113d40330Schristos=pod 213d40330Schristos 313d40330Schristos=head1 NAME 413d40330Schristos 513d40330SchristosBIO_push, BIO_pop, BIO_set_next - add and remove BIOs from a chain 613d40330Schristos 713d40330Schristos=head1 SYNOPSIS 813d40330Schristos 913d40330Schristos #include <openssl/bio.h> 1013d40330Schristos 1121497c5cSchristos BIO *BIO_push(BIO *b, BIO *next); 1213d40330Schristos BIO *BIO_pop(BIO *b); 1313d40330Schristos void BIO_set_next(BIO *b, BIO *next); 1413d40330Schristos 1513d40330Schristos=head1 DESCRIPTION 1613d40330Schristos 1721497c5cSchristosBIO_push() pushes I<b> on I<next>. 1821497c5cSchristosIf I<b> is NULL the function does nothing and returns I<next>. 1921497c5cSchristosOtherwise it prepends I<b>, which may be a single BIO or a chain of BIOs, 2021497c5cSchristosto I<next> (unless I<next> is NULL). 2121497c5cSchristosIt then makes a control call on I<b> and returns I<b>. 2213d40330Schristos 2321497c5cSchristosBIO_pop() removes the BIO I<b> from any chain is is part of. 2421497c5cSchristosIf I<b> is NULL the function does nothing and returns NULL. 2521497c5cSchristosOtherwise it makes a control call on I<b> and 2621497c5cSchristosreturns the next BIO in the chain, or NULL if there is no next BIO. 2721497c5cSchristosThe removed BIO becomes a single BIO with no association with 2821497c5cSchristosthe original chain, it can thus be freed or be made part of a different chain. 2913d40330Schristos 3013d40330SchristosBIO_set_next() replaces the existing next BIO in a chain with the BIO pointed to 3121497c5cSchristosby I<next>. The new chain may include some of the same BIOs from the old chain 3213d40330Schristosor it may be completely different. 3313d40330Schristos 3413d40330Schristos=head1 NOTES 3513d40330Schristos 3613d40330SchristosThe names of these functions are perhaps a little misleading. BIO_push() 3713d40330Schristosjoins two BIO chains whereas BIO_pop() deletes a single BIO from a chain, 3813d40330Schristosthe deleted BIO does not need to be at the end of a chain. 3913d40330Schristos 4013d40330SchristosThe process of calling BIO_push() and BIO_pop() on a BIO may have additional 4121497c5cSchristosconsequences (a control call is made to the affected BIOs). 4221497c5cSchristosAny effects will be noted in the descriptions of individual BIOs. 4313d40330Schristos 44a3b08d93Schristos=head1 RETURN VALUES 45a3b08d93Schristos 4621497c5cSchristosBIO_push() returns the head of the chain, 4721497c5cSchristoswhich usually is I<b>, or I<next> if I<b> is NULL. 48a3b08d93Schristos 4921497c5cSchristosBIO_pop() returns the next BIO in the chain, 5021497c5cSchristosor NULL if there is no next BIO. 51a3b08d93Schristos 5213d40330Schristos=head1 EXAMPLES 5313d40330Schristos 5421497c5cSchristosFor these examples suppose I<md1> and I<md2> are digest BIOs, 5521497c5cSchristosI<b64> is a base64 BIO and I<f> is a file BIO. 5613d40330Schristos 5713d40330SchristosIf the call: 5813d40330Schristos 5913d40330Schristos BIO_push(b64, f); 6013d40330Schristos 6121497c5cSchristosis made then the new chain will be I<b64-f>. After making the calls 6213d40330Schristos 6313d40330Schristos BIO_push(md2, b64); 6413d40330Schristos BIO_push(md1, md2); 6513d40330Schristos 6621497c5cSchristosthe new chain is I<md1-md2-b64-f>. Data written to I<md1> will be digested 6721497c5cSchristosby I<md1> and I<md2>, base64 encoded, and finally written to I<f>. 6813d40330Schristos 6913d40330SchristosIt should be noted that reading causes data to pass in the reverse 7021497c5cSchristosdirection, that is data is read from I<f>, base64 decoded, 7121497c5cSchristosand digested by I<md2> and then I<md1>. 7221497c5cSchristos 7321497c5cSchristosThe call: 7413d40330Schristos 7513d40330Schristos BIO_pop(md2); 7613d40330Schristos 7721497c5cSchristoswill return I<b64> and the new chain will be I<md1-b64-f>. 7821497c5cSchristosData can be written to and read from I<md1> as before, 7921497c5cSchristosexcept that I<md2> will no more be applied. 8013d40330Schristos 8113d40330Schristos=head1 SEE ALSO 8213d40330Schristos 83*b0d17251SchristosL<bio(7)> 8413d40330Schristos 8513d40330Schristos=head1 HISTORY 8613d40330Schristos 8713d40330SchristosThe BIO_set_next() function was added in OpenSSL 1.1.0. 8813d40330Schristos 8913d40330Schristos=head1 COPYRIGHT 9013d40330Schristos 9121497c5cSchristosCopyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved. 9213d40330Schristos 93*b0d17251SchristosLicensed under the Apache License 2.0 (the "License"). You may not use 9413d40330Schristosthis file except in compliance with the License. You can obtain a copy 9513d40330Schristosin the file LICENSE in the source distribution or at 9613d40330SchristosL<https://www.openssl.org/source/license.html>. 9713d40330Schristos 9813d40330Schristos=cut 99