BIO_push, BIO_pop - Add and remove BIOs from a chain.
BIO * BIO_push(
BIO *append ); BIO * BIO_pop(
BIO *b );
The BIO_push() function appends the BIO append to b. It
The BIO_pop() function removes the BIO b from a chain and
returns the next BIO in the chain. The return is NULL if
there are no more BIOs in the chain. The removed BIO then
becomes a single BIO with no association to the original
chain. It can be freed or attached to a different chain.
The names of these functions are somewhat misleading. The
BIO_push() function joins two BIO chains, whereas the
BIO_pop() function 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 the BIO_push() and BIO_pop() functions
on a BIO may have additional consequences (a control
call is made to the affected BIOs). Any effects are noted
in the descriptions of individual BIOs.
The BIO_push() function returns the end of the chain, b.
The BIO_pop() function returns the next BIO in the chain.
If there are no more BIOs in the chain, the return is
For these examples, 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 following calls BIO_push(md2, b64); BIO_push(md1,
the new chain is md1-md2-b64-f. Data written to md1 will
be digested by md1 and md2, base64 encoded and written to
Reading causes data to pass in the reverse direction. Data
is read from f, base64 decoded and digested by md1 and
If the call:
is made, the call will return b64, and the new chain will
be md1-b64-f. Data can be written to md1 as before.
[ Back ]