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 

        #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 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 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 opera-
       tion 1 is placed in retvalue, if the return value is not
       positive it will be immediately returned to the applica-
       tion 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)

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