Checking if a file is in a given directory

Question

I've got a situation where I'd like to check whether a particular path lands inside of a particular directory. My first instinct was to do something like

filepath.HasPrefix(filepath.Clean(path), dir)

but the procedure filepath.HasPrefix is documented as existing for historic reasons only. Am I going to get the same effect by using strings.HasPrefix, or is there something I'm missing?

Answer 1

You're not missing anything, look at the source:

// HasPrefix exists for historical compatibility and should not be used.
func HasPrefix(p, prefix string) bool {
    return strings.HasPrefix(p, prefix)
}

Just use strings.HasPrefix(p, prefix) directly.

Answer 2

While you will get the same functionality with strings.HasPrefix, it doesn't work in general. filepath.HasPrefix is deprecated for a reason and it's approach should be considered deprecated too.

Consider filename=/foo/bar and prefix=/fo. This passes the strings.HasPrefix test but clearly bar is not in /fo.

The proper approach would compare each directory name holistically.

Answer 3

In Go 1.4 method filepath.HasPrefix actually calls strings.HasPrefix so the answer is yes.