include/apr_sdbm.h

/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */

/*
 * sdbm - ndbm work-alike hashed database library
 * based on Per-Ake Larson's Dynamic Hashing algorithms. BIT 18 (1978).
 * author: oz@nexus.yorku.ca
 * status: ex-public domain
 */

#ifndef APR_SDBM_H
#define APR_SDBM_H

#include "apu.h"
#include "apr_errno.h"
#include "apr_file_io.h"   /* for apr_fileperms_t */

/** 
 * @file apr_sdbm.h
 * @brief apr-util SDBM library
 */
/**
 * @defgroup APR_Util_DBM_SDBM SDBM library
 * @ingroup APR_Util_DBM
 * @{
 */

/**
 * Structure for referencing an sdbm
 */
typedef struct apr_sdbm_t apr_sdbm_t;

/**
 * Structure for referencing the datum record within an sdbm
 */
typedef struct {
    /** pointer to the data stored/retrieved */
    char *dptr;
    /** size of data */
    int dsize;
} apr_sdbm_datum_t;

/* The extensions used for the database files */
/** SDBM Directory file extension */
#define APR_SDBM_DIRFEXT	".dir"
/** SDBM page file extension */
#define APR_SDBM_PAGFEXT	".pag"

/* flags to sdbm_store */
#define APR_SDBM_INSERT     0   /**< Insert */
#define APR_SDBM_REPLACE    1   /**< Replace */
#define APR_SDBM_INSERTDUP  2   /**< Insert with duplicates */

/**
 * Open an sdbm database by file name
 * @param db The newly opened database
 * @param name The sdbm file to open
 * @param mode The flag values (APR_READ and APR_BINARY flags are implicit)
 * <PRE>
 *           APR_WRITE          open for read-write access
 *           APR_CREATE         create the sdbm if it does not exist
 *           APR_TRUNCATE       empty the contents of the sdbm
 *           APR_EXCL           fail for APR_CREATE if the file exists
 *           APR_DELONCLOSE     delete the sdbm when closed
 *           APR_SHARELOCK      support locking across process/machines
 * </PRE>
 * @param perms Permissions to apply to if created
 * @param p The pool to use when creating the sdbm
 * @remark The sdbm name is not a true file name, as sdbm appends suffixes 
 * for seperate data and index files.
 */
APU_DECLARE(apr_status_t) apr_sdbm_open(apr_sdbm_t **db, const char *name, 
                                        apr_int32_t mode, 
                                        apr_fileperms_t perms, apr_pool_t *p);

/**
 * Close an sdbm file previously opened by apr_sdbm_open
 * @param db The database to close
 */
APU_DECLARE(apr_status_t) apr_sdbm_close(apr_sdbm_t *db);

/**
 * Lock an sdbm database for concurency of multiple operations
 * @param db The database to lock
 * @param type The lock type
 * <PRE>
 *           APR_FLOCK_SHARED
 *           APR_FLOCK_EXCLUSIVE
 * </PRE>
 * @remark Calls to apr_sdbm_lock may be nested.  All apr_sdbm functions
 * perform implicit locking.  Since an APR_FLOCK_SHARED lock cannot be 
 * portably promoted to an APR_FLOCK_EXCLUSIVE lock, apr_sdbm_store and 
 * apr_sdbm_delete calls will fail if an APR_FLOCK_SHARED lock is held.
 * The apr_sdbm_lock call requires the database to be opened with the
 * APR_SHARELOCK mode value.
 */
APU_DECLARE(apr_status_t) apr_sdbm_lock(apr_sdbm_t *db, int type);

/**
 * Release an sdbm lock previously aquired by apr_sdbm_lock
 * @param db The database to unlock
 */
APU_DECLARE(apr_status_t) apr_sdbm_unlock(apr_sdbm_t *db);

/**
 * Fetch an sdbm record value by key
 * @param db The database 
 * @param value The value datum retrieved for this record
 * @param key The key datum to find this record
 */
APU_DECLARE(apr_status_t) apr_sdbm_fetch(apr_sdbm_t *db, 
                                         apr_sdbm_datum_t *value, 
                                         apr_sdbm_datum_t key);

/**
 * Store an sdbm record value by key
 * @param db The database 
 * @param key The key datum to store this record by
 * @param value The value datum to store in this record
 * @param opt The method used to store the record
 * <PRE>
 *           APR_SDBM_INSERT     return an error if the record exists
 *           APR_SDBM_REPLACE    overwrite any existing record for key
 * </PRE>
 */
APU_DECLARE(apr_status_t) apr_sdbm_store(apr_sdbm_t *db, apr_sdbm_datum_t key,
                                         apr_sdbm_datum_t value, int opt);

/**
 * Delete an sdbm record value by key
 * @param db The database 
 * @param key The key datum of the record to delete
 * @remark It is not an error to delete a non-existent record.
 */
APU_DECLARE(apr_status_t) apr_sdbm_delete(apr_sdbm_t *db, 
                                          const apr_sdbm_datum_t key);

/**
 * Retrieve the first record key from a dbm
 * @param db The database 
 * @param key The key datum of the first record
 * @remark The keys returned are not ordered.  To traverse the list of keys
 * for an sdbm opened with APR_SHARELOCK, the caller must use apr_sdbm_lock
 * prior to retrieving the first record, and hold the lock until after the
 * last call to apr_sdbm_nextkey.
 */
APU_DECLARE(apr_status_t) apr_sdbm_firstkey(apr_sdbm_t *db, apr_sdbm_datum_t *key);

/**
 * Retrieve the next record key from an sdbm
 * @param db The database 
 * @param key The key datum of the next record
 */
APU_DECLARE(apr_status_t) apr_sdbm_nextkey(apr_sdbm_t *db, apr_sdbm_datum_t *key);

/**
 * Returns true if the sdbm database opened for read-only access
 * @param db The database to test
 */
APU_DECLARE(int) apr_sdbm_rdonly(apr_sdbm_t *db);
/** @} */
#endif /* APR_SDBM_H */