Use nested ServeMux with path stripping

Snippets » Go » Use nested ServeMux with path stripping

If you want to nest multiple ServeMux within each other, stripping the path at each level, you tend to end up with problems with trailing slashes and redirects.

This function:

Registers both “/path” and “/path/” to ensure that the mux doesn’t redirect
Strips the prefix
Re-adds a “/” if the prefix became empty

func addSubmux(mux *http.ServeMux, path string, submux *http.ServeMux) {
    wrapper := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        if r.URL.Path = strings.TrimPrefix(r.URL.Path, path); r.URL.Path == "" {
            r.URL.Path = "/"
        }

        submux.ServeHTTP(w, r)
    })

    mux.Handle(path+"/", wrapper)
    mux.Handle(path, wrapper)
}