lib/dns/masterdump.c

	masterdump.c revision 40f53fa8d9c6a4fc38c0014495e7a42b08f52481
/*
 * Copyright (C) 1999, 2000  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: masterdump.c,v 1.29 2000/08/01 01:22:31 tale Exp $ */

#include <config.h>

#include <isc/file.h>
#include <isc/mem.h>
#include <isc/stdio.h>
#include <isc/string.h>
#include <isc/util.h>

#include <dns/db.h>
#include <dns/dbiterator.h>
#include <dns/fixedname.h>
#include <dns/log.h>
#include <dns/masterdump.h>
#include <dns/rdata.h>
#include <dns/rdataset.h>
#include <dns/rdatasetiter.h>
#include <dns/rdatatype.h>
#include <dns/result.h>
#include <dns/time.h>
#include <dns/ttl.h>

#define RETERR(x) do { \
    isc_result_t _r = (x); \
    if (_r != ISC_R_SUCCESS) \
        return (_r); \
    } while (0)

struct dns_master_style {
    unsigned int flags;     /* DNS_STYLEFLAG_* */
    unsigned int ttl_column;
    unsigned int class_column;
    unsigned int type_column;
    unsigned int rdata_column;
    unsigned int line_length;
    unsigned int tab_width;
};

/*
 * Flags affecting master file formatting.  Flags 0x0000FFFF
 * define the formatting of the rdata part and are defined in
 * rdata.h.
 */

/* Omit the owner name when possible. */
#define DNS_STYLEFLAG_OMIT_OWNER    0x00010000U

/*
 * Omit the TTL when possible.  If DNS_STYLEFLAG_TTL is
 * also set, this means no TTLs are ever printed
 * because $TTL directives are generated before every
 * change in the TTL.  In this case, no columns need to
 * be reserved for the TTL.  Master files generated with
 * these options will be rejected by BIND 4.x because it
 * does not recognize the $TTL directive.
 *
 * If DNS_STYLEFLAG_TTL is not also set, the TTL will be
 * omitted when it is equal to the previous TTL.
 * This is correct according to RFC1035, but the
 * TTLs may be silently misinterpreted by older
 * versions of BIND which use the SOA MINTTL as a
 * default TTL value.
 */
#define DNS_STYLEFLAG_OMIT_TTL      0x00020000U

/* Omit the class when possible. */
#define DNS_STYLEFLAG_OMIT_CLASS    0x00040000U

/* Output $TTL directives. */
#define DNS_STYLEFLAG_TTL       0x00080000U

/*
 * Output $ORIGIN directives and print owner names relative to
 * the origin when possible.
 */
#define DNS_STYLEFLAG_REL_OWNER     0x00100000U

/* Print domain names in RR data in relative form when possible.
   For this to take effect, DNS_STYLEFLAG_REL_OWNER must also be set. */
#define DNS_STYLEFLAG_REL_DATA      0x00200000U


/*
 * The maximum length of the newline+indentation that is output
 * when inserting a line break in an RR.  This effectively puts an
 * upper limits on the value of "rdata_column", because if it is
 * very large, the tabs and spaces needed to reach it will not fit.
 */
#define DNS_TOTEXT_LINEBREAK_MAXLEN 100

/*
 * Context structure for a masterfile dump in progress.
 */
typedef struct dns_totext_ctx {
    dns_master_style_t  style;
    isc_boolean_t       class_printed;
    char *          linebreak;
    char            linebreak_buf[DNS_TOTEXT_LINEBREAK_MAXLEN];
    dns_name_t *        origin;
    dns_fixedname_t     origin_fixname;
    isc_uint32_t        current_ttl;
    isc_boolean_t       current_ttl_valid;
} dns_totext_ctx_t;

/*
 * The default master file style.
 *
 * Because the TTL is always omitted, and the class is almost always
 * omitted, neither is allocated any columns.
 */
const dns_master_style_t
dns_master_style_default = {
    DNS_STYLEFLAG_OMIT_OWNER |
    DNS_STYLEFLAG_OMIT_CLASS |
    DNS_STYLEFLAG_REL_OWNER |
    DNS_STYLEFLAG_REL_DATA |
    DNS_STYLEFLAG_OMIT_TTL |
    DNS_STYLEFLAG_TTL |
    DNS_STYLEFLAG_COMMENT |
    DNS_STYLEFLAG_MULTILINE,
    24, 24, 24, 32, 80, 8
};

/*
 * A style suitable for dns_rdataset_totext().
 */
dns_master_style_t
dns_masterfile_style_debug = {
        DNS_STYLEFLAG_REL_OWNER,
    24, 32, 40, 48, 80, 8
};


#define N_SPACES 10
static char spaces[N_SPACES+1] = "          ";

#define N_TABS 10
static char tabs[N_TABS+1] = "\t\t\t\t\t\t\t\t\t\t";


/*
 * Output tabs and spaces to go from column '*current' to
 * column 'to', and update '*current' to reflect the new
 * current column.
 */
static isc_result_t
indent(unsigned int *current, unsigned int to, int tabwidth,
       isc_buffer_t *target)
{
    isc_region_t r;
    unsigned char *p;
    unsigned int from;
    int ntabs, nspaces, t;

    from = *current;

    if (to < from + 1)
        to = from + 1;

    ntabs = to / tabwidth - from / tabwidth;
    if (ntabs < 0)
        ntabs = 0;

    if (ntabs > 0) {
        isc_buffer_availableregion(target, &r);
        if (r.length < (unsigned) ntabs)
            return (ISC_R_NOSPACE);
        p = r.base;

        t = ntabs;
        while (t) {
            int n = t;
            if (n > N_TABS)
                n = N_TABS;
            memcpy(p, tabs, n);
            p += n;
            t -= n;
        }
        isc_buffer_add(target, ntabs);
        from = (to / tabwidth) * tabwidth;
    }

    nspaces = to - from;
    INSIST(nspaces >= 0);

    isc_buffer_availableregion(target, &r);
    if (r.length < (unsigned) nspaces)
        return (ISC_R_NOSPACE);
    p = r.base;

    t = nspaces;
    while (t) {
        int n = t;
        if (n > N_SPACES)
            n = N_SPACES;
        memcpy(p, spaces, n);
        p += n;
        t -= n;
    }
    isc_buffer_add(target, nspaces);

    *current = to;
    return (ISC_R_SUCCESS);
}

static isc_result_t
totext_ctx_init(const dns_master_style_t *style, dns_totext_ctx_t *ctx) {
    isc_result_t result;

    REQUIRE(style->tab_width != 0);

    ctx->style = *style;
    ctx->class_printed = ISC_FALSE;

    dns_fixedname_init(&ctx->origin_fixname);

    /*
     * Set up the line break string if needed.
     */
    if ((ctx->style.flags & DNS_STYLEFLAG_MULTILINE) != 0) {
        isc_buffer_t buf;
        isc_region_t r;
        unsigned int col = 0;

        isc_buffer_init(&buf, ctx->linebreak_buf,
                sizeof(ctx->linebreak_buf));

        isc_buffer_availableregion(&buf, &r);
        if (r.length < 1)
            return (DNS_R_TEXTTOOLONG);
        r.base[0] = '\n';
        isc_buffer_add(&buf, 1);

        result = indent(&col, ctx->style.rdata_column,
                ctx->style.tab_width, &buf);
        /*
         * Do not return ISC_R_NOSPACE if the line break string
         * buffer is too small, because that would just make
         * dump_rdataset() retry indenfinitely with ever
         * bigger target buffers.  That's a different buffer,
         * so it won't help.  Use DNS_R_TEXTTOOLONG as a substitute.
         */
        if (result == ISC_R_NOSPACE)
            return (DNS_R_TEXTTOOLONG);
        if (result != ISC_R_SUCCESS)
            return (result);

        isc_buffer_availableregion(&buf, &r);
        if (r.length < 1)
            return (DNS_R_TEXTTOOLONG);
        r.base[0] = '\0';
        isc_buffer_add(&buf, 1);
        ctx->linebreak = ctx->linebreak_buf;
    } else {
        ctx->linebreak = NULL;
    }

    ctx->origin = NULL;
    ctx->current_ttl = 0;
    ctx->current_ttl_valid = ISC_FALSE;

    return (ISC_R_SUCCESS);
}

#define INDENT_TO(col) \
    do { \
         if ((result = indent(&column, ctx->style.col, \
                      ctx->style.tab_width, target)) \
             != ISC_R_SUCCESS) \
                return (result); \
        } while (0)


/*
 * Convert 'rdataset' to master file text format according to 'ctx',
 * storing the result in 'target'.  If 'owner_name' is NULL, it
 * is omitted; otherwise 'owner_name' must be valid and have at least
 * one label.
 */

static isc_result_t
rdataset_totext(dns_rdataset_t *rdataset,
        dns_name_t *owner_name,
        dns_totext_ctx_t *ctx,
        isc_boolean_t omit_final_dot,
        isc_buffer_t *target)
{
    isc_result_t result;
    unsigned int column;
    isc_boolean_t first = ISC_TRUE;
    isc_uint32_t current_ttl;
    isc_boolean_t current_ttl_valid;

    REQUIRE(DNS_RDATASET_VALID(rdataset));

    result = dns_rdataset_first(rdataset);
    REQUIRE(result == ISC_R_SUCCESS);

    current_ttl = ctx->current_ttl;
    current_ttl_valid = ctx->current_ttl_valid;

    do {
        column = 0;

        /*
         * Owner name.
         */
        if (owner_name != NULL &&
            ! ((ctx->style.flags & DNS_STYLEFLAG_OMIT_OWNER) != 0 &&
               !first))
        {
            unsigned int name_start = target->used;
            RETERR(dns_name_totext(owner_name,
                           omit_final_dot,
                           target));
            column += target->used - name_start;
        }

        /*
         * TTL.
         */
        if (! ((ctx->style.flags & DNS_STYLEFLAG_OMIT_TTL) != 0 &&
               current_ttl_valid &&
               rdataset->ttl == current_ttl))
        {
            char ttlbuf[64];
            isc_region_t r;
            unsigned int length;

            INDENT_TO(ttl_column);
            length = sprintf(ttlbuf, "%u", rdataset->ttl);
            INSIST(length <= sizeof ttlbuf);
            isc_buffer_availableregion(target, &r);
            if (r.length < length)
                return (ISC_R_NOSPACE);
            memcpy(r.base, ttlbuf, length);
            isc_buffer_add(target, length);
            column += length;

            /*
             * If the $TTL directive is not in use, the TTL we
             * just printed becomes the default for subsequent RRs.
             */
            if ((ctx->style.flags & DNS_STYLEFLAG_TTL) == 0) {
                current_ttl = rdataset->ttl;
                current_ttl_valid = ISC_TRUE;
            }
        }

        /*
         * Class.
         */
        if ((ctx->style.flags & DNS_STYLEFLAG_OMIT_CLASS) == 0 ||
            ctx->class_printed == ISC_FALSE)
        {
            unsigned int class_start;
            INDENT_TO(class_column);
            class_start = target->used;
            result = dns_rdataclass_totext(rdataset->rdclass,
                               target);
            if (result != ISC_R_SUCCESS)
                return (result);
            column += (target->used - class_start);
        }

        /*
         * Type.
         */
        {
            unsigned int type_start;
            INDENT_TO(type_column);
            type_start = target->used;
            result = dns_rdatatype_totext(rdataset->type, target);
            if (result != ISC_R_SUCCESS)
                return (result);
            column += (target->used - type_start);
        }

        /*
         * Rdata.
         */
        {
            dns_rdata_t rdata;
            isc_region_t r;

            INDENT_TO(rdata_column);
            dns_rdataset_current(rdataset, &rdata);

            RETERR(dns_rdata_tofmttext(&rdata,
                           ctx->origin,
                           ctx->style.flags,
                           ctx->style.line_length -
                               ctx->style.rdata_column,
                           ctx->linebreak,
                           target));

            isc_buffer_availableregion(target, &r);
            if (r.length < 1)
                return (ISC_R_NOSPACE);
            r.base[0] = '\n';
            isc_buffer_add(target, 1);
        }

        first = ISC_FALSE;
        result = dns_rdataset_next(rdataset);
    } while (result == ISC_R_SUCCESS);

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

    /*
     * Update the ctx state to reflect what we just printed.
     * This is done last, only when we are sure we will return
     * success, because this function may be called multiple
     * times with increasing buffer sizes until it succeeds,
     * and failed attempts must not update the state prematurely.
     */
    ctx->class_printed = ISC_TRUE;
    ctx->current_ttl= current_ttl;
    ctx->current_ttl_valid = current_ttl_valid;

    return (ISC_R_SUCCESS);
}

/*
 * Print the name, type, and class of an empty rdataset,
 * such as those used to represent the question section
 * of a DNS message.
 */
static isc_result_t
question_totext(dns_rdataset_t *rdataset,
        dns_name_t *owner_name,
        dns_totext_ctx_t *ctx,
        isc_boolean_t omit_final_dot,
        isc_buffer_t *target)
{
    unsigned int column;
    isc_result_t result;
    isc_region_t r;

    REQUIRE(DNS_RDATASET_VALID(rdataset));
    result = dns_rdataset_first(rdataset);
    REQUIRE(result == ISC_R_NOMORE);

    column = 0;

    /* Owner name */
    {
        unsigned int name_start = target->used;
        RETERR(dns_name_totext(owner_name,
                       omit_final_dot,
                       target));
        column += target->used - name_start;
    }

    /* Class */
    {
        unsigned int class_start;
        INDENT_TO(class_column);
        class_start = target->used;
        result = dns_rdataclass_totext(rdataset->rdclass, target);
        if (result != ISC_R_SUCCESS)
            return (result);
        column += (target->used - class_start);
    }

    /* Type */
    {
        unsigned int type_start;
        INDENT_TO(type_column);
        type_start = target->used;
        result = dns_rdatatype_totext(rdataset->type, target);
        if (result != ISC_R_SUCCESS)
            return (result);
        column += (target->used - type_start);
    }

    isc_buffer_availableregion(target, &r);
    if (r.length < 1)
        return (ISC_R_NOSPACE);
    r.base[0] = '\n';
    isc_buffer_add(target, 1);

    return (ISC_R_SUCCESS);
}

/*
 * Provide a backwards compatible interface for printing a
 * single rdataset or question section.  This is now used
 * only by wire_test.c.
 */
isc_result_t
dns_rdataset_totext(dns_rdataset_t *rdataset,
            dns_name_t *owner_name,
            isc_boolean_t omit_final_dot,
            isc_boolean_t no_rdata_or_ttl,
            isc_buffer_t *target)
{
    dns_totext_ctx_t ctx;
    isc_result_t result;
    result = totext_ctx_init(&dns_masterfile_style_debug, &ctx);
    if (result != ISC_R_SUCCESS) {
        UNEXPECTED_ERROR(__FILE__, __LINE__,
                 "could not set master file style");
        return (ISC_R_UNEXPECTED);
    }

    /*
     * The caller might want to give us an empty owner
     * name (e.g. if they are outputting into a master
     * file and this rdataset has the same name as the
     * previous one.)
     */
    if (dns_name_countlabels(owner_name) == 0)
        owner_name = NULL;

    if (no_rdata_or_ttl)
        return (question_totext(rdataset, owner_name, &ctx,
                    omit_final_dot, target));
    else
        return (rdataset_totext(rdataset, owner_name, &ctx,
                    omit_final_dot, target));
}

/*
 * Print an rdataset.  'buffer' is a scratch buffer, which must have been
 * dynamically allocated by the caller.  It must be large enough to
 * hold the result from dns_ttl_totext().  If more than that is needed,
 * the buffer will be grown automatically.
 */

static isc_result_t
dump_rdataset(isc_mem_t *mctx, dns_name_t *name, dns_rdataset_t *rdataset,
          dns_totext_ctx_t *ctx,
          isc_buffer_t *buffer, FILE *f)
{
    isc_region_t r;
    isc_result_t result;

    REQUIRE(buffer->length > 0);

    /*
     * Output a $TTL directive if needed.
     */

    if ((ctx->style.flags & DNS_STYLEFLAG_TTL) != 0) {
        if (ctx->current_ttl_valid == ISC_FALSE ||
            ctx->current_ttl != rdataset->ttl)
        {
            if ((ctx->style.flags & DNS_STYLEFLAG_COMMENT) != 0)
            {
                isc_buffer_clear(buffer);
                result = dns_ttl_totext(rdataset->ttl,
                            ISC_TRUE, buffer);
                INSIST(result == ISC_R_SUCCESS);
                isc_buffer_usedregion(buffer, &r);
                fprintf(f, "$TTL %u\t; %.*s\n", rdataset->ttl,
                    (int) r.length, (char *) r.base);
            } else {
                fprintf(f, "$TTL %u\n", rdataset->ttl);
            }
            ctx->current_ttl = rdataset->ttl;
            ctx->current_ttl_valid = ISC_TRUE;
        }
    }

    isc_buffer_clear(buffer);

    /*
     * Generate the text representation of the rdataset into
     * the buffer.  If the buffer is too small, grow it.
     */
    for (;;) {
        int newlength;
        void *newmem;
        result = rdataset_totext(rdataset, name, ctx,
                     ISC_FALSE, buffer);
        if (result != ISC_R_NOSPACE)
            break;

        isc_mem_put(mctx, buffer->base, buffer->length);
        newlength = buffer->length * 2;
        newmem = isc_mem_get(mctx, newlength);
        if (newmem == NULL)
            return (ISC_R_NOMEMORY);
        isc_buffer_init(buffer, newmem, newlength);
    }
    if (result != ISC_R_SUCCESS)
        return (result);

    /*
     * Write the buffer contents to the master file.
     */
    isc_buffer_usedregion(buffer, &r);
    result = isc_stdio_write(r.base, 1, (size_t)r.length, f, NULL);

    if (result != ISC_R_SUCCESS) {
        UNEXPECTED_ERROR(__FILE__, __LINE__,
                 "master file write failed: %s",
                 isc_result_totext(result));
        return (result);
    }

    return (ISC_R_SUCCESS);
}

/*
 * Dump all the rdatasets of a domain name to a master file.
 */
static isc_result_t
dump_rdatasets(isc_mem_t *mctx, dns_name_t *name, dns_rdatasetiter_t *rdsiter,
           dns_totext_ctx_t *ctx,
           isc_buffer_t *buffer, FILE *f)
{
    isc_result_t result;
    dns_rdataset_t rdataset;

    dns_rdataset_init(&rdataset);
    result = dns_rdatasetiter_first(rdsiter);
    while (result == ISC_R_SUCCESS) {
        dns_rdatasetiter_current(rdsiter, &rdataset);
        if (rdataset.type != 0) {
            /*
             * XXX  We only dump the rdataset if it isn't a
             * negative caching entry.  Maybe our dumping routines
             * will learn how to usefully dump such an entry later
             * on.
             */
            result = dump_rdataset(mctx, name, &rdataset, ctx,
                           buffer, f);
        } else
            result = ISC_R_SUCCESS;
        dns_rdataset_disassociate(&rdataset);
        if (result != ISC_R_SUCCESS)
            return (result);
        result = dns_rdatasetiter_next(rdsiter);
        if ((ctx->style.flags & DNS_STYLEFLAG_OMIT_OWNER) != 0)
            name = NULL;
    }
    if (result != ISC_R_NOMORE)
        return (result);
    return (ISC_R_SUCCESS);
}


/*
 * Initial size of text conversion buffer.  The buffer is used
 * for several purposes: converting origin names, rdatasets,
 * $DATE timestamps, and comment strings for $TTL directives.
 *
 * When converting rdatasets, it is dynamically resized, but
 * when converting origins, timestamps, etc it is not.  Therefore,
 * the  initial size must large enough to hold the longest possible
 * text representation of any domain name (for $ORIGIN).
 */
static const int initial_buffer_length = 1200;

/*
 * Dump an entire database into a master file.
 */
isc_result_t
dns_master_dumptostream(isc_mem_t *mctx, dns_db_t *db,
            dns_dbversion_t *version,
            const dns_master_style_t *style,
            FILE *f)
{
    dns_fixedname_t fixname;
    dns_name_t *name;
    dns_dbiterator_t *dbiter = NULL;
    isc_result_t result;
    isc_buffer_t buffer;
    char *bufmem;
    isc_stdtime_t now;
    isc_region_t r;
    dns_totext_ctx_t ctx;

    result = totext_ctx_init(style, &ctx);
    if (result != ISC_R_SUCCESS) {
        UNEXPECTED_ERROR(__FILE__, __LINE__,
                 "could not set master file style");
        return (ISC_R_UNEXPECTED);
    }

    dns_fixedname_init(&fixname);
    name = dns_fixedname_name(&fixname);

    isc_stdtime_get(&now);

    bufmem = isc_mem_get(mctx, initial_buffer_length);
    if (bufmem == NULL)
        return (ISC_R_NOMEMORY);

    isc_buffer_init(&buffer, bufmem, initial_buffer_length);

    /*
     * If the database has cache semantics, output an RFC2540
     * $DATE directive so that the TTLs can be adjusted when
     * it is reloaded.  For zones it is not really needed, and
     * it would make the file incompatible with pre-RFC2540
     * software, so we omit it in the zone case.
     */
    if (dns_db_iscache(db)) {
        result = dns_time32_totext(now, &buffer);
        RUNTIME_CHECK(result == ISC_R_SUCCESS);
        isc_buffer_usedregion(&buffer, &r);
        fprintf(f, "$DATE %.*s\n", (int) r.length, (char *) r.base);
    }

    result = dns_db_createiterator(db,
               ((ctx.style.flags & DNS_STYLEFLAG_REL_OWNER) != 0) ?
                   ISC_TRUE : ISC_FALSE,
               &dbiter);
    if (result != ISC_R_SUCCESS)
        goto create_iter_failure;

    result = dns_dbiterator_first(dbiter);

    while (result == ISC_R_SUCCESS) {
        dns_rdatasetiter_t *rdsiter = NULL;
        dns_dbnode_t *node = NULL;
        result = dns_dbiterator_current(dbiter, &node, name);
        if (result != ISC_R_SUCCESS && result != DNS_R_NEWORIGIN)
            break;
        if (result == DNS_R_NEWORIGIN) {
            dns_name_t *origin =
                dns_fixedname_name(&ctx.origin_fixname);
            result = dns_dbiterator_origin(dbiter, origin);
            RUNTIME_CHECK(result == ISC_R_SUCCESS);
            isc_buffer_clear(&buffer);
            result = dns_name_totext(origin, ISC_FALSE, &buffer);
            RUNTIME_CHECK(result == ISC_R_SUCCESS);
            isc_buffer_usedregion(&buffer, &r);
            fprintf(f, "$ORIGIN %.*s\n", (int) r.length,
                (char *) r.base);
            if ((ctx.style.flags & DNS_STYLEFLAG_REL_DATA) != 0)
                ctx.origin = origin;
        }
        result = dns_db_allrdatasets(db, node, version, now, &rdsiter);
        if (result != ISC_R_SUCCESS) {
            dns_db_detachnode(db, &node);
            goto iter_failure;
        }
        result = dump_rdatasets(mctx, name, rdsiter, &ctx,
                    &buffer, f);
        if (result != ISC_R_SUCCESS) {
            dns_db_detachnode(db, &node);
            goto iter_failure;
        }
        dns_rdatasetiter_destroy(&rdsiter);
        dns_db_detachnode(db, &node);
        result = dns_dbiterator_next(dbiter);
    }
    if (result != ISC_R_NOMORE)
        goto iter_failure;

    result = ISC_R_SUCCESS;

 iter_failure:
    dns_dbiterator_destroy(&dbiter);

 create_iter_failure:
    isc_mem_put(mctx, buffer.base, buffer.length);
    return (result);
}


isc_result_t
dns_master_dump(isc_mem_t *mctx, dns_db_t *db, dns_dbversion_t *version,
        const dns_master_style_t *style, const char *filename)
{
    FILE *f = NULL;
    isc_result_t result;

    result = isc_stdio_open(filename, "w", &f);
    if (result != ISC_R_SUCCESS) {
        isc_log_write(dns_lctx, ISC_LOGCATEGORY_GENERAL,
                  DNS_LOGMODULE_MASTERDUMP, ISC_LOG_ERROR,
                  "dumping master file: %s: open: %s", filename,
                  isc_result_totext(result));
        return (ISC_R_UNEXPECTED);
    }

    result = dns_master_dumptostream(mctx, db, version, style, f);

    result = isc_stdio_close(f);
    if (result != ISC_R_SUCCESS) {
        isc_log_write(dns_lctx, ISC_LOGCATEGORY_GENERAL,
                  DNS_LOGMODULE_MASTERDUMP, ISC_LOG_ERROR,
                  "dumping master file: %s: close: %s", filename,
                  isc_result_totext(result));
        return (ISC_R_UNEXPECTED);
    }

    return (result);
}