Cryptography and SSL/TLS Toolkit



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


 #include <openssl/bio.h>

 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)


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() and BIO_write() 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() set 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.


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.


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");

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_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.


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.


BIO_seek(3), BIO_tell(3), BIO_reset(3), BIO_flush(3), BIO_read(3), BIO_write(3), BIO_puts(3), BIO_gets(3), BIO_printf(3), BIO_set_close(3), BIO_get_close(3)