BIO_push, BIO_pop, BIO_set_next - add and remove BIOs from a chain
#include <openssl/bio.h>
BIO *BIO_push(BIO *b, BIO *next);
BIO *BIO_pop(BIO *b);
void BIO_set_next(BIO *b, BIO *next);
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.
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.
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.
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.
bio(7)
The
BIO_set_next() function was added in OpenSSL 1.1.0.
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>.