include/apr_hash.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.
 */

#ifndef APR_HASH_H
#define APR_HASH_H

/**
 * @file apr_hash.h
 * @brief APR Hash Tables
 */

#include "apr_pools.h"

#ifdef __cplusplus
extern "C" {
#endif

/**
 * @defgroup apr_hash Hash Tables
 * @ingroup APR 
 * @{
 */

/**
 * When passing a key to apr_hash_set or apr_hash_get, this value can be
 * passed to indicate a string-valued key, and have apr_hash compute the
 * length automatically.
 *
 * @remark apr_hash will use strlen(key) for the length. The NUL terminator
 *         is not included in the hash value (why throw a constant in?).
 *         Since the hash table merely references the provided key (rather
 *         than copying it), apr_hash_this() will return the NUL-term'd key.
 */
#define APR_HASH_KEY_STRING     (-1)

/**
 * Abstract type for hash tables.
 */
typedef struct apr_hash_t apr_hash_t;

/**
 * Abstract type for scanning hash tables.
 */
typedef struct apr_hash_index_t apr_hash_index_t;

/**
 * Callback functions for calculating hash values.
 * @param key The key.
 * @param klen The length of the key, or APR_HASH_KEY_STRING to use the string 
 *             length. If APR_HASH_KEY_STRING then returns the actual key length.
 */
typedef unsigned int (*apr_hashfunc_t)(const char *key, apr_ssize_t *klen);

/**
 * The default hash function.
 */
APR_DECLARE_NONSTD(unsigned int) apr_hashfunc_default(const char *key,
                                                      apr_ssize_t *klen);

/**
 * Create a hash table.
 * @param pool The pool to allocate the hash table out of
 * @return The hash table just created
  */
APR_DECLARE(apr_hash_t *) apr_hash_make(apr_pool_t *pool);

/**
 * Create a hash table with a custom hash function
 * @param pool The pool to allocate the hash table out of
 * @param hash_func A custom hash function.
 * @return The hash table just created
  */
APR_DECLARE(apr_hash_t *) apr_hash_make_custom(apr_pool_t *pool, 
                                               apr_hashfunc_t hash_func);

/**
 * Make a copy of a hash table
 * @param pool The pool from which to allocate the new hash table
 * @param h The hash table to clone
 * @return The hash table just created
 * @remark Makes a shallow copy
 */
APR_DECLARE(apr_hash_t *) apr_hash_copy(apr_pool_t *pool,
                                        const apr_hash_t *h);

/**
 * Associate a value with a key in a hash table.
 * @param ht The hash table
 * @param key Pointer to the key
 * @param klen Length of the key. Can be APR_HASH_KEY_STRING to use the string length.
 * @param val Value to associate with the key
 * @remark If the value is NULL the hash entry is deleted.
 */
APR_DECLARE(void) apr_hash_set(apr_hash_t *ht, const void *key,
                               apr_ssize_t klen, const void *val);

/**
 * Look up the value associated with a key in a hash table.
 * @param ht The hash table
 * @param key Pointer to the key
 * @param klen Length of the key. Can be APR_HASH_KEY_STRING to use the string length.
 * @return Returns NULL if the key is not present.
 */
APR_DECLARE(void *) apr_hash_get(apr_hash_t *ht, const void *key,
                                 apr_ssize_t klen);

/**
 * Start iterating over the entries in a hash table.
 * @param p The pool to allocate the apr_hash_index_t iterator. If this
 *          pool is NULL, then an internal, non-thread-safe iterator is used.
 * @param ht The hash table
 * @remark  There is no restriction on adding or deleting hash entries during
 * an iteration (although the results may be unpredictable unless all you do
 * is delete the current entry) and multiple iterations can be in
 * progress at the same time.

 * @example
 */
/**
 * <PRE>
 * 
 * int sum_values(apr_pool_t *p, apr_hash_t *ht)
 * {
 *     apr_hash_index_t *hi;
 *     void *val;
 *     int sum = 0;
 *     for (hi = apr_hash_first(p, ht); hi; hi = apr_hash_next(hi)) {
 *         apr_hash_this(hi, NULL, NULL, &val);
 *         sum += *(int *)val;
 *     }
 *     return sum;
 * }
 * </PRE>
 */
APR_DECLARE(apr_hash_index_t *) apr_hash_first(apr_pool_t *p, apr_hash_t *ht);

/**
 * Continue iterating over the entries in a hash table.
 * @param hi The iteration state
 * @return a pointer to the updated iteration state.  NULL if there are no more  
 *         entries.
 */
APR_DECLARE(apr_hash_index_t *) apr_hash_next(apr_hash_index_t *hi);

/**
 * Get the current entry's details from the iteration state.
 * @param hi The iteration state
 * @param key Return pointer for the pointer to the key.
 * @param klen Return pointer for the key length.
 * @param val Return pointer for the associated value.
 * @remark The return pointers should point to a variable that will be set to the
 *         corresponding data, or they may be NULL if the data isn't interesting.
 */
APR_DECLARE(void) apr_hash_this(apr_hash_index_t *hi, const void **key, 
                                apr_ssize_t *klen, void **val);

/**
 * Get the number of key/value pairs in the hash table.
 * @param ht The hash table
 * @return The number of key/value pairs in the hash table.
 */
APR_DECLARE(unsigned int) apr_hash_count(apr_hash_t *ht);

/**
 * Merge two hash tables into one new hash table. The values of the overlay
 * hash override the values of the base if both have the same key.  Both
 * hash tables must use the same hash function.
 * @param p The pool to use for the new hash table
 * @param overlay The table to add to the initial table
 * @param base The table that represents the initial values of the new table
 * @return A new hash table containing all of the data from the two passed in
 */
APR_DECLARE(apr_hash_t *) apr_hash_overlay(apr_pool_t *p,
                                           const apr_hash_t *overlay, 
                                           const apr_hash_t *base);

/**
 * Merge two hash tables into one new hash table. If the same key
 * is present in both tables, call the supplied merge function to
 * produce a merged value for the key in the new table.  Both
 * hash tables must use the same hash function.
 * @param p The pool to use for the new hash table
 * @param h1 The first of the tables to merge
 * @param h2 The second of the tables to merge
 * @param merger A callback function to merge values, or NULL to
 *  make values from h1 override values from h2 (same semantics as
 *  apr_hash_overlay())
 * @param data Client data to pass to the merger function
 * @return A new hash table containing all of the data from the two passed in
 */
APR_DECLARE(apr_hash_t *) apr_hash_merge(apr_pool_t *p,
                                         const apr_hash_t *h1,
                                         const apr_hash_t *h2,
                                         void * (*merger)(apr_pool_t *p,
                                                     const void *key,
                                                     apr_ssize_t klen,
                                                     const void *h1_val,
                                                     const void *h2_val,
                                                     const void *data),
                                         const void *data);

/**
 * Get a pointer to the pool which the hash table was created in
 */
APR_POOL_DECLARE_ACCESSOR(hash);

/** @} */

#ifdef __cplusplus
}
#endif

#endif	/* !APR_HASH_H */