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=pod
=head1 NAME
BIO_s_fd, BIO_set_fd, BIO_get_fd, BIO_new_fd - file descriptor BIO
=head1 SYNOPSIS
#include <openssl/bio.h>
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);
=head1 DESCRIPTION
BIO_s_fd() returns the file descriptor BIO method. This is a wrapper
round the platforms file descriptor routines such as read() and write().
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 B<ofs> from start of file
using lseek(fd, ofs, 0).
BIO_tell() returns the current file position by calling lseek(fd, 0, 1).
BIO_set_fd() sets the file descriptor of BIO B<b> to B<fd> and the close
flag to B<c>.
BIO_get_fd() places the file descriptor in B<c> if it is not NULL, it also
returns the file descriptor. If B<c> is not NULL it should be of type
(int *).
BIO_new_fd() returns a file descriptor BIO using B<fd> and B<close_flag>.
=head1 NOTES
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 L<BIO_read(3)|BIO_read(3)> and L<BIO_should_retry(3)|BIO_should_retry(3)>
manual pages.
File descriptor BIOs should not be used for socket I/O. Use socket BIOs
instead.
=head1 RETURN VALUES
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 initialized.
BIO_new_fd() returns the newly allocated BIO or NULL is an error
occurred.
=head1 EXAMPLE
This is a file descriptor BIO version of "Hello World":
BIO *out;
out = BIO_new_fd(fileno(stdout), BIO_NOCLOSE);
BIO_printf(out, "Hello World\n");
BIO_free(out);
=head1 SEE ALSO
L<BIO_seek(3)|BIO_seek(3)>, L<BIO_tell(3)|BIO_tell(3)>,
L<BIO_reset(3)|BIO_reset(3)>, L<BIO_read(3)|BIO_read(3)>,
L<BIO_write(3)|BIO_write(3)>, L<BIO_puts(3)|BIO_puts(3)>,
L<BIO_gets(3)|BIO_gets(3)>, L<BIO_printf(3)|BIO_printf(3)>,
L<BIO_set_close(3)|BIO_set_close(3)>, L<BIO_get_close(3)|BIO_get_close(3)>