signer/core: fix encoding of `bytes` nested within array (#31049)

Fixes an incorrect encoding of recursive bytes types.
closes https://github.com/ethereum/go-ethereum/issues/30979

signer/core/apitypes/types.go

@@ -501,7 +501,16 @@ func (typedData *TypedData) encodeArrayValue(encValue interface{}, encType strin
 	for _, item := range arrayValue {
 		if reflect.TypeOf(item).Kind() == reflect.Slice ||
 			reflect.TypeOf(item).Kind() == reflect.Array {
-			encodedData, err := typedData.encodeArrayValue(item, parsedType, depth+1)
+			var (
+				encodedData hexutil.Bytes
+				err         error
+			)
+			if reflect.TypeOf(item).Elem().Kind() == reflect.Uint8 {
+				// the item type is bytes.  encode the bytes array directly instead of recursing.
+				encodedData, err = typedData.EncodePrimitiveValue(parsedType, item, depth+1)
+			} else {
+				encodedData, err = typedData.encodeArrayValue(item, parsedType, depth+1)
+			}
 			if err != nil {
 				return nil, err
 			}

signer/core/signed_data_test.go

@@ -1014,3 +1014,49 @@ func TestComplexTypedDataWithLowercaseReftype(t *testing.T) {
 		t.Fatalf("Error, got %x, wanted %x", sighash, expSigHash)
 	}
 }
+
+var recursiveBytesTypesStandard = apitypes.Types{
+	"EIP712Domain": {
+		{
+			Name: "name",
+			Type: "string",
+		},
+		{
+			Name: "version",
+			Type: "string",
+		},
+		{
+			Name: "chainId",
+			Type: "uint256",
+		},
+		{
+			Name: "verifyingContract",
+			Type: "address",
+		},
+	},
+	"Val": {
+		{
+			Name: "field",
+			Type: "bytes[][]",
+		},
+	},
+}
+
+var recursiveBytesMessageStandard = map[string]interface{}{
+	"field": [][][]byte{{{1}, {2}}, {{3}, {4}}},
+}
+
+var recursiveBytesTypedData = apitypes.TypedData{
+	Types:       recursiveBytesTypesStandard,
+	PrimaryType: "Val",
+	Domain:      domainStandard,
+	Message:     recursiveBytesMessageStandard,
+}
+
+func TestEncodeDataRecursiveBytes(t *testing.T) {
+	typedData := recursiveBytesTypedData
+	_, err := typedData.EncodeData(typedData.PrimaryType, typedData.Message, 0)
+	if err != nil {
+		t.Fatalf("got err %v", err)
+	}
+}