Configure debug logging

logs/pod_watcher.go

@@ -48,10 +48,11 @@ type PodWatcher struct {
 	streamResults chan error
 	dst           io.Writer
 	closeChan     chan struct{}
+	logger        *log.Logger
 }
 
 // NewPodWatcher initializes a new PodWatcher.
-func NewPodWatcher(client KubernetesClient, container string, labelSelector labels.Selector, dst io.Writer) PodWatcherInterface {
+func NewPodWatcher(client KubernetesClient, container string, labelSelector labels.Selector, dst io.Writer, logger *log.Logger) PodWatcherInterface {
 	return &PodWatcher{
 		client:        client,
 		container:     container,
@@ -61,6 +62,7 @@ func NewPodWatcher(client KubernetesClient, container string, labelSelector labe
 		streamResults: make(chan error),
 		dst:           dst,
 		closeChan:     make(chan struct{}),
+		logger:        logger,
 	}
 }
 
@@ -73,7 +75,7 @@ func (pw *PodWatcher) WatchPods(ctx context.Context) error {
 	err := pw.watchPods(ctx, &wg)
 
 	wg.Wait()
-	log.Println("[PodWatcher] all goroutines exited, exiting")
+	pw.logger.Println("[PodWatcher] all goroutines exited, exiting")
 
 	return err
 }
@@ -117,7 +119,7 @@ func (pw *PodWatcher) watchPods(ctx context.Context, wg *sync.WaitGroup) error {
 			for podName, pod := range pw.spec {
 				pod := pod
 				if _, ok := pw.status[podName]; !ok {
-					log.Printf("[PodWatcher] adding pod, name = %s", pod.Name)
+					pw.logger.Printf("[PodWatcher] adding pod, name = %s", pod.Name)
 					pw.status[pod.Name] = true
 					wg.Add(1)
 					go func() {
@@ -163,7 +165,7 @@ func (pw *PodWatcher) watchPods(ctx context.Context, wg *sync.WaitGroup) error {
 }
 
 func (pw *PodWatcher) removePod(podName string) {
-	log.Printf("[PodWatcher] removing pod, name = %s", podName)
+	pw.logger.Printf("[PodWatcher] removing pod, name = %s", podName)
 	delete(pw.status, podName)
 }
 

logs/pod_watcher_test.go

@@ -76,7 +76,7 @@ func TestPodWatcherClose(t *testing.T) {
 	selector := labels.SelectorFromSet(map[string]string{"foo": "bar"})
 
 	var buf bytes.Buffer
-	pw := logs.NewPodWatcher(client, "mycontainer", selector, &buf)
+	pw := logs.NewPodWatcher(client, "mycontainer", selector, &buf, discardLogger())
 
 	go func() {
 		podsWatcher.Add(&corev1.Pod{ObjectMeta: metav1.ObjectMeta{Name: "foo", Namespace: "default"}, Status: corev1.PodStatus{Phase: corev1.PodRunning}})
@@ -148,7 +148,7 @@ func TestPodWatcher(t *testing.T) {
 			selector := labels.SelectorFromSet(map[string]string{"foo": "bar"})
 
 			var buf bytes.Buffer
-			pw := logs.NewPodWatcher(client, "mycontainer", selector, &buf)
+			pw := logs.NewPodWatcher(client, "mycontainer", selector, &buf, discardLogger())
 
 			go func() {
 				for _, pod := range tc.podEvents {

logs/watcher.go

@@ -3,8 +3,10 @@ package logs
 import (
 	"context"
 	"errors"
+	"fmt"
 	"io"
 	"log"
+	"os"
 	"sync"
 	"time"
 
@@ -48,7 +50,7 @@ type PodWatcherInterface interface {
 }
 
 // PodWatcherFunc builds a PodWatcher.
-type PodWatcherFunc func(KubernetesClient, string, labels.Selector, io.Writer) PodWatcherInterface
+type PodWatcherFunc func(KubernetesClient, string, labels.Selector, io.Writer, *log.Logger) PodWatcherInterface
 
 // WatcherParams defines the input parameters of a Watcher.
 type WatcherParams struct {
@@ -70,16 +72,18 @@ type Watcher struct {
 	podWatcherFunc PodWatcherFunc
 	errChan        chan error
 	dst            *concurrentWriter
+	logger         *log.Logger
 }
 
 // NewWatcher creates a new Watcher.
-func NewWatcher(params WatcherParams, client KubernetesClient, podWatcherFunc PodWatcherFunc, dst io.Writer) *Watcher {
+func NewWatcher(params WatcherParams, client KubernetesClient, podWatcherFunc PodWatcherFunc, dst io.Writer, logger *log.Logger) *Watcher {
 	return &Watcher{
 		params:         params,
 		client:         client,
 		podWatcherFunc: podWatcherFunc,
 		errChan:        make(chan error),
 		dst:            &concurrentWriter{w: dst},
+		logger:         logger,
 	}
 }
 
@@ -130,7 +134,7 @@ func (w *Watcher) Watch(ctx context.Context) error {
 				if !ok || err != nil {
 					// matchLabels don't exist or cannot be parsed.
 					// Should this be fatal?
-					log.Printf("warning: unable to parse matchLabels: ok = %t, err = %v", ok, err)
+					w.logger.Printf("warning: unable to parse matchLabels: ok = %t, err = %v", ok, err)
 					continue
 				}
 				selector := labels.SelectorFromSet(selectorAsMap)
@@ -151,7 +155,7 @@ func (w *Watcher) checkResourceExists(ctx context.Context, namespace string, res
 	_, err := w.client.Untyped.Resource(resourceID).Namespace(namespace).Get(ctx, w.params.Name, metav1.GetOptions{})
 	var statusErr *apierrors.StatusError
 	if !w.params.StrictExist && errors.As(err, &statusErr) && statusErr.Status().Reason == metav1.StatusReasonNotFound {
-		log.Printf(`%s "%s" does not exist, waiting`, resourceID.Resource, w.params.Name)
+		fmt.Fprintf(os.Stderr, "%s \"%s\" does not exist, waiting\n", resourceID.Resource, w.params.Name)
 		return nil
 	}
 	return err
@@ -164,7 +168,7 @@ func (w *Watcher) addDeployment(ctx context.Context, resourceUID types.UID, podS
 
 	w.removeDeployment()
 
-	log.Println("[DeploymentWatcher] add podWatcher")
+	w.logger.Println("[DeploymentWatcher] add podWatcher")
 
 	w.resourceUID = resourceUID
 	w.podSelector = podSelector
@@ -173,6 +177,7 @@ func (w *Watcher) addDeployment(ctx context.Context, resourceUID types.UID, podS
 		w.params.Container,
 		w.podSelector,
 		w.dst,
+		w.logger,
 	)
 
 	go func() {
@@ -184,7 +189,7 @@ func (w *Watcher) addDeployment(ctx context.Context, resourceUID types.UID, podS
 
 func (w *Watcher) removeDeployment() {
 	if w.podWatcher != nil {
-		log.Println("[DeploymentWatcher] remove podWatcher")
+		w.logger.Println("[DeploymentWatcher] remove podWatcher")
 		w.podWatcher.Close()
 		w.podWatcher = nil
 	}

logs/watcher_test.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"errors"
 	"io"
+	"log"
 	"strings"
 	"testing"
 	"time"
@@ -30,11 +31,15 @@ func (m *mockPodWatcher) WatchPods(ctx context.Context) error { return m.err }
 func (m *mockPodWatcher) Close()                              {}
 
 func mockPodwatcherFunc(err error) logs.PodWatcherFunc {
-	return func(logs.KubernetesClient, string, labels.Selector, io.Writer) logs.PodWatcherInterface {
+	return func(logs.KubernetesClient, string, labels.Selector, io.Writer, *log.Logger) logs.PodWatcherInterface {
 		return &mockPodWatcher{err: err}
 	}
 }
 
+func discardLogger() *log.Logger {
+	return log.New(io.Discard, "", 0)
+}
+
 func buildDeployment(t *testing.T, name string) *unstructured.Unstructured {
 	deployment := new(unstructured.Unstructured)
 	deployment.SetAPIVersion("v1")
@@ -51,7 +56,7 @@ func TestWatcherStrictExist(t *testing.T) {
 
 	var buf bytes.Buffer
 	params := logs.WatcherParams{Name: "mydeployment", Type: "deployments", Namespace: "default", StrictExist: true}
-	watcher := logs.NewWatcher(params, client, mockPodwatcherFunc(nil), &buf)
+	watcher := logs.NewWatcher(params, client, mockPodwatcherFunc(nil), &buf, discardLogger())
 
 	err := watcher.Watch(context.Background())
 	assert.EqualError(t, err, `deployments.apps "mydeployment" not found`)
@@ -67,7 +72,7 @@ func TestWatcherPodWatcherError(t *testing.T) {
 	var buf bytes.Buffer
 	wantErr := errors.New("foo")
 	params := logs.WatcherParams{Name: "mydeployment", Type: "deployments", Namespace: "default"}
-	watcher := logs.NewWatcher(params, client, mockPodwatcherFunc(wantErr), &buf)
+	watcher := logs.NewWatcher(params, client, mockPodwatcherFunc(wantErr), &buf, discardLogger())
 
 	go func() {
 		defer deploymentsWatcher.Stop()
@@ -89,7 +94,7 @@ func TestWatcherClosedChannel(t *testing.T) {
 
 	var buf bytes.Buffer
 	params := logs.WatcherParams{Name: "mydeployment", Type: "deployments", Namespace: "default"}
-	watcher := logs.NewWatcher(params, client, nil, &buf)
+	watcher := logs.NewWatcher(params, client, nil, &buf, discardLogger())
 	// Immediately stop the watcher, which closes the ResultChan.
 	// This should be expected to be handled.
 	deploymentsWatcher.Stop()
@@ -136,7 +141,7 @@ func TestWatcherWithPodWatcher(t *testing.T) {
 
 	var buf bytes.Buffer
 	params := logs.WatcherParams{Name: "mydeployment", Type: "deployments", Namespace: "default"}
-	watcher := logs.NewWatcher(params, client, logs.NewPodWatcher, &buf)
+	watcher := logs.NewWatcher(params, client, logs.NewPodWatcher, &buf, discardLogger())
 
 	err := watcher.Watch(ctx)
 	require.EqualError(t, err, context.DeadlineExceeded.Error())

main.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"flag"
 	"fmt"
+	"io"
 	"log"
 	"os"
 
@@ -23,11 +24,13 @@ func main() {
 	var (
 		container   string
 		strictExist bool
+		debug       bool
 		version     bool
 	)
 
 	flag.StringVar(&container, "container", "", "name of a specific container")
 	flag.BoolVar(&strictExist, "strict", false, "require deployment to exist on launch")
+	flag.BoolVar(&debug, "debug", false, "enable debug logging to stderr")
 	flag.BoolVar(&version, "version", false, "print version and exit")
 	flag.Parse()
 
@@ -36,6 +39,11 @@ func main() {
 		os.Exit(0)
 	}
 
+	logger := log.New(io.Discard, "", 0)
+	if debug {
+		logger = log.New(os.Stderr, "", 0)
+	}
+
 	var params logs.WatcherParams
 
 	switch len(flag.Args()) {
@@ -79,6 +87,7 @@ func main() {
 		logs.KubernetesClient{Typed: clientset, Untyped: dynamicclient},
 		logs.NewPodWatcher,
 		os.Stdout,
+		logger,
 	)
 	if err := watcher.Watch(ctx); err != nil {
 		log.Fatal(err)