| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | BIO_push, BIO_pop, BIO_set_next - add and remove BIOs from a chain
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| 6 |
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| 7 | =head1 SYNOPSIS
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| 8 |
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| 9 | #include <openssl/bio.h>
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| 10 |
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| 11 | BIO *BIO_push(BIO *b, BIO *next);
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| 12 | BIO *BIO_pop(BIO *b);
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| 13 | void BIO_set_next(BIO *b, BIO *next);
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| 14 |
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| 15 | =head1 DESCRIPTION
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| 16 |
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| 17 | BIO_push() pushes I<b> on I<next>.
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| 18 | If I<b> is NULL the function does nothing and returns I<next>.
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| 19 | Otherwise it prepends I<b>, which may be a single BIO or a chain of BIOs,
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| 20 | to I<next> (unless I<next> is NULL).
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| 21 | It then makes a control call on I<b> and returns I<b>.
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| 22 |
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| 23 | BIO_pop() removes the BIO I<b> from any chain is is part of.
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| 24 | If I<b> is NULL the function does nothing and returns NULL.
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| 25 | Otherwise it makes a control call on I<b> and
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| 26 | returns the next BIO in the chain, or NULL if there is no next BIO.
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| 27 | The removed BIO becomes a single BIO with no association with
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| 28 | the original chain, it can thus be freed or be made part of a different chain.
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| 29 |
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| 30 | BIO_set_next() replaces the existing next BIO in a chain with the BIO pointed to
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| 31 | by I<next>. The new chain may include some of the same BIOs from the old chain
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| 32 | or it may be completely different.
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| 33 |
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| 34 | =head1 NOTES
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| 35 |
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| 36 | The names of these functions are perhaps a little misleading. BIO_push()
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| 37 | joins two BIO chains whereas BIO_pop() deletes a single BIO from a chain,
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| 38 | the deleted BIO does not need to be at the end of a chain.
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| 39 |
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| 40 | The process of calling BIO_push() and BIO_pop() on a BIO may have additional
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| 41 | consequences (a control call is made to the affected BIOs).
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| 42 | Any effects will be noted in the descriptions of individual BIOs.
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| 43 |
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| 44 | =head1 RETURN VALUES
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| 45 |
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| 46 | BIO_push() returns the head of the chain,
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| 47 | which usually is I<b>, or I<next> if I<b> is NULL.
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| 48 |
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| 49 | BIO_pop() returns the next BIO in the chain,
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| 50 | or NULL if there is no next BIO.
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| 51 |
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| 52 | =head1 EXAMPLES
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| 53 |
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| 54 | For these examples suppose I<md1> and I<md2> are digest BIOs,
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| 55 | I<b64> is a base64 BIO and I<f> is a file BIO.
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| 56 |
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| 57 | If the call:
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| 58 |
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| 59 | BIO_push(b64, f);
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| 60 |
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| 61 | is made then the new chain will be I<b64-f>. After making the calls
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| 62 |
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| 63 | BIO_push(md2, b64);
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| 64 | BIO_push(md1, md2);
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| 65 |
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| 66 | the new chain is I<md1-md2-b64-f>. Data written to I<md1> will be digested
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| 67 | by I<md1> and I<md2>, base64 encoded, and finally written to I<f>.
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| 68 |
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| 69 | It should be noted that reading causes data to pass in the reverse
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| 70 | direction, that is data is read from I<f>, base64 decoded,
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| 71 | and digested by I<md2> and then I<md1>.
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| 72 |
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| 73 | The call:
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| 74 |
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| 75 | BIO_pop(md2);
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| 76 |
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| 77 | will return I<b64> and the new chain will be I<md1-b64-f>.
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| 78 | Data can be written to and read from I<md1> as before,
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| 79 | except that I<md2> will no more be applied.
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| 80 |
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| 81 | =head1 SEE ALSO
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| 82 |
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| 83 | L<bio(7)>
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| 84 |
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| 85 | =head1 HISTORY
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| 86 |
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| 87 | The BIO_set_next() function was added in OpenSSL 1.1.0.
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| 88 |
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| 89 | =head1 COPYRIGHT
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| 90 |
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| 91 | Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
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| 92 |
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| 93 | Licensed under the Apache License 2.0 (the "License"). You may not use
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| 94 | this file except in compliance with the License. You can obtain a copy
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| 95 | in the file LICENSE in the source distribution or at
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| 96 | L<https://www.openssl.org/source/license.html>.
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| 97 |
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| 98 | =cut
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