bio — I/O abstraction
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
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
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_null(3), BIO_s_socket(3), BIO_set_callback(3), BIO_should_retry(3)