.\" $OpenBSD: BIO_set_callback.3,v 1.5 2016/12/06 14:45:08 schwarze Exp $ .\" OpenSSL 99d63d46 Oct 26 13:56:48 2016 -0400 .\" .\" This file was written by Dr. Stephen Henson . .\" Copyright (c) 2000, 2016 The OpenSSL Project. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" 3. 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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 6 2016 $ .Dt BIO_SET_CALLBACK 3 .Os .Sh NAME .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 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 *arg" .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 .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 .Sh DESCRIPTION .Fn BIO_set_callback and .Fn BIO_get_callback 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_arg and .Fn BIO_get_callback_arg set and retrieve an argument for use in the callback. .Pp .Fn BIO_debug_callback is a standard debugging callback which prints out information relating to each BIO operation. If the callback argument is set, it is interpreted as a BIO to send the information to, otherwise stderr is used. .Pp .Fn BIO_callback_fn is the type of the callback function. The meaning of each argument is described below. .Pp The BIO the callback is attached to is passed in .Fa b . .Pp .Fa 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 .Fa oper or'ed with .Dv BIO_CB_RETURN . .Pp The meaning of the arguments .Fa argp , .Fa argi and .Fa argl depends on the value of .Fa oper (i.e. the operation being performed). .Pp .Fa ret 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 .Fa ret . If the return value is not positive, it will be immediately returned to the application and the BIO operation will not be performed. .Pp The callback should normally simply return .Fa ret when it has finished processing, unless it specifically wishes to modify the value returned to the application. .Ss Callback operations .Bl -tag -width Ds .It Fn BIO_free b .Fn callback b BIO_CB_FREE NULL 0L 0L 1L is called before the free operation. .It Fn BIO_read b out outl .Fn callback b BIO_CB_READ out outl 0L 1L is called before the read and .Fn callback b BIO_CB_READ|BIO_CB_RETURN out outl 0L ret after. .It Fn BIO_write b in inl .Fn callback b BIO_CB_WRITE in inl 0L 1L is called before the write and .Fn callback b BIO_CB_WRITE|BIO_CB_RETURN in inl 0L ret after. .It Fn BIO_gets b out outl .Fn callback b BIO_CB_GETS out outl 0L 1L is called before the operation and .Fn callback b BIO_CB_GETS|BIO_CB_RETURN out outl 0L ret after. .It Fn BIO_puts b in .Fn callback b BIO_CB_WRITE in 0 0L 1L is called before the operation and .Fn callback b BIO_CB_WRITE|BIO_CB_RETURN in 0 0L ret after. .It Fn BIO_ctrl b oper larg parg .Fn callback b BIO_CB_CTRL parg oper larg 1L is called before the call and .Fn callback b BIO_CB_CTRL|BIO_CB_RETURN parg oper larg ret after. .El .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