bin/named/xfrout.c

	xfrout.c revision 0c32f6b044792f3dc78b6861933bc51fdecba1c5
/*
 * 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.
 */

 /* $Id: xfrout.c,v 1.36 2000/01/12 18:01:11 gson Exp $ */

#include <config.h>

#include <string.h>
#include <stdlib.h>
#include <unistd.h>

#include <sys/types.h>

#include <isc/assertions.h>
#include <isc/error.h>
#include <isc/mem.h>
#include <isc/result.h>
#include <isc/timer.h>

#include <dns/acl.h>
#include <dns/db.h>
#include <dns/dbiterator.h>
#include <dns/fixedname.h>
#include <dns/journal.h>
#include <dns/message.h>
#include <dns/name.h>
#include <dns/rdata.h>
#include <dns/rdatalist.h>
#include <dns/rdataset.h>
#include <dns/rdatasetiter.h>
#include <dns/rdatastruct.h>
#include <dns/result.h>
#include <dns/types.h>
#include <dns/view.h>
#include <dns/zone.h>
#include <dns/zt.h>

#include <named/client.h>
#include <named/globals.h>
#include <named/log.h>
#include <named/server.h>
#include <named/xfrout.h>

/*
 * Outgoing AXFR and IXFR.
 */

/*
 * TODO:
 *  - IXFR over UDP
 */

#define XFROUT_COMMON_LOGARGS \
    ns_g_lctx, NS_LOGCATEGORY_XFER_OUT, NS_LOGMODULE_XFER_OUT

#define XFROUT_PROTOCOL_LOGARGS \
    XFROUT_COMMON_LOGARGS, ISC_LOG_INFO

#define XFROUT_DEBUG_LOGARGS(n) \
    XFROUT_COMMON_LOGARGS, ISC_LOG_DEBUG(n)

/*
 * Fail unconditionally and log as a client error.
 */
#define FAILC(code, msg) \
    do {                            \
        result = (code);                \
        isc_log_write(XFROUT_PROTOCOL_LOGARGS,      \
                  "bad zone transfer request: %s (%s)", \
                      msg, isc_result_totext(code));    \
        goto failure;                   \
    } while (0)

#define CHECK(op) \
        do { result = (op);                     \
        if (result != DNS_R_SUCCESS) goto failure;  \
    } while (0)

/**************************************************************************/
/*
 * A db_rr_iterator_t is an iterator that iterates over an entire database,
 * returning one RR at a time, in some arbitrary order.
 */

typedef struct db_rr_iterator db_rr_iterator_t;

struct db_rr_iterator {
    isc_result_t        result;
    dns_db_t        *db;
        dns_dbiterator_t    *dbit;
    dns_dbversion_t     *ver;
    isc_stdtime_t       now;
    dns_dbnode_t        *node;
    dns_fixedname_t     fixedname;
        dns_rdatasetiter_t  *rdatasetit;
    dns_rdataset_t      rdataset;
    dns_rdata_t     rdata;
};

isc_result_t db_rr_iterator_init(db_rr_iterator_t *it, dns_db_t *db,
                 dns_dbversion_t *ver, isc_stdtime_t now);

isc_result_t db_rr_iterator_first(db_rr_iterator_t *it);

isc_result_t db_rr_iterator_next(db_rr_iterator_t *it);

void db_rr_iterator_current(db_rr_iterator_t *it, dns_name_t **name,
                isc_uint32_t *ttl, dns_rdata_t **rdata);

void db_rr_iterator_destroy(db_rr_iterator_t *it);

isc_result_t
db_rr_iterator_init(db_rr_iterator_t *it, dns_db_t *db, dns_dbversion_t *ver,
            isc_stdtime_t now)
{
    isc_result_t result;
    it->db = db;
    it->dbit = NULL;
    it->ver = ver;
    it->now = now;
    it->node = NULL;
    result = dns_db_createiterator(it->db, ISC_FALSE, &it->dbit);
    if (result != DNS_R_SUCCESS)
        return (result);
    it->rdatasetit = NULL;
    dns_rdataset_init(&it->rdataset);
    dns_fixedname_init(&it->fixedname);
    INSIST(! dns_rdataset_isassociated(&it->rdataset));
    it->result = DNS_R_SUCCESS;
    return (it->result);
}

isc_result_t
db_rr_iterator_first(db_rr_iterator_t *it) {
    it->result = dns_dbiterator_first(it->dbit);
    if (it->result != DNS_R_SUCCESS)
        return (it->result);
    it->result = dns_dbiterator_current(it->dbit, &it->node,
                    dns_fixedname_name(&it->fixedname));
    if (it->result != DNS_R_SUCCESS)
        return (it->result);

    it->result = dns_db_allrdatasets(it->db, it->node,
                     it->ver, it->now,
                     &it->rdatasetit);
    if (it->result != DNS_R_SUCCESS)
        return (it->result);

    it->result = dns_rdatasetiter_first(it->rdatasetit);
    if (it->result != DNS_R_SUCCESS)
        return (it->result);

    dns_rdatasetiter_current(it->rdatasetit, &it->rdataset);

    it->result = dns_rdataset_first(&it->rdataset);
    return (it->result);
}


isc_result_t
db_rr_iterator_next(db_rr_iterator_t *it) {
    if (it->result != DNS_R_SUCCESS)
        return (it->result);

    INSIST(it->dbit != NULL);
    INSIST(it->node != NULL);
    INSIST(it->rdatasetit != NULL);

    it->result = dns_rdataset_next(&it->rdataset);
    if (it->result == DNS_R_NOMORE) {
        dns_rdataset_disassociate(&it->rdataset);
        it->result = dns_rdatasetiter_next(it->rdatasetit);
        while (it->result == DNS_R_NOMORE) {
            dns_rdatasetiter_destroy(&it->rdatasetit);
            dns_db_detachnode(it->db, &it->node);
            it->result = dns_dbiterator_next(it->dbit);
            if (it->result == DNS_R_NOMORE) {
                /* We are at the end of the entire database. */
                return (it->result);
            }
            if (it->result != DNS_R_SUCCESS)
                return (it->result);
            it->result = dns_dbiterator_current(it->dbit,
                    &it->node,
                    dns_fixedname_name(&it->fixedname));
            if (it->result != DNS_R_SUCCESS)
                return (it->result);
            it->result = dns_db_allrdatasets(it->db, it->node,
                     it->ver, it->now,
                     &it->rdatasetit);
            if (it->result != DNS_R_SUCCESS)
                return (it->result);
            it->result = dns_rdatasetiter_first(it->rdatasetit);
        }
        if (it->result != DNS_R_SUCCESS)
            return (it->result);
        dns_rdatasetiter_current(it->rdatasetit, &it->rdataset);
    }
    return (it->result);
}

void
db_rr_iterator_destroy(db_rr_iterator_t *it) {
    if (dns_rdataset_isassociated(&it->rdataset))
        dns_rdataset_disassociate(&it->rdataset);
    if (it->rdatasetit != NULL)
        dns_rdatasetiter_destroy(&it->rdatasetit);
    if (it->node != NULL)
        dns_db_detachnode(it->db, &it->node);
    dns_dbiterator_destroy(&it->dbit);
}

void
db_rr_iterator_current(db_rr_iterator_t *it, dns_name_t **name,
              isc_uint32_t *ttl, dns_rdata_t **rdata)
{
    REQUIRE(name != NULL && *name == NULL);
    REQUIRE(it->result == DNS_R_SUCCESS);
    *name = dns_fixedname_name(&it->fixedname);
    *ttl = it->rdataset.ttl;
    dns_rdataset_current(&it->rdataset, &it->rdata);
    *rdata = &it->rdata;
}

/**************************************************************************/

/* Log an RR (for debugging) */

static void
log_rr(dns_name_t *name, dns_rdata_t *rdata, isc_uint32_t ttl) {
    isc_result_t result;

    isc_buffer_t buf;
    char mem[2000];
    isc_region_t r;
    dns_rdatalist_t rdl;
    dns_rdataset_t rds;

    rdl.type = rdata->type;
    rdl.rdclass = rdata->rdclass;
    rdl.ttl = ttl;
    ISC_LIST_INIT(rdl.rdata);
    ISC_LINK_INIT(&rdl, link);
    dns_rdataset_init(&rds);
    ISC_LIST_APPEND(rdl.rdata, rdata, link);
    RUNTIME_CHECK(dns_rdatalist_tordataset(&rdl, &rds) == DNS_R_SUCCESS);

    isc_buffer_init(&buf, mem, sizeof(mem), ISC_BUFFERTYPE_TEXT);
    result = dns_rdataset_totext(&rds, name,
                     ISC_FALSE, ISC_FALSE, &buf);

    /* Get rid of final newline. */
    INSIST(buf.used >= 1 && ((char *) buf.base)[buf.used-1] == '\n');
    buf.used--;

    if (result == DNS_R_SUCCESS) {
        isc_buffer_used(&buf, &r);
        isc_log_write(XFROUT_DEBUG_LOGARGS(8),
                  "%.*s", (int) r.length, (char *) r.base);
    } else {
        isc_log_write(XFROUT_DEBUG_LOGARGS(8),
                  "<RR too large to print>");
    }
}

/**************************************************************************/
/*
 * An 'rrstream_t' is a polymorphic iterator that returns
 * a stream of resource records.  There are multiple implementations,
 * e.g. for generating AXFR and IXFR records streams.
 */

typedef struct rrstream_methods rrstream_methods_t;

typedef struct rrstream {
    isc_mem_t       *mctx;
    rrstream_methods_t  *methods;
} rrstream_t;

struct rrstream_methods {
    isc_result_t        (*first)(rrstream_t *);
    isc_result_t        (*next)(rrstream_t *);
    void            (*current)(rrstream_t *,
                       dns_name_t **,
                       isc_uint32_t *,
                       dns_rdata_t **);
    void            (*destroy)(rrstream_t **);
};

/**************************************************************************/
/*
 * An 'ixfr_rrstream_t' is an 'rrstream_t' that returns
 * an IXFR-like RR stream from a journal file.
 *
 * The SOA at the beginning of each sequence of additions
 * or deletions are included in the stream, but the extra
 * SOAs at the beginning and end of the entire transfer are
 * not included.
 */

typedef struct ixfr_rrstream {
    rrstream_t      common;
    dns_journal_t       *journal;
} ixfr_rrstream_t;

/* Forward declarations. */
static void ixfr_rrstream_destroy(rrstream_t **sp);
static rrstream_methods_t ixfr_rrstream_methods;

/*
 * Returns: anything dns_journal_open() or dns_journal_iter_init()
 * may return.
 */

static isc_result_t
ixfr_rrstream_create(isc_mem_t *mctx,
             const char *journal_filename,
             isc_uint32_t begin_serial,
             isc_uint32_t end_serial,
             rrstream_t **sp)
{
    ixfr_rrstream_t *s;
    isc_result_t result;

    INSIST(sp != NULL && *sp == NULL);

    s = isc_mem_get(mctx, sizeof(*s));
    if (s == NULL)
        return (DNS_R_NOMEMORY);
    s->common.mctx = mctx;
    s->common.methods = &ixfr_rrstream_methods;
    s->journal = NULL;

    CHECK(dns_journal_open(mctx, journal_filename,
                   ISC_FALSE, &s->journal));
    CHECK(dns_journal_iter_init(s->journal, begin_serial, end_serial));

    *sp = (rrstream_t *) s;
    return (DNS_R_SUCCESS);

 failure:
    ixfr_rrstream_destroy((rrstream_t **) &s);
    return (result);
}

static isc_result_t
ixfr_rrstream_first(rrstream_t *rs)
{
    ixfr_rrstream_t *s = (ixfr_rrstream_t *) rs;
    return (dns_journal_first_rr(s->journal));
}

static isc_result_t
ixfr_rrstream_next(rrstream_t *rs)
{
    ixfr_rrstream_t *s = (ixfr_rrstream_t *) rs;
    return (dns_journal_next_rr(s->journal));
}


static void
ixfr_rrstream_current(rrstream_t *rs,
               dns_name_t **name, isc_uint32_t *ttl,
               dns_rdata_t **rdata)
{
    ixfr_rrstream_t *s = (ixfr_rrstream_t *) rs;
    dns_journal_current_rr(s->journal, name, ttl, rdata);
}

static void
ixfr_rrstream_destroy(rrstream_t **rsp) {
    ixfr_rrstream_t *s = (ixfr_rrstream_t *) *rsp;
    if (s->journal != 0)
        dns_journal_destroy(&s->journal);
    isc_mem_put(s->common.mctx, s, sizeof(*s));
}

static rrstream_methods_t ixfr_rrstream_methods =
{
    ixfr_rrstream_first,
    ixfr_rrstream_next,
    ixfr_rrstream_current,
    ixfr_rrstream_destroy
};

/**************************************************************************/
/*
 * An 'ixfr_rrstream_t' is an 'rrstream_t' that returns
 * an AXFR-like RR stream from a database.
 *
 * The SOAs at the beginning and end of the transfer are
 * not included in the stream.
 */

typedef struct axfr_rrstream {
    rrstream_t      common;
    int             state;
    db_rr_iterator_t        it;
    isc_boolean_t       it_valid;
} axfr_rrstream_t;

/* Forward declarations. */
static void axfr_rrstream_destroy(rrstream_t **rsp);
static rrstream_methods_t axfr_rrstream_methods;

static isc_result_t
axfr_rrstream_create(isc_mem_t *mctx,
              dns_db_t *db,
              dns_dbversion_t *ver,
              rrstream_t **sp)
{
    axfr_rrstream_t *s;
    isc_result_t result;

    INSIST(sp != NULL && *sp == NULL);

    s = isc_mem_get(mctx, sizeof(*s));
    if (s == NULL)
        return (DNS_R_NOMEMORY);
    s->common.mctx = mctx;
    s->common.methods = &axfr_rrstream_methods;
    s->it_valid = ISC_FALSE;

    CHECK(db_rr_iterator_init(&s->it, db, ver, 0));
    s->it_valid = ISC_TRUE;

    *sp = (rrstream_t *) s;
    return (DNS_R_SUCCESS);

 failure:
    axfr_rrstream_destroy((rrstream_t **) &s);
    return (result);
}

static isc_result_t
axfr_rrstream_first(rrstream_t *rs)
{
    axfr_rrstream_t *s = (axfr_rrstream_t *) rs;
    isc_result_t result;
    result = db_rr_iterator_first(&s->it);
    /* Skip SOA records. */
    for (;;) {
        dns_name_t *name_dummy = NULL;
        isc_uint32_t ttl_dummy;
        dns_rdata_t *rdata = NULL;
        db_rr_iterator_current(&s->it, &name_dummy,
                      &ttl_dummy, &rdata);
        if (rdata->type != dns_rdatatype_soa)
            break;
        result = db_rr_iterator_next(&s->it);
        if (result != DNS_R_SUCCESS)
            break;
    }
    return (result);
}

static isc_result_t
axfr_rrstream_next(rrstream_t *rs)
{
    axfr_rrstream_t *s = (axfr_rrstream_t *) rs;
    isc_result_t result;

    /* Skip SOA records. */
    for (;;) {
        dns_name_t *name_dummy = NULL;
        isc_uint32_t ttl_dummy;
        dns_rdata_t *rdata = NULL;
        result = db_rr_iterator_next(&s->it);
        if (result != DNS_R_SUCCESS)
            break;
        db_rr_iterator_current(&s->it, &name_dummy,
                      &ttl_dummy, &rdata);
        if (rdata->type != dns_rdatatype_soa)
            break;
    }
    return (result);
}

static void
axfr_rrstream_current(rrstream_t *rs,
               dns_name_t **name, isc_uint32_t *ttl,
               dns_rdata_t **rdata)
{
    axfr_rrstream_t *s = (axfr_rrstream_t *) rs;
    db_rr_iterator_current(&s->it, name, ttl, rdata);
}

static void
axfr_rrstream_destroy(rrstream_t **rsp) {
    axfr_rrstream_t *s = (axfr_rrstream_t *) *rsp;
    if (s->it_valid)
        db_rr_iterator_destroy(&s->it);
    isc_mem_put(s->common.mctx, s, sizeof(*s));
}

static rrstream_methods_t axfr_rrstream_methods =
{
    axfr_rrstream_first,
    axfr_rrstream_next,
    axfr_rrstream_current,
    axfr_rrstream_destroy
};

/**************************************************************************/
/*
 * An 'soa_rrstream_t' is a degenerate 'rrstream_t' that returns
 * a single SOA record.
 */

typedef struct soa_rrstream {
    rrstream_t      common;
    dns_difftuple_t     *soa_tuple;
} soa_rrstream_t;

/* Forward declarations. */
static void soa_rrstream_destroy(rrstream_t **rsp);
static rrstream_methods_t soa_rrstream_methods;

static isc_result_t
soa_rrstream_create(isc_mem_t *mctx,
            dns_db_t *db,
            dns_dbversion_t *ver,
            rrstream_t **sp)
{
    soa_rrstream_t *s;
    isc_result_t result;

    INSIST(sp != NULL && *sp == NULL);

    s = isc_mem_get(mctx, sizeof(*s));
    if (s == NULL)
        return (DNS_R_NOMEMORY);
    s->common.mctx = mctx;
    s->common.methods = &soa_rrstream_methods;
    s->soa_tuple = NULL;

    CHECK(dns_db_createsoatuple(db, ver, mctx, DNS_DIFFOP_EXISTS,
                    &s->soa_tuple));

    *sp = (rrstream_t *) s;
    return (DNS_R_SUCCESS);

 failure:
    soa_rrstream_destroy((rrstream_t **) &s);
    return (result);
}

static isc_result_t
soa_rrstream_first(rrstream_t *rs) {
    rs = rs; /* Unused */
    return (DNS_R_SUCCESS);
}

static isc_result_t
soa_rrstream_next(rrstream_t *rs) {
    rs = rs; /* Unused */
    return (DNS_R_NOMORE);
}

static void
soa_rrstream_current(rrstream_t *rs,
             dns_name_t **name, isc_uint32_t *ttl,
             dns_rdata_t **rdata)
{
    soa_rrstream_t *s = (soa_rrstream_t *) rs;
    *name = &s->soa_tuple->name;
    *ttl = s->soa_tuple->ttl;
    *rdata = &s->soa_tuple->rdata;
}

static void
soa_rrstream_destroy(rrstream_t **rsp) {
    soa_rrstream_t *s = (soa_rrstream_t *) *rsp;
    if (s->soa_tuple != NULL)
        dns_difftuple_free(&s->soa_tuple);
    isc_mem_put(s->common.mctx, s, sizeof(*s));
}

static rrstream_methods_t soa_rrstream_methods =
{
    soa_rrstream_first,
    soa_rrstream_next,
    soa_rrstream_current,
    soa_rrstream_destroy
};

/**************************************************************************/
/*
 * A 'compound_rrstream_t' objects owns a soa_rrstream
 * and another rrstream, the "data stream".  It returns
 * a concatenated stream consisting of the soa_rrstream, then
 * the data stream, then the soa_rrstream again.
 *
 * The component streams are owned by the compound_rrstream_t
 * and are destroyed with it.
 */

typedef struct compound_rrstream {
    rrstream_t      common;
    rrstream_t      *components[3];
    int         state;
    isc_result_t        result;
} compound_rrstream_t;

/* Forward declarations. */
static void compound_rrstream_destroy(rrstream_t **rsp);
static isc_result_t compound_rrstream_next(rrstream_t *rs);
static rrstream_methods_t compound_rrstream_methods;

/*
 * Requires:
 *  soa_stream != NULL && *soa_stream != NULL
 *  data_stream != NULL && *data_stream != NULL
 *  sp != NULL && *sp == NULL
 *
 * Ensures:
 *  *soa_stream == NULL
 *  *data_stream == NULL
 *  *sp points to a valid compound_rrstream_t
 *  The soa and data streams will be destroyed
 *  when the compound_rrstream_t is destroyed.
 */
static isc_result_t
compound_rrstream_create(isc_mem_t *mctx,
             rrstream_t **soa_stream,
             rrstream_t **data_stream,
             rrstream_t **sp)
{
    compound_rrstream_t *s;

    INSIST(sp != NULL && *sp == NULL);

    s = isc_mem_get(mctx, sizeof(*s));
    if (s == NULL)
        return (DNS_R_NOMEMORY);
    s->common.mctx = mctx;
    s->common.methods = &compound_rrstream_methods;
    s->components[0] = *soa_stream;
    s->components[1] = *data_stream;
    s->components[2] = *soa_stream;
    s->state = -1;
    s->result = ISC_R_FAILURE;

    *soa_stream = NULL;
    *data_stream = NULL;
    *sp = (rrstream_t *) s;
    return (DNS_R_SUCCESS);
}

static isc_result_t
compound_rrstream_first(rrstream_t *rs) {
    compound_rrstream_t *s = (compound_rrstream_t *) rs;
    s->state = 0;
    do {
        rrstream_t *curstream = s->components[s->state];
        s->result = curstream->methods->first(curstream);
    } while (s->result == DNS_R_NOMORE && s->state < 2) ;
    return (s->result);
}

static isc_result_t
compound_rrstream_next(rrstream_t *rs) {
    compound_rrstream_t *s = (compound_rrstream_t *) rs;
    rrstream_t *curstream = s->components[s->state];
    s->result = curstream->methods->next(curstream);
    while (s->result == DNS_R_NOMORE) {
        if (s->state == 2)
            return (DNS_R_NOMORE);
        s->state++;
        curstream = s->components[s->state];
        s->result = curstream->methods->first(curstream);
    }
    return (s->result);
}

static void
compound_rrstream_current(rrstream_t *rs,
             dns_name_t **name, isc_uint32_t *ttl,
             dns_rdata_t **rdata)
{
    compound_rrstream_t *s = (compound_rrstream_t *) rs;
    rrstream_t *curstream;
    INSIST(0 <= s->state && s->state < 3);
    INSIST(s->result == DNS_R_SUCCESS);
    curstream = s->components[s->state];
    curstream->methods->current(curstream, name, ttl, rdata);
}

static void
compound_rrstream_destroy(rrstream_t **rsp) {
    compound_rrstream_t *s = (compound_rrstream_t *) *rsp;
    s->components[0]->methods->destroy(&s->components[0]);
    s->components[1]->methods->destroy(&s->components[1]);
    s->components[2] = NULL; /* Copy of components[0]. */
    isc_mem_put(s->common.mctx, s, sizeof(*s));
}

static rrstream_methods_t compound_rrstream_methods =
{
    compound_rrstream_first,
    compound_rrstream_next,
    compound_rrstream_current,
    compound_rrstream_destroy
};

/**************************************************************************/
/*
 * An 'xfrout_ctx_t' contains the state of an outgoing AXFR or IXFR
 * in progress.
 */

typedef struct {
    isc_mem_t       *mctx;
    ns_client_t     *client;
    unsigned int        id;     /* ID of request */
    dns_name_t      *qname;     /* Question name of request */
    dns_rdatatype_t     qtype;      /* dns_rdatatype_{a,i}xfr */
    dns_db_t        *db;
    dns_dbversion_t     *ver;
    rrstream_t      *stream;    /* The XFR RR stream */
    isc_boolean_t       end_of_stream;  /* EOS has been reached */
    isc_buffer_t        buf;        /* Buffer for message owner
                           names and rdatas */
    isc_buffer_t        txlenbuf;   /* Transmit length buffer */
    isc_buffer_t        txbuf;      /* Transmit message buffer */
    void            *txmem;
    unsigned int        txmemlen;
    unsigned int        nmsg;       /* Number of messages sent */
    dns_tsigkey_t       *tsigkey;   /* Key used to create TSIG */
    dns_rdata_any_tsig_t    *lasttsig;  /* the last TSIG */
    isc_timer_t     *timer;
    int         sends;      /* Send in progress */
    isc_boolean_t       shuttingdown;
} xfrout_ctx_t;

static isc_result_t
xfrout_ctx_create(isc_mem_t *mctx, ns_client_t *client,
          unsigned int id, dns_name_t *qname, dns_rdatatype_t qtype,
          dns_db_t *db, dns_dbversion_t *ver,
          rrstream_t *stream, dns_tsigkey_t *tsigkey,
          dns_rdata_any_tsig_t *lasttsig,
          unsigned int maxtime,
          unsigned int idletime,
          xfrout_ctx_t **xfrp);

static void sendstream(xfrout_ctx_t *xfr);

static void xfrout_senddone(isc_task_t *task, isc_event_t *event);
static void xfrout_timeout(isc_task_t *task, isc_event_t *event);
static void xfrout_fail(xfrout_ctx_t *xfr, isc_result_t result, char *msg);
static void xfrout_maybe_destroy(xfrout_ctx_t *xfr);
static void xfrout_ctx_destroy(xfrout_ctx_t **xfrp);
static void xfrout_client_shutdown(void *arg);

/**************************************************************************/

void
ns_xfr_start(ns_client_t *client, dns_rdatatype_t reqtype)
{
    isc_result_t result;
    dns_name_t *question_name;
    dns_rdataset_t *question_rdataset;
    dns_zone_t *zone = NULL;
    dns_db_t *db = NULL;
    dns_dbversion_t *ver = NULL;
    dns_rdataclass_t question_class;
    rrstream_t *soa_stream = NULL;
    rrstream_t *data_stream = NULL;
    rrstream_t *stream = NULL;
    dns_difftuple_t *current_soa_tuple = NULL;
    dns_name_t *soa_name;
    dns_rdataset_t *soa_rdataset;
    dns_rdata_t soa_rdata;
    isc_boolean_t have_soa = ISC_FALSE;
    char *mnemonic = NULL;
    isc_mem_t *mctx = client->mctx;
    dns_message_t *request = client->message;
    xfrout_ctx_t *xfr = NULL;

    switch (reqtype) {
    case dns_rdatatype_axfr:
        mnemonic = "AXFR";
        break;
    case dns_rdatatype_ixfr:
        mnemonic = "IXFR";
        break;
    default:
        INSIST(0);
        break;
    }

    isc_log_write(XFROUT_DEBUG_LOGARGS(6), "got %s request", mnemonic);

    /*
     * Apply quotas.
     */
    result = ns_client_getquota(client, &ns_g_server->xfroutquota);
    if (result != DNS_R_SUCCESS) {
        isc_log_write(XFROUT_COMMON_LOGARGS, ISC_LOG_WARNING,
                  "zone transfer request denied: %s",
                  isc_result_totext(result));
        goto failure;
    }

    /*
     * Interpret the question section.
     */
    result = dns_message_firstname(request, DNS_SECTION_QUESTION);
    INSIST(result == DNS_R_SUCCESS);

    /*
     * The question section must contain exactly one question, and
     * it must be for AXFR/IXFR as appropriate.
     */
    question_name = NULL;
    dns_message_currentname(request, DNS_SECTION_QUESTION, &question_name);
    question_rdataset = ISC_LIST_HEAD(question_name->list);
    question_class = question_rdataset->rdclass;
    INSIST(question_rdataset->type == reqtype);
    if (ISC_LIST_NEXT(question_rdataset, link) != NULL)
        FAILC(DNS_R_FORMERR,
              "multiple questions in AXFR/IXFR request");
    result = dns_message_nextname(request, DNS_SECTION_QUESTION);
    if (result != DNS_R_NOMORE)
        FAILC(DNS_R_FORMERR,
              "multiple questions in AXFR/IXFR request");

    result = dns_zt_find(client->view->zonetable, question_name, NULL, &zone);
    if (result != DNS_R_SUCCESS)
        FAILC(DNS_R_NOTAUTH,
              "AXFR/IXFR requested for non-authoritative zone");
    switch(dns_zone_gettype(zone)) {
    case dns_zone_master:
    case dns_zone_slave:
        break;  /* Master and slave zones are OK for transfer. */
    default:
        FAILC(DNS_R_NOTAUTH,
              "AXFR/IXFR requested for non-authoritative zone");
    }
    CHECK(dns_zone_getdb(zone, &db));
    dns_db_currentversion(db, &ver);

    isc_log_write(XFROUT_DEBUG_LOGARGS(6), "%s question section OK",
              mnemonic);

    /*
     * Check the authority section.  Look for a SOA record with
     * the same name and class as the question.
     */
    for (result = dns_message_firstname(request, DNS_SECTION_AUTHORITY);
         result == DNS_R_SUCCESS;
         result = dns_message_nextname(request, DNS_SECTION_AUTHORITY))
    {
        soa_name = NULL;
        dns_message_currentname(request, DNS_SECTION_AUTHORITY,
                    &soa_name);

        /* Ignore data whose owner name is not the zone apex. */
        if (! dns_name_equal(soa_name, question_name))
            continue;

        for (soa_rdataset = ISC_LIST_HEAD(soa_name->list);
             soa_rdataset != NULL;
             soa_rdataset = ISC_LIST_NEXT(soa_rdataset, link))
        {
            /* Ignore non-SOA data. */
            if (soa_rdataset->type != dns_rdatatype_soa)
                continue;
            if (soa_rdataset->rdclass != question_class)
                continue;

            CHECK(dns_rdataset_first(soa_rdataset));
            dns_rdataset_current(soa_rdataset, &soa_rdata);
            result = dns_rdataset_next(soa_rdataset);
            if (result == DNS_R_SUCCESS)
                FAILC(DNS_R_FORMERR,
                      "IXFR authority section "
                      "has multiple SOAs");
            have_soa = ISC_TRUE;
            goto got_soa;
        }
    }
 got_soa:
    if (result != DNS_R_NOMORE)
        CHECK(result);

    isc_log_write(XFROUT_DEBUG_LOGARGS(6), "%s authority section OK",
              mnemonic);

    /* Decide whether to allow this transfer. */
    CHECK(dns_acl_checkrequest(client->signer,
                   ns_client_getsockaddr(client),
                   "zone transfer",
                   dns_zone_getxfracl(zone),
                   ns_g_server->transferacl,
                   ISC_TRUE));

    /* AXFR over UDP is not possible. */
    if (reqtype == dns_rdatatype_axfr &&
        (client->attributes & NS_CLIENTATTR_TCP) == 0) {
        FAILC(DNS_R_FORMERR, "attempted AXFR over UDP");
    }

    /* Get a dynamically allocated copy of the current SOA. */
    CHECK(dns_db_createsoatuple(db, ver, mctx, DNS_DIFFOP_EXISTS,
                    &current_soa_tuple));

    if (reqtype == dns_rdatatype_ixfr) {
        isc_uint32_t begin_serial, current_serial;

        if (! have_soa)
            FAILC(DNS_R_FORMERR,
                  "IXFR request missing SOA");

        begin_serial = dns_soa_getserial(&soa_rdata);
        current_serial = dns_soa_getserial(&current_soa_tuple->rdata);

        /*
         * RFC1995 says "If an IXFR query with the same or
         * newer version number than that of the server
         * is received, it is replied to with a single SOA
         * record of the server's current version, just as
         * in AXFR".  The claim about AXFR is incorrect,
         * but other than that, we do as the RFC says.
         *
         * Sending a single SOA record is also how we refuse
         * IXFR over UDP (currently, we always do).
         */
        if (DNS_SERIAL_GE(begin_serial, current_serial) ||
            (client->attributes & NS_CLIENTATTR_TCP) == 0)
            {
            CHECK(soa_rrstream_create(mctx, db, ver, &stream));
            goto have_stream;
        }
        result = ixfr_rrstream_create(mctx,
                          dns_zone_getjournal(zone),
                          begin_serial,
                          current_serial,
                          &data_stream);
        if (result == ISC_R_NOTFOUND ||
            result == DNS_R_RANGE) {
            isc_log_write(XFROUT_DEBUG_LOGARGS(4),
                      "IXFR version not in journal, "
                      "falling back to AXFR");
            goto axfr_fallback;
        }
        CHECK(result);
    } else {
    axfr_fallback:
        CHECK(axfr_rrstream_create(mctx, db, ver,
                       &data_stream));
    }

    /* Bracket the the data stream with SOAs. */
    CHECK(soa_rrstream_create(mctx, db, ver, &soa_stream));
    CHECK(compound_rrstream_create(mctx, &soa_stream, &data_stream,
                       &stream));
    soa_stream = NULL;
    data_stream = NULL;

 have_stream:
    /*
     * Create the xfrout context object.  This transfers the ownership
     * of "stream", "db", and "ver" to the xfrout context object.
     */
    CHECK(xfrout_ctx_create(mctx, client, request->id, question_name,
                reqtype, db, ver, stream, request->tsigkey,
                request->tsig,
                dns_zone_getmaxxfrout(zone),
                dns_zone_getidleout(zone),
                &xfr));
    stream = NULL;
    db = NULL;
    ver = NULL;

    CHECK(xfr->stream->methods->first(xfr->stream));

    /*
     * Hand the context over to sendstream().  Set xfr to NULL;
     * sendstream() is responsible for either passing the
     * context on to a later event handler or destroying it.
     */
    sendstream(xfr);
    xfr = NULL;

    result = DNS_R_SUCCESS;

 failure:
    if (current_soa_tuple != NULL)
        dns_difftuple_free(&current_soa_tuple);
    if (stream != NULL)
        stream->methods->destroy(&stream);
    if (soa_stream != NULL)
        soa_stream->methods->destroy(&soa_stream);
    if (data_stream != NULL)
        data_stream->methods->destroy(&data_stream);
    if (ver != NULL)
        dns_db_closeversion(db, &ver, ISC_FALSE);
    if (db != NULL)
        dns_db_detach(&db);
    if (zone != NULL)
        dns_zone_detach(&zone);
    /* XXX kludge */
    if (xfr != NULL) {
        xfrout_fail(xfr, result, "setting up zone transfer");
    } else if (result != DNS_R_SUCCESS) {
        isc_log_write(XFROUT_DEBUG_LOGARGS(3),
                  "zone transfer setup failed");
        ns_client_error(client, result);
    }
}

static isc_result_t
xfrout_ctx_create(isc_mem_t *mctx, ns_client_t *client, unsigned int id,
          dns_name_t *qname, dns_rdatatype_t qtype,
          dns_db_t *db, dns_dbversion_t *ver,
          rrstream_t *stream, dns_tsigkey_t *tsigkey,
          dns_rdata_any_tsig_t *lasttsig, unsigned int maxtime,
          unsigned int idletime, xfrout_ctx_t **xfrp)
{
    xfrout_ctx_t *xfr;
    isc_result_t result;
    unsigned int len;
    void *mem;
    isc_interval_t maxinterval, idleinterval;
    isc_time_t expires;

    INSIST(xfrp != NULL && *xfrp == NULL);
    xfr = isc_mem_get(mctx, sizeof(*xfr));
    if (xfr == NULL)
        return (DNS_R_NOMEMORY);
    xfr->mctx = mctx;
    xfr->client = client;
    ns_client_wait(client);
    xfr->id = id;
    xfr->qname = qname;
    xfr->qtype = qtype;
    xfr->db = db;
    xfr->ver = ver;
    xfr->stream = stream;
    xfr->end_of_stream = ISC_FALSE;
    xfr->tsigkey = tsigkey;
    xfr->lasttsig = lasttsig;
    xfr->txmem = NULL;
    xfr->txmemlen = 0;
    xfr->nmsg = 0;
    xfr->timer = NULL;
    xfr->sends = 0;
    xfr->shuttingdown = ISC_FALSE;

    /*
     * Allocate a temporary buffer for the uncompressed response
     * message data.  The size should be no more than 65535 bytes
     * so that the compressed data will fit in a TCP message,
     * and no less than 65535 bytes so that an almost maximum-sized
     * RR will fit.  Note that although 65535-byte RRs are allowed
     * in principle, they cannot be zone-transferred (at least not
     * if uncompressible), because the message and RR headers would
     * push the size of the TCP message over the 65536 byte limit.
     */
    len = 65535;
    mem = isc_mem_get(mctx, len);
    if (mem == NULL) {
        result = DNS_R_NOMEMORY;
        goto failure;
    }
    isc_buffer_init(&xfr->buf, mem, len, ISC_BUFFERTYPE_BINARY);

    /*
     * Allocate another temporary buffer for the compressed
     * response message and its TCP length prefix.
     */
    len = 2 + 65535;
    mem = isc_mem_get(mctx, len);
    if (mem == NULL) {
        result = DNS_R_NOMEMORY;
        goto failure;
    }
    isc_buffer_init(&xfr->txlenbuf, mem, 2, ISC_BUFFERTYPE_BINARY);
    isc_buffer_init(&xfr->txbuf, (char *) mem + 2, len - 2,
            ISC_BUFFERTYPE_BINARY);
    xfr->txmem = mem;
    xfr->txmemlen = len;

    isc_interval_set(&maxinterval, maxtime, 0);
    CHECK(isc_time_nowplusinterval(&expires, &maxinterval));
    isc_interval_set(&idleinterval, idletime, 0);

    CHECK(isc_timer_create(ns_g_timermgr, isc_timertype_once,
                   &expires, &idleinterval,
                   xfr->client->task,
                   xfrout_timeout, xfr, &xfr->timer));

    /*
     * Register a shutdown callback with the client, so that we
     * can stop the transfer immediately when the client task
     * gets a shutdown event.
     */
    xfr->client->shutdown = xfrout_client_shutdown;
    xfr->client->shutdown_arg = xfr;

    *xfrp = xfr;
    return (DNS_R_SUCCESS);

failure:
    xfrout_ctx_destroy(&xfr);
    return (result);
}


/*
 * Arrange to send as much as we can of "stream" without blocking.
 *
 * Requires:
 *  The stream iterator is initialized and points at an RR,
 *      or possiby at the end of the stream (that is, the
 *      _first method of the iterator has been called).
 */
static void
sendstream(xfrout_ctx_t *xfr)
{
    dns_message_t *msg = NULL;
    isc_result_t result;
    isc_region_t used;
    isc_region_t region;
    dns_rdataset_t *qrdataset;
    int n_rrs;

    isc_buffer_clear(&xfr->buf);
    isc_buffer_clear(&xfr->txlenbuf);
    isc_buffer_clear(&xfr->txbuf);

    /*
     * Build a response dns_message_t, temporarily storing the raw,
     * uncompressed owner names and RR data contiguously in xfr->buf.
     * We know that if the uncompressed data fits in xfr->buf,
     * the compressed data will surely fit in a TCP message.
     */

    msg = NULL;
    CHECK(dns_message_create(xfr->mctx, DNS_MESSAGE_INTENTRENDER, &msg));

    msg->id = xfr->id;
    msg->rcode = dns_rcode_noerror;
    msg->flags = DNS_MESSAGEFLAG_QR | DNS_MESSAGEFLAG_AA;
    if ((xfr->client->attributes & NS_CLIENTATTR_RA) != 0)
        msg->flags |= DNS_MESSAGEFLAG_RA;
    msg->tsigkey = xfr->tsigkey;
    msg->querytsig = xfr->lasttsig;

    /*
     * Include a question section in the first message only.
     * BIND 8.2.1 will not recognize an IXFR if it does not have a
     * question section.
     */
    if (xfr->nmsg == 0) {
        dns_name_t *qname = NULL;
        isc_region_t r;

        /*
         * Reserve space for the 12-byte message header
         * and 4 bytes of question.
         */
        isc_buffer_add(&xfr->buf, 12 + 4);

        qrdataset = NULL;
        result = dns_message_gettemprdataset(msg, &qrdataset);
        if (result != ISC_R_SUCCESS)
            goto failure;
        dns_rdataset_init(qrdataset);
        dns_rdataset_makequestion(qrdataset,
                      xfr->client->message->rdclass,
                      xfr->qtype);

        result = dns_message_gettempname(msg, &qname);
        if (result != ISC_R_SUCCESS)
            goto failure;
        dns_name_init(qname, NULL);
        isc_buffer_available(&xfr->buf, &r);
        INSIST(r.length >= xfr->qname->length);
        r.length = xfr->qname->length;
        isc_buffer_putmem(&xfr->buf, xfr->qname->ndata,
                  xfr->qname->length);
        dns_name_fromregion(qname, &r);
        ISC_LIST_INIT(qname->list);
        ISC_LIST_APPEND(qname->list, qrdataset, link);

        dns_message_addname(msg, qname, DNS_SECTION_QUESTION);
    }
    else
        msg->tcp_continuation = 1;

    /*
     * Try to fit in as many RRs as possible, unless "one-answer"
     * format has been requested.
     */
    for (n_rrs = 0; ; n_rrs++) {
        dns_name_t *name = NULL;
        isc_uint32_t ttl;
        dns_rdata_t *rdata = NULL;

        dns_name_t *msgname = NULL;
        dns_rdata_t *msgrdata = NULL;
        dns_rdatalist_t *msgrdl = NULL;
        dns_rdataset_t *msgrds = NULL;

        unsigned int size;
        isc_region_t r;

        xfr->stream->methods->current(xfr->stream,
                          &name, &ttl, &rdata);
        size = name->length + 10 + rdata->length;
        isc_buffer_available(&xfr->buf, &r);
        if (size >= r.length) {
            /*
             * RR would not fit.  If there are other RRs in the
             * buffer, send them now and leave this RR to the
             * next message.  If this RR overflows the buffer
             * all by itself, fail.
             *
             * In theory some RRs might fit in a TCP message
             * when compressed even if they do not fit when
             * uncompressed, but surely we don't want
             * to send such monstrosities to an unsuspecting
             * slave.
             */
            if (n_rrs == 0) {
                isc_log_write(XFROUT_COMMON_LOGARGS,
                          ISC_LOG_WARNING,
                          "RR too large for zone transfer "
                          "(%d bytes)", size);
                /* XXX DNS_R_RRTOOLARGE? */
                result = ISC_R_NOSPACE;
                goto failure;
            }
            break;
        }

        log_rr(name, rdata, ttl); /* XXX */

        dns_message_gettempname(msg, &msgname);
        dns_name_init(msgname, NULL);
        isc_buffer_available(&xfr->buf, &r);
        INSIST(r.length >= name->length);
        r.length = name->length;
        isc_buffer_putmem(&xfr->buf, name->ndata, name->length);
        dns_name_fromregion(msgname, &r);

        /* Reserve space for RR header. */
        isc_buffer_add(&xfr->buf, 10);

        dns_message_gettemprdata(msg, &msgrdata);
        isc_buffer_available(&xfr->buf, &r);
        r.length = rdata->length;
        isc_buffer_putmem(&xfr->buf, rdata->data, rdata->length);
        dns_rdata_init(msgrdata);
        dns_rdata_fromregion(msgrdata,
                     rdata->rdclass, rdata->type, &r);

        dns_message_gettemprdatalist(msg, &msgrdl);
        msgrdl->type = rdata->type;
        msgrdl->rdclass = rdata->rdclass;
        msgrdl->ttl = ttl;
        ISC_LIST_INIT(msgrdl->rdata);
        ISC_LINK_INIT(msgrdl, link);
        ISC_LIST_APPEND(msgrdl->rdata, msgrdata, link);

        dns_message_gettemprdataset(msg, &msgrds);
        dns_rdataset_init(msgrds);
        result = dns_rdatalist_tordataset(msgrdl, msgrds);
        INSIST(result == DNS_R_SUCCESS);

        ISC_LIST_APPEND(msgname->list, msgrds, link);

        dns_message_addname(msg, msgname, DNS_SECTION_ANSWER);

        result = xfr->stream->methods->next(xfr->stream);
        if (result == DNS_R_NOMORE) {
            xfr->end_of_stream = ISC_TRUE;
            break;
        }
        CHECK(result);

        /* XXX per-server, too */
        if (ns_g_server->transfer_format == dns_one_answer)
            break;
    }

    if ((xfr->client->attributes & NS_CLIENTATTR_TCP) != 0) {
        CHECK(dns_message_renderbegin(msg, &xfr->txbuf));
        CHECK(dns_message_rendersection(msg, DNS_SECTION_QUESTION, 0));
        CHECK(dns_message_rendersection(msg, DNS_SECTION_ANSWER, 0));
        CHECK(dns_message_renderend(msg));

        isc_buffer_used(&xfr->txbuf, &used);
        isc_buffer_putuint16(&xfr->txlenbuf, used.length);
        region.base = xfr->txlenbuf.base;
        region.length = 2 + used.length;
        isc_log_write(XFROUT_DEBUG_LOGARGS(8),
                  "sending zone transfer TCP message of %d bytes",
                  used.length);
        CHECK(isc_socket_send(xfr->client->tcpsocket, /* XXX */
                      &region, xfr->client->task,
                      xfrout_senddone,
                      xfr));
        xfr->sends++;
    } else {
        isc_log_write(XFROUT_DEBUG_LOGARGS(8),
                  "sending IXFR UDP response");
        /* XXX kludge */
        dns_message_destroy(&xfr->client->message);
        xfr->client->message = msg;
        msg = NULL;
        ns_client_send(xfr->client);
        xfrout_ctx_destroy(&xfr);
        return;
    }

    /* Advance lasttsig to be the last TSIG generated */
    xfr->lasttsig = msg->tsig;

    /* Clear this field so the TSIG is not destroyed */
    msg->tsig = NULL;

    /*
     * If this is the first message, clear this too, since this is
     * also pointed to by the request.
     */
    if (xfr->nmsg == 0)
        msg->querytsig = NULL;

    xfr->nmsg++;

 failure:
    /*
     * XXXRTH  need to cleanup qname and qrdataset...
     */
    if (msg != NULL) {
        dns_message_destroy(&msg);
    }
    if (result == DNS_R_SUCCESS)
        return;

    xfrout_fail(xfr, result, "sending zone data");
}

static void
xfrout_ctx_destroy(xfrout_ctx_t **xfrp) {
    xfrout_ctx_t *xfr = *xfrp;

    INSIST(xfr->sends == 0);

    xfr->client->shutdown = NULL;
    xfr->client->shutdown_arg = NULL;

    if (xfr->timer != NULL)
        isc_timer_detach(&xfr->timer);
    if (xfr->stream != NULL)
        xfr->stream->methods->destroy(&xfr->stream);
    if (xfr->buf.base != NULL)
        isc_mem_put(xfr->mctx, xfr->buf.base, xfr->buf.length);
    if (xfr->txmem != NULL)
        isc_mem_put(xfr->mctx, xfr->txmem, xfr->txmemlen);
    if (xfr->lasttsig != NULL) {
        dns_rdata_freestruct(xfr->lasttsig);
        isc_mem_put(xfr->mctx, xfr->lasttsig, sizeof(*xfr->lasttsig));
    }

    /* XXX */
    if (xfr->ver != NULL)
        dns_db_closeversion(xfr->db, &xfr->ver, ISC_FALSE);
    if (xfr->db != NULL)
        dns_db_detach(&xfr->db);

    ns_client_unwait(xfr->client);

    isc_mem_put(xfr->mctx, xfr, sizeof(*xfr));

    *xfrp = NULL;
}

static void
xfrout_senddone(isc_task_t *task, isc_event_t *event) {
    isc_socketevent_t *sev = (isc_socketevent_t *) event;
    xfrout_ctx_t *xfr = (xfrout_ctx_t *) event->arg;
    isc_result_t evresult = sev->result;
    task = task; /* Unused */
    INSIST(event->type == ISC_SOCKEVENT_SENDDONE);
    isc_event_free(&event);
    xfr->sends--;
    INSIST(xfr->sends == 0);
    if (xfr->shuttingdown == ISC_TRUE) {
        xfrout_maybe_destroy(xfr);
    } else if (evresult != ISC_R_SUCCESS) {
        xfrout_fail(xfr, evresult, "send");
    } else if (xfr->end_of_stream == ISC_FALSE) {
        sendstream(xfr);
    } else {
        /* End of zone transfer stream. */
        isc_log_write(XFROUT_DEBUG_LOGARGS(6),
                  "end of outgoing zone transfer");
        ns_client_next(xfr->client, DNS_R_SUCCESS);
        xfrout_ctx_destroy(&xfr);
    }
}

static void
xfrout_timeout(isc_task_t *task, isc_event_t *event) {
    xfrout_ctx_t *xfr = (xfrout_ctx_t *) event->arg;
    task = task; /* Unused */
    /* This will log "giving up: timeout". */
    xfrout_fail(xfr, ISC_R_TIMEDOUT, "giving up");
    isc_event_free(&event);
}

static void
xfrout_fail(xfrout_ctx_t *xfr, isc_result_t result, char *msg)
{
    xfr->shuttingdown = ISC_TRUE;
    isc_log_write(XFROUT_COMMON_LOGARGS, ISC_LOG_ERROR,
              "outgoing zone transfer: %s: %s",
              msg, isc_result_totext(result));
    xfrout_maybe_destroy(xfr);
}

static void
xfrout_maybe_destroy(xfrout_ctx_t *xfr) {
    INSIST(xfr->shuttingdown == ISC_TRUE);
    if (xfr->sends > 0) {
        /*
         * If we are currently sending, cancel it and wait for
         * cancel event before destroying the context.
         */
        isc_socket_cancel(xfr->client->tcpsocket, xfr->client->task,
                  ISC_SOCKCANCEL_SEND);
    } else {
        ns_client_next(xfr->client, ISC_R_CANCELED);
        xfrout_ctx_destroy(&xfr);
    }
}

static void
xfrout_client_shutdown(void *arg)
{
    xfrout_ctx_t *xfr = (xfrout_ctx_t *) arg;
    xfrout_fail(xfr, ISC_R_SHUTTINGDOWN, "aborted");
}