go/proxyd: Handle nil responses better

.changeset/chatty-dragons-guess.md

+---
+'@eth-optimism/proxyd': minor
+---
+
+Handle nil responses better

go/proxyd/integration_tests/caching_test.go

@@ -16,7 +16,7 @@ func TestCaching(t *testing.T) {
 	require.NoError(t, err)
 	defer redis.Close()
 
-	hdlr := NewRPCResponseHandler(map[string]string{
+	hdlr := NewRPCResponseHandler(map[string]interface{}{
 		"eth_chainId":          "0x420",
 		"net_version":          "0x1234",
 		"eth_blockNumber":      "0x64",
@@ -123,10 +123,25 @@ func TestCaching(t *testing.T) {
 		})
 	}
 
+	t.Run("block numbers update", func(t *testing.T) {
 		hdlr.SetResponse("eth_blockNumber", "0x100")
 		time.Sleep(1500 * time.Millisecond)
 		resRaw, _, err := client.SendRPC("eth_blockNumber", nil)
+		require.NoError(t, err)
 		RequireEqualJSON(t, []byte("{\"id\":999,\"jsonrpc\":\"2.0\",\"result\":\"0x100\"}"), resRaw)
+		backend.Reset()
+	})
+
+	t.Run("nil responses should not be cached", func(t *testing.T) {
+		hdlr.SetResponse("eth_getBlockByNumber", nil)
+		resRaw, _, err := client.SendRPC("eth_getBlockByNumber", []interface{}{"0x123"})
+		require.NoError(t, err)
+		resCache, _, err := client.SendRPC("eth_getBlockByNumber", []interface{}{"0x123"})
+		require.NoError(t, err)
+		RequireEqualJSON(t, []byte("{\"id\":999,\"jsonrpc\":\"2.0\",\"result\":null}"), resRaw)
+		RequireEqualJSON(t, resRaw, resCache)
+		require.Equal(t, 2, countRequests(backend, "eth_getBlockByNumber"))
+	})
 }
 
 func countRequests(backend *MockBackend, name string) int {

go/proxyd/integration_tests/mock_backend_test.go

@@ -33,18 +33,27 @@ func SingleResponseHandler(code int, response string) http.HandlerFunc {
 
 type RPCResponseHandler struct {
 	mtx          sync.RWMutex
-	rpcResponses map[string]string
+	rpcResponses map[string]interface{}
 }
 
-func NewRPCResponseHandler(rpcResponses map[string]string) *RPCResponseHandler {
+func NewRPCResponseHandler(rpcResponses map[string]interface{}) *RPCResponseHandler {
 	return &RPCResponseHandler{
 		rpcResponses: rpcResponses,
 	}
 }
 
-func (h *RPCResponseHandler) SetResponse(method, response string) {
+func (h *RPCResponseHandler) SetResponse(method string, response interface{}) {
 	h.mtx.Lock()
 	defer h.mtx.Unlock()
+
+	switch response.(type) {
+	case string:
+	case nil:
+		break
+	default:
+		panic("invalid response type")
+	}
+
 	h.rpcResponses[method] = response
 }
 

go/proxyd/server.go

@@ -237,7 +237,7 @@ func (s *Server) handleSingleRPC(ctx context.Context, req *RPCReq) (*RPCRes, boo
 		return NewRPCErrorRes(req.ID, err), false
 	}
 
-	if backendRes.Error == nil {
+	if backendRes.Error == nil && backendRes.Result != nil {
 		if err = s.cache.PutRPC(ctx, req, backendRes); err != nil {
 			log.Warn(
 				"cache put error",