lib/model, lib/config: Refactor folder health/error handling (fixes #4445, fixes #4451)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4455
LGTM: AudriusButkevicius, calmh

lib/model/folder.go

@@ -25,7 +25,7 @@ type folder struct {
 	initialScanFinished chan struct{}
 	watchCancel         context.CancelFunc
 	watchChan           chan []string
-	ignoresUpdated      chan struct{} // The ignores changed, we need to restart watcher
+	restartWatchChan    chan struct{}
 }
 
 func newFolder(model *Model, cfg config.FolderConfiguration) folder {
@@ -43,12 +43,25 @@ func newFolder(model *Model, cfg config.FolderConfiguration) folder {
 	}
 }
 
-func (f *folder) IndexUpdated() {
-}
+func (f *folder) BringToFront(string) {}
+
 func (f *folder) DelayScan(next time.Duration) {
 	f.scan.Delay(next)
 }
 
+func (f *folder) IndexUpdated() {
+}
+
+func (f *folder) IgnoresUpdated() {
+	if f.FSWatcherEnabled {
+		f.scheduleWatchRestart()
+	}
+}
+
+func (f *folder) Jobs() ([]string, []string) {
+	return nil, nil
+}
+
 func (f *folder) Scan(subdirs []string) error {
 	<-f.initialScanFinished
 	return f.scan.Scan(subdirs)
@@ -58,13 +71,34 @@ func (f *folder) Stop() {
 	f.cancel()
 }
 
-func (f *folder) Jobs() ([]string, []string) {
-	return nil, nil
+func (f *folder) BlockStats() map[string]int {
+	return nil
 }
 
-func (f *folder) BringToFront(string) {}
+// CheckHealth checks the folder for common errors, updates the folder state
+// and returns the current folder error, or nil if the folder is healthy.
+func (f *folder) CheckHealth() error {
+	err := f.getHealthError()
+	f.setError(err)
+	return err
+}
+
+func (f *folder) getHealthError() error {
+	// Check for folder errors, with the most serious and specific first and
+	// generic ones like out of space on the home disk later.
+
+	if err := f.CheckPath(); err != nil {
+		return err
+	}
+
+	if err := f.CheckFreeSpace(); err != nil {
+		return err
+	}
+
+	if err := f.model.cfg.CheckHomeFreeSpace(); err != nil {
+		return err
+	}
 
-func (f *folder) BlockStats() map[string]int {
 	return nil
 }
 
@@ -72,7 +106,7 @@ func (f *folder) scanSubdirs(subDirs []string) error {
 	if err := f.model.internalScanFolderSubdirs(f.ctx, f.folderID, subDirs); err != nil {
 		// Potentially sets the error twice, once in the scanner just
 		// by doing a check, and once here, if the error returned is
-		// the same one as returned by CheckFolderHealth, though
+		// the same one as returned by CheckHealth, though
 		// duplicate set is handled by setError.
 		f.setError(err)
 		return err
@@ -97,7 +131,7 @@ func (f *folder) scanTimerFired() {
 	f.scan.Reschedule()
 }
 
-func (f *folder) startWatcher() {
+func (f *folder) startWatch() {
 	ctx, cancel := context.WithCancel(f.ctx)
 	f.model.fmut.RLock()
 	ignores := f.model.folderIgnores[f.folderID]
@@ -113,18 +147,45 @@ func (f *folder) startWatcher() {
 	}
 }
 
-func (f *folder) restartWatcher() {
+func (f *folder) restartWatch() {
 	f.watchCancel()
-	f.startWatcher()
+	f.startWatch()
 	f.Scan(nil)
 }
 
-func (f *folder) IgnoresUpdated() {
+func (f *folder) scheduleWatchRestart() {
 	select {
-	case f.ignoresUpdated <- struct{}{}:
+	case f.restartWatchChan <- struct{}{}:
 	default:
 		// We might be busy doing a pull and thus not reading from this
 		// channel. The channel is 1-buffered, so one notification will be
 		// queued to ensure we recheck after the pull.
 	}
 }
+
+func (f *folder) setError(err error) {
+	_, _, oldErr := f.getState()
+	if (err != nil && oldErr != nil && oldErr.Error() == err.Error()) || (err == nil && oldErr == nil) {
+		return
+	}
+
+	if err != nil {
+		if oldErr == nil {
+			l.Warnf("Error on folder %s: %v", f.Description(), err)
+		} else {
+			l.Infof("Error on folder %s changed: %q -> %q", f.Description(), oldErr, err)
+		}
+	} else {
+		l.Infoln("Cleared error on folder", f.Description())
+	}
+
+	if f.FSWatcherEnabled {
+		if err != nil {
+			f.watchCancel()
+		} else {
+			f.scheduleWatchRestart()
+		}
+	}
+
+	f.stateTracker.setError(err)
+}