BIO_set_callback(3) OpenSSL BIO_set_callback(3) NNAAMMEE BIO_set_callback, BIO_get_callback, BIO_set_callback_arg, BIO_get_call- back_arg, BIO_debug_callback - BIO callback functions SSYYNNOOPPSSIISS #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); DDEESSCCRRIIPPTTIIOONN _B_I_O___s_e_t___c_a_l_l_b_a_c_k_(_) and _B_I_O___g_e_t___c_a_l_l_b_a_c_k_(_) 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. _B_I_O___s_e_t___c_a_l_l_b_a_c_k___a_r_g_(_) and _B_I_O___g_e_t___c_a_l_l_b_a_c_k___a_r_g_(_) are macros which can be used to set and retrieve an argument for use in the callback. _B_I_O___d_e_b_u_g___c_a_l_l_b_a_c_k_(_) 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. _c_a_l_l_b_a_c_k_(_) is the callback function itself. The meaning of each argu- ment is described below. The BIO the callback is attached to is passed in bb. ooppeerr is set to the operation being performed. For some operations the callback is called twice, once before and once after the actual opera- tion, the latter case has ooppeerr or'ed with BIO_CB_RETURN. The meaning of the arguments aarrggpp, aarrggii and aarrggll depends on the value of ooppeerr, that is the operation being performed. rreettvvaalluuee 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 rreettvvaalluuee when it has fin- ished processing, unless if specifically wishes to modify the value returned to the application. CCAALLLLBBAACCKK OOPPEERRAATTIIOONNSS BBIIOO__ffrreeee((bb)) callback(b, BIO_CB_FREE, NULL, 0L, 0L, 1L) is called before the free operation. BBIIOO__rreeaadd((bb,, oouutt,, oouuttll)) 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, ret- value) after. BBIIOO__wwrriittee((bb,, iinn,, iinnll)) 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, ret- value) after. BBIIOO__ggeettss((bb,, oouutt,, oouuttll)) 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. BBIIOO__ppuuttss((bb,, iinn)) callback(b, BIO_CB_WRITE, in, 0, 0L, 1L) is called before the oper- ation and callback(b, BIO_CB_WRITE|BIO_CB_RETURN, in, 0, 0L, ret- value) after. BBIIOO__ccttrrll((BBIIOO **bb,, iinntt ccmmdd,, lloonngg llaarrgg,, vvooiidd **ppaarrgg)) 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. EEXXAAMMPPLLEE The _B_I_O___d_e_b_u_g___c_a_l_l_b_a_c_k_(_) function is a good example, its source is in crypto/bio/bio_cb.c SSEEEE AALLSSOO TBA 1.0.2u 2019-12-20 BIO_set_callback(3)