BIO_s_file(3)

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

LIBRARY
libcrypto, -lcrypto

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);

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 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 mode the meaning of 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 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 fp. 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 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 to use file name for reading, writing, append or read write respectively.

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.

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 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.

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);

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.

SEE ALSO
BIO_seek(3), BIO_tell(3), BIO_reset(3), BIO_flush(3), BIO_read_ex(3), BIO_write_ex(3), BIO_puts(3), BIO_gets(3), BIO_printf(3), BIO_set_close(3), BIO_get_close(3)

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 <https://www.openssl.org/source/license.html>.