BIO_PUSH(3) BSD Library Functions Manual BIO_PUSH(3)NAME
BIO_push, BIO_pop — add and remove BIOs from a chain
SYNOPSIS
#include <openssl/bio.h>
BIO *
BIO_push(BIO *b, BIO *append);
BIO *
BIO_pop(BIO *b);
DESCRIPTION
The BIO_push() function appends the BIO append to b and 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.
RETURN VALUESBIO_push() returns the beginning of the chain, b.
BIO_pop() returns the next BIO in the chain, or NULL if there is no next
BIO.
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 addi‐
tional consequences: a control call is made to the affected BIOs. Any
effects will be noted in the descriptions of individual BIOs.
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 direc‐
tion, that is data is read from f, base64 decoded and digested by md1 and
md2. If this call is made:
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.
BSD April 19, 2024 BSD
