isc/assertions.h>
#include <isc/boolean.h>
#include <isc/region.h>
#include <isc/types.h>

#include <dns/message.h>
#include <dns/rdataset.h>
#include <dns/rdata.h>
#include <dns/rdataclass.h>
#include <dns/rdatatype.h>
#include <dns/rdatalist.h>
#include <dns/compress.h>

#define DNS_MESSAGE_OPCODE_MASK     0x7800U
#define DNS_MESSAGE_OPCODE_SHIFT        11
#define DNS_MESSAGE_RCODE_MASK      0x000fU
#define DNS_MESSAGE_FLAG_MASK       0x8ff0U

#define VALID_NAMED_SECTION(s)  (((s) > DNS_SECTION_ANY) \
                 && ((s) < DNS_SECTION_MAX))
#define VALID_SECTION(s)    (((s) >= DNS_SECTION_ANY) \
                 && ((s) < DNS_SECTION_MAX))

/*
 * This is the size of each individual scratchpad buffer, and the numbers
 * of various block allocations used within the server.
 * XXXMLG These should come from a config setting.
 */
#define SCRATCHPAD_SIZE     512
#define NAME_COUNT        8
#define RDATA_COUNT       8
#define RDATALIST_COUNT       8
#define RDATASET_COUNT       RDATALIST_COUNT

/*
 * "helper" type, which consists of a block of some type, and is linkable.
 * For it to work, sizeof(dns_msgblock_t) must be a multiple of the pointer
 * size, or the allocated elements will not be alligned correctly.
 */
struct dns_msgblock {
    unsigned int            count;
    unsigned int            remaining;
    ISC_LINK(dns_msgblock_t)    link;
}; /* dynamically sized */

static inline dns_msgblock_t *
msgblock_allocate(isc_mem_t *, unsigned int, unsigned int);

#define msgblock_get(block, type) \
    ((type *)msgblock_internalget(block, sizeof(type)))

static inline void *
msgblock_internalget(dns_msgblock_t *, unsigned int);

static inline void
msgblock_reset(dns_msgblock_t *);

static inline void
msgblock_free(isc_mem_t *, dns_msgblock_t *, unsigned int);

/*
 * Allocate a new dns_msgblock_t, and return a pointer to it.  If no memory
 * is free, return NULL.
 */
static inline dns_msgblock_t *
msgblock_allocate(isc_mem_t *mctx, unsigned int sizeof_type,
          unsigned int count)
{
    dns_msgblock_t *block;
    unsigned int length;

    length = sizeof(dns_msgblock_t) + (sizeof_type * count);

    block = isc_mem_get(mctx, length);
    if (block == NULL)
        return (NULL);

    block->count = count;
    block->remaining = count;

    ISC_LINK_INIT(block, link);

    return (block);
}

/*
 * Return an element from the msgblock.  If no more are available, return
 * NULL.
 */
static inline void *
msgblock_internalget(dns_msgblock_t *block, unsigned int sizeof_type)
{
    void *ptr;

    if (block->remaining == 0)
        return (NULL);

    block->remaining--;

    ptr = (((unsigned char *)block)
           + sizeof(dns_msgblock_t)
           + (sizeof_type * block->remaining));

    return (ptr);
}

static inline void
msgblock_reset(dns_msgblock_t *block)
{
    block->remaining = block->count;
}

/*
 * Release memory associated with a message block.
 */
static inline void
msgblock_free(isc_mem_t *mctx, dns_msgblock_t *block,
          unsigned int sizeof_type)
{
    unsigned int length;

    length = sizeof(dns_msgblock_t) + (sizeof_type * block->count);

    isc_mem_put(mctx, block, length);
}

/*
 * Allocate a new dynamic buffer, and attach it to this message as the
 * "current" buffer.  (which is always the last on the list, for our
 * uses)
 */
static inline dns_result_t
newbuffer(dns_message_t *msg)
{
    isc_result_t result;
    isc_dynbuffer_t *dynbuf;

    dynbuf = NULL;
    result = isc_dynbuffer_allocate(msg->mctx, &dynbuf, SCRATCHPAD_SIZE,
                    ISC_BUFFERTYPE_BINARY);
    if (result != ISC_R_SUCCESS)
        return (DNS_R_NOMEMORY);

    ISC_LIST_APPEND(msg->scratchpad, dynbuf, link);
    return (DNS_R_SUCCESS);
}

static inline isc_buffer_t *
currentbuffer(dns_message_t *msg)
{
    isc_dynbuffer_t *dynbuf;

    dynbuf = ISC_LIST_TAIL(msg->scratchpad);
    INSIST(dynbuf != NULL);

    return (&dynbuf->buffer);
}

static inline void
releasename(dns_message_t *msg, dns_name_t *name)
{
    ISC_LIST_PREPEND(msg->freename, name, link);
}

static inline dns_name_t *
newname(dns_message_t *msg)
{
    dns_msgblock_t *msgblock;
    dns_name_t *name;

    name = ISC_LIST_HEAD(msg->freename);
    if (name != NULL) {
        ISC_LIST_UNLINK(msg->freename, name, link);
        return (name);
    }

    msgblock = ISC_LIST_TAIL(msg->names);
    name = msgblock_get(msgblock, dns_name_t);
    if (name == NULL) {
        msgblock = msgblock_allocate(msg->mctx, sizeof(dns_name_t),
                         NAME_COUNT);
        if (msgblock == NULL)
            return (NULL);

        ISC_LIST_APPEND(msg->names, msgblock, link);

        name = msgblock_get(msgblock, dns_name_t);
    }

    return (name);
}

static inline void
releaserdata(dns_message_t *msg, dns_rdata_t *rdata)
{
    ISC_LIST_PREPEND(msg->freerdata, rdata, link);
}

static inline dns_rdata_t *
newrdata(dns_message_t *msg)
{
    dns_msgblock_t *msgblock;
    dns_rdata_t *rdata;

    rdata = ISC_LIST_HEAD(msg->freerdata);
    if (rdata != NULL) {
        ISC_LIST_UNLINK(msg->freerdata, rdata, link);
        return (rdata);
    }

    msgblock = ISC_LIST_TAIL(msg->rdatas);
    rdata = msgblock_get(msgblock, dns_rdata_t);
    if (rdata == NULL) {
        msgblock = msgblock_allocate(msg->mctx, sizeof(dns_rdata_t),
                         RDATA_COUNT);
        if (msgblock == NULL)
            return (NULL);

        ISC_LIST_APPEND(msg->rdatas, msgblock, link);

        rdata = msgblock_get(msgblock, dns_rdata_t);
    }

    return (rdata);
}

static inline void
releaserdatalist(dns_message_t *msg, dns_rdatalist_t *rdatalist)
{
    ISC_LIST_PREPEND(msg->freerdatalist, rdatalist, link);
}

static inline dns_rdatalist_t *
newrdatalist(dns_message_t *msg)
{
    dns_msgblock_t *msgblock;
    dns_rdatalist_t *rdatalist;

    rdatalist = ISC_LIST_HEAD(msg->freerdatalist);
    if (rdatalist != NULL) {
        ISC_LIST_UNLINK(msg->freerdatalist, rdatalist, link);
        return (rdatalist);
    }

    msgblock = ISC_LIST_TAIL(msg->rdatalists);
    rdatalist = msgblock_get(msgblock, dns_rdatalist_t);
    if (rdatalist == NULL) {
        msgblock = msgblock_allocate(msg->mctx,
                         sizeof(dns_rdatalist_t),
                         RDATALIST_COUNT);
        if (msgblock == NULL)
            return (NULL);

        ISC_LIST_APPEND(msg->rdatalists, msgblock, link);

        rdatalist = msgblock_get(msgblock, dns_rdatalist_t);
    }

    return (rdatalist);
}

static inline void
releaserdataset(dns_message_t *msg, dns_rdataset_t *rdataset)
{
    ISC_LIST_PREPEND(msg->freerdataset, rdataset, link);
}

static inline dns_rdataset_t *
newrdataset(dns_message_t *msg)
{
    dns_msgblock_t *msgblock;
    dns_rdataset_t *rdataset;

    rdataset = ISC_LIST_HEAD(msg->freerdataset);
    if (rdataset != NULL) {
        ISC_LIST_UNLINK(msg->freerdataset, rdataset, link);
        return (rdataset);
    }

    msgblock = ISC_LIST_TAIL(msg->rdatasets);
    rdataset = msgblock_get(msgblock, dns_rdataset_t);
    if (rdataset == NULL) {
        msgblock = msgblock_allocate(msg->mctx, sizeof(dns_rdataset_t),
                         RDATASET_COUNT);
        if (msgblock == NULL)
            return (NULL);

        ISC_LIST_APPEND(msg->rdatasets, msgblock, link);

        rdataset = msgblock_get(msgblock, dns_rdataset_t);
    }

    return (rdataset);
}

/*
 * Init elements to default state.  Used both when allocating a new element
 * and when resetting one.
 */
static inline void
msginit(dns_message_t *m)
{
    unsigned int i;

    m->id = 0;
    m->flags = 0;
    m->rcode = 0;
    m->opcode = 0;
    m->rdclass = 0;

    for (i = 0 ; i < DNS_SECTION_MAX ; i++) {
        m->cursors[i] = NULL;
        m->counts[i] = 0;
    }
    m->opt = NULL;

    m->state = DNS_SECTION_ANY;  /* indicate nothing parsed or rendered */

    m->reserved = 0;

    m->buffer = NULL;
    m->need_cctx_cleanup = 0;
}

/*
 * Free all but one (or everything) for this message.  This is used by
 * both dns_message_reset() and dns_message_parse().
 */
static void
msgreset(dns_message_t *msg, isc_boolean_t everything)
{
    dns_msgblock_t *msgblock, *next_msgblock;
    isc_dynbuffer_t *dynbuf, *next_dynbuf;
    dns_rdataset_t *rds, *next_rds;
    dns_name_t *name, *next_name;
    dns_rdata_t *rdata;
    dns_rdatalist_t *rdatalist;
    unsigned int i;

    /*
     * Clean up name lists by calling the rdataset disassociate function.
     */
    for (i = 0 ; i < DNS_SECTION_MAX ; i++) {
        name = ISC_LIST_HEAD(msg->sections[i]);
        while (name != NULL) {
            next_name = ISC_LIST_NEXT(name, link);
            ISC_LIST_UNLINK(msg->sections[i], name, link);

            rds = ISC_LIST_HEAD(name->list);
            while (rds != NULL) {
                next_rds = ISC_LIST_NEXT(rds, link);
                ISC_LIST_UNLINK(name->list, rds, link);

                dns_rdataset_disassociate(rds);
                rds = next_rds;
            }
            name = next_name;
        }
    }

    /*
     * Clean up linked lists.
     */

    /*
     * Run through the free lists, and just unlink anything found there.
     * The memory isn't lost since these are part of message blocks we
     * have allocated.
     */
    name = ISC_LIST_HEAD(msg->freename);
    while (name != NULL) {
        ISC_LIST_UNLINK(msg->freename, name, link);
        name = ISC_LIST_HEAD(msg->freename);
    }
    rdata = ISC_LIST_HEAD(msg->freerdata);
    while (rdata != NULL) {
        ISC_LIST_UNLINK(msg->freerdata, rdata, link);
        rdata = ISC_LIST_HEAD(msg->freerdata);
    }
    rdatalist = ISC_LIST_HEAD(msg->freerdatalist);
    while (rdatalist != NULL) {
        ISC_LIST_UNLINK(msg->freerdatalist, rdatalist, link);
        rdatalist = ISC_LIST_HEAD(msg->freerdatalist);
    }
    rds = ISC_LIST_HEAD(msg->freerdataset);
    while (rds != NULL) {
        ISC_LIST_UNLINK(msg->freerdataset, rds, link);
        rds = ISC_LIST_HEAD(msg->freerdataset);
    }

    dynbuf = ISC_LIST_HEAD(msg->scratchpad);
    INSIST(dynbuf != NULL);
    if (!everything) {
        isc_dynbuffer_reset(dynbuf);
        dynbuf = ISC_LIST_NEXT(dynbuf, link);
    }
    while (dynbuf != NULL) {
        next_dynbuf = ISC_LIST_NEXT(dynbuf, link);
        ISC_LIST_UNLINK(msg->scratchpad, dynbuf, link);
        isc_dynbuffer_free(msg->mctx, &dynbuf);
        dynbuf = next_dynbuf;
    }

    msgblock = ISC_LIST_HEAD(msg->names);
    INSIST(msgblock != NULL);
    if (!everything) {
        msgblock_reset(msgblock);
        msgblock = ISC_LIST_NEXT(msgblock, link);
    }
    while (msgblock != NULL) {
        next_msgblock = ISC_LIST_NEXT(msgblock, link);
        ISC_LIST_UNLINK(msg->names, msgblock, link);
        msgblock_free(msg->mctx, msgblock, sizeof(dns_name_t));
        msgblock = next_msgblock;
    }

    msgblock = ISC_LIST_HEAD(msg->rdatas);
    INSIST(msgblock != NULL);
    if (!everything) {
        msgblock_reset(msgblock);
        msgblock = ISC_LIST_NEXT(msgblock, link);
    }
    while (msgblock != NULL) {
        next_msgblock = ISC_LIST_NEXT(msgblock, link);
        ISC_LIST_UNLINK(msg->rdatas, msgblock, link);
        msgblock_free(msg->mctx, msgblock, sizeof(dns_rdata_t));
        msgblock = next_msgblock;
    }

    msgblock = ISC_LIST_HEAD(msg->rdatasets);
    INSIST(msgblock != NULL);
    if (!everything) {
        msgblock_reset(msgblock);
        msgblock = ISC_LIST_NEXT(msgblock, link);
    }
    while (msgblock != NULL) {
        next_msgblock = ISC_LIST_NEXT(msgblock, link);
        ISC_LIST_UNLINK(msg->rdatasets, msgblock, link);
        msgblock_free(msg->mctx, msgblock, sizeof(dns_rdataset_t));
        msgblock = next_msgblock;
    }

    /*
     * rdatalists could be empty.
     */

    msgblock = ISC_LIST_HEAD(msg->rdatalists);
    if (!everything && msgblock != NULL) {
        msgblock_reset(msgblock);
        msgblock = ISC_LIST_NEXT(msgblock, link);
    }
    while (msgblock != NULL) {
        next_msgblock = ISC_LIST_NEXT(msgblock, link);
        ISC_LIST_UNLINK(msg->rdatalists, msgblock, link);
        msgblock_free(msg->mctx, msgblock, sizeof(dns_rdatalist_t));
        msgblock = next_msgblock;
    }

    if (msg->need_cctx_cleanup == 1)
        dns_compress_invalidate(&msg->cctx);

    /*
     * Set other bits to normal default values.
     */
    if (!everything)
        msginit(msg);
}

dns_result_t
dns_message_create(isc_mem_t *mctx, dns_message_t **msgp, unsigned int intent)
{
    dns_message_t *m;
    isc_result_t iresult;
    dns_msgblock_t *msgblock;
    isc_dynbuffer_t *dynbuf;
    unsigned int i;

    REQUIRE(mctx != NULL);
    REQUIRE(msgp != NULL);
    REQUIRE(*msgp == NULL);
    REQUIRE(intent == DNS_MESSAGE_INTENTPARSE
        || intent == DNS_MESSAGE_INTENTRENDER);

    m = isc_mem_get(mctx, sizeof(dns_message_t));
    if (m == NULL)
        return(DNS_R_NOMEMORY);

    m->magic = MESSAGE_MAGIC;
    m->from_to_wire = intent;
    msginit(m);
    for (i = 0 ; i < DNS_SECTION_MAX ; i++)
        ISC_LIST_INIT(m->sections[i]);
    m->mctx = mctx;
    ISC_LIST_INIT(m->scratchpad);
    ISC_LIST_INIT(m->names);
    ISC_LIST_INIT(m->rdatas);
    ISC_LIST_INIT(m->rdatasets);
    ISC_LIST_INIT(m->rdatalists);
    ISC_LIST_INIT(m->freename);
    ISC_LIST_INIT(m->freerdata);
    ISC_LIST_INIT(m->freerdataset);
    ISC_LIST_INIT(m->freerdatalist);

    dynbuf = NULL;
    iresult = isc_dynbuffer_allocate(mctx, &dynbuf, SCRATCHPAD_SIZE,
                     ISC_BUFFERTYPE_BINARY);
    if (iresult != ISC_R_SUCCESS)
        goto cleanup1;
    ISC_LIST_APPEND(m->scratchpad, dynbuf, link);

    msgblock = msgblock_allocate(mctx, sizeof(dns_name_t),
                     NAME_COUNT);
    if (msgblock == NULL)
        goto cleanup2;
    ISC_LIST_APPEND(m->names, msgblock, link);

    msgblock = msgblock_allocate(mctx, sizeof(dns_rdata_t),
                     RDATA_COUNT);
    if (msgblock == NULL)
        goto cleanup3;
    ISC_LIST_APPEND(m->rdatas, msgblock, link);

    msgblock = msgblock_allocate(mctx, sizeof(dns_rdataset_t),
                     RDATASET_COUNT);
    if (msgblock == NULL)
        goto cleanup4;
    ISC_LIST_APPEND(m->rdatasets, msgblock, link);

    if (intent == DNS_MESSAGE_INTENTPARSE) {
        msgblock = msgblock_allocate(mctx, sizeof(dns_rdatalist_t),
                         RDATALIST_COUNT);
        if (msgblock == NULL)
            goto cleanup5;
        ISC_LIST_APPEND(m->rdatalists, msgblock, link);
    }

    *msgp = m;
    return (DNS_R_SUCCESS);

    /*
     * Cleanup for error returns.
     */
 cleanup5:
    msgblock = ISC_LIST_HEAD(m->rdatasets);
    msgblock_free(mctx, msgblock, sizeof(dns_rdataset_t));
 cleanup4:
    msgblock = ISC_LIST_HEAD(m->rdatas);
    msgblock_free(mctx, msgblock, sizeof(dns_rdata_t));
 cleanup3:
    msgblock = ISC_LIST_HEAD(m->names);
    msgblock_free(mctx, msgblock, sizeof(dns_name_t));
 cleanup2:
    dynbuf = ISC_LIST_HEAD(m->scratchpad);
    isc_dynbuffer_free(mctx, &dynbuf);
 cleanup1:
    m->magic = 0;
    isc_mem_put(mctx, m, sizeof(dns_message_t));

    return (DNS_R_NOMEMORY);
}

void
dns_message_reset(dns_message_t *msg)
{
    REQUIRE(VALID_MESSAGE(msg));
    msgreset(msg, ISC_FALSE);
}

void
dns_message_destroy(dns_message_t **msgp)
{
    dns_message_t *msg;

    REQUIRE(msgp != NULL);
    REQUIRE(VALID_MESSAGE(*msgp));

    msg = *msgp;
    *msgp = NULL;

    msgreset(msg, ISC_TRUE);
    msg->magic = 0;
    isc_mem_put(msg->mctx, msg, sizeof(dns_message_t));
}

static dns_result_t
findname(dns_name_t **foundname, dns_name_t *target, dns_namelist_t *section)
{
    dns_name_t *curr;

    for (curr = ISC_LIST_TAIL(*section) ;
         curr != NULL ;
         curr = ISC_LIST_PREV(curr, link)) {
        if (dns_name_equal(curr, target)) {
            if (foundname != NULL)
                *foundname = curr;
            return (DNS_R_SUCCESS);
        }
    }

    return (DNS_R_NOTFOUND);
}

static dns_result_t
findtype(dns_rdataset_t **rdataset, dns_name_t *name, dns_rdatatype_t type)
{
    dns_rdataset_t *curr;

    for (curr = ISC_LIST_TAIL(name->list) ;
         curr != NULL ;
         curr = ISC_LIST_PREV(curr, link)) {
        if (curr->type == type) {
            if (rdataset != NULL)
                *rdataset = curr;
            return (DNS_R_SUCCESS);
        }
    }

    return (DNS_R_NOTFOUND);
}

/*
 * Read a name from buffer "source".
 */
static dns_result_t
getname(dns_name_t *name, isc_buffer_t *source, dns_message_t *msg,
    dns_decompress_t *dctx)
{
    isc_buffer_t *scratch;
    dns_result_t result;
    unsigned int tries;

    scratch = currentbuffer(msg);

    /*
     * First try:  use current buffer.
     * Second try:  allocate a new buffer and use that.
     */
    tries = 0;
    while (tries < 2) {
        dns_name_init(name, NULL);
        result = dns_name_fromwire(name, source, dctx, ISC_FALSE,
                       scratch);

        if (result == DNS_R_NOSPACE) {
            tries++;

            result = newbuffer(msg);
            if (result != DNS_R_SUCCESS)
                return (result);

            scratch = currentbuffer(msg);
        } else {
            return (result);
        }
    }

    INSIST(0);  /* Cannot get here... */
    return (DNS_R_UNEXPECTED);
}

static dns_result_t
getrdata(dns_name_t *name, isc_buffer_t *source, dns_message_t *msg,
     dns_decompress_t *dctx, dns_rdataclass_t rdclass,
     dns_rdatatype_t rdtype, unsigned int rdatalen, dns_rdata_t *rdata)
{
    isc_buffer_t *scratch;
    dns_result_t result;
    unsigned int tries;

    /*
     * In dynamic update messages, the rdata can be empty.
     */
    if (msg->opcode == dns_opcode_update && rdatalen == 0) {
        /*
         * When the rdata is empty, the data pointer is never
         * dereferenced, but it must still be non-NULL.
         */
        rdata->data = (unsigned char *)"";
        rdata->length = 0;
        rdata->class = rdclass;
        rdata->type = rdtype;
        return DNS_R_SUCCESS;
    }

    scratch = currentbuffer(msg);

    isc_buffer_setactive(source, rdatalen);
    dns_decompress_localinit(dctx, name, source);

    /*
     * First try:  use current buffer.
     * Second try:  allocate a new buffer and use that.
     */
    tries = 0;
    while (tries < 2) {
        result = dns_rdata_fromwire(rdata, rdclass, rdtype,
                        source, dctx, ISC_FALSE,
                        scratch);

        if (result == DNS_R_NOSPACE) {
            tries++;

            result = newbuffer(msg);
            if (result != DNS_R_SUCCESS)
                return (result);

            scratch = currentbuffer(msg);
        } else {
            return (result);
        }
    }

    INSIST(0);  /* Cannot get here... */
    return (DNS_R_UNEXPECTED);
}

static dns_result_t
getquestions(isc_buffer_t *source, dns_message_t *msg, dns_decompress_t *dctx)
{
    isc_region_t r;
    unsigned int count;
    dns_name_t *name;
    dns_name_t *name2;
    dns_rdataset_t *rdataset;
    dns_rdatalist_t *rdatalist;
    dns_result_t result;
    dns_rdatatype_t rdtype;
    dns_rdataclass_t rdclass;
    dns_namelist_t *section;

    section = &msg->sections[DNS_SECTION_QUESTION];

    for (count = 0 ; count < msg->counts[DNS_SECTION_QUESTION] ; count++) {
        name = newname(msg);
        if (name == NULL)
            return (DNS_R_NOMEMORY);

        /*
         * Parse the name out of this packet.
         */
        isc_buffer_remaining(source, &r);
        isc_buffer_setactive(source, r.length);
        result = getname(name, source, msg, dctx);
        if (result != DNS_R_SUCCESS)
            return (result);

        /*
         * Run through the section, looking to see if this name
         * is already there.  If it is found, put back the allocated
         * name since we no longer need it, and set our name pointer
         * to point to the name we found.
         */
        result = findname(&name2, name, section);

        /*
         * If it is the first name in the section, accept it.
         *
         * If it is not, but is not the same as the name already
         * in the question section, append to the section.  Note that
         * here in the question section this is illegal, so return
         * FORMERR.  In the future, check the opcode to see if
         * this should be legal or not.  In either case we no longer
         * need this name pointer.
         */
        if (result != DNS_R_SUCCESS) {
            if (ISC_LIST_EMPTY(*section)) {
                ISC_LIST_APPEND(*section, name, link);
            } else {
                return (DNS_R_FORMERR);
            }
        } else {
            name = name2;
        }

        /*
         * Get type and class.
         */
        isc_buffer_remaining(source, &r);
        if (r.length < 4)
            return (DNS_R_UNEXPECTEDEND);
        rdtype = isc_buffer_getuint16(source);
        rdclass = isc_buffer_getuint16(source);

        /*
         * If this class is different than the one we already read,
         * this is an error.
         */
        if (msg->state == DNS_SECTION_ANY) {
            msg->state = DNS_SECTION_QUESTION;
            msg->rdclass = rdclass;
            msg->state = DNS_SECTION_QUESTION;
        } else if (msg->rdclass != rdclass)
            return (DNS_R_FORMERR);

        /*
         * Can't ask the same question twice.
         */
        result = findtype(NULL, name, rdtype);
        if (result == DNS_R_SUCCESS)
            return (DNS_R_FORMERR);

        /*
         * Allocate a new rdatalist.
         */
        rdatalist = newrdatalist(msg);
        if (rdatalist == NULL)
            return (DNS_R_NOMEMORY);
        rdataset = newrdataset(msg);
        if (rdataset == NULL)
            return (DNS_R_NOMEMORY);

        /*
         * Convert rdatalist to rdataset, and attach the latter to
         * the name.
         */
        rdatalist->type = rdtype;
        rdatalist->rdclass = rdclass;
        rdatalist->ttl = 0;
        ISC_LIST_INIT(rdatalist->rdata);

        dns_rdataset_init(rdataset);
        result = dns_rdatalist_tordataset(rdatalist, rdataset);
        if (result != DNS_R_SUCCESS)
            return (result);

        ISC_LIST_APPEND(name->list, rdataset, link);
    }

    return (DNS_R_SUCCESS);
}

static dns_result_t
getsection(isc_buffer_t *source, dns_message_t *msg, dns_decompress_t *dctx,
       dns_section_t sectionid)
{
    isc_region_t r;
    unsigned int count;
    unsigned int rdatalen;
    dns_name_t *name;
    dns_name_t *name2;
    dns_rdataset_t *rdataset;
    dns_rdatalist_t *rdatalist;
    dns_result_t result;
    dns_rdatatype_t rdtype;
    dns_rdataclass_t rdclass;
    dns_rdata_t *rdata;
    dns_ttl_t ttl;
    dns_namelist_t *section;

    for (count = 0 ; count < msg->counts[sectionid] ; count++) {
        section = &msg->sections[sectionid];

        name = newname(msg);
        if (name == NULL)
            return (DNS_R_NOMEMORY);

        /*
         * Parse the name out of this packet.
         */
        isc_buffer_remaining(source, &r);
        isc_buffer_setactive(source, r.length);
        result = getname(name, source, msg, dctx);
        if (result != DNS_R_SUCCESS)
            return (result);

        /*
         * Get type, class, ttl, and rdatalen.  Verify that at least
         * rdatalen bytes remain.  (Some of this is deferred to
         * later.)
         */
        isc_buffer_remaining(source, &r);
        if (r.length < 2 + 2 + 4 + 2)
            return (DNS_R_UNEXPECTEDEND);
        rdtype = isc_buffer_getuint16(source);
        rdclass = isc_buffer_getuint16(source);

        /*
         * If this class is different than the one in the question
         * section, bail.
         */
        if (msg->opcode != dns_opcode_update
            && msg->rdclass != rdclass)
            return (DNS_R_FORMERR);

        /*
         * If it is a tsig, verify that it is in the additional data
         * section, and switch sections for the rest of this rdata.
         */
        if (rdtype == dns_rdatatype_tsig) {
            if (sectionid != DNS_SECTION_ADDITIONAL)
                return (DNS_R_FORMERR);
            section = &msg->sections[DNS_SECTION_TSIG];
        }

        /*
         * ... now get ttl and rdatalen, and check buffer.
         */
        ttl = isc_buffer_getuint32(source);
        rdatalen = isc_buffer_getuint16(source);
        r.length -= (2 + 2 + 4 + 2);
        if (r.length < rdatalen)
            return (DNS_R_UNEXPECTEDEND);

        /*
         * If we are doing a dynamic update don't bother searching
         * for a name, just append this one to the end of the message.
         */
        if (msg->opcode == dns_opcode_update
            || rdtype == dns_rdatatype_tsig) {
            ISC_LIST_APPEND(*section, name, link);
        } else {
            /*
             * Run through the section, looking to see if this name
             * is already there.  If it is found, put back the
             * allocated name since we no longer need it, and set
             * our name pointer to point to the name we found.
             */
            result = findname(&name2, name, section);

            /*
             * If it is a new name, append to the section.
             */
            if (result == DNS_R_SUCCESS) {
                releasename(msg, name);
                name = name2;
            } else {
                ISC_LIST_APPEND(*section, name, link);
            }
        }

        /*
         * If this is an OPT record, There Can Be Only One.
         */
#if 0 /* until there is a dns_rdatatype_opt  XXXMLG */
        if (rdtype == dns_rdatatype_opt && msg->opt != NULL)
            return (DNS_R_FORMERR);
#endif

        /*
         * Search name for the particular type and class.
         * Skip this stage if in update mode, or this is a TSIG.
         */
        if (msg->opcode == dns_opcode_update
            || rdtype == dns_rdatatype_tsig)
            result = DNS_R_NOTFOUND;
        else
            result = findtype(&rdataset, name, rdtype);

        /*
         * If we found an rdataset that matches, we need to
         * append this rdata to that set.  If we did not, we need
         * to create a new rdatalist, store the important bits there,
         * convert it to an rdataset, and link the latter to the name.
         * Yuck.
         */
        if (result == DNS_R_NOTFOUND) {
            rdataset = newrdataset(msg);
            if (rdataset == NULL)
                return (DNS_R_NOMEMORY);
            rdatalist = newrdatalist(msg);
            if (rdatalist == NULL)
                return (DNS_R_NOMEMORY);

            rdatalist->type = rdtype;
            rdatalist->rdclass = rdclass;
            rdatalist->ttl = ttl;
            ISC_LIST_INIT(rdatalist->rdata);

            dns_rdataset_init(rdataset);
            dns_rdatalist_tordataset(rdatalist, rdataset);

            ISC_LIST_APPEND(name->list, rdataset, link);
        }

        /*
         * Read the rdata from the wire format.  Interpret the
         * rdata according to its actual class, even if it had a
         * DynDNS meta-class in the packet.  Then put the meta-class
         * back into the finished rdata.
         */
        rdata = newrdata(msg);
        if (rdata == NULL)
            return (DNS_R_NOMEMORY);
        result = getrdata(name, source, msg, dctx,
                  msg->rdclass, rdtype, rdatalen, rdata);
        if (result != DNS_R_SUCCESS)
            return (result);
        rdata->class = rdclass;

        /*
         * XXXMLG Perform a totally ugly hack here to pull
         * the rdatalist out of the private field in the rdataset,
         * and append this rdata to the rdatalist's linked list
         * of rdata.
         */
        rdatalist = (dns_rdatalist_t *)(rdataset->private1);

        ISC_LIST_APPEND(rdatalist->rdata, rdata, link);

        /*
         * If this is an OPT record, remember it.
         */
#if 0 /* until there is a dns_rdatatype_opt  XXXMLG */
        if (rdtype == dns_rdatatype_opt)
            msg->opt = rdata;
#endif
    }

    return (DNS_R_SUCCESS);
}

dns_result_t
dns_message_parse(dns_message_t *msg, isc_buffer_t *source)
{
    isc_region_t r;
    dns_decompress_t dctx;
    dns_result_t ret;
    isc_uint16_t tmpflags;

    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(source != NULL);
    REQUIRE(msg->from_to_wire == DNS_MESSAGE_INTENTPARSE);

    isc_buffer_remaining(source, &r);
    if (r.length < DNS_MESSAGE_HEADERLEN)
        return (DNS_R_UNEXPECTEDEND);

    msg->id = isc_buffer_getuint16(source);
    tmpflags = isc_buffer_getuint16(source);
    msg->opcode = ((tmpflags & DNS_MESSAGE_OPCODE_MASK)
               >> DNS_MESSAGE_OPCODE_SHIFT);
    msg->rcode = (tmpflags & DNS_MESSAGE_RCODE_MASK);
    msg->flags = (tmpflags & DNS_MESSAGE_FLAG_MASK);
    msg->counts[DNS_SECTION_QUESTION] = isc_buffer_getuint16(source);
    msg->counts[DNS_SECTION_ANSWER] = isc_buffer_getuint16(source);
    msg->counts[DNS_SECTION_AUTHORITY] = isc_buffer_getuint16(source);
    msg->counts[DNS_SECTION_ADDITIONAL] = isc_buffer_getuint16(source);

    /*
     * -1 means no EDNS.
     */
    dns_decompress_init(&dctx, -1, ISC_FALSE);

    if (dns_decompress_edns(&dctx) > 1 || !dns_decompress_strict(&dctx))
        dns_decompress_setmethods(&dctx, DNS_COMPRESS_GLOBAL);
    else
        dns_decompress_setmethods(&dctx, DNS_COMPRESS_GLOBAL14);


    ret = getquestions(source, msg, &dctx);
    if (ret != DNS_R_SUCCESS)
        return (ret);

    ret = getsection(source, msg, &dctx, DNS_SECTION_ANSWER);
    if (ret != DNS_R_SUCCESS)
        return (ret);

    ret = getsection(source, msg, &dctx, DNS_SECTION_AUTHORITY);
    if (ret != DNS_R_SUCCESS)
        return (ret);

    ret = getsection(source, msg, &dctx, DNS_SECTION_ADDITIONAL);
    if (ret != DNS_R_SUCCESS)
        return (ret);

    isc_buffer_remaining(source, &r);
    if (r.length != 0)
        return (DNS_R_FORMERR);

    /*
     * XXXMLG Need to check the tsig(s) here...
     */

    return (DNS_R_SUCCESS);
}

dns_result_t
dns_message_renderbegin(dns_message_t *msg, isc_buffer_t *buffer)
{
    isc_region_t r;
    dns_result_t result;

    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(buffer != NULL);
    REQUIRE(msg->buffer == NULL);
    REQUIRE(msg->from_to_wire == DNS_MESSAGE_INTENTRENDER);

    /*
     * Erase the contents of this buffer.
     */
    isc_buffer_clear(buffer);

    /*
     * Make certain there is enough for at least the header in this
     * buffer.
     */
    isc_buffer_available(buffer, &r);
    REQUIRE(r.length >= DNS_MESSAGE_HEADERLEN);

    result = dns_compress_init(&msg->cctx, -1, msg->mctx);
    if (result != DNS_R_SUCCESS)
        return (result);
    msg->need_cctx_cleanup = 1;

    /*
     * Reserve enough space for the header in this buffer.
     */
    isc_buffer_add(buffer, DNS_MESSAGE_HEADERLEN);

    msg->buffer = buffer;

    return (DNS_R_SUCCESS);
}

dns_result_t
dns_message_renderchangebuffer(dns_message_t *msg, isc_buffer_t *buffer)
{
    isc_region_t r, rn;

    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(buffer != NULL);
    REQUIRE(msg->buffer != NULL);

    /*
     * ensure that the new buffer is empty, and has enough space to
     * hold the current contents.
     */
    isc_buffer_clear(buffer);

    isc_buffer_available(buffer, &rn);
    isc_buffer_used(msg->buffer, &r);
    REQUIRE(rn.length > r.length);

    /*
     * Copy the contents from the old to the new buffer.
     */
    isc_buffer_add(buffer, r.length);
    memcpy(rn.base, r.base, r.length);

    msg->buffer = buffer;

    return (DNS_R_SUCCESS);
}

dns_result_t
dns_message_renderrelease(dns_message_t *msg, unsigned int space)
{
    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(msg->buffer != NULL);

    if (msg->reserved < space)
        return (DNS_R_NOSPACE);

    msg->reserved -= space;

    return (DNS_R_SUCCESS);
}

dns_result_t
dns_message_renderreserve(dns_message_t *msg, unsigned int space)
{
    isc_region_t r;

    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(msg->buffer != NULL);

    isc_buffer_available(msg->buffer, &r);
    if (r.length < (space + msg->reserved))
        return (DNS_R_NOSPACE);

    msg->reserved += space;

    return (DNS_R_SUCCESS);
}

dns_result_t
dns_message_rendersection(dns_message_t *msg, dns_section_t sectionid,
              unsigned int priority, unsigned int options)
{
    dns_namelist_t *section;
    dns_name_t *name, *next_name;
    dns_rdataset_t *rdataset, *next_rdataset;
    unsigned int count, total;
    dns_result_t result;
    isc_buffer_t st; /* for rollbacks */

    (void)priority; /* XXXMLG implement */
    (void)options;  /* XXXMLG implement */

    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(msg->buffer != NULL);
    REQUIRE(VALID_NAMED_SECTION(sectionid));

    section = &msg->sections[sectionid];

    name = ISC_LIST_HEAD(*section);
    if (name == NULL)
        return (DNS_R_SUCCESS);

    /*
     * Shrink the space in the buffer by the reserved amount.
     */
    msg->buffer->length -= msg->reserved;

    total = 0;
    while (name != NULL) {
        next_name = ISC_LIST_NEXT(name, link);

        rdataset = ISC_LIST_HEAD(name->list);
        while (rdataset != NULL) {
            next_rdataset = ISC_LIST_NEXT(rdataset, link);

            if (rdataset->attributes & DNS_RDATASETATTR_RENDERED) {
                rdataset = next_rdataset;
                continue;
            }

            st = *(msg->buffer);

            count = 0;
            result = dns_rdataset_towire(rdataset, name,
                             &msg->cctx,
                             msg->buffer, &count);

            total += count;

            /*
             * If out of space, record stats on what we rendered
             * so far, and return that status.
             *
             * XXXMLG Need to change this when
             * dns_rdataset_towire() can render partial
             * sets starting at some arbitary point in the set.
             * This will include setting a bit in the
             * rdataset to indicate that a partial rendering
             * was done, and some state saved somewhere
             * (probably in the message struct)
             * to indicate where to continue from.
             */
            if (result != DNS_R_SUCCESS) {
                dns_compress_rollback(&msg->cctx, st.used);
                *(msg->buffer) = st;  /* rollback */
                msg->buffer->length += msg->reserved;
                msg->counts[sectionid] += total;
                return (result);
            }

            rdataset->attributes |= DNS_RDATASETATTR_RENDERED;

            rdataset = next_rdataset;
        }

        name = next_name;
    }

    msg->buffer->length += msg->reserved;
    msg->counts[sectionid] += total;

    return (DNS_R_SUCCESS);
}

dns_result_t
dns_message_renderend(dns_message_t *msg)
{
    isc_buffer_t tmpbuf;
    isc_region_t r;
    isc_uint16_t tmp;

    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(msg->buffer != NULL);

    isc_buffer_used(msg->buffer, &r);
    isc_buffer_init(&tmpbuf, r.base, r.length, ISC_BUFFERTYPE_BINARY);

    isc_buffer_putuint16(&tmpbuf, msg->id);

    tmp = ((msg->opcode << DNS_MESSAGE_OPCODE_SHIFT)
           & DNS_MESSAGE_OPCODE_MASK);
    tmp |= (msg->rcode & DNS_MESSAGE_RCODE_MASK);  /* XXX edns? */
    tmp |= (msg->flags & DNS_MESSAGE_FLAG_MASK);

    isc_buffer_putuint16(&tmpbuf, tmp);
    isc_buffer_putuint16(&tmpbuf, msg->counts[DNS_SECTION_QUESTION]);
    isc_buffer_putuint16(&tmpbuf, msg->counts[DNS_SECTION_ANSWER]);
    isc_buffer_putuint16(&tmpbuf, msg->counts[DNS_SECTION_AUTHORITY]);
    tmp  = msg->counts[DNS_SECTION_ADDITIONAL]
        + msg->counts[DNS_SECTION_TSIG];
    isc_buffer_putuint16(&tmpbuf, tmp);

    msg->buffer = NULL;  /* forget about this buffer only on success XXX */

    dns_compress_invalidate(&msg->cctx);
    msg->need_cctx_cleanup = 0;

    return (DNS_R_SUCCESS);
}

dns_result_t
dns_message_firstname(dns_message_t *msg, dns_section_t section)
{
    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(VALID_NAMED_SECTION(section));

    msg->cursors[section] = ISC_LIST_HEAD(msg->sections[section]);

    if (msg->cursors[section] == NULL)
        return (DNS_R_NOMORE);

    return (DNS_R_SUCCESS);
}

dns_result_t
dns_message_nextname(dns_message_t *msg, dns_section_t section)
{
    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(VALID_NAMED_SECTION(section));
    REQUIRE(msg->cursors[section] != NULL);

    msg->cursors[section] = ISC_LIST_NEXT(msg->cursors[section], link);

    if (msg->cursors[section] == NULL)
        return (DNS_R_NOMORE);

    return (DNS_R_SUCCESS);
}

void
dns_message_currentname(dns_message_t *msg, dns_section_t section,
            dns_name_t **name)
{
    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(VALID_NAMED_SECTION(section));
    REQUIRE(name != NULL && *name == NULL);
    REQUIRE(msg->cursors[section] != NULL);

    *name = msg->cursors[section];
}

dns_result_t
dns_message_findname(dns_message_t *msg, dns_section_t section,
             dns_name_t *target, dns_rdatatype_t type,
             dns_name_t **name, dns_rdataset_t **rdataset)
{
    dns_name_t *foundname;
    dns_result_t result;

    /*
     * XXX These requirements are probably too intensive, especially
     * where things can be NULL, but as they are they ensure that if
     * something is NON-NULL, indicating that the caller expects it
     * to be filled in, that we can in fact fill it in.
     */
    REQUIRE(msg != NULL);
    REQUIRE(VALID_SECTION(section));
    REQUIRE(target != NULL);
    if (name != NULL)
        REQUIRE(*name == NULL);
    if (type == dns_rdatatype_any) {
        REQUIRE(rdataset == NULL);
    } else {
        if (rdataset != NULL)
            REQUIRE(*rdataset == NULL);
    }

    /*
     * Search through, looking for the name.
     */
    result = findname(&foundname, target, &msg->sections[section]);
    if (result == DNS_R_NOTFOUND)
        return (DNS_R_NXDOMAIN);
    else if (result != DNS_R_SUCCESS)
        return (result);

    if (name != NULL)
        *name = foundname;

    /*
     * And now look for the type.
     */
    if (type == dns_rdatatype_any)
        return (DNS_R_SUCCESS);

    result = findtype(rdataset, foundname, type);
    if (result == DNS_R_NOTFOUND)
        return (DNS_R_NXRDATASET);

    return (result);
}

void
dns_message_movename(dns_message_t *msg, dns_name_t *name,
             dns_section_t fromsection,
             dns_section_t tosection)
{
    REQUIRE(msg != NULL);
    REQUIRE(msg->from_to_wire == DNS_MESSAGE_INTENTRENDER);
    REQUIRE(name != NULL);
    REQUIRE(VALID_NAMED_SECTION(fromsection));
    REQUIRE(VALID_NAMED_SECTION(tosection));

    /*
     * Unlink the name from the old section
     */
    ISC_LIST_UNLINK(msg->sections[fromsection], name, link);
    ISC_LIST_APPEND(msg->sections[tosection], name, link);
}

void
dns_message_addname(dns_message_t *msg, dns_name_t *name,
            dns_section_t section)
{
    REQUIRE(msg != NULL);
    REQUIRE(msg->from_to_wire == DNS_MESSAGE_INTENTRENDER);
    REQUIRE(name != NULL);
    REQUIRE(VALID_NAMED_SECTION(section));

    ISC_LIST_APPEND(msg->sections[section], name, link);
}

dns_result_t
dns_message_gettempname(dns_message_t *msg, dns_name_t **item)
{
    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(item != NULL && *item == NULL);

    *item = newname(msg);
    if (*item == NULL)
        return (DNS_R_NOMEMORY);

    return (DNS_R_SUCCESS);
}

dns_result_t
dns_message_gettemprdata(dns_message_t *msg, dns_rdata_t **item)
{
    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(item != NULL && *item == NULL);

    *item = newrdata(msg);
    if (*item == NULL)
        return (DNS_R_NOMEMORY);

    return (DNS_R_SUCCESS);
}

dns_result_t
dns_message_gettemprdataset(dns_message_t *msg, dns_rdataset_t **item)
{
    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(item != NULL && *item == NULL);

    *item = newrdataset(msg);
    if (*item == NULL)
        return (DNS_R_NOMEMORY);

    return (DNS_R_SUCCESS);
}

dns_result_t
dns_message_gettemprdatalist(dns_message_t *msg, dns_rdatalist_t **item)
{
    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(item != NULL && *item == NULL);

    *item = newrdatalist(msg);
    if (*item == NULL)
        return (DNS_R_NOMEMORY);

    return (DNS_R_SUCCESS);
}

void
dns_message_puttempname(dns_message_t *msg, dns_name_t **item)
{
    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(item != NULL && *item != NULL);

    releasename(msg, *item);
    *item = NULL;
}

void
dns_message_puttemprdata(dns_message_t *msg, dns_rdata_t **item)
{
    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(item != NULL && *item != NULL);

    releaserdata(msg, *item);
    *item = NULL;
}

void
dns_message_puttemprdataset(dns_message_t *msg, dns_rdataset_t **item)
{
    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(item != NULL && *item != NULL);

    releaserdataset(msg, *item);
    *item = NULL;
}

void
dns_message_puttemprdatalist(dns_message_t *msg, dns_rdatalist_t **item)
{
    REQUIRE(VALID_MESSAGE(msg));
    REQUIRE(item != NULL && *item != NULL);

    releaserdatalist(msg, *item);
    *item = NULL;
}

dns_result_t
dns_message_peekheader(isc_buffer_t *source, dns_messageid_t *idp,
               unsigned int *flagsp)
{
    isc_region_t r;
    isc_buffer_t buffer;
    dns_messageid_t id;
    unsigned int flags;

    REQUIRE(source != NULL);

    buffer = *source;

    isc_buffer_remaining(&buffer, &r);
    if (r.length < DNS_MESSAGE_HEADERLEN)
        return (DNS_R_UNEXPECTEDEND);

    id = isc_buffer_getuint16(source);
    flags = isc_buffer_getuint16(source);
    flags &= DNS_MESSAGE_FLAG_MASK;

    if (flagsp != NULL)
        *flagsp = flags;
    if (idp != NULL)
        *idp = id;

    return (DNS_R_SUCCESS);
}