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=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 2000-2016 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>.

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