- NAME
- SYNOPSIS
- DESCRIPTION
- NOTES
- RETURN VALUES
- HISTORY
- COPYRIGHT

# NAME

DEFINE_STACK_OF, DEFINE_STACK_OF_CONST, DEFINE_SPECIAL_STACK_OF, DEFINE_SPECIAL_STACK_OF_CONST, sk_TYPE_num, sk_TYPE_value, sk_TYPE_new, sk_TYPE_new_null, sk_TYPE_reserve, sk_TYPE_free, sk_TYPE_zero, sk_TYPE_delete, sk_TYPE_delete_ptr, sk_TYPE_push, sk_TYPE_unshift, sk_TYPE_pop, sk_TYPE_shift, sk_TYPE_pop_free, sk_TYPE_insert, sk_TYPE_set, sk_TYPE_find, sk_TYPE_find_ex, sk_TYPE_sort, sk_TYPE_is_sorted, sk_TYPE_dup, sk_TYPE_deep_copy, sk_TYPE_set_cmp_func, sk_TYPE_new_reserve - stack container

# SYNOPSIS

     #include <openssl/safestack.h>

     STACK_OF(TYPE)
     DEFINE_STACK_OF(TYPE)
     DEFINE_STACK_OF_CONST(TYPE)
     DEFINE_SPECIAL_STACK_OF(FUNCTYPE, TYPE)
     DEFINE_SPECIAL_STACK_OF_CONST(FUNCTYPE, TYPE)

     typedef int (*sk_TYPE_compfunc)(const TYPE *const *a, const TYPE *const *b);
     typedef TYPE * (*sk_TYPE_copyfunc)(const TYPE *a);
     typedef void (*sk_TYPE_freefunc)(TYPE *a);

     int sk_TYPE_num(const STACK_OF(TYPE) *sk);
     TYPE *sk_TYPE_value(const STACK_OF(TYPE) *sk, int idx);
     STACK_OF(TYPE) *sk_TYPE_new(sk_TYPE_compfunc compare);
     STACK_OF(TYPE) *sk_TYPE_new_null(void);
     int sk_TYPE_reserve(STACK_OF(TYPE) *sk, int n);
     void sk_TYPE_free(const STACK_OF(TYPE) *sk);
     void sk_TYPE_zero(const STACK_OF(TYPE) *sk);
     TYPE *sk_TYPE_delete(STACK_OF(TYPE) *sk, int i);
     TYPE *sk_TYPE_delete_ptr(STACK_OF(TYPE) *sk, TYPE *ptr);
     int sk_TYPE_push(STACK_OF(TYPE) *sk, const TYPE *ptr);
     int sk_TYPE_unshift(STACK_OF(TYPE) *sk, const TYPE *ptr);
     TYPE *sk_TYPE_pop(STACK_OF(TYPE) *sk);
     TYPE *sk_TYPE_shift(STACK_OF(TYPE) *sk);
     void sk_TYPE_pop_free(STACK_OF(TYPE) *sk, sk_TYPE_freefunc freefunc);
     int sk_TYPE_insert(STACK_OF(TYPE) *sk, TYPE *ptr, int idx);
     TYPE *sk_TYPE_set(STACK_OF(TYPE) *sk, int idx, const TYPE *ptr);
     int sk_TYPE_find(STACK_OF(TYPE) *sk, TYPE *ptr);
     int sk_TYPE_find_ex(STACK_OF(TYPE) *sk, TYPE *ptr);
     void sk_TYPE_sort(const STACK_OF(TYPE) *sk);
     int sk_TYPE_is_sorted(const STACK_OF(TYPE) *sk);
     STACK_OF(TYPE) *sk_TYPE_dup(const STACK_OF(TYPE) *sk);
     STACK_OF(TYPE) *sk_TYPE_deep_copy(const STACK_OF(TYPE) *sk,
                                       sk_TYPE_copyfunc copyfunc,
                                       sk_TYPE_freefunc freefunc);
     sk_TYPE_compfunc (*sk_TYPE_set_cmp_func(STACK_OF(TYPE) *sk,
                                             sk_TYPE_compfunc compare));
     STACK_OF(TYPE) *sk_TYPE_new_reserve(sk_TYPE_compfunc compare, int n);

# DESCRIPTION

Applications can create and use their own stacks by placing any of the macros described below in a header file. These macros define typesafe inline functions that wrap around the utility OPENSSL_sk_ API. In the description here, TYPE is used as a placeholder for any of the OpenSSL datatypes, such as X509.

`STACK_OF()` returns the name for a stack of the specified TYPE. `DEFINE_STACK_OF()` creates set of functions for a stack of TYPE. This will mean that type TYPE is stored in each stack, the type is referenced by STACK_OF(TYPE) and each function name begins with sk_TYPE_. For example:

     TYPE *sk_TYPE_value(STACK_OF(TYPE) *sk, int idx);

`DEFINE_STACK_OF_CONST()` is identical to `DEFINE_STACK_OF()` except each element is constant. For example:

     const TYPE *sk_TYPE_value(STACK_OF(TYPE) *sk, int idx);

`DEFINE_SPECIAL_STACK_OF()` defines a stack of TYPE but each function uses FUNCNAME in the function name. For example:

     TYPE *sk_FUNCNAME_value(STACK_OF(TYPE) *sk, int idx);

`DEFINE_SPECIAL_STACK_OF_CONST()` is similar except that each element is constant:

     const TYPE *sk_FUNCNAME_value(STACK_OF(TYPE) *sk, int idx);

sk_TYPE_num() returns the number of elements in sk or -1 if sk is NULL.

sk_TYPE_value() returns element idx in sk, where idx starts at zero. If idx is out of range then NULL is returned.

sk_TYPE_new() allocates a new empty stack using comparison function compare. If compare is NULL then no comparison function is used. This function is equivalent to sk_TYPE_new_reserve(compare, 0).

sk_TYPE_new_null() allocates a new empty stack with no comparison function. This function is equivalent to sk_TYPE_new_reserve(NULL, 0).

sk_TYPE_reserve() allocates additional memory in the sk structure such that the next n calls to sk_TYPE_insert(), sk_TYPE_push() or sk_TYPE_unshift() will not fail or cause memory to be allocated or reallocated. If n is zero, any excess space allocated in the sk structure is freed. On error sk is unchanged.

sk_TYPE_new_reserve() allocates a new stack. The new stack will have additional memory allocated to hold n elements if n is positive. The next n calls to sk_TYPE_insert(), sk_TYPE_push() or sk_TYPE_unshift() will not fail or cause memory to be allocated or reallocated. If n is zero or less than zero, no memory is allocated. sk_TYPE_new_reserve() also sets the comparison function compare to the newly created stack. If compare is NULL then no comparison function is used.

sk_TYPE_set_cmp_func() sets the comparison function of sk to compare. The previous comparison function is returned or NULL if there was no previous comparison function.

sk_TYPE_free() frees up the sk structure. It does not free up any elements of sk. After this call sk is no longer valid.

sk_TYPE_zero() sets the number of elements in sk to zero. It does not free sk so after this call sk is still valid.

sk_TYPE_pop_free() frees up all elements of sk and sk itself. The free function `freefunc()` is called on each element to free it.

sk_TYPE_delete() deletes element i from sk. It returns the deleted element or NULL if i is out of range.

sk_TYPE_delete_ptr() deletes element matching ptr from sk. It returns the deleted element or NULL if no element matching ptr was found.

sk_TYPE_insert() inserts ptr into sk at position idx. Any existing elements at or after idx are moved downwards. If idx is out of range the new element is appended to sk. sk_TYPE_insert() either returns the number of elements in sk after the new element is inserted or zero if an error (such as memory allocation failure) occurred.

sk_TYPE_push() appends ptr to sk it is equivalent to:

     sk_TYPE_insert(sk, ptr, -1);

sk_TYPE_unshift() inserts ptr at the start of sk it is equivalent to:

     sk_TYPE_insert(sk, ptr, 0);

sk_TYPE_pop() returns and removes the last element from sk.

sk_TYPE_shift() returns and removes the first element from sk.

sk_TYPE_set() sets element idx of sk to ptr replacing the current element. The new element value is returned or NULL if an error occurred: this will only happen if sk is NULL or idx is out of range.

sk_TYPE_find() searches sk for the element ptr. In the case where no comparison function has been specified, the function performs a linear search for a pointer equal to ptr. The index of the first matching element is returned or -1 if there is no match. In the case where a comparison function has been specified, sk is sorted then sk_TYPE_find() returns the index of a matching element or -1 if there is no match. Note that, in this case, the matching element returned is not guaranteed to be the first; the comparison function will usually compare the values pointed to rather than the pointers themselves and the order of elements in sk could change.

sk_TYPE_find_ex() operates like sk_TYPE_find() except when a comparison function has been specified and no matching element is found. Instead of returning -1, sk_TYPE_find_ex() returns the index of the element either before or after the location where ptr would be if it were present in sk.

sk_TYPE_sort() sorts sk using the supplied comparison function.

sk_TYPE_is_sorted() returns 1 if sk is sorted and 0 otherwise.

sk_TYPE_dup() returns a copy of sk. Note the pointers in the copy are identical to the original.

sk_TYPE_deep_copy() returns a new stack where each element has been copied. Copying is performed by the supplied `copyfunc()` and freeing by `freefunc()`. The function `freefunc()` is only called if an error occurs.

# NOTES

Care should be taken when accessing stacks in multi-threaded environments. Any operation which increases the size of a stack such as sk_TYPE_insert() or sk_TYPE_push() can "grow" the size of an internal array and cause race conditions if the same stack is accessed in a different thread. Operations such as sk_TYPE_find() and sk_TYPE_sort() can also reorder the stack.

Any comparison function supplied should use a metric suitable for use in a binary search operation. That is it should return zero, a positive or negative value if a is equal to, greater than or less than b respectively.

Care should be taken when checking the return values of the functions sk_TYPE_find() and sk_TYPE_find_ex(). They return an index to the matching element. In particular 0 indicates a matching first element. A failed search is indicated by a -1 return value.

`STACK_OF()`, `DEFINE_STACK_OF()`, `DEFINE_STACK_OF_CONST()`, and `DEFINE_SPECIAL_STACK_OF()` are implemented as macros.

The underlying utility OPENSSL_sk_ API should not be used directly. It defines these functions: `OPENSSL_sk_deep_copy()`, `OPENSSL_sk_delete()`, `OPENSSL_sk_delete_ptr()`, `OPENSSL_sk_dup()`, `OPENSSL_sk_find()`, `OPENSSL_sk_find_ex()`, `OPENSSL_sk_free()`, `OPENSSL_sk_insert()`, `OPENSSL_sk_is_sorted()`, `OPENSSL_sk_new()`, `OPENSSL_sk_new_null()`, `OPENSSL_sk_num()`, `OPENSSL_sk_pop()`, `OPENSSL_sk_pop_free()`, `OPENSSL_sk_push()`, `OPENSSL_sk_reserve()`, `OPENSSL_sk_set()`, `OPENSSL_sk_set_cmp_func()`, `OPENSSL_sk_shift()`, `OPENSSL_sk_sort()`, `OPENSSL_sk_unshift()`, `OPENSSL_sk_value()`, `OPENSSL_sk_zero()`.

# RETURN VALUES

sk_TYPE_num() returns the number of elements in the stack or -1 if the passed stack is NULL.

sk_TYPE_value() returns a pointer to a stack element or NULL if the index is out of range.

sk_TYPE_new(), sk_TYPE_new_null() and sk_TYPE_new_reserve() return an empty stack or NULL if an error occurs.

sk_TYPE_reserve() returns 1 on successful allocation of the required memory or 0 on error.

sk_TYPE_set_cmp_func() returns the old comparison function or NULL if there was no old comparison function.

sk_TYPE_free(), sk_TYPE_zero(), sk_TYPE_pop_free() and sk_TYPE_sort() do not return values.

sk_TYPE_pop(), sk_TYPE_shift(), sk_TYPE_delete() and sk_TYPE_delete_ptr() return a pointer to the deleted element or NULL on error.

sk_TYPE_insert(), sk_TYPE_push() and sk_TYPE_unshift() return the total number of elements in the stack and 0 if an error occurred.

sk_TYPE_set() returns a pointer to the replacement element or NULL on error.

sk_TYPE_find() and sk_TYPE_find_ex() return an index to the found element or -1 on error.

sk_TYPE_is_sorted() returns 1 if the stack is sorted and 0 if it is not.

sk_TYPE_dup() and sk_TYPE_deep_copy() return a pointer to the copy of the stack.

# HISTORY

Before OpenSSL 1.1.0, this was implemented via macros and not inline functions and was not a public API.

sk_TYPE_reserve() and sk_TYPE_new_reserve() were added in OpenSSL 1.1.1.

# COPYRIGHT

Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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 https://www.openssl.org/source/license.html.