Updated: 2021/Apr/14


BIO_push(3)                         OpenSSL                        BIO_push(3)



NAME
       BIO_push, BIO_pop, BIO_set_next - add and remove BIOs from a chain

LIBRARY
       libcrypto, -lcrypto

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);

DESCRIPTION
       The BIO_push() function appends the BIO append 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 next. The new chain may include some of the same BIOs
       from the old chain or it may be completely different.

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.

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.

EXAMPLES
       For these examples suppose md1 and md2 are digest BIOs, b64 is a base64
       BIO and f is a file BIO.

       If the call:

        BIO_push(b64, f);

       is made then the new chain will be b64-f. After making the calls

        BIO_push(md2, b64);
        BIO_push(md1, md2);

       the new chain is md1-md2-b64-f. Data written to md1 will be digested by
       md1 and md2, base64 encoded and written to f.

       It should be noted that reading causes data to pass in the reverse
       direction, that is data is read from f, base64 decoded and digested by
       md1 and md2. If the call:

        BIO_pop(md2);

       The call will return b64 and the new chain will be md1-b64-f data can
       be written to md1 as before.

SEE ALSO
       bio

HISTORY
       The BIO_set_next() function was added in OpenSSL 1.1.0.

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
       <https://www.openssl.org/source/license.html>.



1.1.1i                            2019-06-09                       BIO_push(3)