inspect symlinks to auto-reload k8s secrets

internal/watch/file_watcher.go

@@ -18,7 +18,9 @@ package watch
 
 import (
 	"log"
+	"os"
 	"path"
+	"path/filepath"
 	"strings"
 
 	"github.com/fsnotify/fsnotify"
@@ -60,15 +62,31 @@ func (f *OSFileWatcher) watch() error {
 	}
 	f.watcher = watcher
 
+	realFile, err := filepath.EvalSymlinks(f.file)
+	if err != nil {
+		return err
+	}
+
 	dir, file := path.Split(f.file)
 	go func(file string) {
 		for {
 			select {
 			case event := <-watcher.Events:
-				if (event.Op&fsnotify.Write == fsnotify.Write ||
-					event.Op&fsnotify.Create == fsnotify.Create) &&
-					strings.HasSuffix(event.Name, file) {
-					f.onEvent()
+				if event.Op&fsnotify.Create == fsnotify.Create ||
+					event.Op&fsnotify.Write == fsnotify.Write {
+					if finfo, err := os.Lstat(event.Name); err != nil {
+						log.Printf("can not lstat file: %v\n", err)
+					} else if finfo.Mode()&os.ModeSymlink != 0 {
+						if currentRealFile, err := filepath.EvalSymlinks(f.file); err == nil &&
+							currentRealFile != realFile {
+							f.onEvent()
+							realFile = currentRealFile
+						}
+						continue
+					}
+					if strings.HasSuffix(event.Name, file) {
+						f.onEvent()
+					}
 				}
 			case err := <-watcher.Errors:
 				if err != nil {

internal/watch/file_watcher_test.go

@@ -19,6 +19,8 @@ package watch
 import (
 	"io/ioutil"
 	"os"
+	"path"
+	"path/filepath"
 	"testing"
 	"time"
 
@@ -67,3 +69,73 @@ func TestFileWatcher(t *testing.T) {
 		t.Fatalf("expected an event shortly after writing a file")
 	}
 }
+
+func TestFileWatcherWithNestedSymlink(t *testing.T) {
+	target1, err := ioutil.TempFile("", "t1")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	defer target1.Close()
+	defer os.Remove(target1.Name())
+	dir := path.Dir(target1.Name())
+
+	innerLink := path.Join(dir, "innerLink")
+	if err = os.Symlink(target1.Name(), innerLink); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	defer os.Remove(innerLink)
+	mainLink := path.Join(dir, "mainLink")
+	if err = os.Symlink(innerLink, mainLink); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	defer os.Remove(mainLink)
+
+	targetName, err := filepath.EvalSymlinks(mainLink)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if targetName != target1.Name() {
+		t.Fatalf("expected symlink to point to %v, not %v", target1.Name(), targetName)
+	}
+
+	count := 0
+	events := make(chan bool, 10)
+	fw, err := NewFileWatcher(mainLink, func() {
+		count++
+		if count != 1 {
+			t.Fatalf("expected 1 but returned %v", count)
+		}
+		if targetName, err = filepath.EvalSymlinks(mainLink); err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		events <- true
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	defer fw.Close()
+
+	target2, err := ioutil.TempFile("", "t2")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	defer target2.Close()
+	defer os.Remove(target2.Name())
+
+	if err = os.Remove(innerLink); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if err = os.Symlink(target2.Name(), innerLink); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	timeoutChan := prepareTimeout()
+	select {
+	case <-events:
+	case <-timeoutChan:
+		t.Fatalf("expected an event shortly after creating a file and relinking")
+	}
+	if targetName != target2.Name() {
+		t.Fatalf("expected symlink to point to %v, not %v", target2.Name(), targetName)
+	}
+}