DragonFly On-Line Manual Pages
BIO(3) DragonFly Library Functions Manual BIO(3)
NAME
BIO -- 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 types 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
to the application. The data may be left unmodified (for example a mes-
sage 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).
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_null(3), BIO_s_socket(3), BIO_set_callback(3), BIO_should_retry(3)
DragonFly 4.7 July 17, 2014 DragonFly 4.7
BIO_read(3) OpenSSL BIO_read(3)
NAME
BIO_read, BIO_write, BIO_gets, BIO_puts - BIO I/O functions
SYNOPSIS
#include <openssl/bio.h>
int BIO_read(BIO *b, void *buf, int len);
int BIO_gets(BIO *b, char *buf, int size);
int BIO_write(BIO *b, const void *buf, int len);
int BIO_puts(BIO *b, const char *buf);
DESCRIPTION
BIO_read() attempts to read len bytes from BIO b and places the data in
buf.
BIO_gets() performs the BIOs "gets" operation and places the data in
buf. Usually this operation will attempt to read a line of data from
the BIO of maximum length len. There are exceptions to this however,
for example BIO_gets() on a digest BIO will calculate and return the
digest and other BIOs may not support BIO_gets() at all.
BIO_write() attempts to write len bytes from buf to BIO b.
BIO_puts() attempts to write a null terminated string buf to BIO b.
RETURN VALUES
All these functions return either the amount of data successfully read
or written (if the return value is positive) or that no data was
successfully read or written if the result is 0 or -1. If the return
value is -2 then the operation is not implemented in the specific BIO
type.
NOTES
A 0 or -1 return is not necessarily an indication of an error. In
particular when the source/sink is non-blocking or of a certain type it
may merely be an indication that no data is currently available and
that the application should retry the operation later.
One technique sometimes used with blocking sockets is to use a system
call (such as select(), poll() or equivalent) to determine when data is
available and then call read() to read the data. The equivalent with
BIOs (that is call select() on the underlying I/O structure and then
call BIO_read() to read the data) should not be used because a single
call to BIO_read() can cause several reads (and writes in the case of
SSL BIOs) on the underlying I/O structure and may block as a result.
Instead select() (or equivalent) should be combined with non blocking
I/O so successive reads will request a retry instead of blocking.
See BIO_should_retry(3) for details of how to determine the cause of a
retry and other I/O issues.
If the BIO_gets() function is not supported by a BIO then it possible
to work around this by adding a buffering BIO BIO_f_buffer(3) to the
chain.
SEE ALSO
BIO_should_retry(3)
TBA
1.0.2h 2016-05-03 BIO_read(3)