BIO_set_callback(3) OpenSSL 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 callback, 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 if 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 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, 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 if specifically wishes
to modify the value returned to the application.
CALLBACK OPERATIONSBIO_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(BIO *b, int cmd, long larg, void *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.
EXAMPLE
The BIO_debug_callback() function is a good example, its
source is in crypto/bio/bio_cb.c
SEE ALSO
TBA
14/Sep/2000 0.9.6j BIO_set_callback(3)
