TestProcessor_BackwardLET, backward LET on empty bridge table

Author: Stefan-Ethernal

bridgesync/processor.go

@@ -1464,6 +1464,12 @@ func (p *processor) ProcessBlock(ctx context.Context, block sync.Block) error {
 				return fmt.Errorf("failed to convert new deposit count to uint64: %w", err)
 			}
 
+			leafIndex, err := aggkitcommon.SafeUint32(newDepositCountU64)
+			if err != nil {
+				return fmt.Errorf("failed to convert new deposit count (uint64) to leaf index (uint32): %w",
+					err)
+			}
+
 			// 1. remove all the bridges whose deposit_count is greater than the one captured by the BackwardLET event
 			deleteBridges := fmt.Sprintf("DELETE from %s WHERE deposit_count > $1", bridgeTableName)
 			_, err = tx.Exec(deleteBridges, newDepositCountU64)
@@ -1473,11 +1479,6 @@ func (p *processor) ProcessBlock(ctx context.Context, block sync.Block) error {
 			}
 
 			// 2. remove all leafs from the exit tree with indices greater than leafIndex in the exit tree
-			leafIndex, err := aggkitcommon.SafeUint32(newDepositCountU64)
-			if err != nil {
-				return fmt.Errorf("failed to convert new deposit count (uint64) to leaf index (uint32): %w",
-					err)
-			}
 			if err := p.exitTree.BackwardToIndex(ctx, tx, leafIndex); err != nil {
 				p.log.Errorf("failed to backward local exit tree to leaf index %d (deposit count: %d)",
 					leafIndex, newDepositCountU64)

bridgesync/processor_test.go

@@ -5377,7 +5377,7 @@ func TestProcessor_BackwardLET(t *testing.T) {
 	collectExpectedBridgesUpTo := func(t *testing.T, blocks []sync.Block, targetDepositCount uint32) []Bridge {
 		t.Helper()
 
-		var bridges []Bridge
+		bridges := make([]Bridge, 0)
 		for _, b := range blocks {
 			for _, e := range b.Events {
 				evt, ok := e.(Event)
@@ -5498,6 +5498,63 @@ func TestProcessor_BackwardLET(t *testing.T) {
 			},
 			targetDepositCount: 3,
 		},
+		{
+			name: "backward let on empty bridge table",
+			setupBlocks: func() []sync.Block {
+				return []sync.Block{
+					{
+						Num:  1,
+						Hash: common.HexToHash("0x1"),
+						Events: []any{
+							Event{BackwardLET: &BackwardLET{
+								BlockNum:             1,
+								BlockPos:             0,
+								PreviousDepositCount: big.NewInt(6),
+								NewDepositCount:      big.NewInt(3),
+							}},
+						},
+					}}
+			},
+			targetDepositCount: 0,
+		},
+		{
+			name: "backward let invalid new deposit count (outside of uint64 range)",
+			setupBlocks: func() []sync.Block {
+				return []sync.Block{
+					{
+						Num:  1,
+						Hash: common.HexToHash("0x1"),
+						Events: []any{
+							Event{BackwardLET: &BackwardLET{
+								BlockNum:             1,
+								BlockPos:             0,
+								PreviousDepositCount: big.NewInt(0),
+								NewDepositCount:      big.NewInt(-3),
+							}},
+						},
+					}}
+			},
+			processBlockErrMsg: "failed to convert new deposit count to uint64",
+		},
+		{
+			name: "backward let invalid new deposit count (outside of uint32 range)",
+			setupBlocks: func() []sync.Block {
+				return []sync.Block{
+					{
+						Num:  1,
+						Hash: common.HexToHash("0x1"),
+						Events: []any{
+							Event{BackwardLET: &BackwardLET{
+								BlockNum:             1,
+								BlockPos:             0,
+								PreviousDepositCount: big.NewInt(0),
+								NewDepositCount:      big.NewInt(4294967296),
+							}},
+						},
+					}}
+			},
+			processBlockErrMsg: "failed to convert new deposit count (uint64) to leaf index (uint32)",
+		},
 		{
 			name: "backward let after a couple of bridges + reorg backward let",
 			setupBlocks: func() []sync.Block {