BIO_callback_fn (3)

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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 callback. The callback is called during most high level operations. It can be used for debugging purposes to trace operations on a or to modify its operation.

BIO_set_callback() and BIO_get_callback() set and retrieve the old format

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

operation. If the callback argument is set it is interpreted as a 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

in the source distribution or at <www.openssl.org/source/license.html>.