source: vbox/trunk/src/libs/openssl-1.1.1g/doc/man3/BIO_s_file.pod@ 83916

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=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);

 BIO_set_fp(BIO *b, FILE *fp, int flags);
 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 file names 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
(although the current implementation never return 0).

BIO_seek() returns the same value as the underlying fseek() function:
0 for success or -1 for failure.

BIO_tell() returns the current file position.

BIO_read_filename(), BIO_write_filename(), BIO_append_filename() and
BIO_rw_filename() return 1 for success or 0 for failure.

=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))
     /* 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"))
     /* 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 2000-2019 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>.

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