NAME
BIO_set_callback,
BIO_get_callback,
BIO_set_callback_arg,
BIO_get_callback_arg,
BIO_debug_callback —
BIO callback functions
SYNOPSIS
#include
<openssl/bio.h>
void
BIO_set_callback(BIO *b,
BIO_callback_fn cb);
BIO_callback_fn
BIO_get_callback(BIO *b);
void
BIO_set_callback_arg(BIO *b,
char *arg);
char *
BIO_get_callback_arg(const BIO
*b);
long
BIO_debug_callback(BIO *bio,
int oper, const char *argp,
int argi, long argl,
long ret);
typedef long
(*BIO_callback_fn)(BIO *b,
int oper, const char *argp,
int argi, long argl,
long ret);
DESCRIPTION
BIO_set_callback()
and
BIO_get_callback()
set and retrieve the BIO callback. The callback is called during most high
level BIO operations. It can be used for debugging purposes to trace
operations on a BIO or to modify its operation.
BIO_set_callback_arg()
and
BIO_get_callback_arg()
set and retrieve an argument for use in the callback.
BIO_debug_callback()
is a standard debugging callback which prints out information relating to
each BIO operation. If the callback argument is set, it is interpreted as a
BIO to send the information to, otherwise stderr is used.
BIO_callback_fn()
is the type of the callback function. The meaning of each argument is
described below.
The BIO the callback is attached to is passed in b.
oper is set to the operation being
performed. For some operations the callback is called twice, once before and
once after the actual operation. The latter case has
oper or'ed with
BIO_CB_RETURN.
The meaning of the arguments argp, argi and argl depends on the value of oper (i.e. the operation being performed).
When oper does not include
BIO_CB_RETURN, i.e. when the callback is invoked
before an operation, the value passed into the callback via
ret is always 1. In this case, if the callback returns
a negative value, the library aborts the requested operation and instead
returns the negative return value from the callback to the application. If
the callback returns a non-negative value, that return value is ignored by
the library, and the operation is performed normally.
When oper includes
BIO_CB_RETURN, i.e. when the callback is invoked
after an operation, the value passed into the callback via
ret is the return value that the operation would
return to the application if no callback were present. When a callback is
present, the operation only passes this value to the callback and instead of
it returns the return value of the callback to the application.
The callback should normally simply return ret when it has finished processing, unless it specifically wishes to abort the operation or to modify the value returned to the application.
Callback operations
BIO_free(b)callback(b, BIO_CB_FREE, NULL, 0L, 0L, 1L) is called before the free operation.BIO_read(b, out, outl)callback(b, BIO_CB_READ, out, outl, 0L, 1L) is called before the read andcallback(b, BIO_CB_READ|BIO_CB_RETURN, out, outl, 0L, ret) after.BIO_write(b, in, inl)callback(b, BIO_CB_WRITE, in, inl, 0L, 1L) is called before the write andcallback(b, BIO_CB_WRITE|BIO_CB_RETURN, in, inl, 0L, ret) after.BIO_gets(b, out, outl)callback(b, BIO_CB_GETS, out, outl, 0L, 1L) is called before the operation andcallback(b, BIO_CB_GETS|BIO_CB_RETURN, out, outl, 0L, ret) after.BIO_puts(b, in)callback(b, BIO_CB_PUTS, in, 0, 0L, 1L) is called before the operation andcallback(b, BIO_CB_PUTS|BIO_CB_RETURN, in, 0, 0L, ret) after.BIO_ctrl(b, oper, larg, parg)callback(b, BIO_CB_CTRL, parg, oper, larg, 1L) is called before the call andcallback(b, BIO_CB_CTRL|BIO_CB_RETURN, parg, oper, larg, ret) after.
RETURN VALUES
BIO_get_callback() returns a pointer to
the function cb previously installed with
BIO_set_callback(), or NULL
if no callback was installed.
BIO_get_callback_arg() returns a pointer
to the arg previously set with
BIO_set_callback_arg(), or
NULL if no such argument was set.
BIO_debug_callback() returns
ret if the bit BIO_CB_RETURN
is set in cmd, or 1 otherwise.
EXAMPLES
The BIO_debug_callback() function is a
good example. Its source is in the file
crypto/bio/bio_cb.c.
SEE ALSO
HISTORY
BIO_set_callback(),
BIO_get_callback(),
BIO_set_callback_arg(), and
BIO_debug_callback() first appeared in SSLeay 0.6.0.
BIO_get_callback_arg() first appeared in SSLeay
0.8.0. All these functions have been available since
OpenBSD 2.4.