chore: Fix indefinite loop bug while fast sync (ethereum-optimism#108)

service/fastsync.go

@@ -43,6 +43,8 @@ func (v *ValidatorInstance) FastSync(startHeight, endHeight uint64) (*FastSyncRe
 			break
 		}
 
+		startHeight = blocks[len(blocks)-1].Height + 1
+
 		// Note: not all the blocks in the range will have votes cast
 		// due to lack of voting power or public randomness, so we may
 		// have gaps during sync
@@ -75,7 +77,6 @@ func (v *ValidatorInstance) FastSync(startHeight, endHeight uint64) (*FastSyncRe
 			return nil, err
 		}
 
-		startHeight = blocks[len(blocks)-1].Height + 1
 		responses = append(responses, res)
 
 		v.logger.WithFields(logrus.Fields{

service/fastsync_test.go

@@ -22,7 +22,6 @@ func FuzzFastSync(f *testing.F) {
 		currentHeight := finalizedHeight + uint64(r.Int63n(10)+1)
 		startingBlock := &types.BlockInfo{Height: randomStartingHeight, LastCommitHash: testutil.GenRandomByteArray(r, 32)}
 		mockClientController := testutil.PrepareMockedClientController(t, r, randomStartingHeight, currentHeight)
-		mockClientController.EXPECT().QueryLatestFinalizedBlocks(gomock.Any()).Return(nil, nil)
 		app, storeValidator, cleanUp := newValidatorAppWithRegisteredValidator(t, r, mockClientController, randomStartingHeight)
 		defer cleanUp()
 		err := app.Start()

service/validator_instance.go

@@ -622,6 +622,18 @@ func (v *ValidatorInstance) tryFastSync(targetBlock *types.BlockInfo) (*FastSync
 	if v.inSync.Load() {
 		return nil, fmt.Errorf("the validator %s is already in sync", v.GetBtcPkHex())
 	}
+
+	if v.GetLastCommittedHeight() <= v.GetLastVotedHeight() {
+		if err := v.SetLastProcessedHeight(targetBlock.Height); err != nil {
+			return nil, err
+		}
+		v.logger.WithFields(logrus.Fields{
+			"btc_pk_hex":   v.GetBtcPkHex(),
+			"block_height": targetBlock.Height,
+		}).Debug("insufficient public randomness, jumping to the latest block")
+		return nil, nil
+	}
+
 	// get the last finalized height
 	lastFinalizedBlocks, err := v.cc.QueryLatestFinalizedBlocks(1)
 	if err != nil {