When it came to NoSQL options, we had a vast variety of solutions at our disposal. This is not the case when it comes to applications that monitor filesystem changes. While Linux flavors have a fairly good built-in solution in inotify, this does restrict the portability of the application.

So it's incredibly helpful that a cross-platform library for handling this exists in Chris Howey's fsnotify.

Fsnotify works on Linux, OSX, and Windows and allows us to detect when files in any given directory are created, deleted, modified, or renamed, which is more than enough for our purposes.

Implementing fsnotify couldn't be easier, either. Best of all it's all non-blocking, so if we throw the listener behind a goroutine, we can have this run as part of the primary server application code.

The following code shows a simple directory listener:

package main

import (
    "github.com/howeyc/fsnotify""fmt"
  "log""
)


func main() {

    scriptDone := make(chan bool)
    dirSpy, err := fsnotify.NewWatcher()
    if err != nil {
        log.Fatal(err)
    }

    go func() {
        for {
            select {
            case fileChange := <-dirSpy.Event:
                log.Println("Something happened to a file:", 
                  fileChange)
            case err := <-dirSpy.Error:
                log.Println("Error with fsnotify:", err)
            }
        }
    }()

    err = dirSpy.Watch("/mnt/sharedir")
    if err != nil {
      fmt.Println(err)
    }

    <-scriptDone

    dirSpy.Close()
}