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CRYPTO_SET_EX_DATA(3) DragonFly Library Functions Manual CRYPTO_SET_EX_DATA(3)
NAME
CRYPTO_EX_new, CRYPTO_EX_free, CRYPTO_EX_dup, CRYPTO_get_ex_new_index,
CRYPTO_set_ex_data, CRYPTO_get_ex_data, CRYPTO_free_ex_data,
CRYPTO_new_ex_data -- functions supporting application-specific data
SYNOPSIS
#include <openssl/crypto.h>
int
CRYPTO_get_ex_new_index(int class_index, long argl, void *argp,
CRYPTO_EX_new *new_func, CRYPTO_EX_dup *dup_func,
CRYPTO_EX_free *free_func);
typedef int
CRYPTO_EX_new(void *parent, void *ptr, CRYPTO_EX_DATA *ad, int idx,
long argl, void *argp);
typedef void
CRYPTO_EX_free(void *parent, void *ptr, CRYPTO_EX_DATA *ad, int idx,
long argl, void *argp);
typedef int
CRYPTO_EX_dup(CRYPTO_EX_DATA *to, const CRYPTO_EX_DATA *from,
void *from_d, int idx, long argl, void *argp);
int
CRYPTO_new_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *ad);
int
CRYPTO_set_ex_data(CRYPTO_EX_DATA *r, int idx, void *arg);
void *
CRYPTO_get_ex_data(CRYPTO_EX_DATA *r, int idx);
void
CRYPTO_free_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *r);
DESCRIPTION
Several OpenSSL structures can have application specific data attached to
them, known as "exdata". The specific structures are:
BIO
DH
DSA
ECDH
ECDSA
ENGINE
RSA
SSL
SSL_CTX
SSL_SESSION
UI
X509
X509_STORE
X509_STORE_CTX
Each is identified by a CRYPTO_EX_INDEX_* constant defined in the
<openssl/crypto.h> header file.
The API described here is used by OpenSSL to manipulate exdata for spe-
cific structures. Since the application data can be anything at all it
is passed and retrieved as a void * type.
The CRYPTO_EX_DATA type is opaque. To initialize the exdata part of a
structure, call CRYPTO_new_ex_data().
Exdata types are identified by an index, an integer guaranteed to be
unique within structures for the lifetime of the program. Applications
using exdata typically call CRYPTO_get_ex_new_index() at startup and
store the result in a global variable, or write a wrapper function to
provide lazy evaluation. The class_index should be one of the
CRYPTO_EX_INDEX_* values. The argl and argp parameters are saved to be
passed to the callbacks but are otherwise not used. In order to trans-
parently manipulate exdata, three callbacks must be provided. The seman-
tics of those callbacks are described below.
When copying or releasing objects with exdata, the callback functions are
called in increasing order of their index value.
To set or get the exdata on an object, the appropriate type-specific rou-
tine must be used. This is because the containing structure is opaque
and the CRYPTO_EX_DATA field is not accessible. In both APIs, the idx
parameter should be an already-created index value.
When setting exdata, the pointer specified with a particular index is
saved, and returned on a subsequent "get" call. If the application is
going to release the data, it must make sure to set a NULL value at the
index, to avoid likely double-free crashes.
The function CRYPTO_free_ex_data() is used to free all exdata attached to
a structure. The appropriate type-specific routine must be used. The
class_index identifies the structure type, the obj is be the pointer to
the actual structure, and r is a pointer to the structure's exdata field.
The callback functions are used as follows.
When a structure is initially allocated (such as by RSA_new(3)), then
new_func is called for every defined index. There is no requirement that
the entire parent, or containing, structure has been set up. The
new_func is typically used only to allocate memory to store the exdata,
and perhaps an "initialized" flag within that memory. The exdata value
should be set by calling CRYPTO_set_ex_data().
When a structure is free'd (such as by SSL_CTX_free(3)), then the
free_func is called for every defined index. Again, the state of the
parent structure is not guaranteed. The free_func may be called with a
NULL pointer.
Both new_func and free_func take the same parameters. The parent is the
pointer to the structure that contains the exdata. The ptr is the cur-
rent exdata item; for new_func this will typically be NULL. The r param-
eter is a pointer to the exdata field of the object. The idx is the
index and is the value returned when the callbacks were initially regis-
tered via CRYPTO_get_ex_new_index() and can be used if the same callback
handles different types of exdata.
dup_func is called when a structure is being copied. This is only done
for SSL and SSL_SESSION objects. The to and from parameters are pointers
to the destination and source CRYPTO_EX_DATA structures, respectively.
The from_d parameter is a pointer to the source exdata. When dup_func
returns, the value in from_d is copied to the destination ex_data. If
the pointer contained in from_d is not modified by the dup_func, then
both to and from will point to the same data. The idx, argl and argp
parameters are as described for the other two callbacks.
CRYPTO_set_ex_data() is used to set application specific data. The data
is supplied in the arg parameter and its precise meaning is up to the
application.
CRYPTO_get_ex_data() is used to retrieve application specific data. The
data is returned to the application; this will be the same value as sup-
plied to a previous CRYPTO_set_ex_data() call.
RETURN VALUES
CRYPTO_get_ex_new_index() returns a new index or -1 on failure; the value
0 is reserved for the legacy "app_data" APIs.
CRYPTO_set_ex_data() returns 1 on success or 0 on failure.
CRYPTO_get_ex_data() returns the application data or NULL on failure;
note that NULL may be a valid value.
dup_func should return 0 for failure and 1 for success.
On failure an error code can be obtained from ERR_get_error(3).
SEE ALSO
BIO_get_ex_new_index(3), DH_get_ex_new_index(3), DSA_get_ex_new_index(3),
RSA_get_ex_new_index(3), X509_STORE_CTX_get_ex_new_index(3)
HISTORY
CRYPTO_get_ex_new_index(), CRYPTO_set_ex_data(), CRYPTO_get_ex_data(),
CRYPTO_free_ex_data(), and CRYPTO_new_ex_data() first appeared in SSLeay
0.9.0 and have been available since OpenBSD 2.4.
CRYPTO_EX_new(), CRYPTO_EX_free(), and CRYPTO_EX_dup() first appeared in
OpenSSL 0.9.5 and have been available since OpenBSD 2.7.
DragonFly 5.5 April 8, 2018 DragonFly 5.5