How to properly instantiate os.FileMode

Question

I have seen countless examples and tutorials that show how to create a file and all of them "cheat" by just setting the permission bits of the file. I would like to know / find out how to properly instantiate os.FileMode to provide to a writer during creation / updating of a file.

A crude example is this below:

func FileWrite(path string, r io.Reader, uid, gid int, perms string) (int64, error){
    w, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0664)
    if err != nil {
        if path == "" {
            w = os.Stdout
        } else {
            return 0, err
        }
    }
    defer w.Close()

    size, err := io.Copy(w, r)

    if err != nil {
        return 0, err
    }
    return size, err
}

In the basic function above permission bits 0664 is set and although this may make sense sometimes I prefer to have a proper way of setting the filemode correctly. As seen above a common example would be that the UID / GID is known and already provided as int values and the perms being octal digits that were previously gathered and inserted into a db as a string.

Answer 1

FileMode is just a uint32. http://golang.org/pkg/os/#FileMode

Setting via constants isn't "cheating", you use it like other numeric values. If you're not using a constant, you can use a conversion on valid numeric values:

mode := int(0777)
os.FileMode(mode)