Evaluate symlinks before starting tailer

ruudk · ruudk · commit e632e589dda2 · 2022-01-01T19:24:43.000+01:00
When the current directory or the absolute path provided to `--file` is a symlink, we need
to convert it to the realpath on the disk.

The reason for this, is that inotify will always emit events with the realpath and not the symlink
path.

Without this change, when the log files exist on the time of starting the tail, everything will be fine.

But when you define log files that do not yet exist at the time of starting, they will never be picked up
if they are located in a symlink path.
diff --git a/local/logs/tailer.go b/local/logs/tailer.go
@@ -147,6 +147,25 @@ func (tailer *Tailer) Watch(pidFile *pid.PidFile) error {
 			if err := inotify.Watch(dir, watcherChan, inotify.Create); err != nil {
 				return errors.Wrap(err, "unable to watch the applog directory")
 			}
+
+			// Evaluate possible symlinks in the applog path, this is needed because
+			// inotify will notify us on source path, and not the symlink path.
+			if _, err := os.Stat(applog); err == nil {
+				realAppLog, err := filepath.EvalSymlinks(applog)
+				if err != nil {
+					return errors.Wrapf(err, "unable to evaluate symlinks for %s", applog)
+				}
+				applog = realAppLog
+			} else if errors.Is(err, os.ErrNotExist) {
+				realDir, err := filepath.EvalSymlinks(dir)
+				if err != nil {
+					return errors.Wrapf(err, "unable to evaluate symlinks for %s", dir)
+				}
+				applog = filepath.Join(realDir, filepath.Base(applog))
+			} else {
+				return errors.Wrapf(err, "unable to evaluate symlinks for %s", applog)
+			}
+
 			go func(applog string) {
 				for {
 					e := <-watcherChan
