1=pod 2 3=head1 NAME 4 5OSSL_CALLBACK, OSSL_PASSPHRASE_CALLBACK - OpenSSL Core type to define callbacks 6 7=head1 SYNOPSIS 8 9 #include <openssl/core.h> 10 typedef int (OSSL_CALLBACK)(const OSSL_PARAM params[], void *arg); 11 typedef int (OSSL_PASSPHRASE_CALLBACK)(char *pass, size_t pass_size, 12 size_t *pass_len, 13 const OSSL_PARAM params[], 14 void *arg); 15 16=head1 DESCRIPTION 17 18For certain events or activities, provider functionality may need help from 19the application or the calling OpenSSL libraries themselves. For example, 20user input or direct (possibly optional) user output could be implemented 21this way. 22 23Callback functions themselves are always provided by or through the calling 24OpenSSL libraries, along with a generic pointer to data I<arg>. As far as 25the function receiving the pointer to the function pointer and I<arg> is 26concerned, the data that I<arg> points at is opaque, and the pointer should 27simply be passed back to the callback function when it's called. 28 29=over 4 30 31=item B<OSSL_CALLBACK> 32 33This is a generic callback function. When calling this callback function, 34the caller is expected to build an L<OSSL_PARAM(3)> array of data it wants or 35is expected to pass back, and pass that as I<params>, as well as the opaque 36data pointer it received, as I<arg>. 37 38=item B<OSSL_PASSPHRASE_CALLBACK> 39 40This is a specialised callback function, used specifically to prompt the 41user for a passphrase. When calling this callback function, a buffer to 42store the pass phrase needs to be given with I<pass>, and its size with 43I<pass_size>. The length of the prompted pass phrase will be given back in 44I<*pass_len>. 45 46Additional parameters can be passed with the L<OSSL_PARAM(3)> array I<params>, 47 48=back 49 50=begin comment RETURN VALUES doesn't make sense for a manual that only 51describes a type, but document checkers still want that section, and 52to have more than just the section title. 53 54=head1 RETURN VALUES 55 56txt 57 58=end comment 59 60=head1 SEE ALSO 61 62L<openssl-core.h(7)> 63 64=head1 HISTORY 65 66The types described here were added in OpenSSL 3.0. 67 68=head1 COPYRIGHT 69 70Copyright 2022 The OpenSSL Project Authors. All Rights Reserved. 71 72Licensed under the Apache License 2.0 (the "License"). You may not use 73this file except in compliance with the License. You can obtain a copy 74in the file LICENSE in the source distribution or at 75L<https://www.openssl.org/source/license.html>. 76 77=cut 78