=pod
=head1 NAME
BIO_s_fd, BIO_set_fd, BIO_get_fd, BIO_new_fd - file descriptor BIO
=head1 SYNOPSIS
#include <openssl/bio.h>
const BIO_METHOD *BIO_s_fd(void);
int BIO_set_fd(BIO *b, int fd, int c);
int BIO_get_fd(BIO *b, int *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_ex() and BIO_write_ex() read or write the underlying descriptor.
BIO_puts() is supported but BIO_gets() is not.
If the close flag is set 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
such as by using B<lseek(fd, 0, 0)>.
BIO_seek() sets the file pointer to position B<ofs> from start of file
such as by using B<lseek(fd, ofs, 0)>.
BIO_tell() returns the current file position such as by calling
B<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.
BIO_new_fd() returns a file descriptor BIO using B<fd> and B<close_flag>.
=head1 NOTES
The behaviour of BIO_read_ex() and BIO_write_ex() 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_ex(3)> and L<BIO_should_retry(3)>
manual pages.
File descriptor BIOs should not be used for socket I/O. Use socket BIOs
instead.
BIO_set_fd() and BIO_get_fd() are implemented as macros.
=head1 RETURN VALUES
BIO_s_fd() returns the file descriptor BIO method.
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 EXAMPLES
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)>, L<BIO_tell(3)>,
L<BIO_reset(3)>, L<BIO_read_ex(3)>,
L<BIO_write_ex(3)>, L<BIO_puts(3)>,
L<BIO_gets(3)>, L<BIO_printf(3)>,
L<BIO_set_close(3)>, L<BIO_get_close(3)>
=head1 COPYRIGHT
Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.
=cut