BIO_push(3)

     BIO_push(3)            0.9.6h (2000-09-14)            BIO_push(3)

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

     SYNOPSIS
           #include <openssl/bio.h>

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

     DESCRIPTION
          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
          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
          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);

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     BIO_push(3)            0.9.6h (2000-09-14)            BIO_push(3)

          The call will return b64 and the new chain will be md1-b64-f
          data can be written to md1 as before.

     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.

     SEE ALSO
          TBA

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