add forwarder contract code check (#253)

ethereum/check_swap_factory_contract.go

@@ -7,6 +7,8 @@ import (
 
 	ethcommon "github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/ethclient"
+
+	"github.com/athanorlabs/go-relayer/impls/gsnforwarder"
 )
 
 // expectedSwapFactoryBytecodeHex is generated by deploying an instance of SwapFactory.sol
@@ -24,7 +26,10 @@ const (
 // blocks. See TestForwarderAddressIndexes to update the values.
 var forwarderAddressIndices = []int{1485, 1523}
 
-var errInvalidSwapContract = errors.New("given contract address does not contain correct code")
+var (
+	errInvalidSwapContract      = errors.New("given contract address does not contain correct SwapFactory code")
+	errInvalidForwarderContract = errors.New("given contract address does not contain correct Forwarder code")
+)
 
 // CheckSwapFactoryContractCode checks that the bytecode at the given address matches the
 // SwapFactory.sol contract. The trusted forwarder address that the contract was deployed
@@ -75,6 +80,36 @@ func CheckSwapFactoryContractCode(
 		return ethcommon.Address{}, errInvalidSwapContract
 	}
 
+	if (forwarderAddress == ethcommon.Address{}) {
+		return forwarderAddress, nil
+	}
+
+	err = checkForwarderContractCode(ctx, ec, forwarderAddress)
+	if err != nil {
+		return ethcommon.Address{}, err
+	}
+
 	// return the trusted forwarder address that was parsed from the deployed contract byte code
 	return forwarderAddress, nil
 }
+
+// checkSwapFactoryForwarder checks that the trusted forwarder contract used by
+// the given swap contract has the expected bytecode.
+func checkForwarderContractCode(
+	ctx context.Context,
+	ec *ethclient.Client,
+	contractAddr ethcommon.Address,
+) error {
+	code, err := ec.CodeAt(ctx, contractAddr, nil)
+	if err != nil {
+		return err
+	}
+
+	expectedCode := ethcommon.FromHex(gsnforwarder.ForwarderMetaData.Bin)
+
+	if !bytes.Contains(expectedCode, code) {
+		return errInvalidForwarderContract
+	}
+
+	return nil
+}

ethereum/check_swap_factory_contract_test.go

@@ -48,6 +48,14 @@ func getContractCode(t *testing.T, trustedForwarder ethcommon.Address) []byte {
 	return code
 }
 
+func TestCheckForwarderContractCode(t *testing.T) {
+	ec, _ := tests.NewEthClient(t)
+	pk := tests.GetMakerTestKey(t)
+	trustedForwarder := deployForwarder(t, ec, pk)
+	err := checkForwarderContractCode(context.Background(), ec, trustedForwarder)
+	require.NoError(t, err)
+}
+
 // This test will fail if the compiled SwapFactory contract is updated, but the
 // expectedSwapFactoryBytecodeHex constant is not updated. Use this test to update the
 // constant.