+++ /dev/null
-=pod
-
-=head1 NAME
-
-DECLARE_LHASH_OF,
-OPENSSL_LH_COMPFUNC, OPENSSL_LH_HASHFUNC, OPENSSL_LH_DOALL_FUNC,
-LHASH_DOALL_ARG_FN_TYPE,
-IMPLEMENT_LHASH_HASH_FN, IMPLEMENT_LHASH_COMP_FN,
-lh_TYPE_new, lh_TYPE_free,
-lh_TYPE_insert, lh_TYPE_delete, lh_TYPE_retrieve,
-lh_TYPE_doall, lh_TYPE_doall_arg, lh_TYPE_error - dynamic hash table
-
-=for comment generic
-
-=head1 SYNOPSIS
-
- #include <openssl/lhash.h>
-
- DECLARE_LHASH_OF(TYPE);
-
- LHASH *lh_TYPE_new();
- void lh_TYPE_free(LHASH_OF(TYPE *table);
-
- TYPE *lh_TYPE_insert(LHASH_OF(TYPE *table, TYPE *data);
- TYPE *lh_TYPE_delete(LHASH_OF(TYPE *table, TYPE *data);
- TYPE *lh_retrieve(LHASH_OFTYPE *table, TYPE *data);
-
- void lh_TYPE_doall(LHASH_OF(TYPE *table, OPENSSL_LH_DOALL_FUNC func);
- void lh_TYPE_doall_arg(LHASH_OF(TYPE) *table, OPENSSL_LH_DOALL_FUNCARG func,
- TYPE, TYPE *arg);
-
- int lh_TYPE_error(LHASH_OF(TYPE) *table);
-
- typedef int (*OPENSSL_LH_COMPFUNC)(const void *, const void *);
- typedef unsigned long (*OPENSSL_LH_HASHFUNC)(const void *);
- typedef void (*OPENSSL_LH_DOALL_FUNC)(const void *);
- typedef void (*LHASH_DOALL_ARG_FN_TYPE)(const void *, const void *);
-
-=head1 DESCRIPTION
-
-This library implements type-checked dynamic hash tables. The hash
-table entries can be arbitrary structures. Usually they consist of key
-and value fields. In the description here, I<TYPE> is used a placeholder
-for any of the OpenSSL datatypes, such as I<SSL_SESSION>.
-
-lh_TYPE_new() creates a new B<LHASH_OF(TYPE)> structure to store
-arbitrary data entries, and specifies the 'hash' and 'compare'
-callbacks to be used in organising the table's entries. The B<hash>
-callback takes a pointer to a table entry as its argument and returns
-an unsigned long hash value for its key field. The hash value is
-normally truncated to a power of 2, so make sure that your hash
-function returns well mixed low order bits. The B<compare> callback
-takes two arguments (pointers to two hash table entries), and returns
-0 if their keys are equal, non-zero otherwise.
-
-If your hash table
-will contain items of some particular type and the B<hash> and
-B<compare> callbacks hash/compare these types, then the
-B<IMPLEMENT_LHASH_HASH_FN> and B<IMPLEMENT_LHASH_COMP_FN> macros can be
-used to create callback wrappers of the prototypes required by
-lh_TYPE_new() as shown in this example:
-
- /*
- * Implement the hash and compare functions; "stuff" can be any word.
- */
- static unsigned long stuff_hash(const TYPE *a)
- {
- ...
- }
- static int stuff_cmp(const TYPE *a, const TYPE *b)
- {
- ...
- }
-
- /*
- * Implement the wrapper functions.
- */
- static IMPLEMENT_LHASH_HASH_FN(stuff, TYPE)
- static IMPLEMENT_LHASH_COMP_FN(stuff, TYPE)
-
-If the type is going to be used in several places, the following macros
-can be used in a common header file to declare the function wrappers:
-
- DECLARE_LHASH_HASH_FN(stuff, TYPE)
- DECLARE_LHASH_COMP_FN(stuff, TYPE)
-
-Then a hash table of TYPE objects can be created using this:
-
- LHASH_OF(TYPE) *htable;
-
- htable = lh_TYPE_new(LHASH_HASH_FN(stuff), LHASH_COMP_FN(stuff));
-
-lh_TYPE_free() frees the B<LHASH_OF(TYPE)> structure
-B<table>. Allocated hash table entries will not be freed; consider
-using lh_TYPE_doall() to deallocate any remaining entries in the
-hash table (see below).
-
-lh_TYPE_insert() inserts the structure pointed to by B<data> into
-B<table>. If there already is an entry with the same key, the old
-value is replaced. Note that lh_TYPE_insert() stores pointers, the
-data are not copied.
-
-lh_TYPE_delete() deletes an entry from B<table>.
-
-lh_TYPE_retrieve() looks up an entry in B<table>. Normally, B<data>
-is a structure with the key field(s) set; the function will return a
-pointer to a fully populated structure.
-
-lh_TYPE_doall() will, for every entry in the hash table, call
-B<func> with the data item as its parameter.
-For example:
-
- /* Cleans up resources belonging to 'a' (this is implemented elsewhere) */
- void TYPE_cleanup_doall(TYPE *a);
-
- /* Implement a prototype-compatible wrapper for "TYPE_cleanup" */
- IMPLEMENT_LHASH_DOALL_FN(TYPE_cleanup, TYPE)
-
- /* Call "TYPE_cleanup" against all items in a hash table. */
- lh_TYPE_doall(hashtable, LHASH_DOALL_FN(TYPE_cleanup));
-
- /* Then the hash table itself can be deallocated */
- lh_TYPE_free(hashtable);
-
-When doing this, be careful if you delete entries from the hash table
-in your callbacks: the table may decrease in size, moving the item
-that you are currently on down lower in the hash table - this could
-cause some entries to be skipped during the iteration. The second
-best solution to this problem is to set hash-E<gt>down_load=0 before
-you start (which will stop the hash table ever decreasing in size).
-The best solution is probably to avoid deleting items from the hash
-table inside a "doall" callback!
-
-lh_TYPE_doall_arg() is the same as lh_TYPE_doall() except that
-B<func> will be called with B<arg> as the second argument and B<func>
-should be of type B<LHASH_DOALL_ARG_FN_TYPE> (a callback prototype
-that is passed both the table entry and an extra argument). As with
-lh_doall(), you can instead choose to declare your callback with a
-prototype matching the types you are dealing with and use the
-declare/implement macros to create compatible wrappers that cast
-variables before calling your type-specific callbacks. An example of
-this is demonstrated here (printing all hash table entries to a BIO
-that is provided by the caller):
-
- /* Prints item 'a' to 'output_bio' (this is implemented elsewhere) */
- void TYPE_print_doall_arg(const TYPE *a, BIO *output_bio);
-
- /* Implement a prototype-compatible wrapper for "TYPE_print" */
- static IMPLEMENT_LHASH_DOALL_ARG_FN(TYPE, const TYPE, BIO)
-
- /* Print out the entire hashtable to a particular BIO */
- lh_TYPE_doall_arg(hashtable, LHASH_DOALL_ARG_FN(TYPE_print), BIO,
- logging_bio);
-
-
-lh_TYPE_error() can be used to determine if an error occurred in the last
-operation.
-
-=head1 RETURN VALUES
-
-lh_TYPE_new() returns B<NULL> on error, otherwise a pointer to the new
-B<LHASH> structure.
-
-When a hash table entry is replaced, lh_TYPE_insert() returns the value
-being replaced. B<NULL> is returned on normal operation and on error.
-
-lh_TYPE_delete() returns the entry being deleted. B<NULL> is returned if
-there is no such value in the hash table.
-
-lh_TYPE_retrieve() returns the hash table entry if it has been found,
-B<NULL> otherwise.
-
-lh_TYPE_error() returns 1 if an error occurred in the last operation, 0
-otherwise.
-
-lh_TYPE_free(), lh_TYPE_doall() and lh_TYPE_doall_arg() return no values.
-
-=head1 NOTE
-
-The various LHASH macros and callback types exist to make it possible
-to write type-checked code without resorting to function-prototype
-casting - an evil that makes application code much harder to
-audit/verify and also opens the window of opportunity for stack
-corruption and other hard-to-find bugs. It also, apparently, violates
-ANSI-C.
-
-The LHASH code regards table entries as constant data. As such, it
-internally represents lh_insert()'d items with a "const void *"
-pointer type. This is why callbacks such as those used by lh_doall()
-and lh_doall_arg() declare their prototypes with "const", even for the
-parameters that pass back the table items' data pointers - for
-consistency, user-provided data is "const" at all times as far as the
-LHASH code is concerned. However, as callers are themselves providing
-these pointers, they can choose whether they too should be treating
-all such parameters as constant.
-
-As an example, a hash table may be maintained by code that, for
-reasons of encapsulation, has only "const" access to the data being
-indexed in the hash table (ie. it is returned as "const" from
-elsewhere in their code) - in this case the LHASH prototypes are
-appropriate as-is. Conversely, if the caller is responsible for the
-life-time of the data in question, then they may well wish to make
-modifications to table item passed back in the lh_doall() or
-lh_doall_arg() callbacks (see the "TYPE_cleanup" example above). If
-so, the caller can either cast the "const" away (if they're providing
-the raw callbacks themselves) or use the macros to declare/implement
-the wrapper functions without "const" types.
-
-Callers that only have "const" access to data they're indexing in a
-table, yet declare callbacks without constant types (or cast the
-"const" away themselves), are therefore creating their own risks/bugs
-without being encouraged to do so by the API. On a related note,
-those auditing code should pay special attention to any instances of
-DECLARE/IMPLEMENT_LHASH_DOALL_[ARG_]_FN macros that provide types
-without any "const" qualifiers.
-
-=head1 BUGS
-
-lh_TYPE_insert() returns B<NULL> both for success and error.
-
-=head1 SEE ALSO
-
-L<lh_stats(3)>
-
-=head1 HISTORY
-
-In OpenSSL 1.0.0, the lhash interface was revamped for better
-type checking.
-
-=head1 COPYRIGHT
-
-Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
-
-Licensed under the OpenSSL license (the "License"). You may not use
-this file except in compliance with the License. You can obtain a copy
-in the file LICENSE in the source distribution or at
-L<https://www.openssl.org/source/license.html>.
-
-=cut
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