Fix watching from resourceVersion=0 in etcd3 watcher

pkg/storage/etcd3/event.go

@@ -30,14 +30,15 @@ type event struct {
 	isCreated bool
 }
 
-func parseKV(kv *mvccpb.KeyValue, prevVal []byte) *event {
+// parseKV converts a KeyValue retrieved from an initial sync() listing to a synthetic isCreated event.
+func parseKV(kv *mvccpb.KeyValue) *event {
 	return &event{
 		key:       string(kv.Key),
 		value:     kv.Value,
-		prevValue: prevVal,
+		prevValue: nil,
 		rev:       kv.ModRevision,
 		isDeleted: false,
-		isCreated: kv.ModRevision == kv.CreateRevision,
+		isCreated: true,
 	}
 }
 

pkg/storage/etcd3/watcher.go

@@ -146,6 +146,7 @@ func (wc *watchChan) ResultChan() <-chan watch.Event {
 
 // sync tries to retrieve existing data and send them to process.
 // The revision to watch will be set to the revision in response.
+// All events sent will have isCreated=true
 func (wc *watchChan) sync() error {
 	opts := []clientv3.OpOption{}
 	if wc.recursive {
@@ -156,17 +157,8 @@ func (wc *watchChan) sync() error {
 		return err
 	}
 	wc.initialRev = getResp.Header.Revision
-
 	for _, kv := range getResp.Kvs {
-		prevResp, err := wc.watcher.client.Get(wc.ctx, string(kv.Key), clientv3.WithRev(kv.ModRevision-1), clientv3.WithSerializable())
-		if err != nil {
-			return err
-		}
-		var prevVal []byte
-		if len(prevResp.Kvs) > 0 {
-			prevVal = prevResp.Kvs[0].Value
-		}
-		wc.sendEvent(parseKV(kv, prevVal))
+		wc.sendEvent(parseKV(kv))
 	}
 	return nil
 }

pkg/storage/etcd3/watcher_test.go

@@ -20,6 +20,7 @@ import (
 	"errors"
 	"fmt"
 	"reflect"
+	"strconv"
 	"sync"
 	"testing"
 	"time"
@@ -141,17 +142,64 @@ func TestDeleteTriggerWatch(t *testing.T) {
 
 // TestWatchFromZero tests that
 // - watch from 0 should sync up and grab the object added before
+// - watch from 0 is able to return events for objects whose previous version has been compacted
 // - watch from non-0 should just watch changes after given version
 func TestWatchFromZero(t *testing.T) {
 	ctx, store, cluster := testSetup(t)
 	defer cluster.Terminate(t)
-	key, storedObj := testPropogateStore(ctx, t, store, &api.Pod{ObjectMeta: api.ObjectMeta{Name: "foo"}})
+	key, storedObj := testPropogateStore(ctx, t, store, &api.Pod{ObjectMeta: api.ObjectMeta{Name: "foo", Namespace: "ns"}})
 
 	w, err := store.Watch(ctx, key, "0", storage.Everything)
 	if err != nil {
 		t.Fatalf("Watch failed: %v", err)
 	}
 	testCheckResult(t, 0, watch.Added, w, storedObj)
+	w.Stop()
+
+	// Update
+	out := &api.Pod{}
+	err = store.GuaranteedUpdate(ctx, key, out, true, nil, storage.SimpleUpdate(
+		func(runtime.Object) (runtime.Object, error) {
+			return &api.Pod{ObjectMeta: api.ObjectMeta{Name: "foo", Namespace: "ns", Annotations: map[string]string{"a": "1"}}}, nil
+		}))
+	if err != nil {
+		t.Fatalf("GuaranteedUpdate failed: %v", err)
+	}
+
+	// Make sure when we watch from 0 we receive an ADDED event
+	w, err = store.Watch(ctx, key, "0", storage.Everything)
+	if err != nil {
+		t.Fatalf("Watch failed: %v", err)
+	}
+	testCheckResult(t, 1, watch.Added, w, out)
+	w.Stop()
+
+	// Update again
+	out = &api.Pod{}
+	err = store.GuaranteedUpdate(ctx, key, out, true, nil, storage.SimpleUpdate(
+		func(runtime.Object) (runtime.Object, error) {
+			return &api.Pod{ObjectMeta: api.ObjectMeta{Name: "foo", Namespace: "ns"}}, nil
+		}))
+	if err != nil {
+		t.Fatalf("GuaranteedUpdate failed: %v", err)
+	}
+
+	// Compact previous versions
+	revToCompact, err := strconv.Atoi(out.ResourceVersion)
+	if err != nil {
+		t.Fatalf("Error converting %q to an int: %v", storedObj.ResourceVersion, err)
+	}
+	_, err = cluster.RandClient().Compact(ctx, int64(revToCompact), clientv3.WithCompactPhysical())
+	if err != nil {
+		t.Fatalf("Error compacting: %v", err)
+	}
+
+	// Make sure we can still watch from 0 and receive an ADDED event
+	w, err = store.Watch(ctx, key, "0", storage.Everything)
+	if err != nil {
+		t.Fatalf("Watch failed: %v", err)
+	}
+	testCheckResult(t, 2, watch.Added, w, out)
 }
 
 // TestWatchFromNoneZero tests that