=pod =head1 NAME BIO_push, BIO_pop, BIO_set_next - add and remove BIOs from a chain =head1 SYNOPSIS #include 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 to B, it returns B. BIO_pop() removes the BIO 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. 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 EXAMPLES For these examples suppose B and B are digest BIOs, B is a base64 BIO and B is a file BIO. If the call: BIO_push(b64, f); is made then the new chain will be B. After making the calls BIO_push(md2, b64); BIO_push(md1, md2); the new chain is B. Data written to B will be digested by B and B, B encoded and written to B. It should be noted that reading causes data to pass in the reverse direction, that is data is read from B, base64 B and digested by B and B. If the call: BIO_pop(md2); The call will return B and the new chain will be B data can be written to B as before. =head1 RETURN VALUES BIO_push() returns the end of the chain, B. BIO_pop() returns the next BIO in the chain, or NULL if there is no next BIO. =head1 SEE ALSO L =head1 HISTORY The BIO_set_next() function was added in OpenSSL version 1.1.0. =head1 COPYRIGHT Copyright 2000-2016 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. =cut