.\" $OpenBSD: BIO_set_callback.3,v 1.10 2022/12/16 23:56:57 schwarze Exp $ .\" full merge up to: OpenSSL 24a535ea Sep 22 13:14:20 2020 +0100 .\" .\" This file is a derived work. .\" The changes are covered by the following Copyright and license: .\" .\" Copyright (c) 2018, 2022 Ingo Schwarze .\" .\" Permission to use, copy, modify, and distribute this software for any .\" purpose with or without fee is hereby granted, provided that the above .\" copyright notice and this permission notice appear in all copies. .\" .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF .\" MERCHANTABILITY AND FITNESS. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: December 16 2022 $ .Dt BIO_SET_CALLBACK 3 .Os .Sh NAME .Nm BIO_callback_fn_ex , .Nm BIO_set_callback_ex , .Nm BIO_get_callback_ex , .Nm BIO_callback_fn , .Nm BIO_set_callback , .Nm BIO_get_callback , .Nm BIO_set_callback_arg , .Nm BIO_get_callback_arg , .Nm BIO_debug_callback .Nd BIO callback functions .Sh SYNOPSIS .In openssl/bio.h .Ft typedef long .Fo (*BIO_callback_fn_ex) .Fa "BIO *b" .Fa "int oper" .Fa "const char *argp" .Fa "size_t len" .Fa "int argi" .Fa "long argl" .Fa "int ret" .Fa "size_t *processed" .Fc .Ft void .Fo BIO_set_callback_ex .Fa "BIO *b" .Fa "BIO_callback_fn_ex cb_ex" .Fc .Ft BIO_callback_fn_ex .Fo BIO_get_callback_ex .Fa "const BIO *b" .Fc .Ft typedef long .Fo (*BIO_callback_fn) .Fa "BIO *b" .Fa "int oper" .Fa "const char *argp" .Fa "int argi" .Fa "long argl" .Fa "long ret" .Fc .Ft void .Fo BIO_set_callback .Fa "BIO *b" .Fa "BIO_callback_fn cb" .Fc .Ft BIO_callback_fn .Fo BIO_get_callback .Fa "BIO *b" .Fc .Ft void .Fo BIO_set_callback_arg .Fa "BIO *b" .Fa "char *pointer" .Fc .Ft char * .Fo BIO_get_callback_arg .Fa "const BIO *b" .Fc .Ft long .Fo BIO_debug_callback .Fa "BIO *bio" .Fa "int oper" .Fa "const char *argp" .Fa "int argi" .Fa "long argl" .Fa "long ret" .Fc .Sh DESCRIPTION .Fn BIO_set_callback_ex and .Fn BIO_get_callback_ex set and retrieve the BIO callback. 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. .Pp .Fn BIO_set_callback and .Fn BIO_get_callback are deprecated functions that set and retrieve the old-style BIO callback, which is only used if no new-style callback is set with .Fn BIO_set_callback_ex . .Pp .Fn BIO_set_callback_arg stores the .Fa pointer internally in .Fa b and .Fn BIO_get_callback_arg retrieves it from .Fa b . The name of these two functions is badly misleading: the .Fa pointer is never passed as an argument to any callback function. But of course, callback functions can call .Fn BIO_get_callback_arg and access the pointer, just like any other code can. .Pp .Fn BIO_debug_callback is a standard debugging callback which prints out information related to each BIO operation. If .Fn BIO_set_callback_arg was called with a .Pf non- Dv NULL argument, information is sent to the BIO pointed to by the .Fa pointer ; otherwise, standard error output is used. .Pp The arguments of the callback functions are as follows: .Bl -tag -width Ds .It Fa b The BIO the callback is attached to. .It Fa oper The operation being performed. For some operations, the callback is called twice, once before and once after the actual operation. The latter case has .Fa oper OR'ed with .Dv BIO_CB_RETURN . .It Fa argp , argi , argl The meaning of these three arguments depends on the value of .Fa oper , that is on the operation being performed. .It Fa len The length of the data requested to be read or written. This is only useful if .Fa oper is .Dv BIO_CB_READ , .Dv BIO_CB_WRITE , or .Dv BIO_CB_GETS . .It Fa ret When .Fa oper does not include .Dv BIO_CB_RETURN , i.e. when the callback is invoked before an operation, the value passed into the callback via .Fa ret is always 1. In this case, if the callback returns a negative value, the library aborts the requested operation and instead returns the negative return value from the callback to the application. If the callback returns a non-negative value, that return value is ignored by the library, and the operation is performed normally. .Pp When .Fa oper includes .Dv BIO_CB_RETURN , i.e. when the callback is invoked after an operation, the value passed into the callback via .Fa ret is the return value that the operation would return to the application if no callback were present. When a callback is present, the operation only passes this value to the callback and instead of it returns the return value of the callback to the application. .It Fa processed The location pointed to is updated with the number of bytes actually read or written. Only used for .Dv BIO_CB_READ , .Dv BIO_CB_WRITE , .Dv BIO_CB_GETS , and .Dv BIO_CB_PUTS . .El .Pp The callback should normally simply return .Fa ret when it has finished processing, unless it specifically wishes to abort the operation or to modify the value returned to the application. .Pp The callbacks are called as follows: .Bl -tag -width 1n .It \&In Fn BIO_free "BIO *b" : .Bd -literal before the free operation: cb_ex(b, BIO_CB_FREE, NULL, 0, 0, 0, 1, NULL) or cb(b, BIO_CB_FREE, NULL, 0, 0, 1) .Ed .It \&In Fn BIO_read "BIO *b" "void *out" "int outl" : .Bd -literal before the read operation: cb_ex(b, BIO_CB_READ, out, outl, 0, 0, 1, NULL) or cb(b, BIO_CB_READ, out, outl, 0, 1) after the read operation: cb_ex(b, BIO_CB_READ|BIO_CB_RETURN, out, outl, 0, 0, ret, &bytes) or cb(b, BIO_CB_READ|BIO_CB_RETURN, out, outl, 0, ret) .Ed .It \&In Fn BIO_write "BIO *b" "const void *in" "int inl" : .Bd -literal before the write operation: cb_ex(b, BIO_CB_WRITE, in, inl, 0, 0, 1, NULL) or cb(b, BIO_CB_WRITE, in, inl, 0, 1) after the write operation: cb_ex(b, BIO_CB_WRITE|BIO_CB_RETURN, in, inl, 0, 0, ret, &bytes) or cb(b, BIO_CB_WRITE|BIO_CB_RETURN, in, inl, 0, ret) .Ed .It \&In Fn BIO_gets "BIO *b" "char *out" "int outl" : .Bd -literal before the read operation: cb_ex(b, BIO_CB_GETS, out, outl, 0, 0, 1, NULL) or cb(b, BIO_CB_GETS, out, outl, 0, 1) after the read operation: cb_ex(b, BIO_CB_GETS|BIO_CB_RETURN, out, outl, 0, 0, ret, &bytes) or cb(b, BIO_CB_GETS|BIO_CB_RETURN, out, outl, 0, ret) .Ed .It \&In Fn BIO_puts "BIO *b" "const char *in" : .Bd -literal before the write operation: cb_ex(b, BIO_CB_PUTS, in, 0, 0, 0, 1, NULL) or cb(b, BIO_CB_PUTS, in, 0, 0, 1) after the write operation: cb_ex(b, BIO_CB_PUTS|BIO_CB_RETURN, in, 0, 0, 0, ret, &bytes) or cb(b, BIO_CB_PUTS|BIO_CB_RETURN, in, 0, 0, ret) .Ed .It \&In Fn BIO_ctrl "BIO *b" "int cmd" "long larg" "void *parg" : .Bd -literal before the control operation: cb_ex(b, BIO_CB_CTRL, parg, 0, cmd, larg, 1, NULL) or cb(b, BIO_CB_CTRL, parg, cmd, larg, 1) after the control operation: cb_ex(b, BIO_CB_CTRL|BIO_CB_RETURN, parg, 0, cmd, larg, ret, NULL) or cb(b, BIO_CB_CTRL|BIO_CB_RETURN, parg, cmd, larg, ret) .Ed .It \&In Fn BIO_callback_ctrl "BIO *b" "int cmd" "BIO_info_cb *fp" : .Bd -literal before the control operation: cb_ex(b, BIO_CB_CTRL, fp, 0, cmd, 0, 1, NULL) or cb(b, BIO_CB_CTRL, fp, cmd, 0, 1) after the control operation: cb_ex(b, BIO_CB_CTRL|BIO_CB_RETURN, fp, 0, cmd, 0, ret, NULL) or cb(b, BIO_CB_CTRL|BIO_CB_RETURN, fp, cmd, 0, ret) .Ed .El .Sh RETURN VALUES .Fn BIO_get_callback_ex returns a pointer to the function .Fa cb_ex previously installed with .Fn BIO_set_callback_cb , or .Dv NULL if no such callback was installed. .Pp .Fn BIO_get_callback returns a pointer to the function .Fa cb previously installed with .Fn BIO_set_callback , or .Dv NULL if no such callback was installed. .Pp .Fn BIO_get_callback_arg returns the .Fa pointer previously set with .Fn BIO_set_callback_arg , or .Dv NULL if no such pointer was set. .Pp .Fn BIO_debug_callback returns .Fa ret if the bit .Dv BIO_CB_RETURN is set in .Fa cmd , or 1 otherwise. .Sh EXAMPLES The .Fn BIO_debug_callback function is a good example. Its source is in the file .Pa crypto/bio/bio_cb.c . .Sh SEE ALSO .Xr BIO_new 3 .Sh HISTORY .Fn BIO_set_callback , .Fn BIO_get_callback , .Fn BIO_set_callback_arg , and .Fn BIO_debug_callback first appeared in SSLeay 0.6.0. .Fn BIO_get_callback_arg first appeared in SSLeay 0.8.0. These functions have been available since .Ox 2.4 . .Pp .Fn BIO_callback_fn first appeared in OpenSSL 1.1.0. .Fn BIO_callback_fn_ex , .Fn BIO_set_callback_ex , and .Fn BIO_get_callback_ex first appeared in OpenSSL 1.1.1. These functions have been available since .Ox 7.1 .