notify

This example shows why it is important to not create leaks by stoping a channel when it's no longer being used.

package main

import (
	"log"
	"path/filepath"
	"time"

	"github.com/syncthing/notify"
)

func main() {
	waitfor := func(path string, e notify.Event, timeout time.Duration) bool {
		dir, file := filepath.Split(path)
		c := make(chan notify.EventInfo, 1)

		if err := notify.Watch(dir, c, e); err != nil {
			log.Fatal(err)
		}
		// Clean up watchpoint associated with c. If Stop was not called upon
		// return the channel would be leaked as notify holds the only reference
		// to it and does not release it on its own.
		defer notify.Stop(c)

		t := time.After(timeout)

		for {
			select {
			case ei := <-c:
				if filepath.Base(ei.Path()) == file {
					return true
				}
			case <-t:
				return false
			}
		}
	}

	if waitfor("index.lock", notify.Create, 5*time.Second) {
		log.Println("The git repository was locked")
	}

	if waitfor("index.lock", notify.Remove, 5*time.Second) {
		log.Println("The git repository was unlocked")
	}
}

Output:

This is a basic example showing how to work with notify.Watch function.

package main

import (
	"log"

	"github.com/syncthing/notify"
)

func main() {
	// Make the channel buffered to ensure no event is dropped. Notify will drop
	// an event if the receiver is not able to keep up the sending pace.
	c := make(chan notify.EventInfo, 1)

	// Set up a watchpoint listening on events within current working directory.
	// Dispatch each create and remove events separately to c.
	if err := notify.Watch(".", c, notify.Create, notify.Remove); err != nil {
		log.Fatal(err)
	}
	defer notify.Stop(c)

	// Block until an event is received.
	ei := <-c
	log.Println("Got event:", ei)
}

Output:

This example shows how to watch changes made on file-system by text editor when saving a file. Usually, either InCloseWrite or InMovedTo (when swapping with a temporary file) event is created.

package main

import (
	"log"

	"github.com/syncthing/notify"
)

func main() {
	// Make the channel buffered to ensure no event is dropped. Notify will drop
	// an event if the receiver is not able to keep up the sending pace.
	c := make(chan notify.EventInfo, 1)

	// Set up a watchpoint listening for inotify-specific events within a
	// current working directory. Dispatch each InCloseWrite and InMovedTo
	// events separately to c.
	if err := notify.Watch(".", c, notify.InCloseWrite, notify.InMovedTo); err != nil {
		log.Fatal(err)
	}
	defer notify.Stop(c)

	// Block until an event is received.
	switch ei := <-c; ei.Event() {
	case notify.InCloseWrite:
		log.Println("Editing of", ei.Path(), "file is done.")
	case notify.InMovedTo:
		log.Println("File", ei.Path(), "was swapped/moved into the watched directory.")
	}
}

Output:

This example shows how to use Sys() method from EventInfo interface to tie two separate events generated by rename(2) function.

package main

import (
	"log"

	"golang.org/x/sys/unix"

	"github.com/syncthing/notify"
)

func main() {
	// Make the channel buffered to ensure no event is dropped. Notify will drop
	// an event if the receiver is not able to keep up the sending pace.
	c := make(chan notify.EventInfo, 2)

	// Set up a watchpoint listening for inotify-specific events within a
	// current working directory. Dispatch each InMovedFrom and InMovedTo
	// events separately to c.
	if err := notify.Watch(".", c, notify.InMovedFrom, notify.InMovedTo); err != nil {
		log.Fatal(err)
	}
	defer notify.Stop(c)

	// Inotify reports move filesystem action by sending two events tied with
	// unique cookie value (uint32): one of the events is of InMovedFrom type
	// carrying move source path, while the second one is of InMoveTo type
	// carrying move destination path.
	moves := make(map[uint32]struct {
		From string
		To   string
	})

	// Wait for moves.
	for ei := range c {
		cookie := ei.Sys().(*unix.InotifyEvent).Cookie

		info := moves[cookie]
		switch ei.Event() {
		case notify.InMovedFrom:
			info.From = ei.Path()
		case notify.InMovedTo:
			info.To = ei.Path()
		}
		moves[cookie] = info

		if cookie != 0 && info.From != "" && info.To != "" {
			log.Println("File:", info.From, "was renamed to", info.To)
			delete(moves, cookie)
		}
	}
}

Output:

This example shows how to set up a recursive watchpoint.

package main

import (
	"log"

	"github.com/syncthing/notify"
)

func main() {
	// Make the channel buffered to ensure no event is dropped. Notify will drop
	// an event if the receiver is not able to keep up the sending pace.
	c := make(chan notify.EventInfo, 1)

	// Set up a watchpoint listening for events within a directory tree rooted
	// at current working directory. Dispatch remove events to c.
	if err := notify.Watch("./...", c, notify.Remove); err != nil {
		log.Fatal(err)
	}
	defer notify.Stop(c)

	// Block until an event is received.
	ei := <-c
	log.Println("Got event:", ei)
}

Output: