op-service/sources: Always validate number of receipts when fetching receipts (#8834)

Even if we're trusting the rpc source. This is a cheap sanity check.

op-service/sources/eth_client.go

@@ -327,6 +327,8 @@ func (s *EthClient) FetchReceipts(ctx context.Context, blockHash common.Hash) (e
 		if err := validateReceipts(block, info.ReceiptHash(), txHashes, receipts); err != nil {
 			return info, nil, fmt.Errorf("invalid receipts: %w", err)
 		}
+	} else if len(txHashes) != len(receipts) {
+		return info, nil, fmt.Errorf("unexpected number of receipts, expected: %d, got: %d", len(txHashes), len(receipts))
 	}
 
 	return info, receipts, nil

op-service/sources/eth_client_test.go

@@ -180,7 +180,54 @@ func TestEthClient_WrongInfoByHash(t *testing.T) {
 	m.Mock.AssertExpectations(t)
 }
 
+type validateReceiptsTest struct {
+	desc        string
+	trustRPC    bool
+	mutReceipts func(types.Receipts) types.Receipts
+	expError    string
+}
+
 func TestEthClient_validateReceipts(t *testing.T) {
+	mutBloom := func(rs types.Receipts) types.Receipts {
+		rs[2].Bloom[0] = 1
+		return rs
+	}
+
+	for _, tt := range []validateReceiptsTest{
+		{
+			desc: "no-trust-valid",
+		},
+		{
+			desc:        "no-trust-invalid-mut-bloom",
+			mutReceipts: mutBloom,
+			expError:    "invalid receipts",
+		},
+		{
+			desc:     "trust-valid",
+			trustRPC: true,
+		},
+		{
+			desc:        "trust-invalid-mut-bloom",
+			trustRPC:    true,
+			mutReceipts: mutBloom, // should still pass if trusting rpc
+		},
+		{
+			desc:     "trust-invalid-truncated",
+			trustRPC: true,
+			mutReceipts: func(rs types.Receipts) types.Receipts {
+				// remove last receipt should invalidate even if trusting RPC
+				return rs[:len(rs)-1]
+			},
+			expError: "unexpected number of receipts",
+		},
+	} {
+		t.Run(tt.desc, func(t *testing.T) {
+			testEthClient_validateReceipts(t, tt)
+		})
+	}
+}
+
+func testEthClient_validateReceipts(t *testing.T, test validateReceiptsTest) {
 	require := require.New(t)
 	mrpc := new(mockRPC)
 	mrp := new(mockReceiptsProvider)
@@ -189,8 +236,9 @@ func TestEthClient_validateReceipts(t *testing.T) {
 	txHashes := receiptTxHashes(receipts)
 	ctx := context.Background()
 
-	// mutate a field to make validation fail.
-	receipts[2].Bloom[0] = 1
+	if mut := test.mutReceipts; mut != nil {
+		receipts = mut(receipts)
+	}
 
 	mrpc.On("CallContext", ctx, mock.AnythingOfType("**sources.rpcBlock"),
 		"eth_getBlockByHash", []any{block.Hash, true}).
@@ -205,10 +253,18 @@ func TestEthClient_validateReceipts(t *testing.T) {
 	ethcl := newEthClientWithCaches(nil, numTxs)
 	ethcl.client = mrpc
 	ethcl.recProvider = mrp
-	ethcl.trustRPC = false
+	ethcl.trustRPC = test.trustRPC
 
-	_, _, err := ethcl.FetchReceipts(ctx, block.Hash)
-	require.ErrorContains(err, "invalid receipts")
+	info, recs, err := ethcl.FetchReceipts(ctx, block.Hash)
+	if test.expError != "" {
+		require.ErrorContains(err, test.expError)
+	} else {
+		require.NoError(err)
+		expInfo, _, err := block.Info(true, false)
+		require.NoError(err)
+		require.Equal(expInfo, info)
+		require.Equal(types.Receipts(receipts), recs)
+	}
 
 	mrpc.AssertExpectations(t)
 	mrp.AssertExpectations(t)