BIO_S_FD(3)                Library Functions Manual                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.

Linux 6.8.2-arch2-1            November 16, 2023           Linux 6.8.2-arch2-1