ZP-832 Check for availability in GlobalWindowSize first before comparing

folder stats, do folderstats comparing only if there is space in
GlobalWindowSize, do not ommit output if folder has no stat.

Released under the Affero GNU General Public License (AGPL) version 3.

src/lib/request/sync.php

@@ -701,8 +701,14 @@ class Sync extends RequestProcessor {
             // TODO we could check against $sc->GetChangedFolderIds() on heartbeat so we do not need to configure all exporter again
             if($status == SYNC_STATUS_SUCCESS && ($sc->GetParameter($spa, "getchanges") || ! $spa->HasSyncKey())) {
 
+                // no need to run the exporter if the globalwindowsize is already full
+                if ($sc->GetGlobalWindowSize() - $this->globallyExportedItems == 0) {
+                    ZLog::Write(LOGLEVEL_DEBUG, sprintf("Sync(): no exporter setup for '%s' as GlobalWindowSize is full.", $spa->GetFolderId()));
+                    $setupExporter = false;
+                }
+
                 // compare the folder statistics if the backend supports this
-                if (self::$backend->HasFolderStats()) {
+                if ($setupExporter && self::$backend->HasFolderStats() && $spa->HasFolderStat()) {
                     // check if the folder stats changed -> if not, don't setup the exporter, there are no changes!
                     $newFolderStat = self::$backend->GetFolderStat(ZPush::GetAdditionalSyncFolderStore($spa->GetFolderId()), $spa->GetFolderId());
                     if ($newFolderStat === $spa->GetFolderStat()) {
@@ -712,12 +718,6 @@ class Sync extends RequestProcessor {
                     }
                 }
 
-                // no need to run the exporter if the globalwindowsize is already full
-                if ($sc->GetGlobalWindowSize() - $this->globallyExportedItems == 0) {
-                    ZLog::Write(LOGLEVEL_DEBUG, "Sync(): no exporter setup as GlobalWindowSize is full.");
-                    $setupExporter = false;
-                }
-
                 // Do a full Exporter setup if we can't avoid it
                 if ($setupExporter) {
                     //make sure the states are loaded
@@ -795,7 +795,8 @@ class Sync extends RequestProcessor {
             }
 
             // Fir AS 14.0+ omit output for folder, if there were no incoming or outgoing changes and no Fetch
-            if (Request::GetProtocolVersion() >= 14.0 && ! $spa->HasNewSyncKey() && $changecount == 0 && empty($actiondata["fetchids"]) && $status == SYNC_STATUS_SUCCESS && $spa->GetFolderStat() === $newFolderStat) {
+            if (Request::GetProtocolVersion() >= 14.0 && ! $spa->HasNewSyncKey() && $changecount == 0 && empty($actiondata["fetchids"]) && $status == SYNC_STATUS_SUCCESS &&
+                    $spa->HasFolderStat() && $spa->GetFolderStat() === $newFolderStat) {
                 ZLog::Write(LOGLEVEL_DEBUG, sprintf("HandleSync: No changes found for %s folder id '%s'. Omitting output.", $spa->GetContentClass(), $spa->GetFolderId()));
                 continue;
             }