Sortix 1.1dev ports manual
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| STACK_OF(3) | Library Functions Manual | STACK_OF(3) |
NAME
STACK_OF — variable-sized arrays of pointers, called OpenSSL stacksSYNOPSIS
#include <openssl/safestack.h> STACK_OF(type);DESCRIPTION
The <openssl/safestack.h> header provides a fragile, unusually complicated system of macro-generated wrappers around the functions described in the OPENSSL_sk_new(3) manual page. It is intended to implement superficially type-safe variable-sized arrays of pointers, somewhat misleadingly called “stacks” by OpenSSL. Due to the excessive number of API functions, it is impossible to properly document this system. In particular, calling man(1) for any of the functions operating on stacks cannot yield any result. Unfortunately, application programs can hardly avoid using the concept because several important OpenSSL APIs rely on it; see the SEE ALSO section for examples. Even though both pages are more complicated than any manual page ought to be, using the concept safely requires a complete understanding of all the details in both this manual page and in OPENSSL_sk_new(3). The STACK_OF() macro takes a type name as its argument, typically the name of a type that has been defined as an alias for a specific struct type using a typedef declaration. It expands to an incomplete struct type which is intended to represent a “stack” of objects of the given type. That type does not actually exist, so it is not possible to define, for example, an automatic variable ‘STACK_OF(X509) my_certificates’; it is
only possible to define pointers to stacks, for example
‘STACK_OF(X509) *my_certificates’. The
only way such pointers can ever be used is by wrapper functions casting them
to the type _STACK * described in
OPENSSL_sk_new(3).
For a considerable number of types, OpenSSL provides one wrapper function for
each function described in
OPENSSL_sk_new(3).
The names of these wrapper functions are usually constructed by inserting the
name of the type and an underscore after the ‘sk_’ prefix of the
function name. Usually, where the real functions take
void * arguments, the wrappers take pointers
to the type in questions, and where the real
functions take _STACK * arguments, the
wrappers take pointers to
STACK_OF(type).
The same applies to return values. Various exceptions to all this exist, but
the above applies to all the types listed below.
Using the above may make sense for the following types because public API
functions exist that take stacks of these types as arguments or return them:
ACCESS_DESCRIPTION,
ASN1_INTEGER,
ASN1_OBJECT,
ASN1_TYPE,
ASN1_UTF8STRING,
CONF_VALUE,
DIST_POINT,
GENERAL_NAME,
GENERAL_SUBTREE,
PKCS12_SAFEBAG,
PKCS7,
PKCS7_RECIP_INFO,
PKCS7_SIGNER_INFO,
POLICY_MAPPING,
POLICYINFO,
POLICYQUALINFO,
X509,
X509_ALGOR,
X509_ATTRIBUTE,
X509_CRL,
X509_EXTENSION,
X509_INFO,
X509_OBJECT,
X509_POLICY_NODE,
X509_PURPOSE,
X509_REVOKED.
Even though the OpenSSL headers declare wrapper functions for many more types
and even though the OpenSSL documentation says that users can declare their
own stack types, using STACK_OF() with any type
not listed here is strongly discouraged. For other types, there may be subtle,
undocumented differences in syntax and semantics, and attempting to declare
custom stack types is very error prone; using plain C arrays of pointers to
the desired type is much simpler and less dangerous.
EXAMPLES
The following program creates a certificate object, puts two pointers to it on a stack, and uses X509_free(3) to clean up properly:
#include <err.h>
#include <stdio.h>
#include <openssl/x509.h>
int
main(void)
{
STACK_OF(X509) *stack;
X509 *x;
if ((stack = sk_X509_new_null()) == NULL)
err(1, NULL);
if ((x = X509_new()) == NULL)
err(1, NULL);
if (sk_X509_push(stack, x) == 0)
err(1, NULL);
if (X509_up_ref(x) == 0)
errx(1, "X509_up_ref failed");
if (sk_X509_push(stack, x) == 0)
err(1, NULL);
printf("%d pointers: %p, %p\n", sk_X509_num(stack),
sk_X509_value(stack, 0), sk_X509_value(stack, 1));
sk_X509_pop_free(stack, X509_free);
return 0;
}
2 pointers: 0x4693ff24c00,
0x4693ff24c00SEE ALSO
crypto(3), OCSP_request_sign(3), OPENSSL_sk_new(3), PKCS12_parse(3), PKCS7_encrypt(3), SSL_CTX_set_client_CA_list(3), SSL_get_ciphers(3), SSL_get_peer_cert_chain(3), SSL_load_client_CA_file(3), X509_CRL_get_REVOKED(3), X509_STORE_CTX_get0_chain(3)HISTORY
The STACK_OF() macro first appeared in OpenSSL 0.9.3 and has been available since OpenBSD 2.6.| June 10, 2019 | Debian |