From 2192c23760c3ccacdb6ce7db6992dbe8e2ecf96b Mon Sep 17 00:00:00 2001
From: Michael Quigley <michael@quigley.com>
Date: Mon, 6 Mar 2023 13:56:54 -0500
Subject: [PATCH] start of infrastructure for positionally resuming tail (#128)

---
 cmd/zrok/metrics.go              | 20 +++++++++++++++++++-
 controller/metrics/agent.go      | 27 +++++++++++++++++++--------
 controller/metrics/fileSource.go | 18 +++++++++++++++---
 3 files changed, 53 insertions(+), 12 deletions(-)

diff --git a/cmd/zrok/metrics.go b/cmd/zrok/metrics.go
index 445348d5..4001c224 100644
--- a/cmd/zrok/metrics.go
+++ b/cmd/zrok/metrics.go
@@ -5,6 +5,10 @@ import (
 	"github.com/openziti/zrok/controller/metrics"
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
 )
 
 func init() {
@@ -33,7 +37,21 @@ func (cmd *metricsCommand) run(_ *cobra.Command, args []string) {
 	}
 	logrus.Infof(cf.Dump(cfg, metrics.GetCfOptions()))
 
-	if err := metrics.Run(cfg); err != nil {
+	ma, err := metrics.Run(cfg)
+	if err != nil {
 		panic(err)
 	}
+
+	c := make(chan os.Signal)
+	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
+	go func() {
+		<-c
+		ma.Stop()
+		ma.Join()
+		os.Exit(0)
+	}()
+
+	for {
+		time.Sleep(30 * time.Minute)
+	}
 }
diff --git a/controller/metrics/agent.go b/controller/metrics/agent.go
index f793b43a..757d033f 100644
--- a/controller/metrics/agent.go
+++ b/controller/metrics/agent.go
@@ -5,23 +5,28 @@ import (
 	"github.com/sirupsen/logrus"
 )
 
-func Run(cfg *Config) error {
+type MetricsAgent struct {
+	src  Source
+	join chan struct{}
+}
+
+func Run(cfg *Config) (*MetricsAgent, error) {
 	logrus.Info("starting")
 	defer logrus.Warn("stopping")
 
 	if cfg.Source == nil {
-		return errors.New("no 'source' configured; exiting")
+		return nil, errors.New("no 'source' configured; exiting")
 	}
 
 	src, ok := cfg.Source.(Source)
 	if !ok {
-		return errors.New("invalid 'source'; exiting")
+		return nil, errors.New("invalid 'source'; exiting")
 	}
 
 	events := make(chan map[string]interface{}, 1024)
-	srcJoin, err := src.Start(events)
+	join, err := src.Start(events)
 	if err != nil {
-		return errors.Wrap(err, "error starting source")
+		return nil, errors.Wrap(err, "error starting source")
 	}
 
 	go func() {
@@ -33,7 +38,13 @@ func Run(cfg *Config) error {
 		}
 	}()
 
-	<-srcJoin
-
-	return nil
+	return &MetricsAgent{src, join}, nil
+}
+
+func (ma *MetricsAgent) Stop() {
+	ma.src.Stop()
+}
+
+func (ma *MetricsAgent) Join() {
+	<-ma.join
 }
diff --git a/controller/metrics/fileSource.go b/controller/metrics/fileSource.go
index db692966..9aba3937 100644
--- a/controller/metrics/fileSource.go
+++ b/controller/metrics/fileSource.go
@@ -19,13 +19,14 @@ func loadFileSourceConfig(v interface{}, opts *cf.Options) (interface{}, error)
 		if err := cf.Bind(cfg, submap, cf.DefaultOptions()); err != nil {
 			return nil, err
 		}
-		return &fileSource{cfg}, nil
+		return &fileSource{cfg: cfg}, nil
 	}
 	return nil, errors.New("invalid config structure for 'file' source")
 }
 
 type fileSource struct {
 	cfg *FileSourceConfig
+	t   *tail.Tail
 }
 
 func (s *fileSource) Start(events chan map[string]interface{}) (chan struct{}, error) {
@@ -45,18 +46,29 @@ func (s *fileSource) Start(events chan map[string]interface{}) (chan struct{}, e
 }
 
 func (s *fileSource) Stop() {
+	if err := s.t.Stop(); err != nil {
+		logrus.Error(err)
+	}
 }
 
 func (s *fileSource) tail(events chan map[string]interface{}) {
-	t, err := tail.TailFile(s.cfg.Path, tail.Config{Follow: true, ReOpen: true})
+	logrus.Infof("started")
+	defer logrus.Infof("stopped")
+
+	var err error
+	s.t, err = tail.TailFile(s.cfg.Path, tail.Config{
+		ReOpen: true,
+		Follow: true,
+	})
 	if err != nil {
 		logrus.Error(err)
 		return
 	}
 
-	for line := range t.Lines {
+	for line := range s.t.Lines {
 		event := make(map[string]interface{})
 		if err := json.Unmarshal([]byte(line.Text), &event); err == nil {
+			logrus.Infof("seekinfo: offset: %d", line.SeekInfo.Offset)
 			events <- event
 		} else {
 			logrus.Errorf("error parsing line #%d: %v", line.Num, err)