The fsmon library provides a callback-based API for monitoring changes to files in the filesystem. It is designed to be operating system-agnostic, although it currently only supports inotify as a backend. Supports subscribing to events on files and folders. Events do not propogate recursively; watching foo will not let you know when changes to foo/bar/foobar occur.

Install it:

goinstall github.com/crazy2be/fsmon

Import it:

import "github.com/crazy2be/fsmon"

Use it:

package main

import (
	"log"
	"github.com/crazy2be/fsmon"
)

type FooHandler int

func (fh *FooHandler) Modified(name string) {
	log.Println(name + " was modified")
}

func (fh *FooHandler) Created(name string) {
	log.Println(name + " was created")
}

func (fh *FooHandler) Deleted(name string) {
	log.Println(name + " was deleted")
}

func main() {
	fh := new(FooHandler)
	
	fsmon.AddWatch("foo", fh)
	log.Println("Listening for events in folder or affecting file 'foo'")
	
	fsmon.Watch()
}

Each different watcher type (InotifyWatcher, Win32APIWatcher, etc) needs only satisfy the Watcher interface, which is fairly simple:

type Watcher interface {
	AddWatch(string, Handler) os.Error
	RemoveWatches(string) os.Error
	Watch()
}

AddWatch() adds another Handler for the path specified. If a handler already exists on that path, it is not affected. Adding a handler to a file gives notifications only for that file, adding a handler to a directory gives all notifications for the immediate desendents of that directory. Directory watches are not recursive. The underlying watcher can "batch" handlers for multiple files in the same directory if it is more efficent. For example, the InotifyWatcher only watches directories rather than files on the underlying watcher, but makes this optimization transparent to users.

RemoveWatches() removes all Handlers for the path specified. As far as I can see, there is no way to allow someone to remove a specific callback, so this removes all of them.

Watch() blocks forever in a loop that listens for events and calls the relevent callbacks. No callbacks will be called before Watch() is called. AddWatch() and RemoveWatches() should be callable after Watch(), and should not be subject to race conditions.

Full function reference available at http://gopkgdoc.appspot.com/pkg/github.com/crazy2be/fsmon.