1=pod 2 3=head1 NAME 4 5LHASH, LHASH_OF, DEFINE_LHASH_OF_EX, DEFINE_LHASH_OF, 6OPENSSL_LH_COMPFUNC, OPENSSL_LH_HASHFUNC, OPENSSL_LH_DOALL_FUNC, 7LHASH_DOALL_ARG_FN_TYPE, 8IMPLEMENT_LHASH_HASH_FN, IMPLEMENT_LHASH_COMP_FN, 9lh_TYPE_new, lh_TYPE_free, lh_TYPE_flush, 10lh_TYPE_insert, lh_TYPE_delete, lh_TYPE_retrieve, 11lh_TYPE_doall, lh_TYPE_doall_arg, lh_TYPE_error, 12OPENSSL_LH_new, OPENSSL_LH_free, OPENSSL_LH_flush, 13OPENSSL_LH_insert, OPENSSL_LH_delete, OPENSSL_LH_retrieve, 14OPENSSL_LH_doall, OPENSSL_LH_doall_arg, OPENSSL_LH_error 15- dynamic hash table 16 17=head1 SYNOPSIS 18 19=for openssl generic 20 21 #include <openssl/lhash.h> 22 23 LHASH_OF(TYPE) 24 25 DEFINE_LHASH_OF_EX(TYPE); 26 27 LHASH_OF(TYPE) *lh_TYPE_new(OPENSSL_LH_HASHFUNC hash, OPENSSL_LH_COMPFUNC compare); 28 void lh_TYPE_free(LHASH_OF(TYPE) *table); 29 void lh_TYPE_flush(LHASH_OF(TYPE) *table); 30 31 TYPE *lh_TYPE_insert(LHASH_OF(TYPE) *table, TYPE *data); 32 TYPE *lh_TYPE_delete(LHASH_OF(TYPE) *table, TYPE *data); 33 TYPE *lh_TYPE_retrieve(LHASH_OF(TYPE) *table, TYPE *data); 34 35 void lh_TYPE_doall(LHASH_OF(TYPE) *table, OPENSSL_LH_DOALL_FUNC func); 36 void lh_TYPE_doall_arg(LHASH_OF(TYPE) *table, OPENSSL_LH_DOALL_FUNCARG func, 37 TYPE *arg); 38 39 int lh_TYPE_error(LHASH_OF(TYPE) *table); 40 41 typedef int (*OPENSSL_LH_COMPFUNC)(const void *, const void *); 42 typedef unsigned long (*OPENSSL_LH_HASHFUNC)(const void *); 43 typedef void (*OPENSSL_LH_DOALL_FUNC)(const void *); 44 typedef void (*LHASH_DOALL_ARG_FN_TYPE)(const void *, const void *); 45 46 OPENSSL_LHASH *OPENSSL_LH_new(OPENSSL_LH_HASHFUNC h, OPENSSL_LH_COMPFUNC c); 47 void OPENSSL_LH_free(OPENSSL_LHASH *lh); 48 void OPENSSL_LH_flush(OPENSSL_LHASH *lh); 49 50 void *OPENSSL_LH_insert(OPENSSL_LHASH *lh, void *data); 51 void *OPENSSL_LH_delete(OPENSSL_LHASH *lh, const void *data); 52 void *OPENSSL_LH_retrieve(OPENSSL_LHASH *lh, const void *data); 53 54 void OPENSSL_LH_doall(OPENSSL_LHASH *lh, OPENSSL_LH_DOALL_FUNC func); 55 void OPENSSL_LH_doall_arg(OPENSSL_LHASH *lh, OPENSSL_LH_DOALL_FUNCARG func, void *arg); 56 57 int OPENSSL_LH_error(OPENSSL_LHASH *lh); 58 59The following macro is deprecated: 60 61 DEFINE_LHASH_OF(TYPE); 62 63=head1 DESCRIPTION 64 65This library implements type-checked dynamic hash tables. The hash 66table entries can be arbitrary structures. Usually they consist of key 67and value fields. In the description here, B<I<TYPE>> is used a placeholder 68for any of the OpenSSL datatypes, such as I<SSL_SESSION>. 69 70To define a new type-checked dynamic hash table, use B<DEFINE_LHASH_OF_EX>(). 71B<DEFINE_LHASH_OF>() was previously used for this purpose, but is now 72deprecated. The B<DEFINE_LHASH_OF_EX>() macro provides all functionality of 73B<DEFINE_LHASH_OF>() except for certain deprecated statistics functions (see 74OPENSSL_LH_stats(3)). 75 76B<lh_I<TYPE>_new>() creates a new B<LHASH_OF>(B<I<TYPE>>) structure to store 77arbitrary data entries, and specifies the 'hash' and 'compare' 78callbacks to be used in organising the table's entries. The I<hash> 79callback takes a pointer to a table entry as its argument and returns 80an unsigned long hash value for its key field. The hash value is 81normally truncated to a power of 2, so make sure that your hash 82function returns well mixed low order bits. The I<compare> callback 83takes two arguments (pointers to two hash table entries), and returns 840 if their keys are equal, nonzero otherwise. 85 86If your hash table 87will contain items of some particular type and the I<hash> and 88I<compare> callbacks hash/compare these types, then the 89B<IMPLEMENT_LHASH_HASH_FN> and B<IMPLEMENT_LHASH_COMP_FN> macros can be 90used to create callback wrappers of the prototypes required by 91B<lh_I<TYPE>_new>() as shown in this example: 92 93 /* 94 * Implement the hash and compare functions; "stuff" can be any word. 95 */ 96 static unsigned long stuff_hash(const TYPE *a) 97 { 98 ... 99 } 100 static int stuff_cmp(const TYPE *a, const TYPE *b) 101 { 102 ... 103 } 104 105 /* 106 * Implement the wrapper functions. 107 */ 108 static IMPLEMENT_LHASH_HASH_FN(stuff, TYPE) 109 static IMPLEMENT_LHASH_COMP_FN(stuff, TYPE) 110 111If the type is going to be used in several places, the following macros 112can be used in a common header file to declare the function wrappers: 113 114 DECLARE_LHASH_HASH_FN(stuff, TYPE) 115 DECLARE_LHASH_COMP_FN(stuff, TYPE) 116 117Then a hash table of B<I<TYPE>> objects can be created using this: 118 119 LHASH_OF(TYPE) *htable; 120 121 htable = B<lh_I<TYPE>_new>(LHASH_HASH_FN(stuff), LHASH_COMP_FN(stuff)); 122 123B<lh_I<TYPE>_free>() frees the B<LHASH_OF>(B<I<TYPE>>) structure 124I<table>. Allocated hash table entries will not be freed; consider 125using B<lh_I<TYPE>_doall>() to deallocate any remaining entries in the 126hash table (see below). 127 128B<lh_I<TYPE>_flush>() empties the B<LHASH_OF>(B<I<TYPE>>) structure I<table>. New 129entries can be added to the flushed table. Allocated hash table entries 130will not be freed; consider using B<lh_I<TYPE>_doall>() to deallocate any 131remaining entries in the hash table (see below). 132 133B<lh_I<TYPE>_insert>() inserts the structure pointed to by I<data> into 134I<table>. If there already is an entry with the same key, the old 135value is replaced. Note that B<lh_I<TYPE>_insert>() stores pointers, the 136data are not copied. 137 138B<lh_I<TYPE>_delete>() deletes an entry from I<table>. 139 140B<lh_I<TYPE>_retrieve>() looks up an entry in I<table>. Normally, I<data> 141is a structure with the key field(s) set; the function will return a 142pointer to a fully populated structure. 143 144B<lh_I<TYPE>_doall>() will, for every entry in the hash table, call 145I<func> with the data item as its parameter. 146For example: 147 148 /* Cleans up resources belonging to 'a' (this is implemented elsewhere) */ 149 void TYPE_cleanup_doall(TYPE *a); 150 151 /* Implement a prototype-compatible wrapper for "TYPE_cleanup" */ 152 IMPLEMENT_LHASH_DOALL_FN(TYPE_cleanup, TYPE) 153 154 /* Call "TYPE_cleanup" against all items in a hash table. */ 155 lh_TYPE_doall(hashtable, LHASH_DOALL_FN(TYPE_cleanup)); 156 157 /* Then the hash table itself can be deallocated */ 158 lh_TYPE_free(hashtable); 159 160When doing this, be careful if you delete entries from the hash table 161in your callbacks: the table may decrease in size, moving the item 162that you are currently on down lower in the hash table - this could 163cause some entries to be skipped during the iteration. The second 164best solution to this problem is to set hash-E<gt>down_load=0 before 165you start (which will stop the hash table ever decreasing in size). 166The best solution is probably to avoid deleting items from the hash 167table inside a "doall" callback! 168 169B<lh_I<TYPE>_doall_arg>() is the same as B<lh_I<TYPE>_doall>() except that 170I<func> will be called with I<arg> as the second argument and I<func> 171should be of type B<LHASH_DOALL_ARG_FN>(B<I<TYPE>>) (a callback prototype 172that is passed both the table entry and an extra argument). As with 173lh_doall(), you can instead choose to declare your callback with a 174prototype matching the types you are dealing with and use the 175declare/implement macros to create compatible wrappers that cast 176variables before calling your type-specific callbacks. An example of 177this is demonstrated here (printing all hash table entries to a BIO 178that is provided by the caller): 179 180 /* Prints item 'a' to 'output_bio' (this is implemented elsewhere) */ 181 void TYPE_print_doall_arg(const TYPE *a, BIO *output_bio); 182 183 /* Implement a prototype-compatible wrapper for "TYPE_print" */ 184 static IMPLEMENT_LHASH_DOALL_ARG_FN(TYPE, const TYPE, BIO) 185 186 /* Print out the entire hashtable to a particular BIO */ 187 lh_TYPE_doall_arg(hashtable, LHASH_DOALL_ARG_FN(TYPE_print), BIO, 188 logging_bio); 189 190 191B<lh_I<TYPE>_error>() can be used to determine if an error occurred in the last 192operation. 193 194OPENSSL_LH_new() is the same as the B<lh_I<TYPE>_new>() except that it is not 195type specific. So instead of returning an B<LHASH_OF(I<TYPE>)> value it returns 196a B<void *>. In the same way the functions OPENSSL_LH_free(), 197OPENSSL_LH_flush(), OPENSSL_LH_insert(), OPENSSL_LH_delete(), 198OPENSSL_LH_retrieve(), OPENSSL_LH_doall(), OPENSSL_LH_doall_arg(), and 199OPENSSL_LH_error() are equivalent to the similarly named B<lh_I<TYPE>> functions 200except that they return or use a B<void *> where the equivalent B<lh_I<TYPE>> 201function returns or uses a B<I<TYPE> *> or B<LHASH_OF(I<TYPE>) *>. B<lh_I<TYPE>> 202functions are implemented as type checked wrappers around the B<OPENSSL_LH> 203functions. Most applications should not call the B<OPENSSL_LH> functions 204directly. 205 206=head1 RETURN VALUES 207 208B<lh_I<TYPE>_new>() and OPENSSL_LH_new() return NULL on error, otherwise a 209pointer to the new B<LHASH> structure. 210 211When a hash table entry is replaced, B<lh_I<TYPE>_insert>() or 212OPENSSL_LH_insert() return the value being replaced. NULL is returned on normal 213operation and on error. 214 215B<lh_I<TYPE>_delete>() and OPENSSL_LH_delete() return the entry being deleted. 216NULL is returned if there is no such value in the hash table. 217 218B<lh_I<TYPE>_retrieve>() and OPENSSL_LH_retrieve() return the hash table entry 219if it has been found, NULL otherwise. 220 221B<lh_I<TYPE>_error>() and OPENSSL_LH_error() return 1 if an error occurred in 222the last operation, 0 otherwise. It's meaningful only after non-retrieve 223operations. 224 225B<lh_I<TYPE>_free>(), OPENSSL_LH_free(), B<lh_I<TYPE>_flush>(), 226OPENSSL_LH_flush(), B<lh_I<TYPE>_doall>() OPENSSL_LH_doall(), 227B<lh_I<TYPE>_doall_arg>() and OPENSSL_LH_doall_arg() return no values. 228 229=head1 NOTE 230 231The LHASH code is not thread safe. All updating operations, as well as 232B<lh_I<TYPE>_error>() or OPENSSL_LH_error() calls must be performed under 233a write lock. All retrieve operations should be performed under a read lock, 234I<unless> accurate usage statistics are desired. In which case, a write lock 235should be used for retrieve operations as well. For output of the usage 236statistics, using the functions from L<OPENSSL_LH_stats(3)>, a read lock 237suffices. 238 239The LHASH code regards table entries as constant data. As such, it 240internally represents lh_insert()'d items with a "const void *" 241pointer type. This is why callbacks such as those used by lh_doall() 242and lh_doall_arg() declare their prototypes with "const", even for the 243parameters that pass back the table items' data pointers - for 244consistency, user-provided data is "const" at all times as far as the 245LHASH code is concerned. However, as callers are themselves providing 246these pointers, they can choose whether they too should be treating 247all such parameters as constant. 248 249As an example, a hash table may be maintained by code that, for 250reasons of encapsulation, has only "const" access to the data being 251indexed in the hash table (i.e. it is returned as "const" from 252elsewhere in their code) - in this case the LHASH prototypes are 253appropriate as-is. Conversely, if the caller is responsible for the 254life-time of the data in question, then they may well wish to make 255modifications to table item passed back in the lh_doall() or 256lh_doall_arg() callbacks (see the "TYPE_cleanup" example above). If 257so, the caller can either cast the "const" away (if they're providing 258the raw callbacks themselves) or use the macros to declare/implement 259the wrapper functions without "const" types. 260 261Callers that only have "const" access to data they're indexing in a 262table, yet declare callbacks without constant types (or cast the 263"const" away themselves), are therefore creating their own risks/bugs 264without being encouraged to do so by the API. On a related note, 265those auditing code should pay special attention to any instances of 266DECLARE/IMPLEMENT_LHASH_DOALL_[ARG_]_FN macros that provide types 267without any "const" qualifiers. 268 269=head1 BUGS 270 271B<lh_I<TYPE>_insert>() and OPENSSL_LH_insert() return NULL both for success 272and error. 273 274=head1 SEE ALSO 275 276L<OPENSSL_LH_stats(3)> 277 278=head1 HISTORY 279 280In OpenSSL 1.0.0, the lhash interface was revamped for better 281type checking. 282 283In OpenSSL 3.1, B<DEFINE_LHASH_OF_EX>() was introduced and B<DEFINE_LHASH_OF>() 284was deprecated. 285 286=head1 COPYRIGHT 287 288Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved. 289 290Licensed under the Apache License 2.0 (the "License"). You may not use 291this file except in compliance with the License. You can obtain a copy 292in the file LICENSE in the source distribution or at 293L<https://www.openssl.org/source/license.html>. 294 295=cut 296