feat: Tail daemon log file instead of using IPC log outputter

src/apps/deskflow-daemon/deskflow-daemon.cpp

@@ -27,6 +27,8 @@
 #include <QCoreApplication>
 #include <QThread>
 
+using namespace deskflow::core;
+
 int main(int argc, char **argv)
 {
 #if SYSAPI_WIN32
@@ -51,13 +53,11 @@ int main(int argc, char **argv)
     using enum DaemonApp::InitResult;
 
   case StartDaemon: {
-    using namespace deskflow::core;
-
     QCoreApplication app(argc, argv);
 
     // Thread must be heap-allocated for deferred deletion on thread exit.
     // Avoid setting Qt ownership to prevent premature deletion (thread may run longer than Qt loop).
-    auto *pDaemonThread = new QThread(); // NOSONAR
+    auto *pDaemonThread = new QThread(); // NOSONAR - Qt memory
     pDaemon->moveToThread(pDaemonThread);
 
     QObject::connect(pDaemonThread, &QThread::started, pDaemon, &DaemonApp::run);
@@ -66,7 +66,7 @@ int main(int argc, char **argv)
     QObject::connect(pDaemonThread, &QThread::finished, QCoreApplication::instance(), &QCoreApplication::quit);
 
     // The daemon app is on it's own thread which doesn't have a Qt event loop, so we need to use direct connection.
-    auto *ipcServer = new ipc::DaemonIpcServer(&app); // NOSONAR
+    auto *ipcServer = new ipc::DaemonIpcServer(&app, QString::fromStdString(pDaemon->logFilename())); // NOSONAR
     QObject::connect(
         ipcServer, &ipc::DaemonIpcServer::logLevelChanged, pDaemon, &DaemonApp::saveLogLevel, //
         Qt::DirectConnection

src/lib/deskflow/DaemonApp.h

@@ -57,6 +57,9 @@ public:
   void applyWatchdogCommand() const;
   void clearWatchdogCommand();
 
+  // Getters
+  std::string logFilename();
+
   static DaemonApp &instance()
   {
     static DaemonApp instance; // NOSONAR - Meyers' Singleton
@@ -69,7 +72,6 @@ private:
 
   void daemonize();
   void handleError(const char *message);
-  std::string logFilename();
   void handleIpcMessage(const Event &e, void *);
 
 #if SYSAPI_WIN32

src/lib/deskflow/ipc/DaemonIpcServer.cpp

@@ -17,9 +17,10 @@ namespace deskflow::core::ipc {
 const auto kAckMessage = "ok\n";
 const auto kErrorMessage = "error\n";
 
-DaemonIpcServer::DaemonIpcServer(QObject *parent)
-    : QObject(parent),                 //
-      m_server{new QLocalServer(this)} // NOSONAR
+DaemonIpcServer::DaemonIpcServer(QObject *parent, const QString &logFilename)
+    : QObject(parent),
+      m_logFilename(logFilename),
+      m_server{new QLocalServer(this)} // NOSONAR - Qt memory
 {
   // Daemon runs as system, but GUI runs as regular user, so we need to allow world access.
   m_server->setSocketOptions(QLocalServer::WorldAccessOption);
@@ -108,7 +109,7 @@ void DaemonIpcServer::processMessage(QLocalSocket *clientSocket, const QString &
   }
 
   const auto &command = parts[0];
-  if (command == "hello") { // NOSONAR
+  if (command == "hello") { // NOSONAR - if-init is confusing here
     clientSocket->write("hello\n");
   } else if (command == "noop") {
     clientSocket->write(kAckMessage);
@@ -128,7 +129,7 @@ void DaemonIpcServer::processMessage(QLocalSocket *clientSocket, const QString &
     clientSocket->write(kAckMessage);
   } else if (command == "logPath") {
     LOG_DEBUG("ipc server got log path request");
-    // TODO: send log path
+    clientSocket->write("logPath=" + m_logFilename.toUtf8());
   } else {
     LOG_WARN("ipc server got unknown message: %s", message.toUtf8().constData());
   }

src/lib/deskflow/ipc/DaemonIpcServer.h

@@ -19,7 +19,7 @@ class DaemonIpcServer : public QObject
   Q_OBJECT
 
 public:
-  explicit DaemonIpcServer(QObject *parent);
+  explicit DaemonIpcServer(QObject *parent, const QString &logFilename);
   ~DaemonIpcServer() override;
 
 signals:
@@ -42,6 +42,7 @@ private slots:
   void handleErrorOccurred();
 
 private:
+  const QString m_logFilename;
   QLocalServer *m_server;
   QSet<QLocalSocket *> m_clients;
 };

src/lib/gui/CMakeLists.txt

@@ -25,6 +25,8 @@ add_library(${target} STATIC
   dotenv.cpp
   dotenv.h
   env_vars.h
+  FileTail.cpp
+  FileTail.h
   Logger.cpp
   Logger.h
   messages.cpp

src/lib/gui/FileTail.cpp

@@ -0,0 +1,45 @@
+/*
+ * Deskflow -- mouse and keyboard sharing utility
+ * SPDX-FileCopyrightText: (C) 2025 Symless Ltd.
+ * SPDX-License-Identifier: GPL-2.0-only WITH LicenseRef-OpenSSL-Exception
+ */
+
+#include "FileTail.h"
+
+#include <QDebug>
+#include <QFile>
+#include <QFileSystemWatcher>
+#include <QObject>
+#include <QTextStream>
+
+namespace deskflow::gui {
+
+FileTail::FileTail(const QString &filePath, QObject *parent)
+    : QObject(parent),
+      m_file(filePath),
+      m_watcher(new QFileSystemWatcher(this))
+{
+  if (!m_file.open(QIODevice::ReadOnly | QIODevice::Text)) {
+    qCritical() << "failed to open file for tail:" << filePath;
+    return;
+  }
+
+  qDebug() << "starting file tail:" << filePath;
+  m_watcher->addPath(filePath);
+  m_lastPos = m_file.size();
+
+  connect(m_watcher, &QFileSystemWatcher::fileChanged, this, &FileTail::handleFileChanged);
+}
+
+void FileTail::handleFileChanged(const QString &)
+{
+  m_file.seek(m_lastPos);
+  QTextStream stream(&m_file);
+  while (!stream.atEnd()) {
+    QString line = stream.readLine();
+    Q_EMIT newLine(line);
+  }
+  m_lastPos = m_file.pos();
+}
+
+} // namespace deskflow::gui

src/lib/gui/FileTail.h

@@ -0,0 +1,35 @@
+/*
+ * Deskflow -- mouse and keyboard sharing utility
+ * SPDX-FileCopyrightText: (C) 2025 Symless Ltd.
+ * SPDX-License-Identifier: GPL-2.0-only WITH LicenseRef-OpenSSL-Exception
+ */
+
+#pragma once
+
+#include <QFile>
+#include <QObject>
+
+class QFileSystemWatcher;
+
+namespace deskflow::gui {
+
+class FileTail : public QObject
+{
+  Q_OBJECT
+
+public:
+  FileTail(const QString &filePath, QObject *parent = nullptr);
+
+signals:
+  void newLine(const QString &line);
+
+private slots:
+  void handleFileChanged(const QString &);
+
+private:
+  QFile m_file;
+  QFileSystemWatcher *m_watcher = nullptr;
+  qint64 m_lastPos;
+};
+
+} // namespace deskflow::gui

src/lib/gui/core/CoreProcess.cpp

@@ -1,6 +1,6 @@
 /*
  * Deskflow -- mouse and keyboard sharing utility
- * SPDX-FileCopyrightText: (C) 2024 Symless Ltd.
+ * SPDX-FileCopyrightText: (C) 2024 - 2025 Symless Ltd.
  * SPDX-License-Identifier: GPL-2.0-only WITH LicenseRef-OpenSSL-Exception
  */
 
@@ -158,6 +158,15 @@ CoreProcess::CoreProcess(const IAppConfig &appConfig, const IServerConfig &serve
       m_pDeps(deps),
       m_daemonIpcClient{new ipc::DaemonIpcClient(this)}
 {
+  if (m_appConfig.processMode() == ProcessMode::kService) {
+    const auto logPath = requestDaemonLogPath();
+    if (!logPath.isEmpty()) {
+      qInfo() << "daemon log path:" << logPath;
+      m_daemonFileTail = new FileTail(logPath, this);
+      connect(m_daemonFileTail, &FileTail::newLine, this, &CoreProcess::handleLogLines);
+    }
+  }
+
   connect(&m_pDeps->process(), &QProcessProxy::finished, this, &CoreProcess::onProcessFinished);
 
   connect(
@@ -743,4 +752,21 @@ QString CoreProcess::correctedAddress() const
   return wrapIpv6(m_address);
 }
 
+QString CoreProcess::requestDaemonLogPath()
+{
+  qDebug() << "requesting daemon log path";
+  const auto logPath = m_daemonIpcClient->requestLogPath();
+  if (logPath.isEmpty()) {
+    qCritical() << "failed to get daemon log path";
+    return QString();
+  }
+
+  if (QFileInfo logFile(logPath); !logFile.exists() || !logFile.isFile()) {
+    qWarning() << "daemon log path file does not exist:" << logPath;
+    return QString();
+  }
+
+  return logPath;
+}
+
 } // namespace deskflow::gui

src/lib/gui/core/CoreProcess.h

@@ -1,22 +1,25 @@
 /*
  * Deskflow -- mouse and keyboard sharing utility
- * SPDX-FileCopyrightText: (C) 2024 Symless Ltd.
+ * SPDX-FileCopyrightText: (C) 2024 - 2025 Symless Ltd.
  * SPDX-License-Identifier: GPL-2.0-only WITH LicenseRef-OpenSSL-Exception
  */
 
 #pragma once
 
+#include "gui/FileTail.h"
 #include "gui/config/IAppConfig.h"
 #include "gui/config/IServerConfig.h"
 #include "gui/ipc/QIpcClient.h"
 #include "gui/proxy/QProcessProxy.h"
 
+#include <memory>
+
+#include <QFileSystemWatcher>
 #include <QMutex>
 #include <QObject>
 #include <QString>
 #include <QStringList>
 #include <QTimer>
-#include <memory>
 
 namespace deskflow::gui {
 
@@ -158,6 +161,7 @@ private:
   void handleLogLines(const QString &text);
   QString correctedInterface() const;
   QString correctedAddress() const;
+  QString requestDaemonLogPath();
 
 #ifdef Q_OS_MAC
   void checkOSXNotification(const QString &line);
@@ -176,6 +180,7 @@ private:
   QTimer m_retryTimer;
   int m_connections = 0;
   deskflow::gui::ipc::DaemonIpcClient *m_daemonIpcClient = nullptr;
+  FileTail *m_daemonFileTail = nullptr;
 };
 
 } // namespace deskflow::gui

src/lib/gui/ipc/DaemonIpcClient.cpp

@@ -18,8 +18,8 @@ namespace deskflow::gui::ipc {
 const auto kTimeout = 1000;
 
 DaemonIpcClient::DaemonIpcClient(QObject *parent)
-    : QObject(parent),                 //
-      m_socket{new QLocalSocket(this)} // NOSONAR
+    : QObject(parent),
+      m_socket{new QLocalSocket(this)} // NOSONAR - Qt memory
 {
 }
 
@@ -58,15 +58,59 @@ void DaemonIpcClient::handleErrorOccurred()
   m_connected = false;
 }
 
+bool DaemonIpcClient::sendMessage(const QString &message, const QString &expectAck, const bool expectConnected)
+{
+  if (expectConnected && !m_connected) {
+    qWarning() << "cannot send command, ipc not connected";
+    return false;
+  }
+
+  QByteArray messageData = message.toUtf8() + "\n";
+  m_socket->write(messageData);
+  if (!m_socket->waitForBytesWritten(kTimeout)) {
+    qWarning() << "ipc failed to write command";
+    return false;
+  }
+
+  if (!expectAck.isEmpty()) {
+    qDebug() << "ipc waiting for ack: " << expectAck;
+
+    if (!m_socket->waitForReadyRead(kTimeout)) {
+      qWarning() << "ipc failed to read response";
+      return false;
+    }
+
+    QByteArray response = m_socket->readAll();
+    if (response.isEmpty()) {
+      qWarning() << "ipc got empty response";
+      return false;
+    }
+
+    QString responseData = QString::fromUtf8(response);
+    if (responseData.isEmpty()) {
+      qWarning() << "ipc failed to convert response to string";
+      return false;
+    }
+
+    if (responseData != expectAck + "\n") {
+      qWarning() << "ipc got unexpected response: " << responseData;
+      return false;
+    }
+  }
+
+  qDebug() << "ipc sent message: " << messageData;
+  return true;
+}
+
 bool DaemonIpcClient::keepAlive()
 {
   if (!isConnected() && !connectToServer()) {
-    qWarning() << "ipc client keep alive failed to connect";
+    qWarning() << "ipc keep alive failed to connect";
     return false;
   }
 
   if (!sendMessage("noop")) {
-    qWarning() << "ipc client keep alive ping failed";
+    qWarning() << "ipc keep alive ping failed";
     m_connected = false;
     return false;
   }
@@ -104,44 +148,45 @@ bool DaemonIpcClient::sendStopProcess()
   return sendMessage("stop");
 }
 
-bool DaemonIpcClient::sendMessage(const QString &message, const QString &expectAck, const bool expectConnected)
+QString DaemonIpcClient::requestLogPath()
 {
-  if (expectConnected && !m_connected) {
-    qWarning() << "cannot send command, ipc not connected";
-    return false;
-  }
+  if (!keepAlive())
+    return QString();
 
-  QByteArray messageData = message.toUtf8() + "\n";
-  m_socket->write(messageData);
-  if (!m_socket->waitForBytesWritten(kTimeout)) {
-    qWarning() << "ipc client failed to write command";
-    return false;
+  if (!sendMessage("logPath", QString())) {
+    return QString();
   }
 
   if (!m_socket->waitForReadyRead(kTimeout)) {
-    qWarning() << "ipc client failed to read response";
-    return false;
+    qWarning() << "ipc failed to read log path response";
+    return QString();
   }
 
   QByteArray response = m_socket->readAll();
   if (response.isEmpty()) {
-    qWarning() << "ipc client got empty response";
-    return false;
+    qWarning() << "ipc got empty log path response";
+    return QString();
   }
 
   QString responseData = QString::fromUtf8(response);
   if (responseData.isEmpty()) {
-    qWarning() << "ipc client failed to convert response to string";
-    return false;
+    qWarning() << "ipc failed to convert log path response to string";
+    return QString();
   }
 
-  if (responseData != expectAck + "\n") {
-    qWarning() << "ipc client got unexpected response: " << responseData;
-    return false;
+  // Trimming removes newline from end of message.
+  QStringList parts = responseData.trimmed().split("=");
+  if (parts.size() != 2) {
+    qWarning() << "ipc got invalid log path response: " << responseData;
+    return QString();
   }
 
-  qDebug() << "ipc client sent message: " << messageData;
-  return true;
+  if (parts[0] != "logPath") {
+    qWarning() << "ipc got unexpected log path response: " << responseData;
+    return QString();
+  }
+
+  return parts[1];
 }
 
 } // namespace deskflow::gui::ipc

src/lib/gui/ipc/DaemonIpcClient.h

@@ -24,6 +24,7 @@ public:
   bool sendLogLevel(const QString &logLevel);
   bool sendStartProcess(const QString &command, ElevateMode elevateMode);
   bool sendStopProcess();
+  QString requestLogPath();
 
   bool isConnected() const
   {