BIO_push, BIO_pop, BIO_set_next - add and remove BIOs from a chain
BIO *BIO_push(BIO *b, BIO *append);
BIO *BIO_pop(BIO *b);
void BIO_set_next(BIO *b, BIO *next);
function appends the BIO append
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.
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.
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()
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.
For these examples suppose md1
are digest BIOs, b64
is a base64 BIO and f
is a file BIO.
If the call:
is made then the new chain will be b64-f
. After making the calls
the new chain is md1-md2-b64-f
. Data written to md1
digested by md1
encoded and written to
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
. If the call:
The call will return b64
and the new chain will be md1-b64-f
can be written to md1
returns the end of the chain, b
returns the next BIO in the chain, or NULL if there is no next
function was added in OpenSSL 1.1.0.
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