=pod =head1 NAME BIO_push, BIO_pop, BIO_set_next - add and remove BIOs from a chain =head1 SYNOPSIS #include <openssl/bio.h> BIO *BIO_push(BIO *b, BIO *append); BIO *BIO_pop(BIO *b); void BIO_set_next(BIO *b, BIO *next); =head1 DESCRIPTION The BIO_push() function appends the BIO B<append> to B<b>, it returns B<b>. BIO_pop() removes the BIO B<b> from a chain and returns the next BIO in the chain, or NULL if there is no next BIO. The removed BIO then becomes a single BIO with no association with the original chain, it can thus be freed or attached to a different chain. BIO_set_next() replaces the existing next BIO in a chain with the BIO pointed to by B<next>. The new chain may include some of the same BIOs from the old chain or it may be completely different. =head1 NOTES The names of these functions are perhaps a little misleading. BIO_push() joins two BIO chains whereas BIO_pop() deletes a single BIO from a chain, the deleted BIO does not need to be at the end of a chain. The process of calling BIO_push() and BIO_pop() on a BIO may have additional consequences (a control call is made to the affected BIOs) any effects will be noted in the descriptions of individual BIOs. =head1 RETURN VALUES BIO_push() returns the end of the chain, B<b>. BIO_pop() returns the next BIO in the chain, or NULL if there is no next BIO. =head1 EXAMPLES For these examples suppose B<md1> and B<md2> are digest BIOs, B<b64> is a base64 BIO and B<f> is a file BIO. If the call: BIO_push(b64, f); is made then the new chain will be B<b64-f>. After making the calls BIO_push(md2, b64); BIO_push(md1, md2); the new chain is B<md1-md2-b64-f>. Data written to B<md1> will be digested by B<md1> and B<md2>, B<base64> encoded and written to B<f>. It should be noted that reading causes data to pass in the reverse direction, that is data is read from B<f>, base64 B<decoded> and digested by B<md1> and B<md2>. If the call: BIO_pop(md2); The call will return B<b64> and the new chain will be B<md1-b64-f> data can be written to B<md1> as before. =head1 SEE ALSO L<bio> =head1 HISTORY The BIO_set_next() function was added in OpenSSL 1.1.0. =head1 COPYRIGHT Copyright 2000-2019 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 LICENSE in the source distribution or at L<https://www.openssl.org/source/license.html>. =cut |