const BIO_METHOD *
returns the null filter BIO method. This is a filter BIO that does nothing.
As may be apparent, a null filter BIO is not particularly useful.
All requests to a null filter BIO are passed through to the next BIO in the chain: this means that a BIO chain containing a null filter BIO behaves just as though the BIO was not there.
A chain containing a null filter BIO cannot be copied with
BIO_dup_chain(3), and any attempt to do so fails and returns
BIO_f_null() returns the null filter BIO
When called on a null filter BIO object,
BIO_method_type(3) returns the constant
BIO_method_name(3) returns a pointer to the static string "NULL
filter", not to be confused with a NUL string nor with a
BIO_f_null() first appeared in SSLeay
0.8.0 and has been available since OpenBSD 2.4.