NAME

       OSSL_CALLBACK, OSSL_PASSPHRASE_CALLBACK - OpenSSL Core type to define callbacks

SYNOPSIS

        #include <openssl/core.h>
        typedef int (OSSL_CALLBACK)(const OSSL_PARAM params[], void *arg);
        typedef int (OSSL_PASSPHRASE_CALLBACK)(char *pass, size_t pass_size,
                                               size_t *pass_len,
                                               const OSSL_PARAM params[],
                                               void *arg);

DESCRIPTION

       For certain events or activities, provider functionality may need help from the
       application or the calling OpenSSL libraries themselves.  For example, user input or
       direct (possibly optional) user output could be implemented this way.

       Callback functions themselves are always provided by or through the calling OpenSSL
       libraries, along with a generic pointer to data arg.  As far as the function receiving the
       pointer to the function pointer and arg is concerned, the data that arg points at is
       opaque, and the pointer should simply be passed back to the callback function when it's
       called.

       OSSL_CALLBACK
           This is a generic callback function.  When calling this callback function, the caller
           is expected to build an OSSL_PARAM(3) array of data it wants or is expected to pass
           back, and pass that as params, as well as the opaque data pointer it received, as arg.

       OSSL_PASSPHRASE_CALLBACK
           This is a specialised callback function, used specifically to prompt the user for a
           passphrase.  When calling this callback function, a buffer to store the pass phrase
           needs to be given with pass, and its size with pass_size.  The length of the prompted
           pass phrase will be given back in *pass_len.

           Additional parameters can be passed with the OSSL_PARAM(3) array params,

SEE ALSO

       openssl-core.h(7)

HISTORY

       The types described here were added in OpenSSL 3.0.

COPYRIGHT

       Copyright 2022 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use this file except
       in compliance with the License.  You can obtain a copy in the file LICENSE in the source
       distribution or at <https://www.openssl.org/source/license.html>.