.Dd $Mdocdate: September 9 2015 $
.Dt BIO 3
.Os
.Sh NAME
.Nm BIO
.Nd I/O abstraction
.Sh SYNOPSIS
.In openssl/bio.h
.Sh 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.
.Pp
There are two types of BIO, a source/sink BIO and a filter BIO.
.Pp
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.
.Pp
A filter BIO takes data from one BIO and passes it through
to another, or to 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.
.Pp
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).
.Sh SEE ALSO
.Xr BIO_ctrl 3 ,
.Xr BIO_f_base64 3 ,
.Xr BIO_f_buffer 3 ,
.Xr BIO_f_cipher 3 ,
.Xr BIO_f_md 3 ,
.Xr BIO_f_null 3 ,
.Xr BIO_f_ssl 3 ,
.Xr BIO_find_type 3 ,
.Xr BIO_new 3 ,
.Xr BIO_new_bio_pair 3 ,
.Xr BIO_push 3 ,
.Xr BIO_read 3 ,
.Xr BIO_s_accept 3 ,
.Xr BIO_s_bio 3 ,
.Xr BIO_s_connect 3 ,
.Xr BIO_s_fd 3 ,
.Xr BIO_s_file 3 ,
.Xr BIO_s_mem 3 ,
.Xr BIO_s_null 3 ,
.Xr BIO_s_socket 3 ,
.Xr BIO_set_callback 3 ,
.Xr BIO_should_retry 3