CLDR-17515 Improve the announcements protocol (#3615)

tools/cldr-apps/js/src/esm/cldrAnnounce.mjs

@@ -28,7 +28,15 @@ let callbackSetData = null;
 let callbackSetCounts = null;
 let callbackSetUnread = null;
 
-let alreadyGotId = 0;
+const MOST_RECENT_ID_UNKNOWN = -1; // must be less than zero
+
+/**
+ * The most recent announcement ID the back end has told us about
+ *
+ * MOST_RECENT_ID_UNKNOWN means the front end hasn't received a response yet;
+ * 0 means the response from the back end indicated no announcements exist yet
+ */
+let alreadyGotId = MOST_RECENT_ID_UNKNOWN;
 
 /**
  * Get the number of unread announcements, to display in the main menu
@@ -70,11 +78,7 @@ async function refresh(viewCallbackSetData, viewCallbackSetCounts) {
   if (schedule.tooSoon()) {
     return;
   }
-  let p = null;
-  if (alreadyGotId) {
-    p = new URLSearchParams();
-    p.append("alreadyGotId", alreadyGotId);
-  }
+  const p = new URLSearchParams().append("alreadyGotId", alreadyGotId);
   const url = cldrAjax.makeApiUrl("announce", p);
   schedule.setRequestTime();
   return await cldrAjax
@@ -90,8 +94,8 @@ function setPosts(json) {
   if (json.unchanged) {
     return;
   }
+  alreadyGotId = json.mostRecentId;
   thePosts = json;
-  setAlreadyGotId(thePosts);
   const totalCount = thePosts.announcements?.length || 0;
   let checkedCount = 0;
   for (let announcement of thePosts.announcements) {
@@ -112,14 +116,6 @@ function setPosts(json) {
   return thePosts;
 }
 
-function setAlreadyGotId(thePosts) {
-  for (let announcement of thePosts.announcements) {
-    if (announcement.id > alreadyGotId) {
-      alreadyGotId = announcement.id;
-    }
-  }
-}
-
 function canAnnounce() {
   return cldrStatus.getPermissions()?.userIsManager || false;
 }
@@ -178,7 +174,7 @@ async function combineAndValidateLocales(locs, validateLocCallback) {
 }
 
 function resetSchedule() {
-  alreadyGotId = 0;
+  alreadyGotId = MOST_RECENT_ID_UNKNOWN;
   schedule.reset();
 }
 

tools/cldr-apps/src/main/java/org/unicode/cldr/web/api/Announcements.java

@@ -63,7 +63,7 @@ public Response getAnnouncements(
             @HeaderParam(Auth.SESSION_HEADER) String sessionString,
             @QueryParam("alreadyGotId")
                     @Schema(description = "The client already got this announcement ID")
-                    @DefaultValue("0")
+                    @DefaultValue("-1")
                     int alreadyGotId) {
         CookieSession session = Auth.getSession(sessionString);
         if (session == null) {
@@ -76,25 +76,39 @@ public Response getAnnouncements(
         if (SurveyMain.isBusted() || !SurveyMain.wasInitCalled() || !SurveyMain.triedToStartUp()) {
             return STError.surveyNotQuiteReady();
         }
-        Boolean unchanged =
-                (alreadyGotId != 0
-                        && alreadyGotId == AnnouncementData.getMostRecentAnnouncementId());
-        AnnouncementResponse response = new AnnouncementResponse(session.user, unchanged);
+        final int mostRecentId = AnnouncementData.getMostRecentAnnouncementId();
+        final Boolean unchanged = alreadyGotId != -1 && alreadyGotId == mostRecentId;
+        final AnnouncementResponse response =
+                new AnnouncementResponse(session.user, unchanged, mostRecentId);
         return Response.ok(response).build();
     }
 
     @Schema(description = "List of announcements")
     public static final class AnnouncementResponse {
-        @Schema(description = "unchanged")
+        @Schema(description = "unchanged (true if request specified ID matching most recent ID)")
         public boolean unchanged;
 
+        /**
+         * This ID is for the most recent announcement ID even if that announcement is filtered out,
+         * for example to exclude locales that are not of interest to the user who made the request.
+         * (The timestamp of the most recent announcement could just as well be used.) This way, the
+         * client will not endlessly keep getting redundant filtered data when there are no new
+         * announcements. The client may get redundant filtered data when a new announcement is made
+         * that doesn't pass the user's filter, but this will not happen more than once per new
+         * announcement. Further optimization would seem to require the back end to keep track of
+         * the most recent announcement ID for each filter, or else to repeat the database query for
+         * each request even if the result would be unchanged -- with dubious benefits.
+         */
+        @Schema(description = "most recent announcement ID (even if filtered out)")
+        public int mostRecentId;
+
         @Schema(description = "announcements")
         public Announcement[] announcements;
 
-        public AnnouncementResponse(UserRegistry.User user, Boolean unchanged) {
+        public AnnouncementResponse(UserRegistry.User user, Boolean unchanged, int mostRecentId) {
             this.unchanged = unchanged;
-
             if (!unchanged) {
+                this.mostRecentId = mostRecentId;
                 List<Announcement> announcementList = new ArrayList<>();
                 AnnouncementData.get(user, announcementList);
                 announcements = announcementList.toArray(new Announcement[0]);