NAME    [Toc]    [Back]

       BIO_push, BIO_pop - add and remove BIOs from a chain.

LIBRARY    [Toc]    [Back]

       libcrypto, -lcrypto

SYNOPSIS    [Toc]    [Back]

        #include <openssl/bio.h>

        BIO *  BIO_push(BIO *b,BIO *append);
        BIO *  BIO_pop(BIO *b);

DESCRIPTION    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       TBA



2001-04-12                    0.9.6g                  BIO_push(3)