Fix exchange capabilities (#14533)

* add proto marshal and unmarshal

* changelog

* Use strings

* fix missing error handling

* fix test

---------

Co-authored-by: terence tsao <terence@prysmaticlabs.com>

beacon-chain/execution/engine_client.go

@@ -297,13 +297,16 @@ func (s *Service) ExchangeCapabilities(ctx context.Context) ([]string, error) {
 	ctx, span := trace.StartSpan(ctx, "powchain.engine-api-client.ExchangeCapabilities")
 	defer span.End()
 
-	result := &pb.ExchangeCapabilities{}
+	var result []string
 	err := s.rpcClient.CallContext(ctx, &result, ExchangeCapabilities, supportedEngineEndpoints)
+	if err != nil {
+		return nil, handleRPCError(err)
+	}
 
 	var unsupported []string
 	for _, s1 := range supportedEngineEndpoints {
 		supported := false
-		for _, s2 := range result.SupportedMethods {
+		for _, s2 := range result {
 			if s1 == s2 {
 				supported = true
 				break
@@ -316,7 +319,7 @@ func (s *Service) ExchangeCapabilities(ctx context.Context) ([]string, error) {
 	if len(unsupported) != 0 {
 		log.Warnf("Please update client, detected the following unsupported engine methods: %s", unsupported)
 	}
-	return result.SupportedMethods, handleRPCError(err)
+	return result, handleRPCError(err)
 }
 
 // GetTerminalBlockHash returns the valid terminal block hash based on total difficulty.

beacon-chain/execution/engine_client_test.go

@@ -1996,11 +1996,10 @@ func Test_ExchangeCapabilities(t *testing.T) {
 			defer func() {
 				require.NoError(t, r.Body.Close())
 			}()
-			exchangeCapabilities := &pb.ExchangeCapabilities{}
 			resp := map[string]interface{}{
 				"jsonrpc": "2.0",
 				"id":      1,
-				"result":  exchangeCapabilities,
+				"result":  []string{},
 			}
 			err := json.NewEncoder(w).Encode(resp)
 			require.NoError(t, err)
@@ -2029,14 +2028,11 @@ func Test_ExchangeCapabilities(t *testing.T) {
 			defer func() {
 				require.NoError(t, r.Body.Close())
 			}()
-			exchangeCapabilities := &pb.ExchangeCapabilities{
-				SupportedMethods: []string{"A", "B", "C"},
-			}
 
 			resp := map[string]interface{}{
 				"jsonrpc": "2.0",
 				"id":      1,
-				"result":  exchangeCapabilities,
+				"result":  []string{"A", "B", "C"},
 			}
 			err := json.NewEncoder(w).Encode(resp)
 			require.NoError(t, err)