Cache response headers along with json-rpc response

.env

@@ -131,6 +131,8 @@ CACHE_INDEFINITELY=false
 # Possible values are testnet, mainnet, etc...
 # CACHE_PREFIX must not contain colon symbol
 CACHE_PREFIX=local-chain
+# WHITELISTED_HEADERS contains comma-separated list of headers which has to be cached along with EVM JSON-RPC response
+WHITELISTED_HEADERS=access-control-expose-headers,server,vary
 
 ##### Database Config
 POSTGRES_PASSWORD=password

config/config.go

@@ -50,6 +50,7 @@ type Config struct {
 	RedisPassword                             string
 	CacheTTL                                  time.Duration
 	CachePrefix                               string
+	WhitelistedHeaders                        []string
 }
 
 const (
@@ -109,6 +110,7 @@ const (
 	CACHE_INDEFINITELY_KEY                                          = "CACHE_INDEFINITELY"
 	CACHE_TTL_ENVIRONMENT_KEY                                       = "CACHE_TTL_SECONDS"
 	CACHE_PREFIX_ENVIRONMENT_KEY                                    = "CACHE_PREFIX"
+	WHITELISTED_HEADERS_ENVIRONMENT_KEY                             = "WHITELISTED_HEADERS"
 )
 
 var ErrEmptyHostMap = errors.New("backend host url map is empty")
@@ -214,6 +216,13 @@ func ReadConfig() Config {
 	parsedProxyBackendHostURLMap, _ := ParseRawProxyBackendHostURLMap(rawProxyBackendHostURLMap)
 	parsedProxyPruningBackendHostURLMap, _ := ParseRawProxyBackendHostURLMap(rawProxyPruningBackendHostURLMap)
 
+	whitelistedHeaders := os.Getenv(WHITELISTED_HEADERS_ENVIRONMENT_KEY)
+	parsedWhitelistedHeaders := strings.Split(whitelistedHeaders, ",")
+	// strings.Split("", sep) returns []string{""} (slice with one empty string) which can be unexpected, so override it with more reasonable behaviour
+	if whitelistedHeaders == "" {
+		parsedWhitelistedHeaders = []string{}
+	}
+
 	return Config{
 		ProxyServicePort:                          os.Getenv(PROXY_SERVICE_PORT_ENVIRONMENT_KEY),
 		LogLevel:                                  EnvOrDefault(LOG_LEVEL_ENVIRONMENT_KEY, DEFAULT_LOG_LEVEL),
@@ -252,5 +261,6 @@ func ReadConfig() Config {
 		CacheTTL:                                  time.Duration(EnvOrDefaultInt(CACHE_TTL_ENVIRONMENT_KEY, 0)) * time.Second,
 		CacheIndefinitely:                         EnvOrDefaultBool(CACHE_INDEFINITELY_KEY, false),
 		CachePrefix:                               os.Getenv(CACHE_PREFIX_ENVIRONMENT_KEY),
+		WhitelistedHeaders:                        parsedWhitelistedHeaders,
 	}
 }

main_test.go

@@ -480,9 +480,9 @@ func TestE2ETestCachingMdwWithBlockNumberParam(t *testing.T) {
 			// check that cached and non-cached responses are equal
 
 			// eth_getBlockByNumber - cache MISS
-			resp1 := mkJsonRpcRequest(t, proxyServiceURL, 1, tc.method, tc.params)
-			require.Equal(t, cachemdw.CacheMissHeaderValue, resp1.Header[cachemdw.CacheHeaderKey][0])
-			body1, err := io.ReadAll(resp1.Body)
+			cacheMissResp := mkJsonRpcRequest(t, proxyServiceURL, 1, tc.method, tc.params)
+			require.Equal(t, cachemdw.CacheMissHeaderValue, cacheMissResp.Header[cachemdw.CacheHeaderKey][0])
+			body1, err := io.ReadAll(cacheMissResp.Body)
 			require.NoError(t, err)
 			err = checkJsonRpcErr(body1)
 			require.NoError(t, err)
@@ -491,16 +491,20 @@ func TestE2ETestCachingMdwWithBlockNumberParam(t *testing.T) {
 			containsKey(t, redisClient, expectedKey)
 
 			// eth_getBlockByNumber - cache HIT
-			resp2 := mkJsonRpcRequest(t, proxyServiceURL, 1, tc.method, tc.params)
-			require.Equal(t, cachemdw.CacheHitHeaderValue, resp2.Header[cachemdw.CacheHeaderKey][0])
-			body2, err := io.ReadAll(resp2.Body)
+			cacheHitResp := mkJsonRpcRequest(t, proxyServiceURL, 1, tc.method, tc.params)
+			require.Equal(t, cachemdw.CacheHitHeaderValue, cacheHitResp.Header[cachemdw.CacheHeaderKey][0])
+			body2, err := io.ReadAll(cacheHitResp.Body)
 			require.NoError(t, err)
 			err = checkJsonRpcErr(body2)
 			require.NoError(t, err)
 			expectKeysNum(t, redisClient, tc.keysNum)
 			containsKey(t, redisClient, expectedKey)
 
+			// check that response bodies are the same
 			require.JSONEq(t, string(body1), string(body2), "blocks should be the same")
+
+			// check that response headers are the same
+			equalHeaders(t, cacheMissResp.Header, cacheHitResp.Header)
 		})
 	}
 
@@ -526,6 +530,27 @@ func TestE2ETestCachingMdwWithBlockNumberParam(t *testing.T) {
 	cleanUpRedis(t, redisClient)
 }
 
+// equalHeaders checks that headers of headersMap1 and headersMap2 are equal
+// NOTE: it completely ignores presence/absence of cachemdw.CacheHeaderKey,
+// it's done in that way to allow comparison of headers for cache miss and cache hit cases
+func equalHeaders(t *testing.T, headersMap1, headersMap2 http.Header) {
+	containsHeaders(t, headersMap1, headersMap2)
+	containsHeaders(t, headersMap2, headersMap1)
+}
+
+// containsHeaders checks that headersMap1 contains all headers from headersMap2 and that values for headers are the same
+// NOTE: it completely ignores presence/absence of cachemdw.CacheHeaderKey,
+// it's done in that way to allow comparison of headers for cache miss and cache hit cases
+func containsHeaders(t *testing.T, headersMap1, headersMap2 http.Header) {
+	for name, value := range headersMap1 {
+		if name == cachemdw.CacheHeaderKey {
+			continue
+		}
+
+		require.Equal(t, value, headersMap2[name])
+	}
+}
+
 func TestE2ETestCachingMdwWithBlockNumberParam_Metrics(t *testing.T) {
 	client, err := ethclient.Dial(proxyServiceURL)
 	require.NoError(t, err)

service/cachemdw/cache.go

@@ -24,8 +24,9 @@ type ServiceCache struct {
 	cacheIndefinitely        bool
 	decodedRequestContextKey any
 	// cachePrefix is used as prefix for any key in the cache
-	cachePrefix  string
-	cacheEnabled bool
+	cachePrefix        string
+	cacheEnabled       bool
+	whitelistedHeaders []string
 
 	*logging.ServiceLogger
 }
@@ -38,6 +39,7 @@ func NewServiceCache(
 	decodedRequestContextKey any,
 	cachePrefix string,
 	cacheEnabled bool,
+	whitelistedHeaders []string,
 	logger *logging.ServiceLogger,
 ) *ServiceCache {
 	return &ServiceCache{
@@ -48,10 +50,19 @@ func NewServiceCache(
 		decodedRequestContextKey: decodedRequestContextKey,
 		cachePrefix:              cachePrefix,
 		cacheEnabled:             cacheEnabled,
+		whitelistedHeaders:       whitelistedHeaders,
 		ServiceLogger:            logger,
 	}
 }
 
+// QueryResponse represents the structure which stored in the cache for every cacheable request
+type QueryResponse struct {
+	// JsonRpcResponseResult is an EVM JSON-RPC response's result
+	JsonRpcResponseResult []byte `json:"json_rpc_response_result"`
+	// HeaderMap is a map of HTTP headers which is cached along with the EVM JSON-RPC response
+	HeaderMap map[string]string `json:"header_map"`
+}
+
 // IsCacheable checks if EVM request is cacheable.
 // In current implementation we consider request is cacheable if it has specific block height
 func IsCacheable(
@@ -89,7 +100,7 @@ func IsCacheable(
 func (c *ServiceCache) GetCachedQueryResponse(
 	ctx context.Context,
 	req *decode.EVMRPCRequestEnvelope,
-) ([]byte, error) {
+) (*QueryResponse, error) {
 	// if request isn't cacheable - there is no point to try to get it from cache so exit early with an error
 	cacheable := IsCacheable(c.ServiceLogger, req)
 	if !cacheable {
@@ -101,25 +112,36 @@ func (c *ServiceCache) GetCachedQueryResponse(
 		return nil, err
 	}
 
-	// get JSON-RPC response's result from the cache
-	result, err := c.cacheClient.Get(ctx, key)
+	// get Query Response from the cache
+	queryResponseInJSON, err := c.cacheClient.Get(ctx, key)
 	if err != nil {
 		return nil, err
 	}
 
+	// Query Response consists of JSON-RPC response's result and headers map.
+	// Unmarshal it and later update JSON-RPC response's result to match JSON-RPC request.
+	var queryResponse QueryResponse
+	if err := json.Unmarshal(queryResponseInJSON, &queryResponse); err != nil {
+		return nil, err
+	}
+
 	// JSON-RPC response's ID and Version should match JSON-RPC request
 	id := strconv.Itoa(int(req.ID))
 	response := JsonRpcResponse{
 		Version: req.JSONRPCVersion,
 		ID:      []byte(id),
-		Result:  result,
+		Result:  queryResponse.JsonRpcResponseResult,
 	}
 	responseInJSON, err := json.Marshal(response)
 	if err != nil {
 		return nil, err
 	}
+	responseInJSON = append(responseInJSON, '\n')
+
+	// update JSON-RPC response's result before returning Query Response
+	queryResponse.JsonRpcResponseResult = responseInJSON
 
-	return responseInJSON, nil
+	return &queryResponse, nil
 }
 
 // CacheQueryResponse calculates cache key for request and then saves response to the cache.
@@ -130,6 +152,7 @@ func (c *ServiceCache) CacheQueryResponse(
 	ctx context.Context,
 	req *decode.EVMRPCRequestEnvelope,
 	responseInBytes []byte,
+	headerMap map[string]string,
 ) error {
 	// don't cache uncacheable requests
 	if !IsCacheable(c.ServiceLogger, req) {
@@ -150,7 +173,17 @@ func (c *ServiceCache) CacheQueryResponse(
 		return err
 	}
 
-	return c.cacheClient.Set(ctx, key, response.Result, c.cacheTTL, c.cacheIndefinitely)
+	// cache JSON-RPC response's result and HTTP Header Map
+	queryResponse := &QueryResponse{
+		JsonRpcResponseResult: response.Result,
+		HeaderMap:             headerMap,
+	}
+	queryResponseInJSON, err := json.Marshal(queryResponse)
+	if err != nil {
+		return err
+	}
+
+	return c.cacheClient.Set(ctx, key, queryResponseInJSON, c.cacheTTL, c.cacheIndefinitely)
 }
 
 func (c *ServiceCache) Healthcheck(ctx context.Context) error {

service/cachemdw/cache_test.go

@@ -82,6 +82,7 @@ func TestUnitTestCacheQueryResponse(t *testing.T) {
 		service.DecodedRequestContextKey,
 		defaultCachePrefixString,
 		true,
+		[]string{},
 		&logger,
 	)
 
@@ -90,12 +91,12 @@ func TestUnitTestCacheQueryResponse(t *testing.T) {
 	require.Equal(t, cache.ErrNotFound, err)
 	require.Empty(t, resp)
 
-	err = serviceCache.CacheQueryResponse(ctxb, req, defaultQueryResp)
+	err = serviceCache.CacheQueryResponse(ctxb, req, defaultQueryResp, map[string]string{})
 	require.NoError(t, err)
 
 	resp, err = serviceCache.GetCachedQueryResponse(ctxb, req)
 	require.NoError(t, err)
-	require.JSONEq(t, string(defaultQueryResp), string(resp))
+	require.JSONEq(t, string(defaultQueryResp), string(resp.JsonRpcResponseResult))
 }
 
 func mkEVMRPCRequestEnvelope(blockNumber string) *decode.EVMRPCRequestEnvelope {

service/cachemdw/caching_middleware.go

@@ -52,10 +52,12 @@ func (c *ServiceCache) CachingMiddleware(
 
 		// if request isn't already cached, request is cacheable and response is present in context - cache the response
 		if !isCached && cacheable && ok {
+			headersToCache := getHeadersToCache(w, c.whitelistedHeaders)
 			if err := c.CacheQueryResponse(
 				r.Context(),
 				decodedReq,
 				typedResponse,
+				headersToCache,
 			); err != nil {
 				c.Logger.Error().Msgf("can't validate and cache response: %v", err)
 			}
@@ -64,3 +66,19 @@ func (c *ServiceCache) CachingMiddleware(
 		next.ServeHTTP(w, r)
 	}
 }
+
+// getHeadersToCache gets header map which has to be cached along with EVM JSON-RPC response
+func getHeadersToCache(w http.ResponseWriter, whitelistedHeaders []string) map[string]string {
+	headersToCache := make(map[string]string, 0)
+
+	for _, headerName := range whitelistedHeaders {
+		headerValue := w.Header().Get(headerName)
+		if headerValue == "" {
+			continue
+		}
+
+		headersToCache[headerName] = headerValue
+	}
+
+	return headersToCache
+}

service/cachemdw/middleware_test.go

@@ -33,6 +33,7 @@ func TestUnitTestServiceCacheMiddleware(t *testing.T) {
 		service.DecodedRequestContextKey,
 		defaultCachePrefixString,
 		true,
+		[]string{},
 		&logger,
 	)
 
@@ -118,6 +119,7 @@ func TestUnitTestServiceCacheMiddleware_CacheIsDisabled(t *testing.T) {
 		service.DecodedRequestContextKey,
 		defaultCachePrefixString,
 		false,
+		[]string{},
 		&logger,
 	)
 

service/middleware.go

@@ -236,7 +236,7 @@ func createProxyRequestMiddleware(next http.Handler, config config.Config, servi
 
 			isCached := cachemdw.IsRequestCached(r.Context())
 			cachedResponse := r.Context().Value(cachemdw.ResponseContextKey)
-			typedCachedResponse, ok := cachedResponse.([]byte)
+			typedCachedResponse, ok := cachedResponse.(*cachemdw.QueryResponse)
 
 			// if cache is enabled, request is cached and response is present in context - serve the request from the cache
 			// otherwise proxy to the actual backend
@@ -250,7 +250,11 @@ func createProxyRequestMiddleware(next http.Handler, config config.Config, servi
 
 				w.Header().Add(cachemdw.CacheHeaderKey, cachemdw.CacheHitHeaderValue)
 				w.Header().Add("Content-Type", "application/json")
-				_, err := w.Write(typedCachedResponse)
+				// add cached headers
+				for headerName, headerValue := range typedCachedResponse.HeaderMap {
+					w.Header().Add(headerName, headerValue)
+				}
+				_, err := w.Write(typedCachedResponse.JsonRpcResponseResult)
 				if err != nil {
 					serviceLogger.Logger.Error().Msg(fmt.Sprintf("can't write cached response: %v", err))
 				}

service/service.go

@@ -215,6 +215,7 @@ func createServiceCache(
 		DecodedRequestContextKey,
 		config.CachePrefix,
 		config.CacheEnabled,
+		config.WhitelistedHeaders,
 		logger,
 	)