Implement --polling option; poll files to detect changes instead of fsnotify

Author: makiuchi-d

README.md

@@ -45,16 +45,17 @@ Usage: arelo [OPTION]... -- COMMAND
 Run the COMMAND and restart when a file matches the pattern has been modified.
 
 Options:
-  -d, --delay duration   duration to delay the restart of the command (default 1s)
-  -f, --filter event     filter file system event (CREATE|WRITE|REMOVE|RENAME|CHMOD)
-  -h, --help             display this message
-  -i, --ignore glob      ignore pathname glob pattern
-  -p, --pattern glob     trigger pathname glob pattern (default "**")
-  -r, --restart          restart the command on exit
-  -s, --signal signal    signal used to stop the command (default "SIGTERM")
-  -t, --target path      observation target path (default "./")
-  -v, --verbose          verbose output
-  -V, --version          display version
+  -d, --delay duration     duration to delay the restart of the command (default 1s)
+  -f, --filter event       filter file system event (CREATE|WRITE|REMOVE|RENAME|CHMOD)
+  -h, --help               display this message
+  -i, --ignore glob        ignore pathname glob pattern
+  -p, --pattern glob       trigger pathname glob pattern (default "**")
+      --polling interval   poll files at given interval instead of using fsnotify
+  -r, --restart            restart the command on exit
+  -s, --signal signal      signal used to stop the command (default "SIGTERM")
+  -t, --target path        observation target path (default "./")
+  -v, --verbose            verbose output
+  -V, --version            display version
 ```
 
 ### Options
@@ -121,6 +122,15 @@ This option is not available on Windows.
 
 Automatically restart the command when it exits, similar to when the pattern matched file is modified.
 
+#### --polling interval
+
+Poll files at the specified interval instead of using fsnotify.
+If not set or set to `0`, fsnotify is used for file monitoring.
+
+This option is useful when fsnotify cannot detect changes, such as on WSL2.
+
+The interval is specified as a number with a unit suffix ("ns", "us" (or "µs"), "ms", "s", "m", "h").
+
 #### -v, --verbose
 
 Output logs verbosely.

arelo.go

@@ -5,7 +5,6 @@ import (
 	"context"
 	"fmt"
 	"io"
-	"io/fs"
 	"log"
 	"os"
 	"os/signal"
@@ -21,6 +20,8 @@ import (
 	"github.com/fsnotify/fsnotify"
 	"github.com/spf13/pflag"
 	"golang.org/x/xerrors"
+
+	"github.com/makiuchi-d/arelo/fspoll"
 )
 
 const (
@@ -44,6 +45,7 @@ Options:
 	help     = pflag.BoolP("help", "h", false, "display this message")
 	showver  = pflag.BoolP("version", "V", false, "display version")
 	filters  = pflag.StringArrayP("filter", "f", nil, "filter file system `event` (CREATE|WRITE|REMOVE|RENAME|CHMOD)")
+	polling  = pflag.Duration("polling", 0, "poll files at given `interval` instead of using fsnotify")
 )
 
 func main() {
@@ -89,7 +91,7 @@ func main() {
 		os.Exit(1)
 	}
 
-	modC, errC, err := watcher(*targets, *patterns, *ignores, filtOp)
+	modC, errC, err := watcher(*targets, *patterns, *ignores, filtOp, *polling)
 	if err != nil {
 		log.Fatalf("[ARELO] wacher error: %v", err)
 	}
@@ -166,12 +168,18 @@ func parseFilters(filters []string) (fsnotify.Op, error) {
 	return op, nil
 }
 
-func watcher(targets, patterns, ignores []string, filtOp fsnotify.Op) (<-chan string, <-chan error, error) {
-	w, err := fsnotify.NewWatcher()
+func newWatcher(interval time.Duration) (fspoll.Watcher, error) {
+	if interval == 0 {
+		return fspoll.Wrap(fsnotify.NewWatcher())
+	}
+	return fspoll.New(interval), nil
+}
+
+func watcher(targets, patterns, ignores []string, filtOp fsnotify.Op, interval time.Duration) (<-chan string, <-chan error, error) {
+	w, err := newWatcher(interval)
 	if err != nil {
 		return nil, nil, err
 	}
-
 	if err := addTargets(w, targets, patterns, ignores); err != nil {
 		return nil, nil, err
 	}
@@ -184,7 +192,7 @@ func watcher(targets, patterns, ignores []string, filtOp fsnotify.Op) (<-chan st
 		defer close(modC)
 		for {
 			select {
-			case event, ok := <-w.Events:
+			case event, ok := <-w.Events():
 				if !ok {
 					errC <- xerrors.Errorf("watcher.Events closed")
 					return
@@ -216,15 +224,15 @@ func watcher(targets, patterns, ignores []string, filtOp fsnotify.Op) (<-chan st
 						// ignore stat errors (notfound, permission, etc.)
 						log.Printf("[ARELO] watcher: %v", err)
 					} else if fi.IsDir() {
-						err := addDirRecursive(w, fi, name, patterns, ignores, modC)
+						err := addDirRecursive(w, name, patterns, ignores, modC)
 						if err != nil {
 							errC <- err
 							return
 						}
 					}
 				}
 
-			case err, ok := <-w.Errors:
+			case err, ok := <-w.Errors():
 				errC <- xerrors.Errorf("watcher.Errors (%v): %w", ok, err)
 				return
 			}
@@ -256,15 +264,15 @@ func matchPatterns(t string, pats []string) (bool, error) {
 	return false, nil
 }
 
-func addTargets(w *fsnotify.Watcher, targets, patterns, ignores []string) error {
+func addTargets(w fspoll.Watcher, targets, patterns, ignores []string) error {
 	for _, t := range targets {
 		t = path.Clean(t)
 		fi, err := os.Stat(t)
 		if err != nil {
 			return xerrors.Errorf("stat: %w", err)
 		}
 		if fi.IsDir() {
-			if err := addDirRecursive(w, fi, t, patterns, ignores, nil); err != nil {
+			if err := addDirRecursive(w, t, patterns, ignores, nil); err != nil {
 				return err
 			}
 		}
@@ -276,7 +284,7 @@ func addTargets(w *fsnotify.Watcher, targets, patterns, ignores []string) error
 	return nil
 }
 
-func addDirRecursive(w *fsnotify.Watcher, fi fs.FileInfo, t string, patterns, ignores []string, ch chan<- string) error {
+func addDirRecursive(w fspoll.Watcher, t string, patterns, ignores []string, ch chan<- string) error {
 	logVerbose("watching target: %q", t)
 	err := w.Add(t)
 	if err != nil {
@@ -301,11 +309,7 @@ func addDirRecursive(w *fsnotify.Watcher, fi fs.FileInfo, t string, patterns, ig
 			}
 		}
 		if de.IsDir() {
-			fi, err := de.Info()
-			if err != nil {
-				return err
-			}
-			err = addDirRecursive(w, fi, name, patterns, ignores, ch)
+			err = addDirRecursive(w, name, patterns, ignores, ch)
 			if err != nil {
 				return err
 			}

arelo_test.go

@@ -7,7 +7,17 @@ import (
 	"time"
 )
 
-func TestWatcher(t *testing.T) {
+func TestWatcherFsnotify(t *testing.T) {
+	t.Parallel()
+	testWatcher(t, 0)
+}
+
+func TestWatcherFspoll(t *testing.T) {
+	t.Parallel()
+	testWatcher(t, time.Second/10)
+}
+
+func testWatcher(t *testing.T, polling time.Duration) {
 	tmpdir := t.TempDir()
 
 	dirs := []string{
@@ -26,7 +36,7 @@ func TestWatcher(t *testing.T) {
 	ignores := []string{"**/ignore"}
 	patterns := []string{"**/file"}
 
-	modC, errC, err := watcher(targets, patterns, ignores, 0)
+	modC, errC, err := watcher(targets, patterns, ignores, 0, polling)
 	if err != nil {
 		t.Fatalf("watcher: %v", err)
 	}
@@ -51,6 +61,7 @@ func TestWatcher(t *testing.T) {
 	for _, test := range tests {
 		<-time.After(time.Second / 5)
 		clearChan(modC, errC)
+		t.Logf("touch %v => detect %v", test.file, test.detect)
 		touchFile(test.file)
 		select {
 		case f := <-modC:

fspoll/fsnotify.go

@@ -0,0 +1,27 @@
+package fspoll
+
+import (
+	"github.com/fsnotify/fsnotify"
+)
+
+// Wrapper of a fsnotify.Watcher.
+type Wrapper struct {
+	*fsnotify.Watcher
+}
+
+var _ Watcher = Wrapper{}
+
+// Wrap returns a wrapping fsnotify.Watcher.
+func Wrap(w *fsnotify.Watcher, err error) (Wrapper, error) {
+	return Wrapper{w}, err
+}
+
+// Events returns Events channel of wrapping fsnotify.Watcher.
+func (w Wrapper) Events() <-chan Event {
+	return w.Watcher.Events
+}
+
+// Errors returns Errors channel of wrapping fsnotify.Watcher.
+func (w Wrapper) Errors() <-chan error {
+	return w.Watcher.Errors
+}

fspoll/fspoll.go

@@ -0,0 +1,45 @@
+// fspoll provides polling file change watcher.
+package fspoll
+
+import (
+	"github.com/fsnotify/fsnotify"
+)
+
+type Event = fsnotify.Event
+type Op = fsnotify.Op
+
+const (
+	Create = fsnotify.Create
+	Write  = fsnotify.Write
+	Remove = fsnotify.Remove
+	Rename = fsnotify.Rename
+	Chmod  = fsnotify.Chmod
+)
+
+var (
+	ErrNonExistentWatch = fsnotify.ErrNonExistentWatch
+	ErrEventOverflow    = fsnotify.ErrEventOverflow
+	ErrClosed           = fsnotify.ErrClosed
+)
+
+// Watcher is a common interface for fspoll and fsnotify
+type Watcher interface {
+
+	// Add starts watching the path for changes.
+	Add(name string) error
+
+	// Close stops all watches and closes the channels.
+	Close() error
+
+	// Remove stops watching the specified path.
+	Remove(name string) error
+
+	// WatchList returns a list of watching path names.
+	WatchList() []string
+
+	// Events returns a channel that receives filesystem events.
+	Events() <-chan Event
+
+	// Errors returns a channel that receives errors.
+	Errors() <-chan error
+}