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, it
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.
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.
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-chain. 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 direction,
that is data is read from
f, base64
decoded and digested by
md1 and
md2. If the call:
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.
RETURN VALUES¶
BIO_push() returns the end of the chain,
b.
BIO_pop() returns the next BIO in the chain, or NULL if there is no next
BIO.
SEE ALSO¶
TBA