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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 of BIO B<b> 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() returns 1 on success or <=0 for failure.

BIO_get_fd() returns the file descriptor or -1 if the BIO has not
been initialized. It also returns zero and negative values if other error occurs.

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 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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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