BIO_push, BIO_pop - add and remove BIOs from a chain.
BIO * BIO_push(BIO *b,BIO *append); BIO * BIO_pop(BIO *b);
The names of these functions are perhaps a little misleading.
The process of calling
For these examples suppose md1 and md2 are digest BIOs, b64 is a base64 BIO and f is a file BIO.
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:
The call will return b64 and the new chain will be md1-b64-f data can be written to md1 as before.