=pod =head1 NAME BIO_push, BIO_pop - add and remove BIOs from a chain. =head1 SYNOPSIS #include BIO * BIO_push(BIO *b,BIO *append); BIO * BIO_pop(BIO *b); =head1 DESCRIPTION The BIO_push() function appends the BIO B 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. =head1 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. =head1 EXAMPLES For these examples suppose B and B are digest BIOs, B is a base64 BIO and B is a file BIO. If the call: BIO_push(b64, f); is made then the new chain will be B. After making the calls BIO_push(md2, b64); BIO_push(md1, md2); the new chain is B. Data written to B will be digested by B and B, B encoded and written to B. It should be noted that reading causes data to pass in the reverse direction, that is data is read from B, base64 B and digested by B and B. If the call: BIO_pop(md2); The call will return B and the new chain will be B data can be written to B as before. =head1 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. =head1 SEE ALSO TBA