Cryptography and SSL/TLS Toolkit



BIO_s_fd, BIO_set_fd, BIO_get_fd, BIO_new_fd - file descriptor BIO


 #include <openssl/bio.h>

 const BIO_METHOD *BIO_s_fd(void);

 int BIO_set_fd(BIO *b, int fd, int c);
 int BIO_get_fd(BIO *b, int *c);

 BIO *BIO_new_fd(int fd, int close_flag);


BIO_s_fd() returns the file descriptor BIO method. This is a wrapper round the platforms file descriptor routines such as read() and write().

BIO_read_ex() and BIO_write_ex() read or write the underlying descriptor. BIO_puts() is supported but BIO_gets() is not.

If the close flag is set then close() is called on the underlying file descriptor when the BIO is freed.

BIO_reset() attempts to change the file pointer to the start of file such as by using lseek(fd, 0, 0).

BIO_seek() sets the file pointer to position ofs from start of file such as by using lseek(fd, ofs, 0).

BIO_tell() returns the current file position such as by calling lseek(fd, 0, 1).

BIO_set_fd() sets the file descriptor of BIO b to fd and the close flag to c.

BIO_get_fd() places the file descriptor in c if it is not NULL, it also returns the file descriptor.

BIO_new_fd() returns a file descriptor BIO using fd and close_flag.


The behaviour of BIO_read_ex() and BIO_write_ex() depends on the behavior of the platforms read() and write() calls on the descriptor. If the underlying file descriptor is in a non blocking mode then the BIO will behave in the manner described in the BIO_read_ex(3) and BIO_should_retry(3) manual pages.

File descriptor BIOs should not be used for socket I/O. Use socket BIOs instead.

BIO_set_fd() and BIO_get_fd() are implemented as macros.


BIO_s_fd() returns the file descriptor BIO method.

BIO_set_fd() always returns 1.

BIO_get_fd() returns the file descriptor or -1 if the BIO has not been initialized.

BIO_new_fd() returns the newly allocated BIO or NULL is an error occurred.


This is a file descriptor BIO version of "Hello World":

 BIO *out;

 out = BIO_new_fd(fileno(stdout), BIO_NOCLOSE);
 BIO_printf(out, "Hello World\n");


BIO_seek(3), BIO_tell(3), BIO_reset(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)

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