feat(BRIDGE-37): Remote notification support

go.mod

@@ -9,7 +9,7 @@ require (
 	github.com/Masterminds/semver/v3 v3.2.0
 	github.com/ProtonMail/gluon v0.17.1-0.20240514133734-79cdd0fec41c
 	github.com/ProtonMail/go-autostart v0.0.0-20210130080809-00ed301c8e9a
-	github.com/ProtonMail/go-proton-api v0.4.1-0.20240827122236-ca6bb6449bba
+	github.com/ProtonMail/go-proton-api v0.4.1-0.20240829112804-d663a2ef90c2
 	github.com/ProtonMail/gopenpgp/v2 v2.7.4-proton
 	github.com/PuerkitoBio/goquery v1.8.1
 	github.com/abiosoft/ishell v2.0.0+incompatible

go.sum

@@ -52,6 +52,10 @@ github.com/ProtonMail/go-proton-api v0.4.1-0.20240827084449-71096377c391 h1:PW6b
 github.com/ProtonMail/go-proton-api v0.4.1-0.20240827084449-71096377c391/go.mod h1:3A0cpdo0BIenIPjTG6u8EbzJ8uuJy7rVvM/NaynjCKA=
 github.com/ProtonMail/go-proton-api v0.4.1-0.20240827122236-ca6bb6449bba h1:QtDxgIbgPqRQg7VT+nIUJlaOyNFAoGyg59oW3Hji/0A=
 github.com/ProtonMail/go-proton-api v0.4.1-0.20240827122236-ca6bb6449bba/go.mod h1:3A0cpdo0BIenIPjTG6u8EbzJ8uuJy7rVvM/NaynjCKA=
+github.com/ProtonMail/go-proton-api v0.4.1-0.20240827132526-849231fc34a1 h1:gATlMoj4raG32WyGGh8SpipoQeR2AlU7g+8NAMicTcw=
+github.com/ProtonMail/go-proton-api v0.4.1-0.20240827132526-849231fc34a1/go.mod h1:3A0cpdo0BIenIPjTG6u8EbzJ8uuJy7rVvM/NaynjCKA=
+github.com/ProtonMail/go-proton-api v0.4.1-0.20240829112804-d663a2ef90c2 h1:yx0iejqB5c21HIN5jn9IsbyzUns0dPUUaGfyUHF3TmQ=
+github.com/ProtonMail/go-proton-api v0.4.1-0.20240829112804-d663a2ef90c2/go.mod h1:3A0cpdo0BIenIPjTG6u8EbzJ8uuJy7rVvM/NaynjCKA=
 github.com/ProtonMail/go-smtp v0.0.0-20231109081432-2b3d50599865 h1:EP1gnxLL5Z7xBSymE9nSTM27nRYINuvssAtDmG0suD8=
 github.com/ProtonMail/go-smtp v0.0.0-20231109081432-2b3d50599865/go.mod h1:qm27SGYgoIPRot6ubfQ/GpiPy/g3PaZAVRxiO/sDUgQ=
 github.com/ProtonMail/go-srp v0.0.7 h1:Sos3Qk+th4tQR64vsxGIxYpN3rdnG9Wf9K4ZloC1JrI=

internal/bridge/bridge.go

@@ -45,6 +45,7 @@ import (
 	"github.com/ProtonMail/proton-bridge/v3/internal/safe"
 	"github.com/ProtonMail/proton-bridge/v3/internal/sentry"
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/imapsmtpserver"
+	"github.com/ProtonMail/proton-bridge/v3/internal/services/notifications"
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/observability"
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/syncservice"
 	"github.com/ProtonMail/proton-bridge/v3/internal/telemetry"
@@ -144,6 +145,9 @@ type Bridge struct {
 
 	// observabilityService is responsible for handling calls to the observability system
 	observabilityService *observability.Service
+
+	// notificationStore is used for notification deduplication
+	notificationStore *notifications.Store
 }
 
 var logPkg = logrus.WithField("pkg", "bridge") //nolint:gochecknoglobals
@@ -307,6 +311,8 @@ func newBridge(
 		unleashService: unleashService,
 
 		observabilityService: observability.NewService(ctx, panicHandler),
+
+		notificationStore: notifications.NewStore(locator.ProvideNotificationsCachePath),
 	}
 
 	bridge.serverManager = imapsmtpserver.NewService(context.Background(),

internal/bridge/types.go

@@ -34,6 +34,7 @@ type Locator interface {
 	Clear(...string) error
 	ProvideIMAPSyncConfigPath() (string, error)
 	ProvideUnleashCachePath() (string, error)
+	ProvideNotificationsCachePath() (string, error)
 }
 
 type ProxyController interface {

internal/bridge/user.go

@@ -569,6 +569,9 @@ func (bridge *Bridge) addUserWithVault(
 		bridge.observabilityService,
 		syncSettingsPath,
 		isNew,
+		bridge.notificationStore,
+		bridge.unleashService.GetFlagValue,
+		bridge.observabilityService.AddMetric,
 	)
 	if err != nil {
 		return fmt.Errorf("failed to create user: %w", err)

internal/events/user.go

@@ -212,3 +212,16 @@ type UserLoadedCheckResync struct {
 func (event UserLoadedCheckResync) String() string {
 	return fmt.Sprintf("UserLoadedCheckResync: UserID: %s", event.UserID)
 }
+
+type UserNotification struct {
+	eventBase
+
+	UserID   string
+	Title    string
+	Subtitle string
+	Body     string
+}
+
+func (event UserNotification) String() string {
+	return fmt.Sprintf("UserNotification: UserID: %s, Title: %s, Subtitle: %s, Body: %s", event.UserID, event.Title, event.Subtitle, event.Body)
+}

internal/frontend/bridge-gui/bridge-gui-tester/Tabs/UsersTab.cpp

@@ -57,6 +57,7 @@ UsersTab::UsersTab(QWidget *parent)
     connect(ui_.checkUsernamePasswordError, &QCheckBox::toggled, this, &UsersTab::updateGUIState);
     connect(ui_.checkSync, &QCheckBox::toggled, this, &UsersTab::onCheckSyncToggled);
     connect(ui_.sliderSync, &QSlider::valueChanged, this, &UsersTab::onSliderSyncValueChanged);
+    connect(ui_.sendNotificationButton, &QPushButton::clicked, this, &UsersTab::onSendUserNotification);
 
     users_.append(defaultUser());
 
@@ -216,6 +217,7 @@ void UsersTab::updateGUIState() {
     ui_.editUsernamePasswordError->setEnabled(ui_.checkUsernamePasswordError->isChecked());
     ui_.spinUsedBytes->setValue(user ? user->usedBytes() : 0.0);
     ui_.groupboxSync->setEnabled(user.get());
+    ui_.groupBoxNotification->setEnabled(hasSelectedUser && (UserState::Connected == state));
 
     if (user)
         ui_.editIMAPLoginFailedUsername->setText(user->primaryEmailOrUsername());
@@ -489,3 +491,41 @@ void UsersTab::onSliderSyncValueChanged(int value) {
     app().grpc().sendEvent(newSyncProgressEvent(user->id(), progress, 1, 1));  // we do not simulate elapsed & remaining.
     this->updateGUIState();
 }
+
+//****************************************************************************************************************************************************
+/// \return the title for the notification.
+//****************************************************************************************************************************************************
+QString UsersTab::notificationTitle() const {
+    return ui_.notificationTitle->text();
+}
+
+//****************************************************************************************************************************************************
+/// \return the subtitle for the notification.
+//****************************************************************************************************************************************************
+QString UsersTab::notificationSubtitle() const {
+    return ui_.notificationSubtitleText->text();
+}
+
+//****************************************************************************************************************************************************
+/// \return the body for the notification.
+//****************************************************************************************************************************************************
+QString UsersTab::notificationBody() const {
+    return ui_.notticationBodyText->text();
+}
+
+
+void UsersTab::onSendUserNotification() {
+    SPUser const user = selectedUser();
+    if (!user) {
+        app().log().error(QString("%1 failed. Unkown user.").arg(__FUNCTION__));
+        return;
+    }
+
+    GRPCService &grpc = app().grpc();
+
+    if (grpc.isStreaming()) {
+        QString const userID = user->id();
+        grpc.sendEvent(newUserNotificationEvent(userID, notificationTitle(), notificationSubtitle(), notificationBody()));
+    }
+}
+

internal/frontend/bridge-gui/bridge-gui-tester/Tabs/UsersTab.h

@@ -23,7 +23,6 @@
 #include "Tabs/ui_UsersTab.h"
 #include "UserTable.h"
 
-
 //****************************************************************************************************************************************************
 /// \brief The 'Users' tab of the main window.
 //****************************************************************************************************************************************************
@@ -50,6 +49,9 @@ public: // member functions.
     bool nextUserTwoPasswordsError() const; ///< Check if next user login should trigger 2nd password error.
     bool nextUserTwoPasswordsAbort() const; ///< Check if next user login should trigger 2nd password abort.
     QString usernamePasswordErrorMessage() const; ///< Return the username password error message.
+    QString notificationTitle() const; ///< Return the user notification title.
+    QString notificationSubtitle() const; ///< Return the user notification subtitle.
+    QString notificationBody() const; ///< Return the user notification body.
 
 public slots:
     void setUserSplitMode(QString const &userID, bool makeItActive); ///< Slot for the split mode.
@@ -69,6 +71,7 @@ private slots:
     void onCheckSyncToggled(bool checked); ///< Slot for the 'Synchronizing' check box.
     void onSliderSyncValueChanged(int value); ///< Slot for the sync 'Progress' slider.
     void updateGUIState(); ///< Update the GUI state.
+    void onSendUserNotification(); ///< Send a user notification event to the GUI.
 
 private: // member functions.
     qint32 selectedIndex() const; ///< Get the index of the selected row.

internal/frontend/bridge-gui/bridge-gui-tester/Tabs/UsersTab.ui

@@ -7,13 +7,19 @@
     <x>0</x>
     <y>0</y>
     <width>1221</width>
-    <height>894</height>
+    <height>408</height>
    </rect>
   </property>
+  <property name="sizePolicy">
+   <sizepolicy hsizetype="Minimum" vsizetype="Minimum">
+    <horstretch>0</horstretch>
+    <verstretch>0</verstretch>
+   </sizepolicy>
+  </property>
   <property name="windowTitle">
    <string>Form</string>
   </property>
-  <layout class="QHBoxLayout" name="horizontalLayout" stretch="1,0">
+  <layout class="QHBoxLayout" name="horizontalLayout" stretch="0,0">
    <item>
     <widget class="QTableView" name="tableUserList">
      <property name="selectionMode">
@@ -30,6 +36,27 @@
      </attribute>
     </widget>
    </item>
+   <item>
+    <widget class="QScrollArea" name="scrollArea">
+     <property name="sizePolicy">
+      <sizepolicy hsizetype="Minimum" vsizetype="Minimum">
+       <horstretch>0</horstretch>
+       <verstretch>0</verstretch>
+      </sizepolicy>
+     </property>
+     <property name="widgetResizable">
+      <bool>true</bool>
+     </property>
+     <widget class="QWidget" name="scrollAreaWidgetContents">
+      <property name="geometry">
+       <rect>
+        <x>0</x>
+        <y>0</y>
+        <width>327</width>
+        <height>905</height>
+       </rect>
+      </property>
+      <layout class="QHBoxLayout" name="horizontalLayout_6">
        <item>
         <layout class="QVBoxLayout" name="verticalLayout">
          <item>
@@ -66,6 +93,68 @@
            </property>
           </spacer>
          </item>
+         <item>
+          <widget class="QGroupBox" name="groupBoxNotification">
+           <property name="enabled">
+            <bool>true</bool>
+           </property>
+           <property name="minimumSize">
+            <size>
+             <width>300</width>
+             <height>0</height>
+            </size>
+           </property>
+           <property name="maximumSize">
+            <size>
+             <width>300</width>
+             <height>400</height>
+            </size>
+           </property>
+           <property name="title">
+            <string>Notification</string>
+           </property>
+           <layout class="QVBoxLayout" name="verticalLayout_9">
+            <item>
+             <layout class="QVBoxLayout" name="verticalLayout_6" stretch="0,0,0,0">
+              <item>
+               <widget class="QLineEdit" name="notificationTitle">
+                <property name="placeholderText">
+                 <string>Title</string>
+                </property>
+               </widget>
+              </item>
+              <item>
+               <widget class="QLineEdit" name="notificationSubtitleText">
+                <property name="minimumSize">
+                 <size>
+                  <width>0</width>
+                  <height>0</height>
+                 </size>
+                </property>
+                <property name="placeholderText">
+                 <string>Subtitle</string>
+                </property>
+               </widget>
+              </item>
+              <item>
+               <widget class="QLineEdit" name="notticationBodyText">
+                <property name="placeholderText">
+                 <string>Body</string>
+                </property>
+               </widget>
+              </item>
+              <item>
+               <widget class="QPushButton" name="sendNotificationButton">
+                <property name="text">
+                 <string>Send</string>
+                </property>
+               </widget>
+              </item>
+             </layout>
+            </item>
+           </layout>
+          </widget>
+         </item>
          <item>
           <widget class="QGroupBox" name="groupboxSync">
            <property name="minimumSize">
@@ -240,7 +329,7 @@
            <property name="minimumSize">
             <size>
              <width>0</width>
-         <height>100</height>
+             <height>250</height>
             </size>
            </property>
            <property name="title">
@@ -360,6 +449,10 @@
        </item>
       </layout>
      </widget>
+    </widget>
+   </item>
+  </layout>
+ </widget>
  <tabstops>
   <tabstop>buttonNewUser</tabstop>
   <tabstop>buttonEditUser</tabstop>

internal/frontend/bridge-gui/bridge-gui/QMLBackend.cpp

@@ -1330,6 +1330,7 @@ void QMLBackend::connectGrpcEvents() {
     connect(client, &GRPCClient::knowledgeBasSuggestionsReceived, this, &QMLBackend::receivedKnowledgeBaseSuggestions);
     connect(client, &GRPCClient::repairStarted, this, &QMLBackend::repairStarted);
     connect(client, &GRPCClient::allUsersLoaded, this, &QMLBackend::allUsersLoaded);
+    connect(client, &GRPCClient::userNotificationReceived, this, &QMLBackend::processUserNotification);
 
     // cache events
     connect(client, &GRPCClient::cantMoveDiskCache, this, &QMLBackend::cantMoveDiskCache);
@@ -1418,3 +1419,25 @@ void QMLBackend::triggerRepair() const {
             app().grpc().triggerRepair();
     )
 }
+
+//****************************************************************************************************************************************************
+/// \param[in] notification The user notification received from the event loop.
+//****************************************************************************************************************************************************
+void QMLBackend::processUserNotification(bridgepp::UserNotification const& notification) {
+    this->userNotificationStack_.push(notification);
+    trayIcon_->showUserNotification(notification.title, notification.subtitle);
+    emit receivedUserNotification(notification);
+}
+
+void QMLBackend::userNotificationDismissed() {
+    if (!this->userNotificationStack_.size()) return;
+
+    // Remove the user notification from the top of the queue as it has been dismissed.
+    this->userNotificationStack_.pop();
+    if (!this->userNotificationStack_.size()) return;
+
+    // Display the user notification that is on top of the queue, if there is one.
+    auto notification = this->userNotificationStack_.top();
+    emit receivedUserNotification(notification);
+}
+

internal/frontend/bridge-gui/bridge-gui/QMLBackend.h

@@ -28,6 +28,7 @@
 #include <bridgepp/GRPC/GRPCClient.h>
 #include <bridgepp/GRPC/GRPCUtils.h>
 #include <bridgepp/Worker/Overseer.h>
+#include <stack>
 
 
 //****************************************************************************************************************************************************
@@ -174,6 +175,8 @@ signals: // Signal used by the Qt property system. Many of them are unused but r
     void isAutostartOnChanged(bool value); ///<Signal for the change of the 'isAutostartOn' property.
     void usersChanged(UserList *users); ///<Signal for the change of the 'users' property.
     void dockIconVisibleChanged(bool value); ///<Signal for the change of the 'dockIconVisible' property.
+    void receivedUserNotification(bridgepp::UserNotification const& notification); ///< Signal to display the userNotification modal
+
 
 public slots: // slot for signals received from QML -> To be forwarded to Bridge via RPC Client calls.
     void toggleAutostart(bool active); ///< Slot for the autostart toggle.
@@ -209,6 +212,7 @@ public slots: // slot for signals received from QML -> To be forwarded to Bridge
     void notifyAutoconfigClicked(QString const &client) const; ///< Slot for gAutoconfigClicked gRPC event.
     void notifyExternalLinkClicked(QString const &article) const; ///< Slot for KBArticleClicked gRPC event.
     void triggerRepair() const; ///< Slot for the triggering of the bridge repair function i.e. 'resync'.
+    void userNotificationDismissed(); ///< Slot to pop the notification from the stack and display the rest.
 
 public slots: // slots for functions that need to be processed locally.
     void setNormalTrayIcon(); ///< Set the tray icon to normal.
@@ -224,6 +228,7 @@ public slots: // slot for signals received from gRPC that need transformation in
     void onLoginAlreadyLoggedIn(QString const &userID); ///< Slot for the LoginAlreadyLoggedIn gRPC event.
     void onUserBadEvent(QString const& userID, QString const& errorMessage); ///< Slot for the userBadEvent gRPC event.
     void onIMAPLoginFailed(QString const& username); ///< Slot the the imapLoginFailed event.
+    void processUserNotification(bridgepp::UserNotification const& notification); ///< Slot for the userNotificationReceived gRCP event.
 
 signals: // Signals received from the Go backend, to be forwarded to QML
     void toggleAutostartFinished(); ///< Signal for the 'toggleAutostartFinished' gRPC stream event.
@@ -310,6 +315,7 @@ private: // data members
     QList<QString> badEventDisplayQueue_; ///< THe queue for displaying 'bad event feedback request dialog'.
     std::unique_ptr<TrayIcon> trayIcon_; ///< The tray icon for the application.
     bridgepp::BugReportFlow reportFlow_;  ///< The bug report flow.
+    std::stack<bridgepp::UserNotification> userNotificationStack_; ///< The stack which holds all of the active notifications that the user needs to acknowledge.
     friend class AppController;
 };
 

internal/frontend/bridge-gui/bridge-gui/Resources.qrc

@@ -71,6 +71,7 @@
         <file>qml/icons/systray-mono-update.png</file>
         <file>qml/icons/systray-mono-warn.png</file>
         <file>qml/icons/systray.svg</file>
+        <file>qml/icons/ic-notification-bell.svg</file>
         <file alias="bridge.svg">../../../../dist/bridge.svg</file>
         <file alias="bridgeMacOS.svg">../../../../dist/bridgeMacOS.svg</file>
         <file>qml/KeychainSettings.qml</file>
@@ -78,6 +79,7 @@
         <file>qml/MainWindow.qml</file>
         <file>qml/NoAccountView.qml</file>
         <file>qml/NotificationDialog.qml</file>
+        <file>qml/UserNotificationDialog.qml</file>
         <file>qml/NotificationPopups.qml</file>
         <file>qml/Notifications/Notification.qml</file>
         <file>qml/Notifications/NotificationFilter.qml</file>

internal/frontend/bridge-gui/bridge-gui/TrayIcon.cpp

@@ -331,6 +331,15 @@ void TrayIcon::showErrorPopupNotification(QString const &title, QString const &m
     this->showMessage(title, message, notificationErrorIcon_);
 }
 
+//****************************************************************************************************************************************************
+/// Used only by user notifications received from the event loop
+/// \param[in] title The title.
+/// \param[in] subtitle The subtitle.
+//****************************************************************************************************************************************************
+void TrayIcon::showUserNotification(QString const &title, QString const &subtitle) {
+    this->showMessage(title, subtitle, QSystemTrayIcon::NoIcon);
+}
+
 
 //****************************************************************************************************************************************************
 /// \param[in] svgPath The path of the SVG file for the icon.

internal/frontend/bridge-gui/bridge-gui/TrayIcon.h

@@ -42,6 +42,8 @@ public: // data members
     TrayIcon& operator=(TrayIcon&&) = delete; ///< Disabled move assignment operator.
     void setState(State state, QString const& stateString, QString const &statusIconPath); ///< Set the state of the icon
     void showErrorPopupNotification(QString const& title, QString const &message); ///< Display a pop up notification.
+    void showUserNotification(QString const& title, QString const &subtitle); ///< Display an OS pop up notification (without icon).
+
 
 signals:
     void selectUser(QString const& userID, bool forceShowWindow); ///< Signal for selecting a user with a given userID

internal/frontend/bridge-gui/bridge-gui/qml/NotificationDialog.qml

@@ -22,6 +22,7 @@ Dialog {
 
     default property alias data: additionalChildrenContainer.children
     property var notification
+    property bool isUserNotification: false
 
     modal: true
     shouldShow: notification && notification.active && !notification.dismissed

internal/frontend/bridge-gui/bridge-gui/qml/NotificationPopups.qml

@@ -109,4 +109,8 @@ Item {
         colorScheme: root.colorScheme
         notification: root.notifications.repairBridge
     }
+    UserNotificationDialog {
+        colorScheme: root.colorScheme
+        notification: root.notifications.userNotification
+    }
 }

internal/frontend/bridge-gui/bridge-gui/qml/Notifications/Notification.qml

@@ -19,7 +19,8 @@ QtObject {
         Info,
         Success,
         Warning,
-        Danger
+        Danger,
+        UserNotification
     }
 
     property list<Action> action
@@ -36,6 +37,9 @@ QtObject {
     readonly property var occurred: active ? new Date() : undefined
     property string title // title is used in dialogs only
     property int type
+    property string subtitle
+    property string username
+
 
     onActiveChanged: {
         dismissed = false;

internal/frontend/bridge-gui/bridge-gui/qml/Notifications/Notifications.qml

@@ -62,7 +62,7 @@ QtObject {
             target: Backend
         }
     }
-    property var all: [root.noInternet, root.imapPortStartupError, root.smtpPortStartupError, root.imapPortChangeError, root.smtpPortChangeError, root.imapConnectionModeChangeError, root.smtpConnectionModeChangeError, root.updateManualReady, root.updateManualRestartNeeded, root.updateManualError, root.updateForce, root.updateForceError, root.updateSilentRestartNeeded, root.updateSilentError, root.updateIsLatestVersion, root.loginConnectionError, root.onlyPaidUsers, root.alreadyLoggedIn, root.enableBeta, root.bugReportSendSuccess, root.bugReportSendError, root.bugReportSendFallback, root.cacheCantMove, root.cacheLocationChangeSuccess, root.enableSplitMode, root.resetBridge, root.changeAllMailVisibility, root.deleteAccount, root.noKeychain, root.rebuildKeychain, root.addressChanged, root.apiCertIssue, root.userBadEvent, root.imapLoginWhileSignedOut, root.genericError, root.genericQuestion, root.hvErrorEvent, root.repairBridge]
+    property var all: [root.noInternet, root.imapPortStartupError, root.smtpPortStartupError, root.imapPortChangeError, root.smtpPortChangeError, root.imapConnectionModeChangeError, root.smtpConnectionModeChangeError, root.updateManualReady, root.updateManualRestartNeeded, root.updateManualError, root.updateForce, root.updateForceError, root.updateSilentRestartNeeded, root.updateSilentError, root.updateIsLatestVersion, root.loginConnectionError, root.onlyPaidUsers, root.alreadyLoggedIn, root.enableBeta, root.bugReportSendSuccess, root.bugReportSendError, root.bugReportSendFallback, root.cacheCantMove, root.cacheLocationChangeSuccess, root.enableSplitMode, root.resetBridge, root.changeAllMailVisibility, root.deleteAccount, root.noKeychain, root.rebuildKeychain, root.addressChanged, root.apiCertIssue, root.userBadEvent, root.imapLoginWhileSignedOut, root.genericError, root.genericQuestion, root.hvErrorEvent, root.repairBridge, root.userNotification]
     property Notification alreadyLoggedIn: Notification {
         brief: qsTr("Already signed in")
         description: qsTr("This account is already signed in.")
@@ -1200,6 +1200,35 @@ QtObject {
 
     }
 
+    property Notification userNotification: Notification {
+        brief: title
+        group: Notifications.Group.Dialogs
+        type: Notification.NotificationType.UserNotification
+        icon: "./icons/ic-exclamation-circle-filled.svg" // If it's not included QML complains
+
+        action: [
+            Action {
+                text: qsTr("Okay")
+                onTriggered: {
+                    root.userNotification.active = false;
+                    Backend.userNotificationDismissed();
+                }
+            }
+        ]
+
+        Connections {
+            function onReceivedUserNotification(notification) {
+                const userPrimaryEmailOrUsername = Backend.users.primaryEmailOrUsername(notification.userID)
+                root.userNotification.title = notification.title
+                root.userNotification.subtitle = notification.subtitle
+                root.userNotification.description = notification.body
+                root.userNotification.username = userPrimaryEmailOrUsername
+                root.userNotification.active = true
+            }
+            target: Backend
+        }
+    }
+
     signal askChangeAllMailVisibility(var isVisibleNow)
     signal askDeleteAccount(var user)
     signal askEnableBeta

internal/frontend/bridge-gui/bridge-gui/qml/Proton/ApplicationWindow.qml

@@ -73,6 +73,11 @@ T.ApplicationWindow {
             if (obj.shouldShow === false) {
                 continue;
             }
+            // User notifications should have display priority
+            if (obj.shouldShow && obj.isUserNotification) {
+                topmost = obj;
+                break;
+            }
             if (topmost && (topmost.popupType > obj.popupType)) {
                 continue;
             }

internal/frontend/bridge-gui/bridge-gui/qml/UserNotificationDialog.qml

@@ -0,0 +1,120 @@
+// Copyright (c) 2024 Proton AG
+// This file is part of Proton Mail Bridge.
+// Proton Mail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// Proton Mail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+// You should have received a copy of the GNU General Public License
+// along with Proton Mail Bridge. If not, see <https://www.gnu.org/licenses/>.
+import QtQml
+import QtQuick
+import QtQuick.Layouts
+import QtQuick.Controls
+import Proton
+import Notifications
+
+Dialog {
+    id: root
+
+    property var notification
+    property bool isUserNotification: true
+    padding: 40
+
+    modal: true
+    shouldShow: notification && notification.active && !notification.dismissed
+
+    ColumnLayout {
+        spacing: 0
+
+        Image {
+            Layout.alignment: Qt.AlignHCenter
+            Layout.bottomMargin: 16
+            Layout.preferredHeight: 64
+            Layout.preferredWidth: 64
+            source: {
+                if (!root.notification) {
+                    return "";
+                }
+                switch (root.notification.type) {
+                    case Notification.NotificationType.UserNotification:
+                        return "/qml/icons/ic-notification-bell.svg"
+                }
+            }
+            sourceSize.height: 64
+            sourceSize.width: 64
+            visible: source != ""
+        }
+        // Title Label
+        Label {
+            Layout.alignment: Qt.AlignHCenter
+            Layout.bottomMargin: 4
+            Layout.preferredWidth: 320
+            colorScheme: root.colorScheme
+            horizontalAlignment: Text.AlignHCenter
+            text: root.notification.title
+            wrapMode: Text.WordWrap
+            type: Label.LabelType.Title
+        }
+        // Username or primary email
+        Label {
+            Layout.alignment: Qt.AlignHCenter
+            Layout.bottomMargin: 24
+            Layout.preferredWidth: 320
+            colorScheme: root.colorScheme
+            horizontalAlignment: Text.AlignHCenter
+            text: root.notification.username
+            wrapMode: Text.WordWrap
+            visible: root.notification.username.length > 0
+            type: Label.LabelType.Caption
+        }
+        // Subtitle
+        Label {
+            Layout.alignment: Qt.AlignHCenter
+            Layout.bottomMargin: 24
+            Layout.fillWidth: true
+            Layout.preferredWidth: 320
+            colorScheme: root.colorScheme
+            horizontalAlignment: Text.AlignHCenter
+            text: root.notification.subtitle
+            wrapMode: Text.WordWrap
+            visible: root.notification.subtitle.length > 0
+            type: Label.LabelType.Lead
+            color: root.colorScheme.text_weak
+        }
+        Label {
+            Layout.bottomMargin: 24
+            Layout.fillWidth: true
+            Layout.preferredWidth: 320
+            colorScheme: root.colorScheme
+            horizontalAlignment: Text.AlignHCenter
+            text: root.notification.description
+            type: Label.LabelType.Body
+            wrapMode: Text.WordWrap
+
+            onLinkActivated: function (link) {
+                Backend.openExternalLink(link);
+            }
+        }
+
+
+        ColumnLayout {
+            spacing: 40
+
+            Repeater {
+                model: root.notification.action
+
+                delegate: Button {
+                    Layout.fillWidth: true
+                    action: modelData
+                    colorScheme: root.colorScheme
+                    loading: modelData.loading
+                    secondary: index > 0
+                }
+            }
+        }
+    }
+}

internal/frontend/bridge-gui/bridge-gui/qml/icons/ic-notification-bell.svg

@@ -0,0 +1,37 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="64" height="64" fill="none" viewBox="0 0 64 64">
+    <g clip-path="url(#a)">
+        <circle cx="13.031" cy="5.288" r="3.166" fill="#2C83DC" transform="rotate(-30 13.031 5.288)"/>
+        <path fill="url(#b)" d="M3.599 27.28A19.757 19.757 0 0 1 36.793 8.115L53.92 25.808a12.42 12.42 0 0 0 4.581 2.998c3.454 1.288 5.556 4.214 3.201 7.05-2.76 3.325-8.795 8.475-21.796 15.981S19.428 61.994 15.169 62.723c-3.634.621-5.117-2.662-4.506-6.298a12.422 12.422 0 0 0-.306-5.466L3.6 27.28Z"/>
+        <path fill="url(#c)" d="M3.599 27.28A19.757 19.757 0 0 1 36.793 8.115L53.92 25.808a12.42 12.42 0 0 0 4.581 2.998c3.454 1.288 5.556 4.214 3.201 7.05-2.76 3.325-8.795 8.475-21.796 15.981S19.428 61.994 15.169 62.723c-3.634.621-5.117-2.662-4.506-6.298a12.422 12.422 0 0 0-.306-5.466L3.6 27.28Z"/>
+        <ellipse cx="37.094" cy="46.965" fill="url(#d)" rx="26.875" ry="3.75" transform="rotate(-30 37.094 46.965)"/>
+        <ellipse cx="37.094" cy="46.965" fill="url(#e)" rx="26.875" ry="3.75" transform="rotate(-30 37.094 46.965)"/>
+        <path fill="#fff" fill-opacity=".2" d="m48.156 19.855-2.032-2.1c-6.302 1.79-12.908 4.57-19.41 8.324-7.591 4.383-14.103 9.553-19.19 14.959l.914 3.201c4.88-5.52 11.835-11.152 20.16-15.958 6.703-3.87 13.425-6.704 19.558-8.426Z"/>
+        <circle cx="36.469" cy="45.883" r="2.5" fill="url(#f)" transform="rotate(-30 36.469 45.883)"/>
+    </g>
+    <defs>
+        <linearGradient id="d" x1="49.16" x2="37.094" y1="30.878" y2="49.439" gradientUnits="userSpaceOnUse">
+            <stop stop-color="#256097"/>
+            <stop offset="1" stop-color="#2C83DC"/>
+        </linearGradient>
+        <linearGradient id="e" x1="49.68" x2="49.037" y1="46.478" y2="51.592" gradientUnits="userSpaceOnUse">
+            <stop stop-color="#27ABF4" stop-opacity="0"/>
+            <stop offset="1" stop-color="#27ABF4" stop-opacity=".5"/>
+        </linearGradient>
+        <linearGradient id="f" x1="35.719" x2="36.469" y1="43.133" y2="48.383" gradientUnits="userSpaceOnUse">
+            <stop offset=".345" stop-color="#B2EAFE" stop-opacity="0"/>
+            <stop offset="1" stop-color="#B2EAFE"/>
+        </linearGradient>
+        <radialGradient id="b" cx="0" cy="0" r="1" gradientTransform="rotate(131.347 12.11 6.294) scale(52.6374 54.7116)" gradientUnits="userSpaceOnUse">
+            <stop stop-color="#B2EAFE"/>
+            <stop offset="1" stop-color="#27ABF4"/>
+        </radialGradient>
+        <radialGradient id="c" cx="0" cy="0" r="1" gradientTransform="rotate(60 -23.22 57.501) scale(21.25 76.0937)" gradientUnits="userSpaceOnUse">
+            <stop stop-color="#fff" stop-opacity="0"/>
+            <stop offset=".46" stop-color="#fff" stop-opacity=".4"/>
+            <stop offset=".58" stop-color="#B2EAFE" stop-opacity=".5"/>
+        </radialGradient>
+        <clipPath id="a">
+            <path fill="#fff" d="M0 0h64v64H0z"/>
+        </clipPath>
+    </defs>
+</svg>

internal/frontend/bridge-gui/bridgepp/bridgepp/GRPC/EventFactory.cpp

@@ -729,4 +729,23 @@ SPStreamEvent newGenericErrorEvent(grpc::ErrorCode errorCode) {
 }
 
 
+//****************************************************************************************************************************************************
+/// \param[in] userID The user ID that received the notification.
+/// \param[in] title The title of the notification.
+/// \param[in] subtitle The subtitle of the notification.
+/// \param[in] body The body of the notification.
+/// \return The event.
+//****************************************************************************************************************************************************
+SPStreamEvent newUserNotificationEvent(QString const &userID, QString const title, QString const subtitle, QString const body) {
+    auto event = new grpc::UserNotificationEvent;
+    event->set_userid(userID.toStdString());
+    event->set_body(body.toStdString());
+    event->set_subtitle(subtitle.toStdString());
+    event->set_title(title.toStdString());
+    auto appEvent = new grpc::AppEvent;
+    appEvent->set_allocated_usernotification(event);
+    return wrapAppEvent(appEvent);
+}
+
+
 } // namespace bridgepp

internal/frontend/bridge-gui/bridgepp/bridgepp/GRPC/EventFactory.h

@@ -94,6 +94,9 @@ SPStreamEvent newSyncProgressEvent(QString const &userID, double progress, qint6
 // Generic error event
 SPStreamEvent newGenericErrorEvent(grpc::ErrorCode errorCode); ///< Create a new GenericErrrorEvent event.
 
+// User notification event
+SPStreamEvent newUserNotificationEvent(QString const &userID, QString const title, QString const subtitle, QString const body);
+
 } // namespace bridgepp
 
 

internal/frontend/bridge-gui/bridgepp/bridgepp/GRPC/GRPCClient.cpp

@@ -1206,6 +1206,17 @@ void GRPCClient::processAppEvent(AppEvent const &event) {
         this->logTrace("App event received: AllUsersLoaded");
         emit allUsersLoaded();
         break;
+    case AppEvent::kUserNotification: {
+        this->logTrace("App event received: UserNotification");
+        UserNotification notification{
+                .title = QString::fromStdString(event.usernotification().title()),
+                .subtitle = QString::fromStdString(event.usernotification().subtitle()),
+                .body = QString::fromStdString(event.usernotification().body()),
+                .userID = QString::fromStdString(event.usernotification().userid()),
+        };
+        emit userNotificationReceived(notification);
+        break;
+    }
     default:
         this->logError("Unknown App event received.");
     }

internal/frontend/bridge-gui/bridgepp/bridgepp/GRPC/GRPCClient.h

@@ -56,6 +56,24 @@ public:
 };
 
 
+//****************************************************************************************************************************************************
+/// \brief A struct for user notitifications.
+//****************************************************************************************************************************************************
+    struct UserNotification {
+        //  The following lines make the type transmissible to QML (but not instanciable there)
+    Q_GADGET
+        Q_PROPERTY(QString title MEMBER title)
+        Q_PROPERTY(QString subtitle MEMBER subtitle)
+        Q_PROPERTY(QString body MEMBER body)
+        Q_PROPERTY(QString userID MEMBER userID)
+    public:
+        QString title; ///< The title of the notification.
+        QString subtitle; ///< The subtitle of the notification.
+        QString body; ///< The body of the notification.
+        QString userID; ///< The userID that received the notification.
+    };
+
+
 //****************************************************************************************************************************************************
 /// \brief gRPC client class. This class encapsulate the gRPC service, abstracting all data type conversions.
 //****************************************************************************************************************************************************
@@ -125,6 +143,7 @@ signals: // app related signals
     void knowledgeBasSuggestionsReceived(QList<KnowledgeBaseSuggestion> const& suggestions);
     void repairStarted();
     void allUsersLoaded();
+    void userNotificationReceived(UserNotification const& notification);
 
 
 public: // cache related calls

internal/frontend/cli/frontend.go

@@ -20,6 +20,7 @@ package cli
 
 import (
 	"errors"
+	"fmt"
 	"os"
 	"runtime"
 
@@ -500,6 +501,18 @@ func (f *frontendCLI) watchEvents(eventCh <-chan events.Event) { // nolint:gocyc
 
 		case events.Raise:
 			f.Printf("Hello!")
+
+		case events.UserNotification:
+			user, err := f.bridge.GetUserInfo(event.UserID)
+			if err != nil {
+				return
+			}
+
+			fmt.Printf("\n--- NOTIFICATION ---\n\n")
+			fmt.Printf("Sent to: %s\n", user.Username)
+			fmt.Printf("Title: %s\n", event.Title)
+			fmt.Printf("Subtitle: %s\n", event.Subtitle)
+			fmt.Printf("Message: %s\n\n", event.Body)
 		}
 	}
 

internal/frontend/grpc/bridge.proto

@@ -277,6 +277,7 @@ message AppEvent {
     KnowledgeBaseSuggestionsEvent knowledgeBaseSuggestions = 12;
     RepairStartedEvent repairStarted = 13;
     AllUsersLoadedEvent allUsersLoaded = 14;
+    UserNotificationEvent userNotification = 15;
   }
 }
 
@@ -545,6 +546,14 @@ message SyncProgressEvent {
   int64 remainingMs = 4;
 }
 
+message UserNotificationEvent {
+  string title = 1;
+  string subtitle = 2;
+  string body = 3;
+  string userID = 4;
+}
+
+
 //**********************************************************
 // Generic errors
 //**********************************************************

internal/frontend/grpc/event_factory.go

@@ -18,6 +18,7 @@
 package grpc
 
 import (
+	"github.com/ProtonMail/proton-bridge/v3/internal/events"
 	"github.com/ProtonMail/proton-bridge/v3/internal/kb"
 	"github.com/bradenaw/juniper/xslices"
 )
@@ -249,6 +250,16 @@ func NewAllUsersLoadedEvent() *StreamEvent {
 	return appEvent(&AppEvent{Event: &AppEvent_AllUsersLoaded{AllUsersLoaded: &AllUsersLoadedEvent{}}})
 }
 
+func NewUserNotificationEvent(event events.UserNotification) *StreamEvent {
+	return appEvent(&AppEvent{Event: &AppEvent_UserNotification{
+		UserNotification: &UserNotificationEvent{
+			UserID:   event.UserID,
+			Title:    event.Title,
+			Subtitle: event.Subtitle,
+			Body:     event.Body,
+		}}})
+}
+
 // Event category factory functions.
 
 func appEvent(appEvent *AppEvent) *StreamEvent {

internal/frontend/grpc/service.go

@@ -404,6 +404,9 @@ func (s *Service) watchEvents() {
 
 		case events.AllUsersLoaded:
 			_ = s.SendEvent(NewAllUsersLoadedEvent())
+
+		case events.UserNotification:
+			_ = s.SendEvent(NewUserNotificationEvent(event))
 		}
 	}
 }

internal/locations/locations.go

@@ -248,6 +248,10 @@ func (l *Locations) getUpdatesPath() string {
 	return filepath.Join(l.userData, "updates")
 }
 
+func (l *Locations) getNotificationsCachePath() string {
+	return filepath.Join(l.userCache, "notifications")
+}
+
 func (l *Locations) getStatsPath() string {
 	return filepath.Join(l.userData, "stats")
 }
@@ -276,3 +280,13 @@ func (l *Locations) ClearUpdates() error {
 func (l *Locations) CleanGoIMAPCache() error {
 	return files.Remove(l.getGoIMAPCachePath()).Do()
 }
+
+// ProvideNotificationsCachePath returns a location for notification deduplication data.
+// It creates it if it doesn't already exist.
+func (l *Locations) ProvideNotificationsCachePath() (string, error) {
+	if err := os.MkdirAll(l.getNotificationsCachePath(), 0o700); err != nil {
+		return "", err
+	}
+
+	return l.getNotificationsCachePath(), nil
+}

internal/services/notifications/metrics.go

@@ -0,0 +1,51 @@
+// Copyright (c) 2024 Proton AG
+//
+// This file is part of Proton Mail Bridge.
+//
+// Proton Mail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Proton Mail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Proton Mail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+package notifications
+
+import (
+	"time"
+
+	"github.com/ProtonMail/go-proton-api"
+)
+
+func generatedNotificationDisplayedMetric(status string, value int) proton.ObservabilityMetric {
+	// Value cannot be zero or negative
+	if value < 1 {
+		value = 1
+	}
+
+	return proton.ObservabilityMetric{
+		Name:      "bridge_remoteNotification_displayed_total",
+		Version:   1,
+		Timestamp: time.Now().Unix(),
+		Data: map[string]interface{}{
+			"Value": value,
+			"Labels": map[string]string{
+				"status": status,
+			},
+		},
+	}
+}
+
+func GenerateReceivedMetric(count int) proton.ObservabilityMetric {
+	return generatedNotificationDisplayedMetric("received", count)
+}
+
+func GenerateProcessedMetric(count int) proton.ObservabilityMetric {
+	return generatedNotificationDisplayedMetric("processed", count)
+}

internal/services/notifications/notification_test.go

@@ -0,0 +1,112 @@
+// Copyright (c) 2024 Proton AG
+//
+// This file is part of Proton Mail Bridge.
+//
+// Proton Mail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Proton Mail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Proton Mail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+package notifications
+
+import (
+	"testing"
+	"time"
+
+	"github.com/ProtonMail/go-proton-api"
+	"github.com/stretchr/testify/require"
+)
+
+func TestIsBodyBitfieldValid(t *testing.T) {
+	tests := []struct {
+		notification proton.NotificationEvent
+		isValid      bool
+	}{
+		{notification: proton.NotificationEvent{Payload: proton.NotificationPayload{Body: ""}}, isValid: true},
+		{notification: proton.NotificationEvent{Payload: proton.NotificationPayload{Body: "HELLO"}}, isValid: true},
+		{notification: proton.NotificationEvent{Payload: proton.NotificationPayload{Body: "What is up?"}}, isValid: true},
+		{notification: proton.NotificationEvent{Payload: proton.NotificationPayload{Body: "123 Hello"}}, isValid: true},
+		{notification: proton.NotificationEvent{Payload: proton.NotificationPayload{Body: "\\123Hello"}}, isValid: false},
+		{notification: proton.NotificationEvent{Payload: proton.NotificationPayload{Body: "\\123 Hello"}}, isValid: false},
+		{notification: proton.NotificationEvent{Payload: proton.NotificationPayload{Body: "\\1test"}}, isValid: false},
+		{notification: proton.NotificationEvent{Payload: proton.NotificationPayload{Body: "\\1 test"}}, isValid: false},
+	}
+
+	for _, test := range tests {
+		isValid := isBodyBitfieldValid(test.notification)
+		require.Equal(t, isValid, !test.isValid)
+	}
+}
+
+// The notification TTL is defined as timestamp by server + predefined duration.
+func TestShouldSendAndStore(t *testing.T) {
+	getDirFn := func(dir string) func() (string, error) {
+		return func() (string, error) {
+			return dir, nil
+		}
+	}
+
+	dir1 := t.TempDir()
+	dir2 := t.TempDir()
+
+	store := NewStore(getDirFn(dir1))
+
+	notification1 := proton.NotificationEvent{ID: "1", Payload: proton.NotificationPayload{Title: "test1", Subtitle: "test1", Body: "test1"}, Time: time.Now().Unix()}
+	notification2 := proton.NotificationEvent{ID: "2", Payload: proton.NotificationPayload{Title: "test2", Subtitle: "test2", Body: "test2"}, Time: time.Now().Unix()}
+	notification3 := proton.NotificationEvent{ID: "3", Payload: proton.NotificationPayload{Title: "test3", Subtitle: "test3", Body: "test3"}, Time: time.Now().Unix()}
+	notificationAlt1 := proton.NotificationEvent{ID: "1", Payload: proton.NotificationPayload{Title: "testAlt1", Subtitle: "test1", Body: "test1"}, Time: time.Now().Unix()}
+	notificationAlt2 := proton.NotificationEvent{ID: "1", Payload: proton.NotificationPayload{Title: "test2", Subtitle: "testAlt2", Body: "test2"}, Time: time.Now().Unix()}
+
+	require.Equal(t, true, store.shouldSendAndStore(notification1))
+	require.Equal(t, true, store.shouldSendAndStore(notification2))
+	require.Equal(t, true, store.shouldSendAndStore(notification3))
+	require.Equal(t, true, store.shouldSendAndStore(notificationAlt1))
+	require.Equal(t, true, store.shouldSendAndStore(notificationAlt2))
+
+	require.Equal(t, false, store.shouldSendAndStore(notification1))
+	require.Equal(t, false, store.shouldSendAndStore(notification2))
+	require.Equal(t, false, store.shouldSendAndStore(notification3))
+
+	store = NewStore(getDirFn(dir1))
+
+	// These should be cached in the file
+	require.Equal(t, false, store.shouldSendAndStore(notification1))
+	require.Equal(t, false, store.shouldSendAndStore(notification2))
+	require.Equal(t, false, store.shouldSendAndStore(notification3))
+
+	store = NewStore(getDirFn(dir2))
+	timeOffset = 1 * time.Second
+
+	// We're basing the time based on when the notification is sent
+	// Let's reset it.
+	notification1 = proton.NotificationEvent{ID: "1", Payload: proton.NotificationPayload{Title: "test1", Subtitle: "test1", Body: "test1"}, Time: time.Now().Unix()}
+	notification2 = proton.NotificationEvent{ID: "2", Payload: proton.NotificationPayload{Title: "test2", Subtitle: "test2", Body: "test2"}, Time: time.Now().Unix()}
+	notification3 = proton.NotificationEvent{ID: "3", Payload: proton.NotificationPayload{Title: "test3", Subtitle: "test3", Body: "test3"}, Time: time.Now().Unix()}
+
+	require.Equal(t, true, store.shouldSendAndStore(notification1))
+	require.Equal(t, true, store.shouldSendAndStore(notification2))
+	require.Equal(t, true, store.shouldSendAndStore(notification3))
+
+	require.Equal(t, false, store.shouldSendAndStore(notification1))
+	require.Equal(t, false, store.shouldSendAndStore(notification2))
+	require.Equal(t, false, store.shouldSendAndStore(notification3))
+
+	time.Sleep(1200 * time.Millisecond)
+
+	require.Equal(t, true, store.shouldSendAndStore(notification1))
+	require.Equal(t, true, store.shouldSendAndStore(notification2))
+	require.Equal(t, true, store.shouldSendAndStore(notification3))
+
+	store = NewStore(getDirFn(dir2))
+	require.Equal(t, true, store.shouldSendAndStore(notification1))
+	require.Equal(t, true, store.shouldSendAndStore(notification2))
+	require.Equal(t, true, store.shouldSendAndStore(notification3))
+}

internal/services/notifications/service.go

@@ -0,0 +1,156 @@
+// Copyright (c) 2024 Proton AG
+//
+// This file is part of Proton Mail Bridge.
+//
+// Proton Mail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Proton Mail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Proton Mail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+package notifications
+
+import (
+	"context"
+	"fmt"
+	"regexp"
+	"strings"
+
+	"github.com/ProtonMail/go-proton-api"
+	"github.com/ProtonMail/proton-bridge/v3/internal/events"
+	"github.com/ProtonMail/proton-bridge/v3/internal/logging"
+	"github.com/ProtonMail/proton-bridge/v3/internal/services/observability"
+	"github.com/ProtonMail/proton-bridge/v3/internal/services/orderedtasks"
+	"github.com/ProtonMail/proton-bridge/v3/internal/services/userevents"
+	"github.com/ProtonMail/proton-bridge/v3/internal/unleash"
+	"github.com/sirupsen/logrus"
+)
+
+type Service struct {
+	userID string
+
+	log *logrus.Entry
+
+	eventService   userevents.Subscribable
+	subscription   *userevents.EventChanneledSubscriber
+	eventPublisher events.EventPublisher
+
+	store *Store
+
+	getFlagValueFn            unleash.GetFlagValueFn
+	pushObservabilityMetricFn observability.PushObsMetricFn
+}
+
+const bitfieldRegexPattern = `^\\\d+`
+const disableNotificationsKillSwitch = "InboxBridgeEventLoopNotificationDisabled"
+
+func NewService(userID string, service userevents.Subscribable, eventPublisher events.EventPublisher, store *Store,
+	getFlagFn unleash.GetFlagValueFn, pushMetricFn observability.PushObsMetricFn) *Service {
+	return &Service{
+		userID: userID,
+
+		log: logrus.WithFields(logrus.Fields{
+			"user":    userID,
+			"service": "notification",
+		}),
+
+		eventService: service,
+		subscription: userevents.NewEventSubscriber(
+			fmt.Sprintf("notifications-%v", userID)),
+		eventPublisher: eventPublisher,
+
+		store: store,
+
+		getFlagValueFn:            getFlagFn,
+		pushObservabilityMetricFn: pushMetricFn,
+	}
+}
+
+func (s *Service) Start(ctx context.Context, group *orderedtasks.OrderedCancelGroup) {
+	group.Go(ctx, s.userID, "notification-service", s.run)
+}
+
+func (s *Service) run(ctx context.Context) {
+	s.log.Info("Starting service main loop")
+	defer s.log.Info("Exiting service main loop")
+
+	eventHandler := userevents.EventHandler{
+		NotificationHandler: s,
+	}
+
+	s.eventService.Subscribe(s.subscription)
+	defer s.eventService.Unsubscribe(s.subscription)
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case e, ok := <-s.subscription.OnEventCh():
+			if !ok {
+				continue
+			}
+			e.Consume(func(event proton.Event) error { return eventHandler.OnEvent(ctx, event) })
+		}
+	}
+}
+
+func (s *Service) HandleNotificationEvents(ctx context.Context, notificationEvents []proton.NotificationEvent) error {
+	if s.getFlagValueFn(disableNotificationsKillSwitch) {
+		s.log.Info("Received notification events. Skipping as kill switch is enabled.")
+		return nil
+	}
+
+	s.log.Debug("Handling notification events")
+
+	// Publish observability metrics that we've received notifications
+	s.pushObservabilityMetricFn(GenerateReceivedMetric(len(notificationEvents)))
+
+	for _, event := range notificationEvents {
+		ctx = logging.WithLogrusField(ctx, "notificationID", event.ID)
+		switch strings.ToLower(event.Type) {
+		case "bridge_modal":
+			{
+				// We currently don't support any notification types with bitfields in the body.
+				if isBodyBitfieldValid(event) {
+					continue
+				}
+
+				shouldSend := s.store.shouldSendAndStore(event)
+				if !shouldSend {
+					s.log.Info("Skipping notification event. Notification was displayed previously")
+					continue
+				}
+
+				s.log.Info("Publishing notification event. notificationID:", event.ID) // \todo BRIDGE-141 - change this to UID once it is available
+				s.eventPublisher.PublishEvent(ctx, events.UserNotification{UserID: s.userID, Title: event.Payload.Title,
+					Subtitle: event.Payload.Subtitle, Body: event.Payload.Body})
+
+				// Publish observability metric that we've successfully processed notifications
+				s.pushObservabilityMetricFn(GenerateProcessedMetric(1))
+			}
+
+		default:
+			s.log.Debug("Skipping notification event. Notification type is not related to bridge:", event.Type)
+			continue
+		}
+	}
+	return nil
+}
+
+// We will (potentially) encode different notification functionalities based on a starting bitfield "\NUMBER" in the
+// payload Body. Currently, we don't support this, but we might in the future. This is so versions of Bridge that don't
+// support this functionality won't be display such a message.
+func isBodyBitfieldValid(notification proton.NotificationEvent) bool {
+	match, err := regexp.MatchString(bitfieldRegexPattern, notification.Payload.Body)
+	if err != nil {
+		return false
+	}
+	return match
+}

internal/services/notifications/store.go

@@ -0,0 +1,161 @@
+// Copyright (c) 2024 Proton AG
+//
+// This file is part of Proton Mail Bridge.
+//
+// Proton Mail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Proton Mail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Proton Mail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+package notifications
+
+import (
+	"crypto"
+	"encoding/hex"
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"sync"
+	"time"
+
+	"github.com/ProtonMail/go-proton-api"
+	"github.com/sirupsen/logrus"
+	"golang.org/x/exp/maps"
+)
+
+// not-const so we can unit test the functionality.
+var timeOffset = 24 * time.Hour //nolint:gochecknoglobals
+const filename = "notification_cache"
+
+type Store struct {
+	displayedMessages     map[string]time.Time
+	displayedMessagesLock sync.Mutex
+
+	useCache      bool
+	cacheFilepath string
+	cacheLock     sync.Mutex
+
+	log *logrus.Entry
+}
+
+func NewStore(getCachePath func() (string, error)) *Store {
+	log := logrus.WithField("pkg", "notification-store")
+
+	useCacheFile := true
+	cachePath, err := getCachePath()
+	if err != nil {
+		useCacheFile = false
+		log.WithError(err).Error("Could not obtain cache directory")
+	}
+
+	store := &Store{
+		displayedMessages: make(map[string]time.Time),
+
+		useCache:      useCacheFile,
+		cacheFilepath: filepath.Clean(filepath.Join(cachePath, filename)),
+
+		log: log,
+	}
+
+	store.readCache()
+
+	return store
+}
+
+func generateHash(payload proton.NotificationPayload) string {
+	hash := crypto.SHA256.New()
+	hash.Write([]byte(payload.Body + payload.Subtitle + payload.Title))
+	return hex.EncodeToString(hash.Sum(nil))
+}
+
+func (s *Store) shouldSendAndStore(notification proton.NotificationEvent) bool {
+	s.displayedMessagesLock.Lock()
+	defer s.displayedMessagesLock.Unlock()
+
+	// \todo BRIDGE-141 - Add an additional check for the API returned UID
+	uid := generateHash(notification.Payload)
+
+	value, ok := s.displayedMessages[uid]
+	if !ok {
+		s.displayedMessages[uid] = time.Unix(notification.Time, 0).Add(timeOffset)
+		s.writeCache()
+		return true
+	}
+
+	if !time.Now().After(value) {
+		return false
+	}
+
+	s.displayedMessages[uid] = time.Unix(notification.Time, 0).Add(timeOffset)
+	s.writeCache()
+	return true
+}
+
+func (s *Store) readCache() {
+	if !s.useCache {
+		return
+	}
+
+	s.cacheLock.Lock()
+	defer s.cacheLock.Unlock()
+
+	file, err := os.Open(s.cacheFilepath)
+	if err != nil {
+		s.log.WithError(err).Error("Unable to open cache file")
+		return
+	}
+
+	defer func(file *os.File) {
+		err := file.Close()
+		if err != nil {
+			s.log.WithError(err).Error("Unable to close cache file after read")
+		}
+	}(file)
+
+	s.displayedMessagesLock.Lock()
+	defer s.displayedMessagesLock.Unlock()
+	if err = json.NewDecoder(file).Decode(&s.displayedMessages); err != nil {
+		s.log.WithError(err).Error("Unable to decode cache file")
+	}
+
+	// Remove redundant data
+	curTime := time.Now()
+	maps.DeleteFunc(s.displayedMessages, func(_ string, value time.Time) bool {
+		return curTime.After(value)
+	})
+}
+
+func (s *Store) writeCache() {
+	if !s.useCache {
+		return
+	}
+
+	s.cacheLock.Lock()
+	defer s.cacheLock.Unlock()
+
+	file, err := os.Create(s.cacheFilepath)
+	if err != nil {
+		s.log.WithError(err).Info("Unable to create cache file.")
+		return
+	}
+
+	defer func(file *os.File) {
+		err := file.Close()
+		if err != nil {
+			s.log.WithError(err).Error("Unable to close cache file after write")
+		}
+	}(file)
+
+	// We don't lock the mutex here as the parent does that already
+	if err = json.NewEncoder(file).Encode(s.displayedMessages); err != nil {
+		s.log.WithError(err).Error("Unable to encode data to cache file")
+	}
+}

internal/services/observability/service.go

@@ -36,6 +36,8 @@ const (
 	maxBatchSize   = 1000
 )
 
+type PushObsMetricFn func(metric proton.ObservabilityMetric)
+
 type client struct {
 	isTelemetryEnabled func(context.Context) bool
 	sendMetrics        func(context.Context, proton.ObservabilityBatch) error

internal/services/userevents/subscription.go

@@ -38,6 +38,7 @@ type EventHandler struct {
 	MessageHandler      MessageEventHandler
 	UsedSpaceHandler    UserUsedSpaceEventHandler
 	UserSettingsHandler UserSettingsHandler
+	NotificationHandler NotificationEventHandler
 }
 
 func (e EventHandler) OnEvent(ctx context.Context, event proton.Event) error {
@@ -87,6 +88,12 @@ func (e EventHandler) OnEvent(ctx context.Context, event proton.Event) error {
 		}
 	}
 
+	if len(event.Notifications) != 0 && e.NotificationHandler != nil {
+		if err := e.NotificationHandler.HandleNotificationEvents(ctx, event.Notifications); err != nil {
+			return fmt.Errorf("failed to apply notification events: %w", err)
+		}
+	}
+
 	return nil
 }
 
@@ -116,3 +123,7 @@ type LabelEventHandler interface {
 type MessageEventHandler interface {
 	HandleMessageEvents(ctx context.Context, events []proton.MessageEvent) error
 }
+
+type NotificationEventHandler interface {
+	HandleNotificationEvents(ctx context.Context, events []proton.NotificationEvent) error
+}

internal/unleash/service.go

@@ -37,6 +37,7 @@ var pollJitter = 2 * time.Minute  //nolint:gochecknoglobals
 const filename = "unleash_flags"
 
 type requestFeaturesFn func(ctx context.Context) (proton.FeatureFlagResult, error)
+type GetFlagValueFn func(key string) bool
 
 type Service struct {
 	panicHandler async.PanicHandler

internal/user/user.go

@@ -31,6 +31,7 @@ import (
 	"github.com/ProtonMail/proton-bridge/v3/internal/events"
 	"github.com/ProtonMail/proton-bridge/v3/internal/safe"
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/imapservice"
+	"github.com/ProtonMail/proton-bridge/v3/internal/services/notifications"
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/observability"
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/orderedtasks"
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/sendrecorder"
@@ -40,6 +41,7 @@ import (
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/userevents"
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/useridentity"
 	"github.com/ProtonMail/proton-bridge/v3/internal/telemetry"
+	"github.com/ProtonMail/proton-bridge/v3/internal/unleash"
 	"github.com/ProtonMail/proton-bridge/v3/internal/usertypes"
 	"github.com/ProtonMail/proton-bridge/v3/internal/vault"
 	"github.com/ProtonMail/proton-bridge/v3/pkg/algo"
@@ -86,6 +88,7 @@ type User struct {
 	smtpService         *smtp.Service
 	imapService         *imapservice.Service
 	telemetryService    *telemetryservice.Service
+	notificationService *notifications.Service
 
 	observabilityService *observability.Service
 
@@ -110,6 +113,9 @@ func New(
 	observabilityService *observability.Service,
 	syncConfigDir string,
 	isNew bool,
+	notificationStore *notifications.Store,
+	getFlagValFn unleash.GetFlagValueFn,
+	pushObservabilityMetric observability.PushObsMetricFn,
 ) (*User, error) {
 	user, err := newImpl(
 		ctx,
@@ -129,6 +135,9 @@ func New(
 		observabilityService,
 		syncConfigDir,
 		isNew,
+		notificationStore,
+		getFlagValFn,
+		pushObservabilityMetric,
 	)
 	if err != nil {
 		// Cleanup any pending resources on error
@@ -161,6 +170,9 @@ func newImpl(
 	observabilityService *observability.Service,
 	syncConfigDir string,
 	isNew bool,
+	notificationStore *notifications.Store,
+	getFlagValueFn unleash.GetFlagValueFn,
+	pushObservabilityMetric observability.PushObsMetricFn,
 ) (*User, error) {
 	logrus.WithField("userID", apiUser.ID).Info("Creating new user")
 
@@ -278,6 +290,8 @@ func newImpl(
 		showAllMail,
 	)
 
+	user.notificationService = notifications.NewService(user.id, user.eventService, user, notificationStore, getFlagValueFn, pushObservabilityMetric)
+
 	// Check for status_progress when triggered.
 	user.goStatusProgress = user.tasks.PeriodicOrTrigger(configstatus.ProgressCheckInterval, 0, func(ctx context.Context) {
 		user.SendConfigStatusProgress(ctx)
@@ -329,6 +343,9 @@ func newImpl(
 	// Add user client to observability service
 	observabilityService.RegisterUserClient(user.id, client, user.telemetryService)
 
+	// Start Notification service
+	user.notificationService.Start(ctx, user.serviceGroup)
+
 	// Start SMTP Service
 	if err := user.smtpService.Start(ctx, user.serviceGroup); err != nil {
 		return user, fmt.Errorf("failed to start smtp service: %w", err)

internal/user/user_test.go

@@ -29,6 +29,7 @@ import (
 	"github.com/ProtonMail/proton-bridge/v3/internal/certs"
 	"github.com/ProtonMail/proton-bridge/v3/internal/events"
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/imapservice"
+	"github.com/ProtonMail/proton-bridge/v3/internal/services/notifications"
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/observability"
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/smtp"
 	"github.com/ProtonMail/proton-bridge/v3/internal/telemetry/mocks"
@@ -168,6 +169,13 @@ func withUser(tb testing.TB, ctx context.Context, _ *server.Server, m *proton.Ma
 		observability.NewService(context.Background(), nil),
 		"",
 		true,
+		notifications.NewStore(func() (string, error) {
+			return "", nil
+		}),
+		func(_ string) bool {
+			return false
+		},
+		func(_ proton.ObservabilityMetric) {},
 	)
 	require.NoError(tb, err)
 	defer user.Close()

tests/features/observability/remote_notification.feature

@@ -0,0 +1,17 @@
+Feature: Bridge send remote notification observability metrics
+  Background:
+    Given there exists an account with username "[user:user1]" and password "password"
+    And there exists an account with username "[user:user2]" and password "password"
+    Then it succeeds
+    When bridge starts
+    Then it succeeds
+
+
+  Scenario: Send notification 'received' and 'processed' observability metric
+    When the user logs in with username "[user:user1]" and password "password"
+    And the user with username "[user:user1]" sends the following remote notification observability metric "received"
+    Then it succeeds
+    And the user with username "[user:user1]" sends the following remote notification observability metric "processed"
+    Then it succeeds
+
+

tests/steps_test.go

@@ -216,4 +216,8 @@ func (s *scenario) steps(ctx *godog.ScenarioContext) {
 	ctx.Step(`^the contact "([^"]*)" of user "([^"]*)" has encryption "([^"]*)"$`, s.contactOfUserHasEncryption)
 	ctx.Step(`^the contact "([^"]*)" of user "([^"]*)" has public key:$`, s.contactOfUserHasPubKey)
 	ctx.Step(`^the contact "([^"]*)" of user "([^"]*)" has public key from file "([^"]*)"$`, s.contactOfUserHasPubKeyFromFile)
+
+	// ==== OBSERVABILITY METRICS ====
+	ctx.Step(`^the user with username "([^"]*)" sends the following remote notification observability metric "([^"]*)"`,
+		s.userRemoteNotificationMetricTest)
 }

tests/user_test.go

@@ -23,11 +23,13 @@ import (
 	"fmt"
 	"net/mail"
 	"strings"
+	"time"
 
 	"github.com/ProtonMail/gluon/rfc822"
 	"github.com/ProtonMail/go-proton-api"
 	"github.com/ProtonMail/gopenpgp/v2/crypto"
 	"github.com/ProtonMail/proton-bridge/v3/internal/bridge"
+	"github.com/ProtonMail/proton-bridge/v3/internal/services/notifications"
 	"github.com/ProtonMail/proton-bridge/v3/internal/vault"
 	"github.com/ProtonMail/proton-bridge/v3/pkg/algo"
 	"github.com/bradenaw/juniper/iterator"
@@ -690,3 +692,24 @@ func matchSettings(have proton.MailSettings, want MailSettings) error {
 
 	return nil
 }
+
+func (s *scenario) userRemoteNotificationMetricTest(username string, metricName string) error {
+	var metricToTest proton.ObservabilityMetric
+	switch strings.ToLower(metricName) {
+	case "processed":
+		metricToTest = notifications.GenerateProcessedMetric(1)
+	case "received":
+		metricToTest = notifications.GenerateReceivedMetric(1)
+	default:
+		return fmt.Errorf("invalid metric name specified")
+	}
+
+	// Account for endpoint throttle
+	time.Sleep(time.Second * 5)
+
+	return s.t.withClientPass(context.Background(), username, s.t.getUserByName(username).userPass, func(ctx context.Context, c *proton.Client) error {
+		batch := proton.ObservabilityBatch{Metrics: []proton.ObservabilityMetric{metricToTest}}
+		err := c.SendObservabilityBatch(ctx, batch)
+		return err
+	})
+}