BIO_F_NULL(3) | Library Functions Manual | BIO_F_NULL(3)

# NAME

`BIO_f_null` — null filter

# SYNOPSIS

library “libcrypto”
`#include <openssl/bio.h>`

const BIO_METHOD *
`BIO_f_null`(void);

# DESCRIPTION

`BIO_f_null`() 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 `NULL`.

# RETURN VALUES

`BIO_f_null`() returns the null filter BIO method.

When called on a null filter BIO object, BIO_method_type(3) returns the constant `BIO_TYPE_NULL_FILTER` and BIO_method_name(3) returns a pointer to the static string "NULL filter", not to be confused with a NUL string nor with a `NULL pointer`.

# SEE ALSO

BIO_new(3)

# HISTORY

`BIO_f_null`() first appeared in SSLeay 0.8.0 and has been available since OpenBSD 2.4.

June 8, 2025 | Debian