BIO_S_FD(3)

NAME
BIO_s_fd, BIO_set_fd, BIO_get_fd, BIO_new_fd, BIO_fd_non_fatal_error, BIO_fd_should_retry - file descriptor BIO

SYNOPSIS
#include <openssl/bio.h>
const BIO_METHOD *
BIO_s_fd(void);
long
BIO_set_fd(BIO *b, int fd, long close_flag);
long
BIO_get_fd(BIO *b, int *c);
BIO *
BIO_new_fd(int fd, int close_flag);
int
BIO_fd_non_fatal_error(int errnum);
int
BIO_fd_should_retry(int retval);

DESCRIPTION
BIO_s_fd() returns the file descriptor BIO method. This is a wrapper around the platform's file descriptor routines such as read(2) and write(2).

BIO_read(3) and BIO_write(3) read or write the underlying descriptor. BIO_puts(3) is supported but BIO_gets(3) is not.

If the close flag is set, close(2) is called on the underlying file descriptor when the BIO is freed.

BIO_reset(3) attempts to set the file pointer to the start of the file using lseek(fd, 0, 0).

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

BIO_tell(3) returns the current file position by calling lseek(fd, 0, 1).

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

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

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

BIO_fd_non_fatal_error() determines whether the error status code errnum represents a recoverable error. BIO_fd_should_retry() determines whether a recoverable error occurred by inspecting both errno(2) and retval, which is supposed to usually be the return value of a previously called function like BIO_read(3) or BIO_write(3). These two functions are mostly used internally; in application code, it is usually easier and more robust to use BIO_should_retry(3), which works for any BIO type.

The behaviour of BIO_read(3) and BIO_write(3) depends on the behavior of the platform's read(2) and write(2) 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(3) and BIO_should_retry(3) manual pages.

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

BIO_ctrl(3) cmd arguments correspond to macros as follows:
cmd constant | corresponding macro
BIO_C_FILE_SEEK | BIO_seek(3)
BIO_C_FILE_TELL | BIO_tell(3)
BIO_C_GET_FD | BIO_get_fd()
BIO_C_SET_FD | BIO_set_fd()
BIO_CTRL_GET_CLOSE | BIO_get_close(3)
BIO_CTRL_RESET | BIO_reset(3)
BIO_CTRL_SET_CLOSE | BIO_set_close(3)

RETURN VALUES
BIO_s_fd() returns the file descriptor BIO method.

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

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 if an error occurred.

BIO_fd_non_fatal_error() returns 1 if errnum is EAGAIN, EALREADY, EINPROGRESS, EINTR, or ENOTCONN and 0 otherwise, even if errnum is 0.

BIO_fd_should_retry() returns 1 if BIO_fd_non_fatal_error(errno) is 1 and retval is either 0 or -1, or 0 otherwise.

EXAMPLES
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_free(out);

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

HISTORY
BIO_s_fd(), BIO_set_fd(), and BIO_get_fd() first appeared in SSLeay 0.6.0, BIO_fd_should_retry() in SSLeay 0.6.5, and BIO_new_fd() and BIO_fd_non_fatal_error() in SSLeay 0.8.0. All these functions have been available since OpenBSD 2.4.