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Title "BIO_PUSH 3" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
BIO_push, BIO_pop, BIO_set_next - add and remove BIOs from a chain Header "SYNOPSIS" .Vb 1 #include <openssl/bio.h> \& BIO *BIO_push(BIO *b, BIO *next); BIO *BIO_pop(BIO *b); void BIO_set_next(BIO *b, BIO *next); .Ve Header "DESCRIPTION" \fBBIO_push() pushes b on next. If b is \s-1NULL\s0 the function does nothing and returns next. Otherwise it prepends b, which may be a single \s-1BIO\s0 or a chain of BIOs, to next (unless next is \s-1NULL\s0). It then makes a control call on b and returns b.

\fBBIO_pop() removes the \s-1BIO\s0 b from any chain is is part of. If b is \s-1NULL\s0 the function does nothing and returns \s-1NULL.\s0 Otherwise it makes a control call on b and returns the next \s-1BIO\s0 in the chain, or \s-1NULL\s0 if there is no next \s-1BIO.\s0 The removed \s-1BIO\s0 becomes a single \s-1BIO\s0 with no association with the original chain, it can thus be freed or be made part of a different chain.

\fBBIO_set_next() replaces the existing next \s-1BIO\s0 in a chain with the \s-1BIO\s0 pointed to by next. The new chain may include some of the same BIOs from the old chain or it may be completely different.

Header "NOTES" The names of these functions are perhaps a little misleading. BIO_push() joins two \s-1BIO\s0 chains whereas BIO_pop() deletes a single \s-1BIO\s0 from a chain, the deleted \s-1BIO\s0 does not need to be at the end of a chain.

The process of calling BIO_push() and BIO_pop() on a \s-1BIO\s0 may have additional consequences (a control call is made to the affected BIOs). Any effects will be noted in the descriptions of individual BIOs.

Header "RETURN VALUES" \fBBIO_push() returns the head of the chain, which usually is b, or next if b is \s-1NULL.\s0

\fBBIO_pop() returns the next \s-1BIO\s0 in the chain, or \s-1NULL\s0 if there is no next \s-1BIO.\s0

Header "EXAMPLES" For these examples suppose md1 and md2 are digest BIOs, \fIb64 is a base64 \s-1BIO\s0 and f is a file \s-1BIO.\s0

If the call:

.Vb 1 BIO_push(b64, f); .Ve

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

.Vb 2 BIO_push(md2, b64); BIO_push(md1, md2); .Ve

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:

.Vb 1 BIO_pop(md2); .Ve

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.

Header "SEE ALSO" bio Header "HISTORY" The BIO_set_next() function was added in OpenSSL 1.1.0. Header "COPYRIGHT" Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.