---
name: "bio"
section: "3ssl"
platform: "linux"
package: "libssl-doc"
version: "1.1.0l-1~deb9u1"
release: "Debian 9 (Stretch)"
platforms: ["linux"]
url: "https://new.carta.tech/bio/3ssl"
---

# bio(3ssl)

Basic I/O abstraction

## NAME

bio - Basic I/O abstraction

## SYNOPSIS

```
 #include <openssl/bio.h>
```

## DESCRIPTION

A BIO is an I/O abstraction, it hides many of the underlying I/O details from an application. If an application uses a BIO for its I/O it can transparently handle SSL connections, unencrypted network connections and file I/O.

There are two type of BIO, a source/sink BIO and a filter BIO.

As its name implies a source/sink BIO is a source and/or sink of data, examples include a socket BIO and a file BIO.

A filter BIO takes data from one BIO and passes it through to another, or the application. The data may be left unmodified (for example a message digest BIO) or translated (for example an encryption BIO). The effect of a filter BIO may change according to the I/O operation it is performing: for example an encryption BIO will encrypt data if it is being written to and decrypt data if it is being read from.

BIOs can be joined together to form a chain (a single BIO is a chain with one component). A chain normally consist of one source/sink BIO and one or more filter BIOs. Data read from or written to the first BIO then traverses the chain to the end (normally a source/sink BIO).

Some BIOs (such as memory BIOs) can be used immediately after calling *BIO\_new()*. Others (such as file BIOs) need some additional initialization, and frequently a utility function exists to create and initialize such BIOs.

If *BIO\_free()* is called on a BIO chain it will only free one BIO resulting in a memory leak.

Calling *BIO\_free\_all()* a single BIO has the same effect as calling *BIO\_free()* on it other than the discarded return value.

Normally the **type** argument is supplied by a function which returns a pointer to a BIO\_METHOD. There is a naming convention for such functions: a source/sink BIO is normally called BIO\_s\_\*() and a filter BIO BIO\_f\_\*();

## EXAMPLE

Create a memory BIO:

```
 BIO *mem = BIO_new(BIO_s_mem());
```

## SEE ALSO

*BIO\_ctrl*(3), *BIO\_f\_base64*(3), *BIO\_f\_buffer*(3), *BIO\_f\_cipher*(3), *BIO\_f\_md*(3), *BIO\_f\_null*(3), *BIO\_f\_ssl*(3), *BIO\_find\_type*(3), *BIO\_new*(3), *BIO\_new\_bio\_pair*(3), *BIO\_push*(3), *BIO\_read*(3), *BIO\_s\_accept*(3), *BIO\_s\_bio*(3), *BIO\_s\_connect*(3), *BIO\_s\_fd*(3), *BIO\_s\_file*(3), *BIO\_s\_mem*(3), *BIO\_s\_mem*(3), *BIO\_s\_null*(3), *BIO\_s\_socket*(3), *BIO\_set\_callback*(3), *BIO\_should\_retry*(3)

## COPYRIGHT

Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License").  You may not use this file except in compliance with the License.  You can obtain a copy in the file LICENSE in the source distribution or at \<https://www.openssl.org/source/license.html\>.