initialize_copy

static VALUE
rb_io_init_copy(VALUE dest, VALUE io)
{
    rb_io_t *fptr, *orig;
    int fd;
    VALUE write_io;
    off_t pos;

    io = rb_io_get_io(io);
    if (dest == io) return dest;
    GetOpenFile(io, orig);
    MakeOpenFile(dest, fptr);

    rb_io_flush(io);

    /* copy rb_io_t structure */
    fptr->mode = orig->mode & ~FMODE_PREP;
    fptr->encs = orig->encs;
    fptr->pid = orig->pid;
    fptr->lineno = orig->lineno;
    if (!NIL_P(orig->pathv)) fptr->pathv = orig->pathv;
    fptr->finalize = orig->finalize;
#if defined (__CYGWIN__) || !defined(HAVE_FORK)
    if (fptr->finalize == pipe_finalize)
        pipe_add_fptr(fptr);
#endif

    fd = ruby_dup(orig->fd);
    fptr->fd = fd;
    pos = io_tell(orig);
    if (0 <= pos)
        io_seek(fptr, pos, SEEK_SET);
    if (fptr->mode & FMODE_BINMODE) {
        rb_io_binmode(dest);
    }

    write_io = GetWriteIO(io);
    if (io != write_io) {
        write_io = rb_obj_dup(write_io);
        fptr->tied_io_for_writing = write_io;
        rb_ivar_set(dest, rb_intern("@tied_io_for_writing"), write_io);
    }

    return dest;
}