| yuezonghe | 824eb0c | 2024-06-27 02:32:26 -0700 | [diff] [blame^] | 1 | =pod |
| 2 | |
| 3 | =head1 NAME |
| 4 | |
| 5 | BIO_push, BIO_pop, BIO_set_next - add and remove BIOs from a chain |
| 6 | |
| 7 | =head1 SYNOPSIS |
| 8 | |
| 9 | #include <openssl/bio.h> |
| 10 | |
| 11 | BIO *BIO_push(BIO *b, BIO *next); |
| 12 | BIO *BIO_pop(BIO *b); |
| 13 | void BIO_set_next(BIO *b, BIO *next); |
| 14 | |
| 15 | =head1 DESCRIPTION |
| 16 | |
| 17 | BIO_push() pushes I<b> on I<next>. |
| 18 | If I<b> is NULL the function does nothing and returns I<next>. |
| 19 | Otherwise it prepends I<b>, which may be a single BIO or a chain of BIOs, |
| 20 | to I<next> (unless I<next> is NULL). |
| 21 | It then makes a control call on I<b> and returns I<b>. |
| 22 | |
| 23 | BIO_pop() removes the BIO I<b> from any chain is is part of. |
| 24 | If I<b> is NULL the function does nothing and returns NULL. |
| 25 | Otherwise it makes a control call on I<b> and |
| 26 | returns the next BIO in the chain, or NULL if there is no next BIO. |
| 27 | The removed BIO becomes a single BIO with no association with |
| 28 | the original chain, it can thus be freed or be made part of a different chain. |
| 29 | |
| 30 | BIO_set_next() replaces the existing next BIO in a chain with the BIO pointed to |
| 31 | by I<next>. The new chain may include some of the same BIOs from the old chain |
| 32 | or it may be completely different. |
| 33 | |
| 34 | =head1 NOTES |
| 35 | |
| 36 | The names of these functions are perhaps a little misleading. BIO_push() |
| 37 | joins two BIO chains whereas BIO_pop() deletes a single BIO from a chain, |
| 38 | the deleted BIO does not need to be at the end of a chain. |
| 39 | |
| 40 | The process of calling BIO_push() and BIO_pop() on a BIO may have additional |
| 41 | consequences (a control call is made to the affected BIOs). |
| 42 | Any effects will be noted in the descriptions of individual BIOs. |
| 43 | |
| 44 | =head1 RETURN VALUES |
| 45 | |
| 46 | BIO_push() returns the head of the chain, |
| 47 | which usually is I<b>, or I<next> if I<b> is NULL. |
| 48 | |
| 49 | BIO_pop() returns the next BIO in the chain, |
| 50 | or NULL if there is no next BIO. |
| 51 | |
| 52 | =head1 EXAMPLES |
| 53 | |
| 54 | For these examples suppose I<md1> and I<md2> are digest BIOs, |
| 55 | I<b64> is a base64 BIO and I<f> is a file BIO. |
| 56 | |
| 57 | If the call: |
| 58 | |
| 59 | BIO_push(b64, f); |
| 60 | |
| 61 | is made then the new chain will be I<b64-f>. After making the calls |
| 62 | |
| 63 | BIO_push(md2, b64); |
| 64 | BIO_push(md1, md2); |
| 65 | |
| 66 | the new chain is I<md1-md2-b64-f>. Data written to I<md1> will be digested |
| 67 | by I<md1> and I<md2>, base64 encoded, and finally written to I<f>. |
| 68 | |
| 69 | It should be noted that reading causes data to pass in the reverse |
| 70 | direction, that is data is read from I<f>, base64 decoded, |
| 71 | and digested by I<md2> and then I<md1>. |
| 72 | |
| 73 | The call: |
| 74 | |
| 75 | BIO_pop(md2); |
| 76 | |
| 77 | will return I<b64> and the new chain will be I<md1-b64-f>. |
| 78 | Data can be written to and read from I<md1> as before, |
| 79 | except that I<md2> will no more be applied. |
| 80 | |
| 81 | =head1 SEE ALSO |
| 82 | |
| 83 | L<bio> |
| 84 | |
| 85 | =head1 HISTORY |
| 86 | |
| 87 | The BIO_set_next() function was added in OpenSSL 1.1.0. |
| 88 | |
| 89 | =head1 COPYRIGHT |
| 90 | |
| 91 | Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved. |
| 92 | |
| 93 | Licensed under the OpenSSL license (the "License"). You may not use |
| 94 | this file except in compliance with the License. You can obtain a copy |
| 95 | in the file LICENSE in the source distribution or at |
| 96 | L<https://www.openssl.org/source/license.html>. |
| 97 | |
| 98 | =cut |