BIO_set_callback(3)         OpenSSL         BIO_set_callback(3)





NAME
       BIO_set_callback, BIO_get_callback, BIO_set_call-
       back_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);

DESCRIPTION
       BIO_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 opera-
       tions. 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 opera-
       tion. 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 per-
       formed.

       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 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(BIO *b, int cmd, long larg, void *parg)
           callback(b,BIO_CB_CTRL,parg,cmd,larg,1L) is called
           before the call and call-
           back(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



0.9.7c                     2000-09-14       BIO_set_callback(3)
