RSA_get_ex_new_index, RSA_set_ex_data, RSA_get_ex_data — add application specific data to RSA structures
RSA_get_ex_new_index(long argl, void *argp, CRYPTO_EX_new *new_func,
CRYPTO_EX_dup *dup_func, CRYPTO_EX_free *free_func);
RSA_set_ex_data(RSA *r, int idx, void *arg);
*r, int idx);
typedef int new_func(void *parent, void
*ptr, CRYPTO_EX_DATA *ad, int idx, long argl, void *argp);
void free_func(void *parent, void *ptr, CRYPTO_EX_DATA *ad, int
idx, long argl, void *argp);
typedef int dup_func(CRYPTO_EX_DATA
*to, CRYPTO_EX_DATA *from, void *from_d, int idx, long argl, void
Several OpenSSL structures can have application specific data
attached to them. This has several potential uses, it can be used
to cache data associated with a structure (for example the hash
of some part of the structure) or some additional data (for example
a handle to the data in an external library).
Since the application data can be anything at all it is passed
and retrieved as a void * type.
The RSA_get_ex_new_index() function is
initially called to "register" some new application specific data.
It takes three optional function pointers which are called when
the parent structure (in this case an RSA structure) is initially
created, when it is copied and when it is freed up. If any or all
of these function pointer arguments are not used they should be
set to NULL. The precise manner in which these function pointers
are called is described in more detail below. RSA_get_ex_new_index() also
takes additional long and pointer parameters which will be passed
to the supplied functions but which otherwise have no special meaning.
It returns an index which should be stored
(typically in a static variable) and passed used in the idx parameter in
the remaining functions. Each successful call to RSA_get_ex_new_index() will
return an index greater than any previously returned, this is important
because the optional functions are called in order of increasing index
RSA_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.
RSA_get_ex_data() is used to retrieve
application specific data. The data is returned to the application,
this will be the same value as supplied to a previous RSA_set_ex_data() call.
new_func() is called when a structure
is initially allocated (for example with RSA_new().
The parent structure members will not have any meaningful values
at this point. This function will typically be used to allocate any
application specific structure.
free_func() is called when a structure
is being freed up. The dynamic parent structure members should not
be accessed because they will be freed up when this function is
new_func() and free_func() take
the same parameters. parent is a pointer to
the parent RSA structure. ptr is a the application
specific data (this wont be of much use in new_func(). ad is
a pointer to the CRYPTO_EX_DATA structure from
the parent RSA structure: the functions CRYPTO_get_ex_data() and CRYPTO_set_ex_data() can
be called to manipulate it. The idx parameter
is the index: this will be the same value returned by RSA_get_ex_new_index() when
the functions were initially registered. Finally the argl and argp parameters
are the values originally passed to the same corresponding parameters
when RSA_get_ex_new_index() was called.
dup_func() is called when a structure
is being copied. Pointers to the destination and source CRYPTO_EX_DATA structures
are passed in the to and from parameters
respectively. The from_d parameter is passed
a pointer to the source application data when the function is called,
when the function returns the value is copied to the destination:
the application can thus modify the data pointed to by from_d and
have different values in the source and destination. The idx, argl and argp parameters
are the same as those in new_func() and free_func().
RSA_get_ex_new_index() returns a new
index or -1 on failure (note 0 is a valid index value).
RSA_set_ex_data() returns 1 on success
or 0 on failure.
RSA_get_ex_data() returns the application
data or 0 on failure. 0 may also be valid application data but currently
it can only fail if given an invalid idx parameter.
new_func() and dup_func() should
return 0 for failure and 1 for success.
On failure an error code can be obtained from ERR_get_error(3).
dup_func() is currently never called.
The return value of new_func() is ignored.
The new_func() function isn't very useful
because no meaningful values are present in the parent RSA structure
when it is called.
RSA_get_ex_new_index(), RSA_set_ex_data() and RSA_get_ex_data()
are available since SSLeay 0.9.0.