=pod

=head1 NAME

BIO_s_file, BIO_new_file, BIO_new_fp, BIO_set_fp, BIO_get_fp,
BIO_read_filename, BIO_write_filename, BIO_append_filename,
BIO_rw_filename - FILE bio

=head1 SYNOPSIS

 #include <openssl/bio.h>

 const BIO_METHOD *BIO_s_file(void);
 BIO *BIO_new_file(const char *filename, const char *mode);
 BIO *BIO_new_fp(FILE *stream, int flags);

 long BIO_set_fp(BIO *b, FILE *fp, int flags);
 long BIO_get_fp(BIO *b, FILE **fpp);

 int BIO_read_filename(BIO *b, char *name);
 int BIO_write_filename(BIO *b, char *name);
 int BIO_append_filename(BIO *b, char *name);
 int BIO_rw_filename(BIO *b, char *name);

=head1 DESCRIPTION

BIO_s_file() returns the BIO file method. As its name implies it
is a wrapper round the stdio FILE structure and it is a
source/sink BIO.

Calls to BIO_read_ex() and BIO_write_ex() read and write data to the
underlying stream. BIO_gets() and BIO_puts() are supported on file BIOs.

BIO_flush() on a file BIO calls the fflush() function on the wrapped
stream.

BIO_reset() attempts to change the file pointer to the start of file
using fseek(stream, 0, 0).

BIO_seek() sets the file pointer to position B<ofs> from start of file
using fseek(stream, ofs, 0).

BIO_eof() calls feof().

Setting the BIO_CLOSE flag calls fclose() on the stream when the BIO
is freed.

BIO_new_file() creates a new file BIO with mode B<mode> the meaning
of B<mode> is the same as the stdio function fopen(). The BIO_CLOSE
flag is set on the returned BIO.

BIO_new_fp() creates a file BIO wrapping B<stream>. Flags can be:
BIO_CLOSE, BIO_NOCLOSE (the close flag) BIO_FP_TEXT (sets the underlying
stream to text mode, default is binary: this only has any effect under
Win32).

BIO_set_fp() sets the fp of a file BIO to B<fp>. B<flags> has the same
meaning as in BIO_new_fp(), it is a macro.

BIO_get_fp() retrieves the fp of a file BIO, it is a macro.

BIO_seek() is a macro that sets the position pointer to B<offset> bytes
from the start of file.

BIO_tell() returns the value of the position pointer.

BIO_read_filename(), BIO_write_filename(), BIO_append_filename() and
BIO_rw_filename() set the file BIO B<b> to use file B<name> for
reading, writing, append or read write respectively.

=head1 NOTES

When wrapping stdout, stdin or stderr the underlying stream should not
normally be closed so the BIO_NOCLOSE flag should be set.

Because the file BIO calls the underlying stdio functions any quirks
in stdio behaviour will be mirrored by the corresponding BIO.

On Windows BIO_new_files reserves for the filename argument to be
UTF-8 encoded. In other words if you have to make it work in multi-
lingual environment, encode filenames in UTF-8.

=head1 RETURN VALUES

BIO_s_file() returns the file BIO method.

BIO_new_file() and BIO_new_fp() return a file BIO or NULL if an error
occurred.

BIO_set_fp() and BIO_get_fp() return 1 for success or <=0 for failure.

BIO_seek() returns 0 for success or negative values for failure.

BIO_tell() returns the current file position or negative values for failure.

BIO_read_filename(), BIO_write_filename(), BIO_append_filename() and
BIO_rw_filename() return 1 for success or <=0 for failure. An error is also
returned if the file does not exist.

=head1 EXAMPLES

File BIO "hello world":

 BIO *bio_out;

 bio_out = BIO_new_fp(stdout, BIO_NOCLOSE);
 BIO_printf(bio_out, "Hello World\n");

Alternative technique:

 BIO *bio_out;

 bio_out = BIO_new(BIO_s_file());
 if (bio_out == NULL)
     /* Error */
 if (BIO_set_fp(bio_out, stdout, BIO_NOCLOSE) <= 0)
     /* Error */
 BIO_printf(bio_out, "Hello World\n");

Write to a file:

 BIO *out;

 out = BIO_new_file("filename.txt", "w");
 if (!out)
     /* Error */
 BIO_printf(out, "Hello World\n");
 BIO_free(out);

Alternative technique:

 BIO *out;

 out = BIO_new(BIO_s_file());
 if (out == NULL)
     /* Error */
 if (BIO_write_filename(out, "filename.txt") <= 0)
     /* Error */
 BIO_printf(out, "Hello World\n");
 BIO_free(out);

=head1 BUGS

BIO_reset() and BIO_seek() are implemented using fseek() on the underlying
stream. The return value for fseek() is 0 for success or -1 if an error
occurred this differs from other types of BIO which will typically return
1 for success and a non positive value if an error occurred.

=head1 SEE ALSO

L<BIO_seek(3)>, L<BIO_tell(3)>,
L<BIO_reset(3)>, L<BIO_flush(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 2000-2026 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>.

=cut
