BIO_set_callback, BIO_get_callback, BIO_set_callback_arg, BIO_get_callback_arg,
BIO_debug_callback - BIO callback functions
#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);
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.
are macros which
can be used to set and retrieve an argument for use in the 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.
is the callback function itself. The meaning of each argument
is described below.
The BIO the callback is attached to is passed in b
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
the value of oper
, that is the operation being performed.
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
The callback should normally simply return retvalue
when it has finished
processing, unless if specifically wishes to modify the value returned to the
- callback(b, BIO_CB_FREE, NULL, 0L, 0L, 1L) is called before the free
- 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)
- 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)
- 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)
- 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.
function is a good example, its source is in