Micro log fixes (#1570)

runtime/default.go

@@ -251,6 +251,18 @@ func (r *runtime) Create(s *Service, opts ...CreateOption) error {
 	return nil
 }
 
+// exists returns whether the given file or directory exists
+func exists(path string) (bool, error) {
+	_, err := os.Stat(path)
+	if err == nil {
+		return true, nil
+	}
+	if os.IsNotExist(err) {
+		return false, nil
+	}
+	return true, err
+}
+
 // @todo: Getting existing lines is not supported yet.
 // The reason for this is because it's hard to calculate line offset
 // as opposed to character offset.
@@ -265,18 +277,41 @@ func (r *runtime) Logs(s *Service, options ...LogsOption) (LogStream, error) {
 		stream:  make(chan LogRecord),
 		stop:    make(chan bool),
 	}
-	t, err := tail.TailFile(logFile(s.Name), tail.Config{Follow: true, Location: &tail.SeekInfo{
-		Whence: 2,
-		Offset: 0,
+
+	fpath := logFile(s.Name)
+	if ex, err := exists(fpath); err != nil {
+		return nil, err
+	} else if !ex {
+		return nil, fmt.Errorf("Log file %v does not exists", fpath)
+	}
+
+	whence := 2
+	// Multiply by length of an average line of log in bytes
+	offset := -1 * lopts.Count * 200
+
+	t, err := tail.TailFile(logFile(s.Name), tail.Config{Follow: lopts.Stream, Location: &tail.SeekInfo{
+		Whence: whence,
+		Offset: int64(offset),
 	}, Logger: tail.DiscardingLogger})
 	if err != nil {
 		return nil, err
 	}
+
 	ret.tail = t
 	go func() {
-		for line := range t.Lines {
-			ret.stream <- LogRecord{Message: line.Text}
+		for {
+			select {
+			case line, ok := <-t.Lines:
+				if !ok {
+					ret.Stop()
+					return
+				}
+				ret.stream <- LogRecord{Message: line.Text}
+			case <-ret.stop:
+				return
+			}
 		}
+
 	}()
 	return ret, nil
 }
@@ -301,16 +336,17 @@ func (l *logStream) Error() error {
 func (l *logStream) Stop() error {
 	l.Lock()
 	defer l.Unlock()
-	// @todo seems like this is causing a hangup
-	//err := l.tail.Stop()
-	//if err != nil {
-	//	return err
-	//}
+
 	select {
 	case <-l.stop:
 		return nil
 	default:
 		close(l.stop)
+		close(l.stream)
+		err := l.tail.Stop()
+		if err != nil {
+			return err
+		}
 	}
 	return nil
 }