offchain - json marshal fix for generic addresses (#546)

# Motivation
The `common.Address` json representation is all in lower-case while the
new `cciptypes.Address` is eip55.
This leads to some incompatibility issues and nodes not reaching
consensus due to seeing different results.

# Solution
Make cciptypes.Address json marshal/unmarshal behave similar to
common.ADdress

core/services/ocr2/plugins/ccip/cciptypes/models.go

@@ -2,10 +2,29 @@ package cciptypes
 
 import (
 	"encoding/hex"
+	"fmt"
+	"strings"
+
+	"github.com/ethereum/go-ethereum/common"
 )
 
 type Address string
 
+// TODO: make JSON marshal/unmarshal non-evm specific.
+// Make sure we have casing compatibility with old versions.
+func (a *Address) UnmarshalJSON(bytes []byte) error {
+	vStr := strings.Trim(string(bytes), `"`)
+	if !common.IsHexAddress(vStr) {
+		return fmt.Errorf("invalid address: %s", vStr)
+	}
+	*a = Address(common.HexToAddress(vStr).String())
+	return nil
+}
+
+func (a *Address) MarshalJSON() ([]byte, error) {
+	return []byte(`"` + strings.ToLower(string(*a)) + `"`), nil
+}
+
 type Hash [32]byte
 
 func (h Hash) String() string {

core/services/ocr2/plugins/ccip/cciptypes/models_test.go

@@ -1,7 +1,15 @@
 package cciptypes
 
 import (
+	"encoding/json"
+	"fmt"
+	"strings"
 	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/stretchr/testify/assert"
+
+	"github.com/smartcontractkit/chainlink/v2/core/chains/evm/utils"
 )
 
 func TestHash_String(t *testing.T) {
@@ -34,3 +42,28 @@ func TestHash_String(t *testing.T) {
 		})
 	}
 }
+
+func TestAddress_JSON(t *testing.T) {
+	addr1 := utils.RandomAddress()
+
+	addrArr := []Address{Address(addr1.String())}
+	evmAddrArr := []common.Address{addr1}
+
+	b, err := json.Marshal(addrArr)
+	assert.NoError(t, err)
+	assert.Equal(t, fmt.Sprintf(`["%s"]`, strings.ToLower(addr1.String())), string(b))
+
+	b2, err := json.Marshal(evmAddrArr)
+	assert.NoError(t, err)
+	assert.Equal(t, string(b), string(b2), "marshal should produce the same result for common.Address and cciptypes.Address")
+
+	var unmarshalledAddr []Address
+	err = json.Unmarshal(b, &unmarshalledAddr)
+	assert.NoError(t, err)
+	assert.Equal(t, addrArr[0], unmarshalledAddr[0])
+
+	var unmarshalledEvmAddr []common.Address
+	err = json.Unmarshal(b, &unmarshalledEvmAddr)
+	assert.NoError(t, err)
+	assert.Equal(t, evmAddrArr[0], unmarshalledEvmAddr[0])
+}