Added experimental HIGHESTMODSEQ support

app/src/main/java/eu/faircode/email/Core.java

@@ -2460,6 +2460,7 @@ class Core {
             boolean sync_flagged = prefs.getBoolean("sync_flagged", false);
             boolean sync_kept = prefs.getBoolean("sync_kept", true);
             boolean delete_unseen = prefs.getBoolean("delete_unseen", false);
+            boolean use_modseq = prefs.getBoolean("use_modseq", BuildConfig.DEBUG);
             boolean perform_expunge = prefs.getBoolean("perform_expunge", true);
 
             Log.i(folder.name + " start sync after=" + sync_days + "/" + keep_days +
@@ -2482,6 +2483,23 @@ class Core {
                 Log.w(folder.name, ex);
             }
 
+            // https://tools.ietf.org/html/rfc4551
+            // https://wiki.mozilla.org/Thunderbird:IMAP_RFC_4551_Implementation
+            boolean modified = true;
+            try {
+                if (use_modseq &&
+                        !force && initialize == 0 &&
+                        MessageHelper.hasCapability(ifolder, "CONDSTORE")) {
+                    long modseq = ifolder.getHighestModSeq();
+                    Log.i(folder.name + " modseq=" + modseq + "/" + folder.modseq);
+                    modified = (folder.modseq == null || !folder.modseq.equals(modseq));
+                    folder.modseq = modseq;
+                    db.folder().setFolderModSeq(folder.id, folder.modseq);
+                }
+            } catch (MessagingException ex) {
+                Log.w(folder.name, ex);
+            }
+
             // Get reference times
             Calendar cal_sync = Calendar.getInstance();
             cal_sync.add(Calendar.DAY_OF_MONTH, -sync_days);
@@ -2562,7 +2580,47 @@ class Core {
             stats.search_ms = (SystemClock.elapsedRealtime() - search);
             Log.i(folder.name + " remote count=" + imessages.length + " search=" + stats.search_ms + " ms");
 
+            Long[] ids = new Long[imessages.length];
+            if (!modified) {
+                Log.i(folder.name + " quick check");
+                long fetch = SystemClock.elapsedRealtime();
+
+                FetchProfile fp = new FetchProfile();
+                fp.add(UIDFolder.FetchProfileItem.UID);
+                ifolder.fetch(imessages, fp);
+
+                stats.flags = imessages.length;
+                stats.flags_ms = (SystemClock.elapsedRealtime() - fetch);
+                Log.i(folder.name + " remote fetched=" + stats.flags_ms + " ms");
+
+                try {
+                    for (int i = 0; i < imessages.length && state.isRunning() && state.isRecoverable(); i++) {
+                        long uid = ifolder.getUID(imessages[i]);
+                        ids[i] = db.message().getMessageMsgIdByUid(folder.id, uid);
+                        if (ids[i] == null) {
+                            Log.i(folder.name + " missing uid=" + uid);
+                            modified = true;
+                            break;
+                        } else
+                            uids.remove(uid);
+                    }
+                } catch (Throwable ex) {
+                    Log.w(ex);
+                    modified = true;
+                    db.folder().setFolderModSeq(folder.id, null);
+                }
+
+                if (uids.size() > 0) {
+                    Log.i(folder.name + " remaining=" + uids.size());
+                    modified = true;
+                }
+
+                EntityLog.log(context, folder.name + " modified=" + modified);
+            }
+
+            if (modified) {
                 long fetch = SystemClock.elapsedRealtime();
+
                 FetchProfile fp = new FetchProfile();
                 fp.add(UIDFolder.FetchProfileItem.UID); // To check if message exists
                 fp.add(FetchProfile.Item.FLAGS); // To update existing messages
@@ -2756,7 +2814,6 @@ class Core {
 
                 // Add/update local messages
                 int synced = 0;
-            Long[] ids = new Long[imessages.length];
                 Log.i(folder.name + " add=" + imessages.length);
                 for (int i = imessages.length - 1; i >= 0 && state.isRunning() && state.isRecoverable(); i -= SYNC_BATCH_SIZE) {
                     int from = Math.max(0, i - SYNC_BATCH_SIZE + 1);
@@ -2841,6 +2898,7 @@ class Core {
                             ((IMAPMessage) isub[j]).invalidateHeaders();
                         }
                 }
+            }
 
             // Delete not synchronized messages without uid
             if (!EntityFolder.isOutgoing(folder.type)) {

app/src/main/java/eu/faircode/email/DaoMessage.java

@@ -296,6 +296,12 @@ public interface DaoMessage {
             " AND uid = :uid")
     EntityMessage getMessageByUid(long folder, long uid);
 
+    @Query("SELECT id" +
+            " FROM message" +
+            " WHERE folder = :folder" +
+            " AND uid = :uid")
+    Long getMessageMsgIdByUid(long folder, long uid);
+
     @Query("SELECT id" +
             " FROM message" +
             " WHERE folder = :folder" +

app/src/main/java/eu/faircode/email/FragmentOptionsMisc.java

@@ -112,6 +112,7 @@ public class FragmentOptionsMisc extends FragmentBase implements SharedPreferenc
     private SwitchCompat swDebug;
     private SwitchCompat swQueries;
     private SwitchCompat swWal;
+    private SwitchCompat swModSeq;
     private SwitchCompat swExpunge;
     private SwitchCompat swAuthPlain;
     private SwitchCompat swAuthLogin;
@@ -139,7 +140,9 @@ public class FragmentOptionsMisc extends FragmentBase implements SharedPreferenc
             "classification", "class_min_probability", "class_min_difference",
             "language", "watchdog", "updates",
             "experiments", "wal", "query_threads", "crash_reports", "cleanup_attachments",
-            "protocol", "debug", "log_level", "perform_expunge", "auth_plain", "auth_login", "auth_ntlm", "auth_sasl"
+            "protocol", "debug", "log_level",
+            "use_modseq", "perform_expunge",
+            "auth_plain", "auth_login", "auth_ntlm", "auth_sasl"
     };
 
     private final static String[] RESET_QUESTIONS = new String[]{
@@ -213,6 +216,7 @@ public class FragmentOptionsMisc extends FragmentBase implements SharedPreferenc
         swDebug = view.findViewById(R.id.swDebug);
         swQueries = view.findViewById(R.id.swQueries);
         swWal = view.findViewById(R.id.swWal);
+        swModSeq = view.findViewById(R.id.swModSeq);
         swExpunge = view.findViewById(R.id.swExpunge);
         swAuthPlain = view.findViewById(R.id.swAuthPlain);
         swAuthLogin = view.findViewById(R.id.swAuthLogin);
@@ -529,11 +533,19 @@ public class FragmentOptionsMisc extends FragmentBase implements SharedPreferenc
             }
         });
 
+        swModSeq.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
+            @Override
+            public void onCheckedChanged(CompoundButton compoundButton, boolean checked) {
+                prefs.edit().putBoolean("use_modseq", checked).apply();
+                ServiceSynchronize.reload(compoundButton.getContext(), null, true, "use_modseq");
+            }
+        });
+
         swExpunge.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
             @Override
             public void onCheckedChanged(CompoundButton compoundButton, boolean checked) {
                 prefs.edit().putBoolean("perform_expunge", checked).apply();
-                ServiceSynchronize.reload(getContext(), null, true, "perform_expunge");
+                ServiceSynchronize.reload(compoundButton.getContext(), null, true, "perform_expunge");
             }
         });
 
@@ -918,6 +930,7 @@ public class FragmentOptionsMisc extends FragmentBase implements SharedPreferenc
         swDebug.setChecked(prefs.getBoolean("debug", false));
         swQueries.setChecked(prefs.getInt("query_threads", 4) < 4);
         swWal.setChecked(prefs.getBoolean("wal", true));
+        swModSeq.setChecked(prefs.getBoolean("use_modseq", BuildConfig.DEBUG));
         swExpunge.setChecked(prefs.getBoolean("perform_expunge", true));
         swAuthPlain.setChecked(prefs.getBoolean("auth_plain", true));
         swAuthLogin.setChecked(prefs.getBoolean("auth_login", true));

app/src/main/res/layout/fragment_options_misc.xml

@@ -529,6 +529,18 @@
             app:layout_constraintTop_toBottomOf="@id/tvQueriesRemark"
             app:switchPadding="12dp" />
 
+        <androidx.appcompat.widget.SwitchCompat
+            android:id="@+id/swModSeq"
+            android:layout_width="0dp"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="12dp"
+            android:checked="true"
+            android:text="@string/title_advanced_modseq"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toBottomOf="@id/swWal"
+            app:switchPadding="12dp" />
+
         <androidx.appcompat.widget.SwitchCompat
             android:id="@+id/swExpunge"
             android:layout_width="0dp"
@@ -538,7 +550,7 @@
             android:text="@string/title_advanced_expunge"
             app:layout_constraintEnd_toEndOf="parent"
             app:layout_constraintStart_toStartOf="parent"
-            app:layout_constraintTop_toBottomOf="@id/swWal"
+            app:layout_constraintTop_toBottomOf="@id/swModSeq"
             app:switchPadding="12dp" />
 
         <androidx.appcompat.widget.SwitchCompat
@@ -694,7 +706,7 @@
             android:layout_height="0dp"
             app:constraint_referenced_ids="
             swQueries,tvQueriesHint,tvQueriesRemark,swWal,
-            swExpunge,
+            swModSeq,swExpunge,
             swAuthPlain,swAuthLogin,swAuthNtlm,swAuthSasl,
             tvProcessors,tvMemoryClass,tvMemoryUsage,tvStorageUsage,
             tvFingerprint,

app/src/main/res/values/strings.xml

@@ -536,6 +536,7 @@
     <string name="title_advanced_language">Language</string>
     <string name="title_advanced_language_system">System</string>
     <string name="title_advanced_watchdog">Periodically check if FairEmail is still active</string>
+    <string name="title_advanced_modseq" translatable="false">MODSEQ (debug only)</string>
     <string name="title_advanced_expunge" translatable="false">EXPUNGE (debug only)</string>
     <string name="title_advanced_auth_plain" translatable="false">PLAIN (debug only)</string>
     <string name="title_advanced_auth_login" translatable="false">LOGIN (debug only)</string>