BIO_SET_CALLBACK(3) BSD Library Functions Manual BIO_SET_CALLBACK(3)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>
#define BIO_set_callback(b,cb) ((b)->callback=(cb))
#define BIO_get_callback(b) ((b)->callback)
#define BIO_set_callback_arg(b,arg) ((b)->cb_arg=(char *)(arg))
#define BIO_get_callback_arg(b) ((b)->cb_arg)
long
BIO_debug_callback(BIO *bio, int cmd, const char *argp, int argi,
long argl, long ret);
typedef long *
callback(BIO *b, int oper, const char *argp, int argi, long argl,
long retvalue);
DESCRIPTIONBIO_set_callback() and BIO_get_callback() set and retrieve the BIO call‐
back, they are both macros. 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() are macros which can be
used to 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.
callback() is the callback function itself. 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 opera‐
tion. 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, that is the operation being performed.
retvalue is the return value that would be returned to the application if
no callback were present. The actual value returned is the return value
of the callback itself. In the case of callbacks called before the
actual BIO operation, 1 is placed in retvalue. If the return value is
not positive, it will be immediately returned to the application and the
BIO operation will not be performed.
The callback should normally simply return retvalue when it has finished
processing, unless it specifically wishes 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 and callback(b, BIO_CB_READ|BIO_CB_RETURN, out, outl, 0L,
retvalue) after.
BIO_write(b, in, inl)
callback(b, BIO_CB_WRITE, in, inl, 0L, 1L) is called before the
write and callback(b, BIO_CB_WRITE|BIO_CB_RETURN, in, inl, 0L,
retvalue) after.
BIO_gets(b, out, outl)
callback(b, BIO_CB_GETS, out, outl, 0L, 1L) is called before the
operation and callback(b, BIO_CB_GETS|BIO_CB_RETURN, out, outl,
0L, retvalue) after.
BIO_puts(b, in)
callback(b, BIO_CB_WRITE, in, 0, 0L, 1L) is called before the
operation and callback(b, BIO_CB_WRITE|BIO_CB_RETURN, in, 0, 0L,
retvalue) after.
BIO_ctrl(b, cmd, larg, parg)
callback(b, BIO_CB_CTRL, parg, cmd, larg, 1L) is called before
the call and callback(b, BIO_CB_CTRL|BIO_CB_RETURN, parg, cmd,
larg, ret) after.
EXAMPLES
The BIO_debug_callback() function is a good example, its source is in the
file crypto/bio/bio_cb.c.
BSD April 20, 2024 BSD
