:-'Generic Commit'
This commit is contained in:
Your Name
239
dropshell-tool/openssl-1.1.1w/doc/man3/OPENSSL_LH_COMPFUNC.pod
Normal file
239
dropshell-tool/openssl-1.1.1w/doc/man3/OPENSSL_LH_COMPFUNC.pod
Normal file
@ -0,0 +1,239 @@
|
||||
=pod
|
||||
|
||||
=head1 NAME
|
||||
|
||||
LHASH, 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
|
||||
|
||||
=head1 SYNOPSIS
|
||||
|
||||
=for comment generic
|
||||
|
||||
#include <openssl/lhash.h>
|
||||
|
||||
DECLARE_LHASH_OF(TYPE);
|
||||
|
||||
LHASH *lh_TYPE_new(OPENSSL_LH_HASHFUNC hash, OPENSSL_LH_COMPFUNC compare);
|
||||
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_TYPE_retrieve(LHASH_OF(TYPE) *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 *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, nonzero 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. It's meaningful only after non-retrieve operations.
|
||||
|
||||
lh_TYPE_free(), lh_TYPE_doall() and lh_TYPE_doall_arg() return no values.
|
||||
|
||||
=head1 NOTE
|
||||
|
||||
The LHASH code is not thread safe. All updating operations, as well as
|
||||
lh_TYPE_error call must be performed under a write lock. All retrieve
|
||||
operations should be performed under a read lock, I<unless> accurate
|
||||
usage statistics are desired. In which case, a write lock should be used
|
||||
for retrieve operations as well. For output of the usage statistics,
|
||||
using the functions from L<OPENSSL_LH_stats(3)>, a read lock suffices.
|
||||
|
||||
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 (i.e. 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<OPENSSL_LH_stats(3)>
|
||||
|
||||
=head1 HISTORY
|
||||
|
||||
In OpenSSL 1.0.0, the lhash interface was revamped for better
|
||||
type checking.
|
||||
|
||||
=head1 COPYRIGHT
|
||||
|
||||
Copyright 2000-2022 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
|
||||
Reference in New Issue
Block a user