/usr/man/cat.3/BIO_set_callback.3(/usr/man/cat.3/BIO_set_callback.3)

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);

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 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

1.0.2t               Last change: 2019-09-10                    1

BIO_set_callback(3)          OpenSSL          BIO_set_callback(3)

     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
         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

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See also BIO_debug_callback(3)
See also BIO_get_callback(3)
See also BIO_get_callback_arg(3)
See also BIO_set_callback_arg(3)