Improve get-cached-response method (#52)

service/cachemdw/cache.go

@@ -90,6 +90,12 @@ func (c *ServiceCache) GetCachedQueryResponse(
 	ctx context.Context,
 	req *decode.EVMRPCRequestEnvelope,
 ) ([]byte, 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 {
+		return nil, ErrRequestIsNotCacheable
+	}
+
 	key, err := GetQueryKey(c.cachePrefix, req)
 	if err != nil {
 		return nil, err

service/cachemdw/errors.go

@@ -0,0 +1,5 @@
+package cachemdw
+
+import "errors"
+
+var ErrRequestIsNotCacheable = errors.New("request is not cacheable")

service/cachemdw/is_cached_middleware.go

@@ -61,7 +61,7 @@ func (c *ServiceCache) IsCachedMiddleware(
 		// 1. if not cached or we encounter an error then mark as uncached and forward to next middleware
 		// 2. if cached then mark as cached, set cached response in context and forward to next middleware
 		cachedQueryResponse, err := c.GetCachedQueryResponse(r.Context(), decodedReq)
-		if err != nil && err != cache.ErrNotFound {
+		if err != nil && err != cache.ErrNotFound && err != ErrRequestIsNotCacheable {
 			// log unexpected error
 			c.Logger.Error().
 				Err(err).