mirror of https://github.com/openssl/openssl.git
132 lines
3.9 KiB
Plaintext
132 lines
3.9 KiB
Plaintext
=pod
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=head1 NAME
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BIO_set_callback, BIO_get_callback, BIO_set_callback_arg, BIO_get_callback_arg,
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BIO_debug_callback - BIO callback functions
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=head1 SYNOPSIS
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#include <openssl/bio.h>
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typedef long (*BIO_callback_fn)(BIO *b, int oper, const char *argp, int argi,
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long argl, long ret);
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void BIO_set_callback(BIO *b, BIO_callack_fn cb);
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BIO_callack_fn BIO_get_callback(BIO *b);
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void BIO_set_callback_arg(BIO *b, char *arg);
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char *BIO_get_callback_arg(const BIO *b);
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long BIO_debug_callback(BIO *bio, int cmd, const char *argp, int argi,
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long argl, long ret);
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=head1 DESCRIPTION
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BIO_set_callback() and BIO_get_callback() set and retrieve the BIO callback,
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they are both macros. The callback is called during most high level BIO
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operations. It can be used for debugging purposes to trace operations on
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a BIO or to modify its operation.
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BIO_set_callback_arg() and BIO_get_callback_arg() are macros which can be
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used to set and retrieve an argument for use in the callback.
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BIO_debug_callback() is a standard debugging callback which prints
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out information relating to each BIO operation. If the callback
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argument is set it is interpreted as a BIO to send the information
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to, otherwise stderr is used.
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BIO_callback_fn() is the type of the callback function. The meaning of each
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argument is described below:
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=over
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=item B<b>
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The BIO the callback is attached to is passed in B<b>.
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=item B<oper>
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B<oper> is set to the operation being performed. For some operations
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the callback is called twice, once before and once after the actual
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operation, the latter case has B<oper> or'ed with BIO_CB_RETURN.
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=item B<argp> B<argi> B<argl>
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The meaning of the arguments B<argp>, B<argi> and B<argl> depends on
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the value of B<oper>, that is the operation being performed.
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=item B<ret>
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B<ret> is the return value that would be returned to the
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application if no callback were present. The actual value returned
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is the return value of the callback itself. In the case of callbacks
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called before the actual BIO operation 1 is placed in B<ret>, if
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the return value is not positive it will be immediately returned to
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the application and the BIO operation will not be performed.
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=back
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The callback should normally simply return B<ret> when it has
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finished processing, unless it specifically wishes to modify the
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value returned to the application.
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=head1 CALLBACK OPERATIONS
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In the notes below, B<callback> defers to the actual callback
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function that is called.
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=over 4
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=item B<BIO_free(b)>
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callback(b, BIO_CB_FREE, NULL, 0L, 0L, 1L) is called before the
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free operation.
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=item B<BIO_read(b, out, outl)>
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callback(b, BIO_CB_READ, out, outl, 0L, 1L) is called before
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the read and callback(b, BIO_CB_READ|BIO_CB_RETURN, out, outl, 0L, retvalue)
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after.
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=item B<BIO_write(b, in, inl)>
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callback(b, BIO_CB_WRITE, in, inl, 0L, 1L) is called before
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the write and callback(b, BIO_CB_WRITE|BIO_CB_RETURN, in, inl, 0L, retvalue)
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after.
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=item B<BIO_gets(b, out, outl)>
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callback(b, BIO_CB_GETS, out, outl, 0L, 1L) is called before
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the operation and callback(b, BIO_CB_GETS|BIO_CB_RETURN, out, outl, 0L, retvalue)
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after.
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=item B<BIO_puts(b, in)>
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callback(b, BIO_CB_WRITE, in, 0, 0L, 1L) is called before
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the operation and callback(b, BIO_CB_WRITE|BIO_CB_RETURN, in, 0, 0L, retvalue)
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after.
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=item B<BIO_ctrl(BIO *b, int cmd, long larg, void *parg)>
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callback(b, BIO_CB_CTRL, parg, cmd, larg, 1L) is called before the call and
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callback(b, BIO_CB_CTRL|BIO_CB_RETURN, parg, cmd, larg, ret) after.
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=back
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=head1 EXAMPLE
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The BIO_debug_callback() function is a good example, its source is
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in crypto/bio/bio_cb.c
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=head1 COPYRIGHT
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Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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