DragonFly On-Line Manual Pages
BIO(3) DragonFly Library Functions Manual BIO(3)
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
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).
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_s_fd(3) OpenSSL BIO_s_fd(3)
BIO_s_fd, BIO_set_fd, BIO_get_fd, BIO_new_fd - file descriptor BIO
BIO_METHOD * BIO_s_fd(void);
#define BIO_set_fd(b,fd,c) BIO_int_ctrl(b,BIO_C_SET_FD,c,fd)
#define BIO_get_fd(b,c) BIO_ctrl(b,BIO_C_GET_FD,0,(char *)c)
BIO *BIO_new_fd(int fd, int close_flag);
BIO_s_fd() returns the file descriptor BIO method. This is a wrapper
round the platforms file descriptor routines such as read() and
BIO_read() and BIO_write() read or write the underlying descriptor.
BIO_puts() is supported but BIO_gets() is not.
If the close flag is set then then close() is called on the underlying
file descriptor when the BIO is freed.
BIO_reset() attempts to change the file pointer to the start of file
using lseek(fd, 0, 0).
BIO_seek() sets the file pointer to position ofs from start of file
using lseek(fd, ofs, 0).
BIO_tell() returns the current file position by calling lseek(fd, 0,
BIO_set_fd() sets the file descriptor of BIO b to fd and the close flag
BIO_get_fd() places the file descriptor in c if it is not NULL, it also
returns the file descriptor. If c is not NULL it should be of type (int
BIO_new_fd() returns a file descriptor BIO using fd and close_flag.
The behaviour of BIO_read() and BIO_write() depends on the behavior of
the platforms read() and write() calls on the descriptor. If the
underlying file descriptor is in a non blocking mode then the BIO will
behave in the manner described in the BIO_read(3) and
BIO_should_retry(3) manual pages.
File descriptor BIOs should not be used for socket I/O. Use socket BIOs
BIO_s_fd() returns the file descriptor BIO method.
BIO_reset() returns zero for success and -1 if an error occurred.
BIO_seek() and BIO_tell() return the current file position or -1 is an
error occurred. These values reflect the underlying lseek() behaviour.
BIO_set_fd() always returns 1.
BIO_get_fd() returns the file descriptor or -1 if the BIO has not been
BIO_new_fd() returns the newly allocated BIO or NULL is an error
This is a file descriptor BIO version of "Hello World":
out = BIO_new_fd(fileno(stdout), BIO_NOCLOSE);
BIO_printf(out, "Hello World\n");
BIO_seek(3), BIO_tell(3), BIO_reset(3), BIO_read(3), BIO_write(3),
BIO_puts(3), BIO_gets(3), BIO_printf(3), BIO_set_close(3),
1.0.2h 2016-05-03 BIO_s_fd(3)