Go event emitter and listener with builtin file watcher package.
// Create a new observer
o := observer.Observer{}
o.Open()
// Register a listener method.
o.AddListener(func(e interface{}) {
log.Printf("Received: %v.\n", e)
})
// Emit an event.
o.Emit("Hello")
// Watch and emit events on file modifications.
o.Watch([]string{"*.html", "css/*.scss"})This observer implements event emitter and listener pattern in go, the observer register a list of listener functions and implement an event emitter, once an event is emitted, all listener functions will be called.
This observer also abstracts watching for file changes, users can register a list for files to watch, once a file is watched, events will be emitted automatically on each file modification. Common use cases are watching for changing in config files, and wating for code changes.
This observer is using golang channels for emiting events and fsnotify for watching file changes.
$ go get -u github.com/golang/dep/cmd/dep
$ make vendor
$ make
$ ./observe
go get -u github.com/yaacov/observer
Install using go get will install the package and the CLI tool observer
observer is a cli tool for watching files and executing shell commands on file modification, it is used to call an action on file change, examples of use can be restart and app when config file changes, recompile code when code updates and send image to server when image change.
inotify-tools, are a set of linux tools that monitor files for changes, they may be better choice for file monitoring on more complex cases.
observer -hobserver -r "curl -X POST http://127.0.0.1:8000/api/v1/-/restart" -w "/root/.aws/config"See examples for usage examples.
| Method | Description |
|---|---|
| Open() | Open the observer channels |
| Close() | Close the observer channels |
| AddListener(callback Listener) | Add a listener function to run on event |
| Emit(event interface{}) | Emit event |
| Watch(files []string) | Watch for file changes, and emit a file change events |
| SetBufferDuration(d time.Duration) | Set the event buffer damping duration |
| Type | Description | |
|---|---|---|
| WatchEvent | struct{ Name string, Op uint32 } | Event type emitted by file watcher |
| Listener | func(interface{}) | Function type for listeners |
| Observer | struct{ Verbose bool } | The observer object |
Watching files can be done using exact file name, or shell pattern matching.
Watch([]string{"./aws/config", "./aws/credentials"})Watch([]string{"./kube/*.yml"})We can not expand tilde to home directory, ~/.config will not work as expected.
If needed users can use golang's os/user/ package.
Example of event listener and emitter.
// Open an observer and start running
o := observer.Observer{}
o.Open()
defer o.Close()
// Add a listener that logs events
o.AddListener(func(e interface{}) {
log.Printf("Received: %s.\n", e.(string))
})
// This event will be picked by the listener
o.Emit("Hello")Example of file watching and listener.
// Open an observer and start watching for files by file name
o := observer.Observer{}
o.Watch([]string{"../LICENSE"})
defer o.Close()
// Add a listener that logs events
o.AddListener(func(e interface{}) {
watchEvent := e.(observer.WatchEvent)
log.Printf("File modified: %s.\n", e.Name)
})// Open an observer and start watching for file matching shell pattern
o := observer.Observer{}
o.Watch([]string{"*.html", "css/*.scss"})
defer o.Close()
// Add a listener that logs events
o.AddListener(func(e interface{}) {
log.Printf("File modified: %v.\n", e)
})o.Open()
o.SetBufferDuration(1 * time.Second)
o.AddListener(func(e interface{}) {
output = e.([]interface{}) // => ["done", "done", "done", "done"]
})
// All this events will be grouped together, and sent only once to the listener.
o.Emit("done")
o.Emit("done")
o.Emit("done")
o.Emit("done")
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