feat: implement and test tailer file component

pkg/monitor/monitor.go

@@ -0,0 +1,54 @@
+package monitor
+
+import (
+	"fmt"
+	"github.com/nxadm/tail"
+	"go.uber.org/zap"
+	"regexp"
+)
+
+type Monitor interface {
+	Close() error
+	Watch(filename string, filter *regexp.Regexp, lineChan chan<- string) error
+}
+
+func New() *LogMonitor {
+	return &LogMonitor{
+		cancel: make(chan interface{}),
+	}
+}
+
+type LogMonitor struct {
+	cancel chan interface{}
+}
+
+func (l *LogMonitor) Close() error {
+	close(l.cancel)
+	return nil
+}
+
+func (l *LogMonitor) Watch(filename string, filter *regexp.Regexp, lineChan chan<- string) error {
+	t, err := tail.TailFile(filename, tail.Config{Follow: true, ReOpen: true, Logger: tail.DiscardingLogger})
+	if err != nil {
+		return fmt.Errorf("unable to begin to tail file '%s': %w", filename, err)
+	}
+
+	for {
+		select {
+		case line := <-t.Lines:
+			if line.Err != nil {
+				zap.S().Errorf("tail error: %v", err)
+				continue
+			}
+			zap.S().Infof("new line: '%s'", line.Text)
+			if filter.MatchString(line.Text) {
+				lineChan <- line.Text
+			}
+		case <-l.cancel:
+			t.Stop()
+			t.Cleanup()
+			return nil
+		}
+	}
+	return nil
+}