Provided by: libssl-doc_1.1.0g-2ubuntu4_all bug

NAME

       BIO_set_callback_ex, BIO_get_callback_ex, BIO_set_callback, BIO_get_callback,
       BIO_set_callback_arg, BIO_get_callback_arg, BIO_debug_callback, BIO_callback_fn_ex,
       BIO_callback_fn - BIO callback functions

SYNOPSIS

        #include <openssl/bio.h>

        typedef long (*BIO_callback_fn_ex)(BIO *b, int oper, const char *argp,
                                           size_t len, int argi,
                                           long argl, int ret, size_t *processed);
        typedef long (*BIO_callback_fn)(BIO *b, int oper, const char *argp, int argi,
                                        long argl, long ret);

        void BIO_set_callback_ex(BIO *b, BIO_callback_fn_ex callback);
        BIO_callback_fn_ex BIO_get_callback_ex(const BIO *b);

        void BIO_set_callback(BIO *b, BIO_callack_fn cb);
        BIO_callack_fn BIO_get_callback(BIO *b);
        void BIO_set_callback_arg(BIO *b, char *arg);
        char *BIO_get_callback_arg(const BIO *b);

        long BIO_debug_callback(BIO *bio, int cmd, const char *argp, int argi,
                                long argl, long ret);

DESCRIPTION

       BIO_set_callback_ex() and 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.

       BIO_set_callback() and BIO_get_callback() set and retrieve the old format BIO callback.
       New code should not use these functions, but they are retained for backwards compatbility.
       Any callback set via BIO_set_callback_ex() will get called in preference to any set by
       BIO_set_callback().

       BIO_set_callback_arg() and BIO_get_callback_arg() are macros which can be used to set and
       retrieve an argument for use in the callback.

       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.

       BIO_callback_fn_ex() is the type of the callback function and BIO_callback_fn() is the
       type of the old format callback function. The meaning of each argument is described below:

       b   The BIO the callback is attached to is passed in b.

       oper
           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
           oper or'ed with BIO_CB_RETURN.

       len The length of the data requested to be read or written. This is only useful if oper is
           BIO_CB_READ, BIO_CB_WRITE or BIO_CB_GETS.

       argp argi argl
           The meaning of the arguments argp, argi and argl depends on the value of oper, that is
           the operation being performed.

       processed
           processed is a pointer to a location which will be updated with the amount of data
           that was actually read or written. Only used for BIO_CB_READ, BIO_CB_WRITE,
           BIO_CB_GETS and BIO_CB_PUTS.

       ret 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 ret, 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 ret when it has finished processing, unless it
       specifically wishes to modify the value returned to the application.

CALLBACK OPERATIONS

       In the notes below, callback defers to the actual callback function that is called.

       BIO_free(b)
            callback_ex(b, BIO_CB_FREE, NULL, 0, 0, 0L, 1L, NULL)

           or

            callback(b, BIO_CB_FREE, NULL, 0L, 0L, 1L)

           is called before the free operation.

       BIO_read_ex(b, data, dlen, readbytes)
            callback_ex(b, BIO_CB_READ, data, dlen, 0, 0L, 1L, readbytes)

           or

            callback(b, BIO_CB_READ, data, dlen, 0L, 1L)

           is called before the read and

            callback_ex(b, BIO_CB_READ | BIO_CB_RETURN, data, dlen, 0, 0L, retvalue, readbytes)

           or

            callback(b, BIO_CB_READ|BIO_CB_RETURN, data, dlen, 0L, retvalue)

           after.

       BIO_write(b, data, dlen, written)
            callback_ex(b, BIO_CB_WRITE, data, dlen, 0, 0L, 1L, written)

           or

            callback(b, BIO_CB_WRITE, datat, dlen, 0L, 1L)

           is called before the write and

            callback_ex(b, BIO_CB_WRITE | BIO_CB_RETURN, data, dlen, 0, 0L, retvalue, written)

           or

            callback(b, BIO_CB_WRITE|BIO_CB_RETURN, data, dlen, 0L, retvalue)

           after.

       BIO_gets(b, buf, size)
            callback_ex(b, BIO_CB_GETS, buf, size, 0, 0L, 1, NULL, NULL)

           or

            callback(b, BIO_CB_GETS, buf, size, 0L, 1L)

           is called before the operation and

            callback_ex(b, BIO_CB_GETS | BIO_CB_RETURN, buf, size, 0, 0L, retvalue, readbytes)

           or

            callback(b, BIO_CB_GETS|BIO_CB_RETURN, buf, size, 0L, retvalue)

           after.

       BIO_puts(b, buf)
            callback_ex(b, BIO_CB_PUTS, buf, 0, 0, 0L, 1L, NULL);

           or

            callback(b, BIO_CB_PUTS, buf, 0, 0L, 1L)

           is called before the operation and

            callback_ex(b, BIO_CB_PUTS | BIO_CB_RETURN, buf, 0, 0, 0L, retvalue, written)

           or

            callback(b, BIO_CB_WRITE|BIO_CB_RETURN, buf, 0, 0L, retvalue)

           after.

       BIO_ctrl(BIO *b, int cmd, long larg, void *parg)
            callback_ex(b, BIO_CB_CTRL, parg, 0, cmd, larg, 1L, NULL)

           or

            callback(b, BIO_CB_CTRL, parg, cmd, larg, 1L)

           is called before the call and

            callback_ex(b, BIO_CB_CTRL | BIO_CB_RETURN, parg, 0, cmd, larg, ret, NULL)

           or

            callback(b, BIO_CB_CTRL|BIO_CB_RETURN, parg, cmd, larg, ret)

           after.

EXAMPLE

       The BIO_debug_callback() function is a good example, its source is in crypto/bio/bio_cb.c

COPYRIGHT

       Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (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>.