fix(httpcache): raw files return 304 after a change when the new commit is older (#39435)

modules/httpcache/httpcache.go

@@ -99,7 +99,9 @@ func handleGenericETagTimeCache(req *http.Request, w http.ResponseWriter, etag s
 			return true
 		}
 	}
-	if lastModified != nil && !lastModified.IsZero() {
+	// https://www.rfc-editor.org/rfc/rfc9110#section-13.1.3
+	// A recipient MUST ignore If-Modified-Since if the request contains an If-None-Match header field
+	if lastModified != nil && !lastModified.IsZero() && req.Header.Get("If-None-Match") == "" {
 		ifModifiedSince := req.Header.Get("If-Modified-Since")
 		if ifModifiedSince != "" {
 			t, err := time.Parse(http.TimeFormat, ifModifiedSince)

modules/httpcache/httpcache_test.go

@@ -76,6 +76,19 @@ func TestHandleGenericETagCache(t *testing.T) {
 			wantHeaders: map[string]string{"Last-Modified": lastModified, "Cache-Control": "", "Etag": weakEtag},
 			wantStatus:  http.StatusNotModified,
 		},
+		{
+			name:        "If-Modified-Since without If-None-Match",
+			reqHeaders:  map[string]string{"If-Modified-Since": lastModified},
+			wantHandled: true,
+			wantHeaders: map[string]string{"Last-Modified": lastModified, "Cache-Control": "", "Etag": matchedEtag},
+			wantStatus:  http.StatusNotModified,
+		},
+		{
+			name:        "Mismatched If-None-Match takes precedence over If-Modified-Since",
+			reqHeaders:  map[string]string{"If-None-Match": `"mismatched-etag"`, "If-Modified-Since": lastModified},
+			wantHandled: false,
+			wantHeaders: map[string]string{"Last-Modified": lastModified, "Cache-Control": cacheControl, "Etag": matchedEtag},
+		},
 		{
 			name:        "Multiple Matched If-None-Match",
 			reqHeaders:  map[string]string{"If-None-Match": `"mismatched-etag", ` + matchedEtag},