cv3/mirror: Fetch the most recent prefix revision

When a user sets up a Mirror with a restricted user that doesn't have
access to the `foo` path, we will fail to get the most recent revision
due to permissions issues.

With this change, when a prefix is provided we will get the initial
revision from the prefix rather than /foo. This allows restricted users
to setup sync.

client/v3/mirror/syncer.go

@@ -18,7 +18,7 @@ package mirror
 import (
 	"context"
 
-	"go.etcd.io/etcd/client/v3"
+	clientv3 "go.etcd.io/etcd/client/v3"
 )
 
 const (
@@ -52,7 +52,13 @@ func (s *syncer) SyncBase(ctx context.Context) (<-chan clientv3.GetResponse, cha
 
 	// if rev is not specified, we will choose the most recent revision.
 	if s.rev == 0 {
-		resp, err := s.c.Get(ctx, "foo")
+		// If len(s.prefix) == 0, we will check a random key to fetch the most recent
+		// revision (foo), otherwise we use the provided prefix.
+		checkPath := "foo"
+		if len(s.prefix) != 0 {
+			checkPath = s.prefix
+		}
+		resp, err := s.c.Get(ctx, checkPath)
 		if err != nil {
 			errchan <- err
 			close(respchan)

tests/integration/clientv3/mirror_test.go

@@ -23,8 +23,10 @@ import (
 	"time"
 
 	"go.etcd.io/etcd/api/v3/mvccpb"
+	clientv3 "go.etcd.io/etcd/client/v3"
 	"go.etcd.io/etcd/client/v3/mirror"
 	"go.etcd.io/etcd/tests/v3/integration"
+	"google.golang.org/grpc"
 )
 
 func TestMirrorSync(t *testing.T) {
@@ -124,3 +126,75 @@ func TestMirrorSyncBase(t *testing.T) {
 		t.Errorf("unexpected kv count: %d", count)
 	}
 }
+
+func TestMirrorSync_Authenticated(t *testing.T) {
+	integration.BeforeTest(t)
+	clus := integration.NewClusterV3(t, &integration.ClusterConfig{Size: 1})
+	defer clus.Terminate(t)
+
+	initialClient := clus.Client(0)
+
+	// Create a user to run the mirror process that only has access to /syncpath
+	initialClient.RoleAdd(context.Background(), "syncer")
+	initialClient.RoleGrantPermission(context.Background(), "syncer", "/syncpath", clientv3.GetPrefixRangeEnd("/syncpath"), clientv3.PermissionType(clientv3.PermReadWrite))
+	initialClient.UserAdd(context.Background(), "syncer", "syncfoo")
+	initialClient.UserGrantRole(context.Background(), "syncer", "syncer")
+
+	// Seed /syncpath with some initial data
+	_, err := initialClient.KV.Put(context.TODO(), "/syncpath/foo", "bar")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Require authentication
+	authSetupRoot(t, initialClient.Auth)
+
+	// Create a client as the `syncer` user.
+	cfg := clientv3.Config{
+		Endpoints:   initialClient.Endpoints(),
+		DialTimeout: 5 * time.Second,
+		DialOptions: []grpc.DialOption{grpc.WithBlock()},
+		Username:    "syncer",
+		Password:    "syncfoo",
+	}
+	syncClient, err := integration.NewClient(t, cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer syncClient.Close()
+
+	// Now run the sync process, create changes, and get the initial sync state
+	syncer := mirror.NewSyncer(syncClient, "/syncpath", 0)
+	gch, ech := syncer.SyncBase(context.TODO())
+	wkvs := []*mvccpb.KeyValue{{Key: []byte("/syncpath/foo"), Value: []byte("bar"), CreateRevision: 2, ModRevision: 2, Version: 1}}
+
+	for g := range gch {
+		if !reflect.DeepEqual(g.Kvs, wkvs) {
+			t.Fatalf("kv = %v, want %v", g.Kvs, wkvs)
+		}
+	}
+
+	for e := range ech {
+		t.Fatalf("unexpected error %v", e)
+	}
+
+	// Start a continuous sync
+	wch := syncer.SyncUpdates(context.TODO())
+
+	// Update state
+	_, err = syncClient.KV.Put(context.TODO(), "/syncpath/foo", "baz")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Wait for the updated state to sync
+	select {
+	case r := <-wch:
+		wkv := &mvccpb.KeyValue{Key: []byte("/syncpath/foo"), Value: []byte("baz"), CreateRevision: 2, ModRevision: 3, Version: 2}
+		if !reflect.DeepEqual(r.Events[0].Kv, wkv) {
+			t.Fatalf("kv = %v, want %v", r.Events[0].Kv, wkv)
+		}
+	case <-time.After(time.Second):
+		t.Fatal("failed to receive update in one second")
+	}
+}