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

SYNOPSIS
libcrypto
#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);
long
BIO_read_filename(BIO *b, char *name);
long
BIO_write_filename(BIO *b, char *name);
long
BIO_append_filename(BIO *b, char *name);
long
BIO_rw_filename(BIO *b, char *name);

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

Calls to BIO_read(3) and BIO_write(3) read and write data to the underlying stream. BIO_gets(3) and BIO_puts(3) are supported on file BIOs.

BIO_flush(3) on a file BIO calls the fflush(3) function on the wrapped stream.

BIO_reset(3) attempts to change the file pointer to the start of file using fseek(stream, 0, 0).

BIO_seek(3) sets the file pointer to position ofs from the start of the file using fseek(stream, ofs, 0).

BIO_eof(3) calls feof(3).

Setting the BIO_CLOSE flag calls fclose(3) 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 for the stdio function fopen(3). 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 file pointer of a file BIO to fp. flags has the same meaning as in BIO_new_fp().

BIO_get_fp() retrieves the file pointer of a file BIO.

BIO_seek(3) sets the position pointer to offset bytes from the start of file.

BIO_tell(3) 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.

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 a multi-lingual environment, encode file names in UTF-8.

The following BIO_ctrl(3) cmd constants correspond to macros:
cmd constant | corresponding macro
BIO_C_FILE_SEEK | BIO_seek(3)
BIO_C_FILE_TELL | BIO_tell(3)
BIO_C_GET_FILE_PTR | BIO_get_fp()
BIO_C_SET_FILE_PTR | BIO_set_fp()
BIO_C_SET_FILENAME | various, see below
BIO_CTRL_EOF | BIO_eof(3)
BIO_CTRL_FLUSH | BIO_flush(3)
BIO_CTRL_GET_CLOSE | BIO_get_close(3)
BIO_CTRL_RESET | BIO_reset(3)
BIO_CTRL_SET_CLOSE | BIO_set_close(3)

The meaning of BIO_C_SET_FILENAME depends on the flags passed in the BIO_ctrl(3) larg argument:
larg argument | corresponding macro
BIO_CLOSE | BIO_FP_READ | BIO_read_filename()
BIO_CLOSE | BIO_FP_WRITE | BIO_write_filename()
BIO_CLOSE | BIO_FP_APPEND | BIO_append_filename()
BIO_CLOSE | BIO_FP_READ | BIO_FP_WRITE | BIO_rw_filename()

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.

When called on a file BIO object, BIO_method_type(3) returns the constant BIO_TYPE_FILE and BIO_method_name(3) returns a pointer to the static string "FILE pointer".

BIO_set_fp() and BIO_get_fp() return 1 for success or 0 for failure (although the current implementation never returns 0).

BIO_seek(3) returns the same value as the underlying fseek(3) function: 0 for success or -1 for failure.

BIO_tell(3) 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.

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 occurred */
    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);

SEE ALSO
BIO_new(3), BIO_read(3), BIO_seek(3)

HISTORY
BIO_s_file(), BIO_set_fp(), BIO_get_fp(), BIO_read_filename(), BIO_write_filename(), and BIO_append_filename() first appeared in SSLeay 0.6.0. BIO_new_file() and BIO_new_fp() first appeared in SSLeay 0.8.0. All these functions have been available since OpenBSD 2.4.

BIO_rw_filename() first appeared in SSLeay 0.9.1 and has been available since OpenBSD 2.6.

BUGS
BIO_reset(3) and BIO_seek(3) are implemented using fseek(3) on the underlying stream. The return value for fseek(3) 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.