---
name: "libressl-BIO_f_null"
section: "3"
platform: "linux"
package: "libressl"
version: "4.4.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/libressl-BIO_f_null"
---

# libressl-BIO\_f\_null(3)

null filter

## NAME

**BIO\_f\_null** – null filter

## SYNOPSIS

Crypto Library (libcrypto, -lcrypto)

**#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.