lock.c

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/* Copyright 2000-2005 The Apache Software Foundation or its licensors, as
 * applicable.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
** DAV filesystem lock implementation
*/

#include "apr.h"
#include "apr_strings.h"
#include "apr_file_io.h"
#include "apr_uuid.h"

#define APR_WANT_MEMFUNC
#include "apr_want.h"

#include "httpd.h"
#include "http_log.h"

#include "mod_dav.h"
#include "repos.h"


/* ---------------------------------------------------------------
**
** Lock database primitives
**
*/

/*
** LOCK DATABASES
** 
** Lockdiscovery information is stored in the single lock database specified
** by the DAVLockDB directive.  Information about this db is stored in the
** global server configuration.
**
** KEY
**
** The database is keyed by a key_type unsigned char (DAV_TYPE_INODE or
** DAV_TYPE_FNAME) followed by inode and device number if possible,
** otherwise full path (in the case of Win32 or lock-null resources).
**
** VALUE
**
** The value consists of a list of elements.
**    DIRECT LOCK:     [char      (DAV_LOCK_DIRECT),
**                      char      (dav_lock_scope),
**                      char      (dav_lock_type),
**                      int        depth,
**                      time_t     expires,
**                      apr_uuid_t locktoken,
**                      char[]     owner,
**                      char[]     auth_user]
**
**    INDIRECT LOCK:   [char      (DAV_LOCK_INDIRECT),
**                      apr_uuid_t locktoken,
**                      time_t     expires,
**                      apr_size_t key_size,
**                      char[]     key]
**       The key is to the collection lock that resulted in this indirect lock
*/

#define DAV_TRUE                1
#define DAV_FALSE               0

#define DAV_CREATE_LIST         23
#define DAV_APPEND_LIST         24

/* Stored lock_discovery prefix */
#define DAV_LOCK_DIRECT         1
#define DAV_LOCK_INDIRECT       2

#define DAV_TYPE_INODE          10
#define DAV_TYPE_FNAME          11


/* ack. forward declare. */
static dav_error * dav_fs_remove_locknull_member(apr_pool_t *p,
                                                 const char *filename,
                                                 dav_buffer *pbuf);

/*
** Use the opaquelock scheme for locktokens
*/
struct dav_locktoken {
    apr_uuid_t uuid;
};
#define dav_compare_locktoken(plt1, plt2) \
                memcmp(&(plt1)->uuid, &(plt2)->uuid, sizeof((plt1)->uuid))


/* #################################################################
** ### keep these structures (internal) or move fully to dav_lock?
*/

/*
** We need to reliably size the fixed-length portion of
** dav_lock_discovery; best to separate it into another 
** struct for a convenient sizeof, unless we pack lock_discovery.
*/
typedef struct dav_lock_discovery_fixed
{
    char scope;
    char type;
    int depth;
    time_t timeout;
} dav_lock_discovery_fixed;

typedef struct dav_lock_discovery
{
    struct dav_lock_discovery_fixed f;

    dav_locktoken *locktoken;
    const char *owner;          /* owner field from activelock */
    const char *auth_user;      /* authenticated user who created the lock */
    struct dav_lock_discovery *next;
} dav_lock_discovery;

/* Indirect locks represent locks inherited from containing collections.
 * They reference the lock token for the collection the lock is
 * inherited from. A lock provider may also define a key to the
 * inherited lock, for fast datbase lookup. The key is opaque outside
 * the lock provider.
 */
typedef struct dav_lock_indirect
{
    dav_locktoken *locktoken;
    apr_datum_t key;
    struct dav_lock_indirect *next;
    time_t timeout;
} dav_lock_indirect;

/* ################################################################# */


/*
** Stored direct lock info - full lock_discovery length:  
** prefix + Fixed length + lock token + 2 strings + 2 nulls (one for each string)
*/
#define dav_size_direct(a)      (1 + sizeof(dav_lock_discovery_fixed) \
                                 + sizeof(apr_uuid_t) \
                                 + ((a)->owner ? strlen((a)->owner) : 0) \
                                 + ((a)->auth_user ? strlen((a)->auth_user) : 0) \
                                 + 2)

/* Stored indirect lock info - lock token and apr_datum_t */
#define dav_size_indirect(a)    (1 + sizeof(apr_uuid_t) \
                                 + sizeof(time_t) \
                                 + sizeof((a)->key.dsize) + (a)->key.dsize)

/*
** The lockdb structure.
**
** The <db> field may be NULL, meaning one of two things:
** 1) That we have not actually opened the underlying database (yet). The
**    <opened> field should be false.
** 2) We opened it readonly and it wasn't present.
**
** The delayed opening (determined by <opened>) makes creating a lockdb
** quick, while deferring the underlying I/O until it is actually required.
**
** We export the notion of a lockdb, but hide the details of it. Most
** implementations will use a database of some kind, but it is certainly
** possible that alternatives could be used.
*/
struct dav_lockdb_private
{
    request_rec *r;                     /* for accessing the uuid state */
    apr_pool_t *pool;                   /* a pool to use */
    const char *lockdb_path;            /* where is the lock database? */

    int opened;                         /* we opened the database */
    dav_db *db;                         /* if non-NULL, the lock database */
};
typedef struct
{
    dav_lockdb pub;
    dav_lockdb_private priv;
} dav_lockdb_combined;

/*
** The private part of the lock structure.
*/
struct dav_lock_private
{
    apr_datum_t key;    /* key into the lock database */
};
typedef struct
{
    dav_lock pub;
    dav_lock_private priv;
    dav_locktoken token;
} dav_lock_combined;

/*
** This must be forward-declared so the open_lockdb function can use it.
*/
extern const dav_hooks_locks dav_hooks_locks_fs;


/* internal function for creating locks */
static dav_lock *dav_fs_alloc_lock(dav_lockdb *lockdb, apr_datum_t key,
                                   const dav_locktoken *locktoken)
{
    dav_lock_combined *comb;

    comb = apr_pcalloc(lockdb->info->pool, sizeof(*comb));
    comb->pub.rectype = DAV_LOCKREC_DIRECT;
    comb->pub.info = &comb->priv;
    comb->priv.key = key;

    if (locktoken == NULL) {
        comb->pub.locktoken = &comb->token;
        apr_uuid_get(&comb->token.uuid);
    }
    else {
        comb->pub.locktoken = locktoken;
    }

    return &comb->pub;
}

/*
** dav_fs_parse_locktoken
**
** Parse an opaquelocktoken URI into a locktoken.
*/
static dav_error * dav_fs_parse_locktoken(
    apr_pool_t *p,
    const char *char_token,
    dav_locktoken **locktoken_p)
{
    dav_locktoken *locktoken;

    if (ap_strstr_c(char_token, "opaquelocktoken:") != char_token) {
        return dav_new_error(p,
                             HTTP_BAD_REQUEST, DAV_ERR_LOCK_UNK_STATE_TOKEN,
                             "The lock token uses an unknown State-token "
                             "format and could not be parsed.");
    }
    char_token += 16;

    locktoken = apr_pcalloc(p, sizeof(*locktoken));
    if (apr_uuid_parse(&locktoken->uuid, char_token)) {
        return dav_new_error(p, HTTP_BAD_REQUEST, DAV_ERR_LOCK_PARSE_TOKEN,
                             "The opaquelocktoken has an incorrect format "
                             "and could not be parsed.");
    }
    
    *locktoken_p = locktoken;
    return NULL;
}

/*
** dav_fs_format_locktoken
**
** Generate the URI for a locktoken
*/
static const char *dav_fs_format_locktoken(
    apr_pool_t *p,
    const dav_locktoken *locktoken)
{
    char buf[APR_UUID_FORMATTED_LENGTH + 1];

    apr_uuid_format(buf, &locktoken->uuid);
    return apr_pstrcat(p, "opaquelocktoken:", buf, NULL);
}

/*
** dav_fs_compare_locktoken
**
** Determine whether two locktokens are the same
*/
static int dav_fs_compare_locktoken(
    const dav_locktoken *lt1,
    const dav_locktoken *lt2)
{
    return dav_compare_locktoken(lt1, lt2);
}

/*
** dav_fs_really_open_lockdb:
**
** If the database hasn't been opened yet, then open the thing.
*/
static dav_error * dav_fs_really_open_lockdb(dav_lockdb *lockdb)
{
    dav_error *err;

    if (lockdb->info->opened)
        return NULL;

    err = dav_dbm_open_direct(lockdb->info->pool,
                              lockdb->info->lockdb_path,
                              lockdb->ro,
                              &lockdb->info->db);
    if (err != NULL) {
        return dav_push_error(lockdb->info->pool,
                              HTTP_INTERNAL_SERVER_ERROR,
                              DAV_ERR_LOCK_OPENDB,
                              "Could not open the lock database.",
                              err);
    }

    /* all right. it is opened now. */
    lockdb->info->opened = 1;

    return NULL;
}

/*
** dav_fs_open_lockdb:
**
** "open" the lock database, as specified in the global server configuration.
** If force is TRUE, then the database is opened now, rather than lazily.
**
** Note that only one can be open read/write.
*/
static dav_error * dav_fs_open_lockdb(request_rec *r, int ro, int force,
                                      dav_lockdb **lockdb)
{
    dav_lockdb_combined *comb;

    comb = apr_pcalloc(r->pool, sizeof(*comb));
    comb->pub.hooks = &dav_hooks_locks_fs;
    comb->pub.ro = ro;
    comb->pub.info = &comb->priv;
    comb->priv.r = r;
    comb->priv.pool = r->pool;

    comb->priv.lockdb_path = dav_get_lockdb_path(r);
    if (comb->priv.lockdb_path == NULL) {
        return dav_new_error(r->pool, HTTP_INTERNAL_SERVER_ERROR,
                             DAV_ERR_LOCK_NO_DB,
                             "A lock database was not specified with the "
                             "DAVLockDB directive. One must be specified "
                             "to use the locking functionality.");
    }

    /* done initializing. return it. */
    *lockdb = &comb->pub;

    if (force) {
        /* ### add a higher-level comment? */
        return dav_fs_really_open_lockdb(*lockdb);
    }

    return NULL;
}

/*
** dav_fs_close_lockdb:
**
** Close it. Duh.
*/
static void dav_fs_close_lockdb(dav_lockdb *lockdb)
{
    if (lockdb->info->db != NULL)
        dav_dbm_close(lockdb->info->db);
}

/*
** dav_fs_build_fname_key
**
** Given a pathname, build a DAV_TYPE_FNAME lock database key.
*/
static apr_datum_t dav_fs_build_fname_key(apr_pool_t *p, const char *pathname)
{
    apr_datum_t key;

    /* ### does this allocation have a proper lifetime? need to check */
    /* ### can we use a buffer for this? */

    /* size is TYPE + pathname + null */
    key.dsize = strlen(pathname) + 2;
    key.dptr = apr_palloc(p, key.dsize);
    *key.dptr = DAV_TYPE_FNAME;
    memcpy(key.dptr + 1, pathname, key.dsize - 1);
    if (key.dptr[key.dsize - 2] == '/')
        key.dptr[--key.dsize - 1] = '\0';
    return key;
}

/*
** dav_fs_build_key:  Given a resource, return a apr_datum_t key
**    to look up lock information for this file.
**
**    (inode/dev not supported or file is lock-null):
**       apr_datum_t->dvalue = full path
**
**    (inode/dev supported and file exists ):
**       apr_datum_t->dvalue = inode, dev
*/
static apr_datum_t dav_fs_build_key(apr_pool_t *p,
                                    const dav_resource *resource)
{
    const char *file = dav_fs_pathname(resource);
    apr_datum_t key;
    apr_finfo_t finfo;
    apr_status_t rv;

    /* ### use lstat() ?? */
    /*
     * XXX: What for platforms with no IDENT (dev/inode)?
     */
    rv = apr_stat(&finfo, file, APR_FINFO_IDENT, p);
    if ((rv == APR_SUCCESS || rv == APR_INCOMPLETE)
        && ((finfo.valid & APR_FINFO_IDENT) == APR_FINFO_IDENT))
    {
        /* ### can we use a buffer for this? */
        key.dsize = 1 + sizeof(finfo.inode) + sizeof(finfo.device);
        key.dptr = apr_palloc(p, key.dsize);
        *key.dptr = DAV_TYPE_INODE;
        memcpy(key.dptr + 1, &finfo.inode, sizeof(finfo.inode));
        memcpy(key.dptr + 1 + sizeof(finfo.inode), &finfo.device,
               sizeof(finfo.device));

        return key;
    }

    return dav_fs_build_fname_key(p, file);
}

/*
** dav_fs_lock_expired:  return 1 (true) if the given timeout is in the past
**    or present (the lock has expired), or 0 (false) if in the future
**    (the lock has not yet expired).
*/
static int dav_fs_lock_expired(time_t expires)
{
    return expires != DAV_TIMEOUT_INFINITE && time(NULL) >= expires;
}

/*
** dav_fs_save_lock_record:  Saves the lock information specified in the
**    direct and indirect lock lists about path into the lock database.
**    If direct and indirect == NULL, the key is removed.
*/
static dav_error * dav_fs_save_lock_record(dav_lockdb *lockdb, apr_datum_t key,
                                           dav_lock_discovery *direct,
                                           dav_lock_indirect *indirect)
{
    dav_error *err;
    apr_datum_t val = { 0 };
    char *ptr;
    dav_lock_discovery *dp = direct;
    dav_lock_indirect *ip = indirect;

#if DAV_DEBUG
    if (lockdb->ro) {
        return dav_new_error(lockdb->info->pool,
                             HTTP_INTERNAL_SERVER_ERROR, 0,
                             "INTERNAL DESIGN ERROR: the lockdb was opened "
                             "readonly, but an attempt to save locks was "
                             "performed.");
    }
#endif

    if ((err = dav_fs_really_open_lockdb(lockdb)) != NULL) {
        /* ### add a higher-level error? */
        return err;
    }

    /* If nothing to save, delete key */
    if (dp == NULL && ip == NULL) {
        /* don't fail if the key is not present */
        /* ### but what about other errors? */
        (void) dav_dbm_delete(lockdb->info->db, key);
        return NULL;
    }
                
    while(dp) {
        val.dsize += dav_size_direct(dp);
        dp = dp->next;
    }
    while(ip) {
        val.dsize += dav_size_indirect(ip);
        ip = ip->next;
    }

    /* ### can this be apr_palloc() ? */
    /* ### hmmm.... investigate the use of a buffer here */
    ptr = val.dptr = apr_pcalloc(lockdb->info->pool, val.dsize);
    dp  = direct;
    ip  = indirect;

    while(dp) {
        *ptr++ = DAV_LOCK_DIRECT;       /* Direct lock - lock_discovery struct follows */
        memcpy(ptr, dp, sizeof(dp->f)); /* Fixed portion of struct */
        ptr += sizeof(dp->f);
        memcpy(ptr, dp->locktoken, sizeof(*dp->locktoken));
        ptr += sizeof(*dp->locktoken);
        if (dp->owner == NULL) {
            *ptr++ = '\0';
        }
        else {
            memcpy(ptr, dp->owner, strlen(dp->owner) + 1);      
            ptr += strlen(dp->owner) + 1;
        }
        if (dp->auth_user == NULL) {
            *ptr++ = '\0';
        }
        else {
            memcpy(ptr, dp->auth_user, strlen(dp->auth_user) + 1);
            ptr += strlen(dp->auth_user) + 1;
        }

        dp = dp->next;
    }

    while(ip) {
        *ptr++ = DAV_LOCK_INDIRECT;     /* Indirect lock prefix */
        memcpy(ptr, ip->locktoken, sizeof(*ip->locktoken));     /* Locktoken */
        ptr += sizeof(*ip->locktoken);
        memcpy(ptr, &ip->timeout, sizeof(ip->timeout));         /* Expire time */
        ptr += sizeof(ip->timeout);
        memcpy(ptr, &ip->key.dsize, sizeof(ip->key.dsize));     /* Size of key */
        ptr += sizeof(ip->key.dsize);
        memcpy(ptr, ip->key.dptr, ip->key.dsize);       /* Key data */
        ptr += ip->key.dsize;
        ip = ip->next;
    }

    if ((err = dav_dbm_store(lockdb->info->db, key, val)) != NULL) {
        /* ### more details? add an error_id? */
        return dav_push_error(lockdb->info->pool,
                              HTTP_INTERNAL_SERVER_ERROR,
                              DAV_ERR_LOCK_SAVE_LOCK,
                              "Could not save lock information.",
                              err);
    }

    return NULL;
}

/*
** dav_load_lock_record:  Reads lock information about key from lock db;
**    creates linked lists of the direct and indirect locks.
**
**    If add_method = DAV_APPEND_LIST, the result will be appended to the
**    head of the direct and indirect lists supplied.
**
**    Passive lock removal:  If lock has timed out, it will not be returned.
**    ### How much "logging" does RFC 2518 require?
*/
static dav_error * dav_fs_load_lock_record(dav_lockdb *lockdb, apr_datum_t key,
                                           int add_method,
                                           dav_lock_discovery **direct,
                                           dav_lock_indirect **indirect)
{
    apr_pool_t *p = lockdb->info->pool;
    dav_error *err;
    apr_size_t offset = 0;
    int need_save = DAV_FALSE;
    apr_datum_t val = { 0 };
    dav_lock_discovery *dp;
    dav_lock_indirect *ip;
    dav_buffer buf = { 0 };

    if (add_method != DAV_APPEND_LIST) {
        *direct = NULL;
        *indirect = NULL;
    }

    if ((err = dav_fs_really_open_lockdb(lockdb)) != NULL) {
        /* ### add a higher-level error? */
        return err;
    }

    /*
    ** If we opened readonly and the db wasn't there, then there are no
    ** locks for this resource. Just exit.
    */
    if (lockdb->info->db == NULL)
        return NULL;

    if ((err = dav_dbm_fetch(lockdb->info->db, key, &val)) != NULL)
        return err;
        
    if (!val.dsize)
        return NULL;

    while (offset < val.dsize) {
        switch (*(val.dptr + offset++)) {
        case DAV_LOCK_DIRECT:
            /* Create and fill a dav_lock_discovery structure */

            dp = apr_pcalloc(p, sizeof(*dp));
            memcpy(dp, val.dptr + offset, sizeof(dp->f));
            offset += sizeof(dp->f);
            dp->locktoken = apr_palloc(p, sizeof(*dp->locktoken));
            memcpy(dp->locktoken, val.dptr + offset, sizeof(*dp->locktoken));
            offset += sizeof(*dp->locktoken);
            if (*(val.dptr + offset) == '\0') {
                ++offset;
            }
            else {
                dp->owner = apr_pstrdup(p, val.dptr + offset);
                offset += strlen(dp->owner) + 1;
            }

            if (*(val.dptr + offset) == '\0') {
                ++offset;
            } 
            else {
                dp->auth_user = apr_pstrdup(p, val.dptr + offset);
                offset += strlen(dp->auth_user) + 1;
            }

            if (!dav_fs_lock_expired(dp->f.timeout)) {
                dp->next = *direct;
                *direct = dp;
            }
            else {
                need_save = DAV_TRUE;

                /* Remove timed-out locknull fm .locknull list */
                if (*key.dptr == DAV_TYPE_FNAME) {
                    const char *fname = key.dptr + 1;
                    apr_finfo_t finfo;
                    apr_status_t rv;

                    /* if we don't see the file, then it's a locknull */
                    rv = apr_lstat(&finfo, fname, APR_FINFO_MIN, p);
                    if (rv != APR_SUCCESS && rv != APR_INCOMPLETE) {
                        if ((err = dav_fs_remove_locknull_member(p, fname, &buf)) != NULL) {
                            /* ### push a higher-level description? */
                            return err;
                        }
                    }
                }
            }
            break;

        case DAV_LOCK_INDIRECT:
            /* Create and fill a dav_lock_indirect structure */

            ip = apr_pcalloc(p, sizeof(*ip));
            ip->locktoken = apr_palloc(p, sizeof(*ip->locktoken));
            memcpy(ip->locktoken, val.dptr + offset, sizeof(*ip->locktoken));
            offset += sizeof(*ip->locktoken);
            memcpy(&ip->timeout, val.dptr + offset, sizeof(ip->timeout));
            offset += sizeof(ip->timeout);
            memcpy(&ip->key.dsize, val.dptr + offset, sizeof(ip->key.dsize)); /* length of datum */
            offset += sizeof(ip->key.dsize);
            ip->key.dptr = apr_palloc(p, ip->key.dsize); 
            memcpy(ip->key.dptr, val.dptr + offset, ip->key.dsize);
            offset += ip->key.dsize;

            if (!dav_fs_lock_expired(ip->timeout)) {
                ip->next = *indirect;
                *indirect = ip;
            }
            else {
                need_save = DAV_TRUE;
                /* A locknull resource will never be locked indirectly */
            }

            break;

        default:
            dav_dbm_freedatum(lockdb->info->db, val);

            /* ### should use a computed_desc and insert corrupt token data */
            --offset;
            return dav_new_error(p,
                                 HTTP_INTERNAL_SERVER_ERROR,
                                 DAV_ERR_LOCK_CORRUPT_DB,
                                 apr_psprintf(p,
                                             "The lock database was found to "
                                             "be corrupt. offset %"
                                             APR_SIZE_T_FMT ", c=%02x",
                                             offset, val.dptr[offset]));
        }
    }

    dav_dbm_freedatum(lockdb->info->db, val);

    /* Clean up this record if we found expired locks */
    /*
    ** ### shouldn't do this if we've been opened READONLY. elide the
    ** ### timed-out locks from the response, but don't save that info back
    */
    if (need_save == DAV_TRUE) {
        return dav_fs_save_lock_record(lockdb, key, *direct, *indirect);
    }

    return NULL;
}

/* resolve <indirect>, returning <*direct> */
static dav_error * dav_fs_resolve(dav_lockdb *lockdb,
                                  dav_lock_indirect *indirect,
                                  dav_lock_discovery **direct,
                                  dav_lock_discovery **ref_dp,
                                  dav_lock_indirect **ref_ip)
{
    dav_error *err;
    dav_lock_discovery *dir;
    dav_lock_indirect *ind;
        
    if ((err = dav_fs_load_lock_record(lockdb, indirect->key,
                                       DAV_CREATE_LIST,
                                       &dir, &ind)) != NULL) {
        /* ### insert a higher-level description? */
        return err;
    }
    if (ref_dp != NULL) {
        *ref_dp = dir;
        *ref_ip = ind;
    }
                
    for (; dir != NULL; dir = dir->next) {
        if (!dav_compare_locktoken(indirect->locktoken, dir->locktoken)) {
            *direct = dir;
            return NULL;
        }
    }

    /* No match found (but we should have found one!) */

    /* ### use a different description and/or error ID? */
    return dav_new_error(lockdb->info->pool,
                         HTTP_INTERNAL_SERVER_ERROR,
                         DAV_ERR_LOCK_CORRUPT_DB,
                         "The lock database was found to be corrupt. "
                         "An indirect lock's direct lock could not "
                         "be found.");
}

/* ---------------------------------------------------------------
**
** Property-related lock functions
**
*/

/*
** dav_fs_get_supportedlock:  Returns a static string for all supportedlock
**    properties. I think we save more returning a static string than
**    constructing it every time, though it might look cleaner.
*/
static const char *dav_fs_get_supportedlock(const dav_resource *resource)
{
    static const char supported[] = DEBUG_CR
        "<D:lockentry>" DEBUG_CR
        "<D:lockscope><D:exclusive/></D:lockscope>" DEBUG_CR
        "<D:locktype><D:write/></D:locktype>" DEBUG_CR
        "</D:lockentry>" DEBUG_CR
        "<D:lockentry>" DEBUG_CR
        "<D:lockscope><D:shared/></D:lockscope>" DEBUG_CR
        "<D:locktype><D:write/></D:locktype>" DEBUG_CR
        "</D:lockentry>" DEBUG_CR;

    return supported;
}

/* ---------------------------------------------------------------
**
** General lock functions
**
*/

/* ---------------------------------------------------------------
**
** Functions dealing with lock-null resources
**
*/

/*
** dav_fs_load_locknull_list:  Returns a dav_buffer dump of the locknull file
**    for the given directory.
*/
static dav_error * dav_fs_load_locknull_list(apr_pool_t *p, const char *dirpath,
                                             dav_buffer *pbuf) 
{
    apr_finfo_t finfo;
    apr_file_t *file = NULL;
    dav_error *err = NULL;
    apr_size_t amt;
    apr_status_t rv;

    dav_buffer_init(p, pbuf, dirpath);

    if (pbuf->buf[pbuf->cur_len - 1] == '/')
        pbuf->buf[--pbuf->cur_len] = '\0';

    dav_buffer_place(p, pbuf, "/" DAV_FS_STATE_DIR "/" DAV_FS_LOCK_NULL_FILE);

    /* reset this in case we leave w/o reading into the buffer */
    pbuf->cur_len = 0;

    if (apr_file_open(&file, pbuf->buf, APR_READ | APR_BINARY, APR_OS_DEFAULT,
                p) != APR_SUCCESS) {
        return NULL;
    }

    rv = apr_file_info_get(&finfo, APR_FINFO_SIZE, file);
    if (rv != APR_SUCCESS) {
        err = dav_new_error(p, HTTP_INTERNAL_SERVER_ERROR, 0,
                            apr_psprintf(p,
                                        "Opened but could not stat file %s",
                                        pbuf->buf));
        goto loaderror;
    }

    if (finfo.size != (apr_size_t)finfo.size) {
        err = dav_new_error(p, HTTP_INTERNAL_SERVER_ERROR, 0,
                            apr_psprintf(p,
                                        "Opened but rejected huge file %s",
                                        pbuf->buf));
        goto loaderror;
    }

    amt = (apr_size_t)finfo.size;
    dav_set_bufsize(p, pbuf, amt);
    if (apr_file_read(file, pbuf->buf, &amt) != APR_SUCCESS
        || amt != finfo.size) {
        err = dav_new_error(p, HTTP_INTERNAL_SERVER_ERROR, 0,
                            apr_psprintf(p,
                                        "Failure reading locknull file "
                                        "for %s", dirpath));

        /* just in case the caller disregards the returned error */
        pbuf->cur_len = 0;
        goto loaderror;
    }

  loaderror:
    apr_file_close(file);
    return err;
}

/*
** dav_fs_save_locknull_list:  Saves contents of pbuf into the
**    locknull file for dirpath.
*/
static dav_error * dav_fs_save_locknull_list(apr_pool_t *p, const char *dirpath,
                                             dav_buffer *pbuf)
{
    const char *pathname;
    apr_file_t *file = NULL;
    dav_error *err = NULL;
    apr_size_t amt;

    if (pbuf->buf == NULL)
        return NULL;

    dav_fs_ensure_state_dir(p, dirpath);
    pathname = apr_pstrcat(p,
                          dirpath,
                          dirpath[strlen(dirpath) - 1] == '/' ? "" : "/",
                          DAV_FS_STATE_DIR "/" DAV_FS_LOCK_NULL_FILE,
                          NULL);

    if (pbuf->cur_len == 0) {
        /* delete the file if cur_len == 0 */
        if (apr_file_remove(pathname, p) != 0) {
            return dav_new_error(p, HTTP_INTERNAL_SERVER_ERROR, 0,
                                 apr_psprintf(p,
                                             "Error removing %s", pathname));
        }
        return NULL;
    }

    if (apr_file_open(&file, pathname,
                APR_WRITE | APR_CREATE | APR_TRUNCATE | APR_BINARY,
                APR_OS_DEFAULT, p) != APR_SUCCESS) {
        return dav_new_error(p, HTTP_INTERNAL_SERVER_ERROR, 0,
                             apr_psprintf(p,
                                         "Error opening %s for writing",
                                         pathname));
    }

    amt = pbuf->cur_len;
    if (apr_file_write(file, pbuf->buf, &amt) != APR_SUCCESS
        || amt != pbuf->cur_len) {
        err = dav_new_error(p, HTTP_INTERNAL_SERVER_ERROR, 0,
                            apr_psprintf(p,
                                        "Error writing %" APR_SIZE_T_FMT 
                                        " bytes to %s",
                                        pbuf->cur_len, pathname));
    }

    apr_file_close(file);
    return err;
}

/*
** dav_fs_remove_locknull_member:  Removes filename from the locknull list
**    for directory path.
*/
static dav_error * dav_fs_remove_locknull_member(apr_pool_t *p,
                                                 const char *filename,
                                                 dav_buffer *pbuf)
{
    dav_error *err;
    apr_size_t len;
    apr_size_t scanlen;
    char *scan;
    const char *scanend;
    char *dirpath = apr_pstrdup(p, filename);
    char *fname = strrchr(dirpath, '/');
    int dirty = 0;

    if (fname != NULL)
        *fname++ = '\0';
    else
        fname = dirpath;
    len = strlen(fname) + 1;

    if ((err = dav_fs_load_locknull_list(p, dirpath, pbuf)) != NULL) {
        /* ### add a higher level description? */
        return err;
    }

    for (scan = pbuf->buf, scanend = scan + pbuf->cur_len;
         scan < scanend;
         scan += scanlen) {
        scanlen = strlen(scan) + 1;
        if (len == scanlen && memcmp(fname, scan, scanlen) == 0) {
            pbuf->cur_len -= scanlen;
            memmove(scan, scan + scanlen, scanend - (scan + scanlen));
            dirty = 1;
            break;
        }
    }

    if (dirty) {
        if ((err = dav_fs_save_locknull_list(p, dirpath, pbuf)) != NULL) {
            /* ### add a higher level description? */
            return err;
        }
    }

    return NULL;
}

/* Note: used by dav_fs_repos.c */
dav_error * dav_fs_get_locknull_members(
    const dav_resource *resource,
    dav_buffer *pbuf)
{
    const char *dirpath;

    /* ### should test this result value... */
    (void) dav_fs_dir_file_name(resource, &dirpath, NULL);
    return dav_fs_load_locknull_list(dav_fs_pool(resource), dirpath, pbuf);
}

/* ### fold into append_lock? */
/* ### take an optional buf parameter? */
static dav_error * dav_fs_add_locknull_state(
    dav_lockdb *lockdb,
    const dav_resource *resource)
{
    dav_buffer buf = { 0 };
    apr_pool_t *p = lockdb->info->pool;
    const char *dirpath;
    const char *fname;
    dav_error *err;

    /* ### should test this result value... */
    (void) dav_fs_dir_file_name(resource, &dirpath, &fname);

    if ((err = dav_fs_load_locknull_list(p, dirpath, &buf)) != NULL) {
        return dav_push_error(p, HTTP_INTERNAL_SERVER_ERROR, 0,
                              "Could not load .locknull file.", err);
    }

    dav_buffer_append(p, &buf, fname);
    buf.cur_len++;      /* we want the null-term here */

    if ((err = dav_fs_save_locknull_list(p, dirpath, &buf)) != NULL) {
        return dav_push_error(p, HTTP_INTERNAL_SERVER_ERROR, 0,
                              "Could not save .locknull file.", err);
    }

    return NULL;
}

/*
** dav_fs_remove_locknull_state:  Given a request, check to see if r->filename
**    is/was a lock-null resource.  If so, return it to an existant state.
**
**    ### this function is broken... it doesn't check!
**
**    In this implementation, this involves two things:
**    (a) remove it from the list in the appropriate .DAV/locknull file
**    (b) on *nix, convert the key from a filename to an inode.
*/
static dav_error * dav_fs_remove_locknull_state(
    dav_lockdb *lockdb,
    const dav_resource *resource)
{
    dav_buffer buf = { 0 };
    dav_error *err;
    apr_pool_t *p = lockdb->info->pool;
    const char *pathname = dav_fs_pathname(resource);

    if ((err = dav_fs_remove_locknull_member(p, pathname, &buf)) != NULL) {
        /* ### add a higher-level description? */
        return err;
    }

    {
        dav_lock_discovery *ld;
        dav_lock_indirect  *id;
        apr_datum_t key;

        /*
        ** Fetch the lock(s) that made the resource lock-null. Remove
        ** them under the filename key. Obtain the new inode key, and
        ** save the same lock information under it.
        */
        key = dav_fs_build_fname_key(p, pathname);
        if ((err = dav_fs_load_lock_record(lockdb, key, DAV_CREATE_LIST,
                                           &ld, &id)) != NULL) {
            /* ### insert a higher-level error description */
            return err;
        }

        if ((err = dav_fs_save_lock_record(lockdb, key, NULL, NULL)) != NULL) {
            /* ### insert a higher-level error description */
            return err;
        }

        key = dav_fs_build_key(p, resource);
        if ((err = dav_fs_save_lock_record(lockdb, key, ld, id)) != NULL) {
            /* ### insert a higher-level error description */
            return err;
        }
    }

    return NULL;
}

static dav_error * dav_fs_create_lock(dav_lockdb *lockdb,
                                      const dav_resource *resource,
                                      dav_lock **lock)
{
    apr_datum_t key;

    key = dav_fs_build_key(lockdb->info->pool, resource);

    *lock = dav_fs_alloc_lock(lockdb,
                              key,
                              NULL);

    (*lock)->is_locknull = !resource->exists;

    return NULL;
}

static dav_error * dav_fs_get_locks(dav_lockdb *lockdb,
                                    const dav_resource *resource,
                                    int calltype,
                                    dav_lock **locks)
{
    apr_pool_t *p = lockdb->info->pool;
    apr_datum_t key;
    dav_error *err;
    dav_lock *lock = NULL;
    dav_lock *newlock;
    dav_lock_discovery *dp;
    dav_lock_indirect *ip;

#if DAV_DEBUG
    if (calltype == DAV_GETLOCKS_COMPLETE) {
        return dav_new_error(lockdb->info->pool,
                             HTTP_INTERNAL_SERVER_ERROR, 0,
                             "INTERNAL DESIGN ERROR: DAV_GETLOCKS_COMPLETE "
                             "is not yet supported");
    }
#endif

    key = dav_fs_build_key(p, resource);
    if ((err = dav_fs_load_lock_record(lockdb, key, DAV_CREATE_LIST,
                                       &dp, &ip)) != NULL) {
        /* ### push a higher-level desc? */
        return err;
    }

    /* copy all direct locks to the result list */
    for (; dp != NULL; dp = dp->next) {
        newlock = dav_fs_alloc_lock(lockdb, key, dp->locktoken);
        newlock->is_locknull = !resource->exists;
        newlock->scope = dp->f.scope;
        newlock->type = dp->f.type;
        newlock->depth = dp->f.depth;
        newlock->timeout = dp->f.timeout;
        newlock->owner = dp->owner;
        newlock->auth_user = dp->auth_user;

        /* hook into the result list */
        newlock->next = lock;
        lock = newlock;
    }

    /* copy all the indirect locks to the result list. resolve as needed. */
    for (; ip != NULL; ip = ip->next) {
        newlock = dav_fs_alloc_lock(lockdb, ip->key, ip->locktoken);
        newlock->is_locknull = !resource->exists;

        if (calltype == DAV_GETLOCKS_RESOLVED) {
            if ((err = dav_fs_resolve(lockdb, ip, &dp, NULL, NULL)) != NULL) {
                /* ### push a higher-level desc? */
                return err;
            }

            newlock->scope = dp->f.scope;
            newlock->type = dp->f.type;
            newlock->depth = dp->f.depth;
            newlock->timeout = dp->f.timeout;
            newlock->owner = dp->owner;
            newlock->auth_user = dp->auth_user;
        }
        else {
            /* DAV_GETLOCKS_PARTIAL */
            newlock->rectype = DAV_LOCKREC_INDIRECT_PARTIAL;
        }

        /* hook into the result list */
        newlock->next = lock;
        lock = newlock;
    }

    *locks = lock;
    return NULL;
}

static dav_error * dav_fs_find_lock(dav_lockdb *lockdb,
                                    const dav_resource *resource,
                                    const dav_locktoken *locktoken,
                                    int partial_ok,
                                    dav_lock **lock)
{
    dav_error *err;
    apr_datum_t key;
    dav_lock_discovery *dp;
    dav_lock_indirect *ip;

    *lock = NULL;

    key = dav_fs_build_key(lockdb->info->pool, resource);
    if ((err = dav_fs_load_lock_record(lockdb, key, DAV_CREATE_LIST,
                                       &dp, &ip)) != NULL) {
        /* ### push a higher-level desc? */
        return err;
    }

    for (; dp != NULL; dp = dp->next) {
        if (!dav_compare_locktoken(locktoken, dp->locktoken)) {
            *lock = dav_fs_alloc_lock(lockdb, key, locktoken);
            (*lock)->is_locknull = !resource->exists;
            (*lock)->scope = dp->f.scope;
            (*lock)->type = dp->f.type;
            (*lock)->depth = dp->f.depth;
            (*lock)->timeout = dp->f.timeout;
            (*lock)->owner = dp->owner;
            (*lock)->auth_user = dp->auth_user;
            return NULL;
        }
    }

    for (; ip != NULL; ip = ip->next) {
        if (!dav_compare_locktoken(locktoken, ip->locktoken)) {
            *lock = dav_fs_alloc_lock(lockdb, ip->key, locktoken);
            (*lock)->is_locknull = !resource->exists;

            /* ### nobody uses the resolving right now! */
            if (partial_ok) {
                (*lock)->rectype = DAV_LOCKREC_INDIRECT_PARTIAL;
            }
            else {
                (*lock)->rectype = DAV_LOCKREC_INDIRECT;
                if ((err = dav_fs_resolve(lockdb, ip, &dp,
                                          NULL, NULL)) != NULL) {
                    /* ### push a higher-level desc? */
                    return err;
                }
                (*lock)->scope = dp->f.scope;
                (*lock)->type = dp->f.type;
                (*lock)->depth = dp->f.depth;
                (*lock)->timeout = dp->f.timeout;
                (*lock)->owner = dp->owner;
                (*lock)->auth_user = dp->auth_user;
            }
            return NULL;
        }
    }

    return NULL;
}

static dav_error * dav_fs_has_locks(dav_lockdb *lockdb,
                                    const dav_resource *resource,
                                    int *locks_present)
{
    dav_error *err;
    apr_datum_t key;

    *locks_present = 0;

    if ((err = dav_fs_really_open_lockdb(lockdb)) != NULL) {
        /* ### insert a higher-level error description */
        return err;
    }

    /*
    ** If we opened readonly and the db wasn't there, then there are no
    ** locks for this resource. Just exit.
    */
    if (lockdb->info->db == NULL)
        return NULL;

    key = dav_fs_build_key(lockdb->info->pool, resource);

    *locks_present = dav_dbm_exists(lockdb->info->db, key);

    return NULL;
}

static dav_error * dav_fs_append_locks(dav_lockdb *lockdb,
                                       const dav_resource *resource,
                                       int make_indirect,
                                       const dav_lock *lock)
{
    apr_pool_t *p = lockdb->info->pool;
    dav_error *err;
    dav_lock_indirect *ip;
    dav_lock_discovery *dp;
    apr_datum_t key;

    key = dav_fs_build_key(lockdb->info->pool, resource);
    if ((err = dav_fs_load_lock_record(lockdb, key, 0, &dp, &ip)) != NULL) {
        /* ### maybe add in a higher-level description */
        return err;
    }

    /*
    ** ### when we store the lock more directly, we need to update
    ** ### lock->rectype and lock->is_locknull
    */

    if (make_indirect) {
        for (; lock != NULL; lock = lock->next) {

            /* ### this works for any <lock> rectype */
            dav_lock_indirect *newi = apr_pcalloc(p, sizeof(*newi));

            /* ### shut off the const warning for now */
            newi->locktoken = (dav_locktoken *)lock->locktoken;
            newi->timeout   = lock->timeout;
            newi->key       = lock->info->key;
            newi->next      = ip;
            ip              = newi;
        }
    }
    else {
        for (; lock != NULL; lock = lock->next) {
            /* create and link in the right kind of lock */

            if (lock->rectype == DAV_LOCKREC_DIRECT) {
                dav_lock_discovery *newd = apr_pcalloc(p, sizeof(*newd));

                newd->f.scope = lock->scope;
                newd->f.type = lock->type;
                newd->f.depth = lock->depth;
                newd->f.timeout = lock->timeout;
                /* ### shut off the const warning for now */
                newd->locktoken = (dav_locktoken *)lock->locktoken;
                newd->owner = lock->owner;
                newd->auth_user = lock->auth_user;
                newd->next = dp;
                dp = newd;
            }
            else {
                /* DAV_LOCKREC_INDIRECT(_PARTIAL) */

                dav_lock_indirect *newi = apr_pcalloc(p, sizeof(*newi));

                /* ### shut off the const warning for now */
                newi->locktoken = (dav_locktoken *)lock->locktoken;
                newi->key       = lock->info->key;
                newi->next      = ip;
                ip              = newi;
            }
        }
    }

    if ((err = dav_fs_save_lock_record(lockdb, key, dp, ip)) != NULL) {
        /* ### maybe add a higher-level description */
        return err;
    }

    /* we have a special list for recording locknull resources */
    /* ### ack! this can add two copies to the locknull list */
    if (!resource->exists
        && (err = dav_fs_add_locknull_state(lockdb, resource)) != NULL) {
        /* ### maybe add a higher-level description */
        return err;
    }

    return NULL;
}

static dav_error * dav_fs_remove_lock(dav_lockdb *lockdb,
                                      const dav_resource *resource,
                                      const dav_locktoken *locktoken)
{
    dav_error *err;
    dav_buffer buf = { 0 };
    dav_lock_discovery *dh = NULL;
    dav_lock_indirect *ih =