#include <openssl/bio.h> BIO * BIO_push(BIO *b,BIO *append); BIO * BIO_pop(BIO *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.
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.
If the call:
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 direction, that is data is read from f, base64 decoded and digested by md1 and md2. If the call: