Updated: 2022/Sep/29

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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 *next);
        BIO *BIO_pop(BIO *b);
        void BIO_set_next(BIO *b, BIO *next);

DESCRIPTION
       BIO_push() pushes b on next.  If b is NULL the function does nothing
       and returns next.  Otherwise it prepends b, which may be a single BIO
       or a chain of BIOs, to next (unless next is NULL).  It then makes a
       control call on b and returns b.

       BIO_pop() removes the BIO b from any chain is is part of.  If b is NULL
       the function does nothing and returns NULL. Otherwise it makes a
       control call on b and returns the next BIO in the chain, or NULL if
       there is no next BIO. The removed BIO becomes a single BIO with no
       association with the original chain, it can thus be freed or be made
       part of 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 head of the chain, which usually is b, or next
       if b is NULL.

       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 finally 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
       md2 and then md1.

       The call:

        BIO_pop(md2);

       will return b64 and the new chain will be md1-b64-f.  Data can be
       written to and read from md1 as before, except that md2 will no more be
       applied.

SEE ALSO
       bio(7)

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

COPYRIGHT
       Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (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>.



3.0.12                            2023-05-07                       BIO_push(3)