1=pod 2 3=head1 NAME 4 5BIO_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 *append); 12 BIO *BIO_pop(BIO *b); 13 void BIO_set_next(BIO *b, BIO *next); 14 15=head1 DESCRIPTION 16 17The BIO_push() function appends the BIO B<append> to B<b>, it returns 18B<b>. 19 20BIO_pop() removes the BIO B<b> from a chain and returns the next BIO 21in the chain, or NULL if there is no next BIO. The removed BIO then 22becomes a single BIO with no association with the original chain, 23it can thus be freed or attached to a different chain. 24 25BIO_set_next() replaces the existing next BIO in a chain with the BIO pointed to 26by B<next>. The new chain may include some of the same BIOs from the old chain 27or it may be completely different. 28 29=head1 NOTES 30 31The names of these functions are perhaps a little misleading. BIO_push() 32joins two BIO chains whereas BIO_pop() deletes a single BIO from a chain, 33the deleted BIO does not need to be at the end of a chain. 34 35The process of calling BIO_push() and BIO_pop() on a BIO may have additional 36consequences (a control call is made to the affected BIOs) any effects will 37be noted in the descriptions of individual BIOs. 38 39=head1 EXAMPLES 40 41For these examples suppose B<md1> and B<md2> are digest BIOs, B<b64> is 42a base64 BIO and B<f> is a file BIO. 43 44If the call: 45 46 BIO_push(b64, f); 47 48is made then the new chain will be B<b64-f>. After making the calls 49 50 BIO_push(md2, b64); 51 BIO_push(md1, md2); 52 53the new chain is B<md1-md2-b64-f>. Data written to B<md1> will be digested 54by B<md1> and B<md2>, B<base64> encoded and written to B<f>. 55 56It should be noted that reading causes data to pass in the reverse 57direction, that is data is read from B<f>, base64 B<decoded> and digested 58by B<md1> and B<md2>. If the call: 59 60 BIO_pop(md2); 61 62The call will return B<b64> and the new chain will be B<md1-b64-f> data can 63be written to B<md1> as before. 64 65=head1 RETURN VALUES 66 67BIO_push() returns the end of the chain, B<b>. 68 69BIO_pop() returns the next BIO in the chain, or NULL if there is no next 70BIO. 71 72=head1 SEE ALSO 73 74L<bio> 75 76=head1 HISTORY 77 78The BIO_set_next() function was added in OpenSSL 1.1.0. 79 80=head1 COPYRIGHT 81 82Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved. 83 84Licensed under the OpenSSL license (the "License"). You may not use 85this file except in compliance with the License. You can obtain a copy 86in the file LICENSE in the source distribution or at 87L<https://www.openssl.org/source/license.html>. 88 89=cut 90