BIO_s_null - null data sink
BIO_METHOD * BIO_s_null(void);
returns the null sink BIO method. Data written to the null
sink is discarded, reads return EOF.
A null sink BIO behaves in a similar manner to the Unix /dev/null device.
A null bio can be placed on the end of a chain to discard any data passed
A null sink is useful if, for example, an application wishes to digest some data
by writing through a digest bio but not send the digested data anywhere. Since
a BIO chain must normally include a source/sink BIO this can be achieved by
adding a null sink BIO to the end of the chain
returns the null sink BIO method.