Set X-Cache and X-Cache-Lookup headers for cache (#8794)

X-Cache sets cache status of HIT if object is
served from the disk cache, or MISS otherwise.
X-Cache-Lookup is set to HIT if object was found
in the cache even if not served (for e.g. if cache
 entry was invalidated by ETag verification)

cmd/api-headers.go

@@ -91,7 +91,10 @@ func setObjectHeaders(w http.ResponseWriter, objInfo ObjectInfo, rs *HTTPRangeSp
 	if !objInfo.Expires.IsZero() {
 		w.Header().Set(xhttp.Expires, objInfo.Expires.UTC().Format(http.TimeFormat))
 	}
-
+	if globalCacheConfig.Enabled {
+		w.Header().Set(xhttp.XCache, objInfo.CacheStatus.String())
+		w.Header().Set(xhttp.XCacheLookup, objInfo.CacheLookupStatus.String())
+	}
 	// Set all other user defined metadata.
 	for k, v := range objInfo.UserDefined {
 		if HasPrefix(k, ReservedMetadataPrefix) {