cyberark/secretless-broker

package configfile

import (
    "log"
    "time"

    "github.com/fsnotify/fsnotify"
)

var logFatal = log.Fatal

// AttachWatcher adds a listener of chenge event to a filepath
func AttachWatcher(filename string, runner func()) {
    watcher, err := fsnotify.NewWatcher()
    if err != nil {
        logFatal(err)
    }

    go func() {
        defer watcher.Close()

        for {
            select {
            case event := <-watcher.Events:
                if event.Op&fsnotify.Write == fsnotify.Write {
                    log.Printf("WARN: Watched file '%s' modified!", filename)
                    go runner()
                } else if event.Op&fsnotify.Remove == fsnotify.Remove ||
                    event.Op&fsnotify.Rename == fsnotify.Rename {
                    log.Printf("WARN: Watched file '%s' has been removed!",
                        filename)

                    // Some editors remove the old file and replace it with a new one
                    // so we need to give it a bit of time and try to reattach the notifier
                    time.Sleep(1 * time.Second)
                    log.Printf("WARN: Trying to reattach to '%s'...", filename)
                    AttachWatcher(filename, runner)

                    // If the file disappeared, we know it changed so run the trigger
                    go runner()
                }
            case err := <-watcher.Errors:
                log.Println("error:", err)
                break
            }
        }
    }()

    log.Printf("Attaching filesystem notifier onto %s", filename)
    err = watcher.Add(filename)
    if err != nil {
        logFatal(err)
        watcher.Close()
    }
}