diff --git a/src/lib/arch/unix/ArchNetworkBSD.cpp b/src/lib/arch/unix/ArchNetworkBSD.cpp
index 064bd4c3b..5ab65c7db 100644
--- a/src/lib/arch/unix/ArchNetworkBSD.cpp
+++ b/src/lib/arch/unix/ArchNetworkBSD.cpp
@@ -751,7 +751,7 @@ const int *ArchNetworkBSD::getUnblockPipeForThread(ArchThread thread)
   return unblockPipe;
 }
 
-void ArchNetworkBSD::throwError(int err)
+void ArchNetworkBSD::throwError(int err) const
 {
   switch (err) {
   case EINTR:
@@ -822,7 +822,7 @@ void ArchNetworkBSD::throwError(int err)
   }
 }
 
-void ArchNetworkBSD::throwNameError(int err)
+void ArchNetworkBSD::throwNameError(int err) const
 {
   static const char *s_msg[] = {
       "The specified host is unknown", "The requested name is valid but does not have an IP address",
diff --git a/src/lib/arch/unix/ArchNetworkBSD.h b/src/lib/arch/unix/ArchNetworkBSD.h
index 8fc68c896..530a96ddc 100644
--- a/src/lib/arch/unix/ArchNetworkBSD.h
+++ b/src/lib/arch/unix/ArchNetworkBSD.h
@@ -123,8 +123,8 @@ private:
   const int *getUnblockPipe();
   const int *getUnblockPipeForThread(ArchThread);
   void setBlockingOnSocket(int fd, bool blocking);
-  void throwError(int);
-  void throwNameError(int);
+  void throwError(int) const;
+  void throwNameError(int) const;
 
 private:
   std::shared_ptr<Deps> m_pDeps;
diff --git a/src/lib/base/LogOutputters.cpp b/src/lib/base/LogOutputters.cpp
index 08185f577..a7b2277d0 100644
--- a/src/lib/base/LogOutputters.cpp
+++ b/src/lib/base/LogOutputters.cpp
@@ -72,8 +72,9 @@ bool ConsoleLogOutputter::write(ELevel level, const char *msg)
   return true;
 }
 
-void ConsoleLogOutputter::flush()
+void ConsoleLogOutputter::flush() const
 {
+  // do nothing
 }
 
 //
diff --git a/src/lib/base/LogOutputters.h b/src/lib/base/LogOutputters.h
index 3df6c4800..a2d3f925d 100644
--- a/src/lib/base/LogOutputters.h
+++ b/src/lib/base/LogOutputters.h
@@ -47,7 +47,7 @@ public:
   void close() override;
   void show(bool showIfEmpty) override;
   bool write(ELevel level, const char *message) override;
-  void flush();
+  void flush() const;
 };
 
 //! Write log to file
diff --git a/src/lib/deskflow/App.cpp b/src/lib/deskflow/App.cpp
index 8a874f734..0c060343f 100644
--- a/src/lib/deskflow/App.cpp
+++ b/src/lib/deskflow/App.cpp
@@ -135,7 +135,7 @@ void App::setupFileLogging()
   }
 }
 
-void App::loggingFilterWarning()
+void App::loggingFilterWarning() const
 {
   if (CLOG->getFilter() > CLOG->getConsoleMaxLevel()) {
     if (argsBase().m_logFile == nullptr) {
diff --git a/src/lib/deskflow/App.h b/src/lib/deskflow/App.h
index e6c756325..dbf88be0c 100644
--- a/src/lib/deskflow/App.h
+++ b/src/lib/deskflow/App.h
@@ -80,7 +80,7 @@ public:
   int run(int argc, char **argv);
   int daemonMainLoop(int, const char **);
   void setupFileLogging();
-  void loggingFilterWarning();
+  void loggingFilterWarning() const;
   void initApp(int argc, const char **argv) override;
   void initApp(int argc, char **argv)
   {
diff --git a/src/lib/deskflow/ArgParser.cpp b/src/lib/deskflow/ArgParser.cpp
index 9f0b09f4c..307193083 100644
--- a/src/lib/deskflow/ArgParser.cpp
+++ b/src/lib/deskflow/ArgParser.cpp
@@ -143,7 +143,7 @@ bool ArgParser::parsePlatformArgs(
 #endif
 }
 
-bool ArgParser::parseGenericArgs(int argc, const char *const *argv, int &i)
+bool ArgParser::parseGenericArgs(int argc, const char *const *argv, int &i) const
 {
   if (isArg(i, argc, argv, "-a", "--address", 1)) {
     argsBase().m_deskflowAddress = argv[++i];
@@ -197,7 +197,7 @@ bool ArgParser::parseGenericArgs(int argc, const char *const *argv, int &i)
   return true;
 }
 
-bool ArgParser::parseDeprecatedArgs(int argc, const char *const *argv, int &i)
+bool ArgParser::parseDeprecatedArgs(int argc, const char *const *argv, int &i) const
 {
   static const std::vector<const char *> deprecatedArgs = {
       "--crypto-pass", "--res-w", "--res-h", "--prm-wc", "--prm-hc"
@@ -353,13 +353,13 @@ ArgParser::assembleCommand(std::vector<std::string> &argsArray, std::string igno
   return result;
 }
 
-void ArgParser::updateCommonArgs(const char *const *argv)
+void ArgParser::updateCommonArgs(const char *const *argv) const
 {
   argsBase().m_name = ARCH->getHostName();
   argsBase().m_pname = QFileInfo(argv[0]).fileName().toLocal8Bit().constData();
 }
 
-bool ArgParser::checkUnexpectedArgs()
+bool ArgParser::checkUnexpectedArgs() const
 {
 #if SYSAPI_WIN32
   // suggest that user installs as a windows service. when launched as
diff --git a/src/lib/deskflow/ArgParser.h b/src/lib/deskflow/ArgParser.h
index 8e9acba07..f5075a4fe 100644
--- a/src/lib/deskflow/ArgParser.h
+++ b/src/lib/deskflow/ArgParser.h
@@ -26,9 +26,9 @@ public:
   bool parseServerArgs(deskflow::ServerArgs &args, int argc, const char *const *argv);
   bool parseClientArgs(deskflow::ClientArgs &args, int argc, const char *const *argv);
   bool parsePlatformArgs(deskflow::ArgsBase &argsBase, const int &argc, const char *const *argv, int &i, bool isServer);
-  bool parseGenericArgs(int argc, const char *const *argv, int &i);
-  bool parseDeprecatedArgs(int argc, const char *const *argv, int &i);
-  void setArgsBase(deskflow::ArgsBase &argsBase)
+  bool parseGenericArgs(int argc, const char *const *argv, int &i) const;
+  bool parseDeprecatedArgs(int argc, const char *const *argv, int &i) const;
+  void setArgsBase(deskflow::ArgsBase &argsBase) const
   {
     m_argsBase = &argsBase;
   }
@@ -49,8 +49,8 @@ public:
   }
 
 private:
-  void updateCommonArgs(const char *const *argv);
-  bool checkUnexpectedArgs();
+  void updateCommonArgs(const char *const *argv) const;
+  bool checkUnexpectedArgs() const;
 
 private:
   App *m_app;
diff --git a/src/lib/deskflow/ClientApp.cpp b/src/lib/deskflow/ClientApp.cpp
index 19a3f38e5..9da13fcdf 100644
--- a/src/lib/deskflow/ClientApp.cpp
+++ b/src/lib/deskflow/ClientApp.cpp
@@ -204,17 +204,18 @@ void ClientApp::updateStatus()
   updateStatus("");
 }
 
-void ClientApp::updateStatus(const std::string &msg)
+void ClientApp::updateStatus(const std::string &msg) const
 {
+  // do nothing
 }
 
-void ClientApp::resetRestartTimeout()
+void ClientApp::resetRestartTimeout() const
 {
   // retry time can nolonger be changed
   // s_retryTime = 0.0;
 }
 
-double ClientApp::nextRestartTimeout()
+double ClientApp::nextRestartTimeout() const
 {
   // retry at a constant rate (Issue 52)
   return RETRY_TIME;
diff --git a/src/lib/deskflow/ClientApp.h b/src/lib/deskflow/ClientApp.h
index dc4fc91d0..4b61286b4 100644
--- a/src/lib/deskflow/ClientApp.h
+++ b/src/lib/deskflow/ClientApp.h
@@ -62,9 +62,9 @@ public:
   //
 
   void updateStatus();
-  void updateStatus(const std::string &msg);
-  void resetRestartTimeout();
-  double nextRestartTimeout();
+  void updateStatus(const std::string &msg) const;
+  void resetRestartTimeout() const;
+  double nextRestartTimeout() const;
   void handleScreenError(const Event &, void *);
   deskflow::Screen *openClientScreen();
   void closeClientScreen(deskflow::Screen *screen);
diff --git a/src/lib/deskflow/KeyState.h b/src/lib/deskflow/KeyState.h
index 56ecbb753..67f159c86 100644
--- a/src/lib/deskflow/KeyState.h
+++ b/src/lib/deskflow/KeyState.h
@@ -72,7 +72,7 @@ public:
   int32_t pollActiveGroup() const override = 0;
   void pollPressedKeys(KeyButtonSet &pressedKeys) const override = 0;
 
-  int32_t getKeyState(KeyButton keyButton)
+  int32_t getKeyState(KeyButton keyButton) const
   {
     return m_keys[keyButton];
   }
diff --git a/src/lib/deskflow/Screen.cpp b/src/lib/deskflow/Screen.cpp
index 6606e8a83..a3e23b493 100644
--- a/src/lib/deskflow/Screen.cpp
+++ b/src/lib/deskflow/Screen.cpp
@@ -225,7 +225,7 @@ void Screen::mouseMove(int32_t x, int32_t y)
   m_screen->fakeMouseMove(x, y);
 }
 
-void Screen::mouseRelativeMove(int32_t dx, int32_t dy)
+void Screen::mouseRelativeMove(int32_t dx, int32_t dy) const
 {
   assert(!m_isPrimary);
   m_screen->fakeMouseRelativeMove(dx, dy);
@@ -400,12 +400,12 @@ void Screen::disableSecondary()
   m_screen->closeScreensaver();
 }
 
-void Screen::enterPrimary()
+void Screen::enterPrimary() const
 {
   // do nothing
 }
 
-void Screen::enterSecondary(KeyModifierMask)
+void Screen::enterSecondary(KeyModifierMask) const
 {
   // do nothing
 }
diff --git a/src/lib/deskflow/Screen.h b/src/lib/deskflow/Screen.h
index fc52de579..7de62a069 100644
--- a/src/lib/deskflow/Screen.h
+++ b/src/lib/deskflow/Screen.h
@@ -153,7 +153,7 @@ public:
   Synthesize mouse events to generate mouse motion by the relative
   amount \c xRel,yRel.
   */
-  void mouseRelativeMove(int32_t xRel, int32_t yRel);
+  void mouseRelativeMove(int32_t xRel, int32_t yRel) const;
 
   //! Notify of mouse wheel motion
   /*!
@@ -285,8 +285,8 @@ protected:
   void disablePrimary();
   void disableSecondary();
 
-  void enterPrimary();
-  void enterSecondary(KeyModifierMask toggleMask);
+  void enterPrimary() const;
+  void enterSecondary(KeyModifierMask toggleMask) const;
   void leavePrimary();
   void leaveSecondary();
 
diff --git a/src/lib/deskflow/ServerApp.cpp b/src/lib/deskflow/ServerApp.cpp
index 578d98173..9d2b3ec8b 100644
--- a/src/lib/deskflow/ServerApp.cpp
+++ b/src/lib/deskflow/ServerApp.cpp
@@ -269,8 +269,9 @@ void ServerApp::updateStatus()
   updateStatus("");
 }
 
-void ServerApp::updateStatus(const std::string &msg)
+void ServerApp::updateStatus(const std::string &msg) const
 {
+  // do nothing
 }
 
 void ServerApp::closeClientListener(ClientListener *listen)
@@ -603,6 +604,7 @@ void ServerApp::handleNoClients(const Event &, void *)
 
 void ServerApp::handleScreenSwitched(const Event &e, void *)
 {
+  // do nothing
 }
 
 ISocketFactory *ServerApp::getSocketFactory() const
diff --git a/src/lib/deskflow/ServerApp.h b/src/lib/deskflow/ServerApp.h
index af25c9bf1..b82e11cb9 100644
--- a/src/lib/deskflow/ServerApp.h
+++ b/src/lib/deskflow/ServerApp.h
@@ -86,7 +86,7 @@ public:
   void closeServer(Server *server);
   void stopRetryTimer();
   void updateStatus();
-  void updateStatus(const std::string &msg);
+  void updateStatus(const std::string &msg) const;
   void closeClientListener(ClientListener *listen);
   void stopServer();
   void closePrimaryClient(PrimaryClient *primaryClient);
diff --git a/src/lib/gui/MainWindow.cpp b/src/lib/gui/MainWindow.cpp
index c1b2c9fc0..b1f0d6e1d 100644
--- a/src/lib/gui/MainWindow.cpp
+++ b/src/lib/gui/MainWindow.cpp
@@ -701,7 +701,7 @@ void MainWindow::applyConfig()
   updateModeControls(coreMode == Settings::CoreMode::Server);
 }
 
-void MainWindow::saveSettings()
+void MainWindow::saveSettings() const
 {
   if (ui->rbModeClient->isChecked()) {
     Settings::setValue(Settings::Core::CoreMode, Settings::CoreMode::Client);
@@ -1116,7 +1116,7 @@ void MainWindow::setHostName()
   applyConfig();
 }
 
-QString MainWindow::trustedFingerprintDatabase()
+QString MainWindow::trustedFingerprintDatabase() const
 {
   const bool isClient = m_coreProcess.mode() == CoreMode::Client;
   return isClient ? Settings::tlsTrustedServersDb() : Settings::tlsTrustedClientsDb();
diff --git a/src/lib/gui/MainWindow.h b/src/lib/gui/MainWindow.h
index 741c34c70..11095ebe5 100644
--- a/src/lib/gui/MainWindow.h
+++ b/src/lib/gui/MainWindow.h
@@ -142,7 +142,7 @@ private:
   void handleLogLine(const QString &line);
   void updateLocalFingerprint();
   void updateScreenName();
-  void saveSettings();
+  void saveSettings() const;
   void showConfigureServer(const QString &message);
   void restoreWindow();
   void setupControls();
@@ -159,7 +159,7 @@ private:
    * @brief trustedFingerprintDatabase get the FingerprintDatabase for the trusted clients or trusted servers.
    * @return The path to the trusted fingerprint file
    */
-  QString trustedFingerprintDatabase();
+  QString trustedFingerprintDatabase() const;
 
   // Generate prints if they are missing
   // Returns true if successful
diff --git a/src/lib/gui/ServerConfig.cpp b/src/lib/gui/ServerConfig.cpp
index 9fc4ae527..ac22557f2 100644
--- a/src/lib/gui/ServerConfig.cpp
+++ b/src/lib/gui/ServerConfig.cpp
@@ -454,12 +454,12 @@ void ServerConfig::addClient(const QString &clientName)
   m_Screens.addScreenByPriority(Screen(clientName));
 }
 
-void ServerConfig::setConfigFile(const QString &configFile)
+void ServerConfig::setConfigFile(const QString &configFile) const
 {
   Settings::setValue(Settings::Server::ExternalConfigFile, configFile);
 }
 
-void ServerConfig::setUseExternalConfig(bool useExternalConfig)
+void ServerConfig::setUseExternalConfig(bool useExternalConfig) const
 {
   Settings::setValue(Settings::Server::ExternalConfig, useExternalConfig);
 }
diff --git a/src/lib/gui/ServerConfig.h b/src/lib/gui/ServerConfig.h
index 8665abe58..39ba13368 100644
--- a/src/lib/gui/ServerConfig.h
+++ b/src/lib/gui/ServerConfig.h
@@ -241,8 +241,8 @@ private:
   {
     m_ClipboardSharing = on;
   }
-  void setConfigFile(const QString &configFile);
-  void setUseExternalConfig(bool useExternalConfig);
+  void setConfigFile(const QString &configFile) const;
+  void setUseExternalConfig(bool useExternalConfig) const;
   size_t setClipboardSharingSize(size_t size);
   QList<bool> &switchCorners()
   {
diff --git a/src/lib/gui/core/CoreProcess.cpp b/src/lib/gui/core/CoreProcess.cpp
index 667a59520..2d7d14a85 100644
--- a/src/lib/gui/core/CoreProcess.cpp
+++ b/src/lib/gui/core/CoreProcess.cpp
@@ -700,7 +700,7 @@ QString CoreProcess::requestDaemonLogPath()
   return logPath;
 }
 
-void CoreProcess::persistLogDir()
+void CoreProcess::persistLogDir() const
 {
   QDir(QFileInfo(Settings::value(Settings::Log::File).toString()).absolutePath()).mkpath(".");
 }
diff --git a/src/lib/gui/core/CoreProcess.h b/src/lib/gui/core/CoreProcess.h
index 2388a512f..7c3c588c5 100644
--- a/src/lib/gui/core/CoreProcess.h
+++ b/src/lib/gui/core/CoreProcess.h
@@ -147,7 +147,7 @@ private:
   QString correctedInterface() const;
   QString correctedAddress() const;
   QString requestDaemonLogPath();
-  void persistLogDir();
+  void persistLogDir() const;
 
 #ifdef Q_OS_MAC
   void checkOSXNotification(const QString &line);
diff --git a/src/lib/gui/dialogs/AboutDialog.cpp b/src/lib/gui/dialogs/AboutDialog.cpp
index 1467cc26a..ec1917a5b 100644
--- a/src/lib/gui/dialogs/AboutDialog.cpp
+++ b/src/lib/gui/dialogs/AboutDialog.cpp
@@ -45,7 +45,7 @@ AboutDialog::AboutDialog(QWidget *parent) : QDialog(parent), ui{std::make_unique
   setMinimumSize(size());
 }
 
-void AboutDialog::copyVersionText()
+void AboutDialog::copyVersionText() const
 {
   QString infoString = QStringLiteral("Deskflow: %1 (%2)\nQt: %3\nSystem: %4")
                            .arg(kVersion, kVersionGitSha, qVersion(), QSysInfo::prettyProductName());
diff --git a/src/lib/gui/dialogs/AboutDialog.h b/src/lib/gui/dialogs/AboutDialog.h
index 86ce0c058..245762986 100644
--- a/src/lib/gui/dialogs/AboutDialog.h
+++ b/src/lib/gui/dialogs/AboutDialog.h
@@ -23,7 +23,7 @@ public:
 
 private:
   std::unique_ptr<Ui::AboutDialog> ui;
-  void copyVersionText();
+  void copyVersionText() const;
 
   inline static const auto s_awesomeDevs = QStringList{
       // Chris is the ultimate creator, and the one who started it all in 2001.
diff --git a/src/lib/gui/dialogs/AddClientDialog.h b/src/lib/gui/dialogs/AddClientDialog.h
index f9b9f8d14..7ab746e8e 100644
--- a/src/lib/gui/dialogs/AddClientDialog.h
+++ b/src/lib/gui/dialogs/AddClientDialog.h
@@ -32,7 +32,7 @@ public:
   AddClientDialog(const QString &clientName, QWidget *parent = nullptr);
   ~AddClientDialog() override;
 
-  int addResult()
+  int addResult() const
   {
     return m_AddResult;
   }
diff --git a/src/lib/gui/dialogs/SettingsDialog.cpp b/src/lib/gui/dialogs/SettingsDialog.cpp
index 94a3135c4..300b66e14 100644
--- a/src/lib/gui/dialogs/SettingsDialog.cpp
+++ b/src/lib/gui/dialogs/SettingsDialog.cpp
@@ -54,7 +54,7 @@ SettingsDialog::SettingsDialog(QWidget *parent, const IServerConfig &serverConfi
   initConnections();
 }
 
-void SettingsDialog::initConnections()
+void SettingsDialog::initConnections() const
 {
   connect(this, &SettingsDialog::shown, this, &SettingsDialog::showReadOnlyMessage, Qt::QueuedConnection);
 
@@ -281,7 +281,7 @@ void SettingsDialog::updateControls()
   updateTlsControls();
 }
 
-void SettingsDialog::updateRequestedKeySize()
+void SettingsDialog::updateRequestedKeySize() const
 {
   if (ui->comboTlsKeyLength->currentText() == Settings::value(Settings::Security::KeySize).toString())
     return;
diff --git a/src/lib/gui/dialogs/SettingsDialog.h b/src/lib/gui/dialogs/SettingsDialog.h
index 36091424f..7ad0c99af 100644
--- a/src/lib/gui/dialogs/SettingsDialog.h
+++ b/src/lib/gui/dialogs/SettingsDialog.h
@@ -34,7 +34,7 @@ signals:
   void shown();
 
 private:
-  void initConnections();
+  void initConnections() const;
   void regenCertificates();
   void browseCertificatePath();
   void browseLogPath();
@@ -56,7 +56,7 @@ private:
   void updateControls();
 
   /// @brief updates the setting vaule for key size.
-  void updateRequestedKeySize();
+  void updateRequestedKeySize() const;
 
   std::unique_ptr<Ui::SettingsDialog> ui;
   const IServerConfig &m_serverConfig;
diff --git a/src/lib/gui/tls/TlsCertificate.cpp b/src/lib/gui/tls/TlsCertificate.cpp
index 8efba6c1b..68ad8fbe1 100644
--- a/src/lib/gui/tls/TlsCertificate.cpp
+++ b/src/lib/gui/tls/TlsCertificate.cpp
@@ -48,7 +48,7 @@ bool TlsCertificate::generateCertificate(const QString &path, int keyLength)
   return generateFingerprint(path);
 }
 
-bool TlsCertificate::generateFingerprint(const QString &certificateFilename)
+bool TlsCertificate::generateFingerprint(const QString &certificateFilename) const
 {
   qDebug("generating tls fingerprint");
   const std::string certPath = certificateFilename.toStdString();
@@ -57,12 +57,12 @@ bool TlsCertificate::generateFingerprint(const QString &certificateFilename)
   return db.write(Settings::tlsLocalDb());
 }
 
-int TlsCertificate::getCertKeyLength(const QString &path)
+int TlsCertificate::getCertKeyLength(const QString &path) const
 {
   return deskflow::getCertLength(path.toStdString());
 }
 
-bool TlsCertificate::isCertificateValid(const QString &path)
+bool TlsCertificate::isCertificateValid(const QString &path) const
 {
   OpenSSL_add_all_algorithms();
   ERR_load_crypto_strings();
diff --git a/src/lib/gui/tls/TlsCertificate.h b/src/lib/gui/tls/TlsCertificate.h
index 172d50be4..4c82bd3cc 100644
--- a/src/lib/gui/tls/TlsCertificate.h
+++ b/src/lib/gui/tls/TlsCertificate.h
@@ -16,8 +16,8 @@ class TlsCertificate : public QObject
 public:
   explicit TlsCertificate(QObject *parent = nullptr);
 
-  bool isCertificateValid(const QString &path);
+  bool isCertificateValid(const QString &path) const;
   bool generateCertificate(const QString &path, int keyLength);
-  bool generateFingerprint(const QString &certificateFilename);
-  int getCertKeyLength(const QString &path);
+  bool generateFingerprint(const QString &certificateFilename) const;
+  int getCertKeyLength(const QString &path) const;
 };
diff --git a/src/lib/net/FingerprintDatabase.cpp b/src/lib/net/FingerprintDatabase.cpp
index 68a325583..22762b541 100644
--- a/src/lib/net/FingerprintDatabase.cpp
+++ b/src/lib/net/FingerprintDatabase.cpp
@@ -87,7 +87,7 @@ void FingerprintDatabase::addTrusted(const Fingerprint &fingerprint)
   m_fingerprints.append(fingerprint);
 }
 
-bool FingerprintDatabase::isTrusted(const Fingerprint &fingerprint)
+bool FingerprintDatabase::isTrusted(const Fingerprint &fingerprint) const
 {
   return m_fingerprints.contains(fingerprint);
 }
diff --git a/src/lib/net/FingerprintDatabase.h b/src/lib/net/FingerprintDatabase.h
index 5c61966fe..57e9f9881 100644
--- a/src/lib/net/FingerprintDatabase.h
+++ b/src/lib/net/FingerprintDatabase.h
@@ -22,7 +22,7 @@ public:
 
   void clear();
   void addTrusted(const Fingerprint &fingerprint);
-  bool isTrusted(const Fingerprint &fingerprint);
+  bool isTrusted(const Fingerprint &fingerprint) const;
 
   const QList<Fingerprint> &fingerprints() const
   {
diff --git a/src/lib/net/NetworkAddress.cpp b/src/lib/net/NetworkAddress.cpp
index d9a163075..16d0d9b17 100644
--- a/src/lib/net/NetworkAddress.cpp
+++ b/src/lib/net/NetworkAddress.cpp
@@ -201,7 +201,7 @@ std::string NetworkAddress::getHostname() const
   return m_hostname;
 }
 
-void NetworkAddress::checkPort()
+void NetworkAddress::checkPort() const
 {
   // check port number
   if (m_port < 0 || m_port > 65535) {
diff --git a/src/lib/net/NetworkAddress.h b/src/lib/net/NetworkAddress.h
index 2d7edd9cb..30b88ca0a 100644
--- a/src/lib/net/NetworkAddress.h
+++ b/src/lib/net/NetworkAddress.h
@@ -105,7 +105,7 @@ public:
   //@}
 
 private:
-  void checkPort();
+  void checkPort() const;
 
 private:
   ArchNetAddress m_address = nullptr;
diff --git a/src/lib/net/SecureSocket.cpp b/src/lib/net/SecureSocket.cpp
index a5e5b5fd7..14cf63b47 100644
--- a/src/lib/net/SecureSocket.cpp
+++ b/src/lib/net/SecureSocket.cpp
@@ -287,7 +287,7 @@ int SecureSocket::secureWrite(const void *buffer, int size, int &wrote)
   return wrote;
 }
 
-bool SecureSocket::isSecureReady()
+bool SecureSocket::isSecureReady() const
 {
   return m_secureReady;
 }
@@ -643,7 +643,7 @@ void SecureSocket::disconnect()
   sendEvent(EventTypes::StreamInputShutdown);
 }
 
-bool SecureSocket::verifyCertFingerprint(const QString &FingerprintDatabasePath)
+bool SecureSocket::verifyCertFingerprint(const QString &FingerprintDatabasePath) const
 {
   const auto cert = SSL_get_peer_certificate(m_ssl->m_ssl);
   const auto sha256 = deskflow::sslCertFingerprint(cert, Fingerprint::Type::SHA256);
diff --git a/src/lib/net/SecureSocket.h b/src/lib/net/SecureSocket.h
index cddc7c577..22bbd6959 100644
--- a/src/lib/net/SecureSocket.h
+++ b/src/lib/net/SecureSocket.h
@@ -57,7 +57,7 @@ public:
   {
     m_fatal = b;
   }
-  bool isSecureReady();
+  bool isSecureReady() const;
   void secureConnect();
   void secureAccept();
   int secureRead(void *buffer, int size, int &read);
@@ -77,7 +77,7 @@ private:
   bool showCertificate() const;
   void checkResult(int n, int &retry);
   void disconnect();
-  bool verifyCertFingerprint(const QString &FingerprintDatabasePath);
+  bool verifyCertFingerprint(const QString &FingerprintDatabasePath) const;
 
   ISocketMultiplexerJob *serviceConnect(ISocketMultiplexerJob *, bool, bool, bool);
 
diff --git a/src/lib/net/TCPSocket.h b/src/lib/net/TCPSocket.h
index 8c2b0c9a6..3e1f5c290 100644
--- a/src/lib/net/TCPSocket.h
+++ b/src/lib/net/TCPSocket.h
@@ -79,11 +79,11 @@ protected:
 
   void setJob(ISocketMultiplexerJob *);
 
-  bool isReadable()
+  bool isReadable() const
   {
     return m_readable;
   }
-  bool isWritable()
+  bool isWritable() const
   {
     return m_writable;
   }
diff --git a/src/lib/platform/EiScreen.cpp b/src/lib/platform/EiScreen.cpp
index 7bf3681fa..699cb77c7 100644
--- a/src/lib/platform/EiScreen.cpp
+++ b/src/lib/platform/EiScreen.cpp
@@ -91,7 +91,7 @@ EiScreen::~EiScreen()
   delete portal_input_capture_;
 }
 
-void EiScreen::handle_ei_log_event(ei *ei, ei_log_priority priority, const char *message, ei_log_context *context)
+void EiScreen::handle_ei_log_event(ei *ei, ei_log_priority priority, const char *message, ei_log_context *context) const
 {
   switch (priority) {
   case EI_LOG_PRIORITY_DEBUG:
@@ -693,7 +693,7 @@ void EiScreen::on_motion_event(ei_event *event)
   }
 }
 
-void EiScreen::on_abs_motion_event(ei_event *event)
+void EiScreen::on_abs_motion_event(ei_event *event) const
 {
   assert(is_primary_);
 }
diff --git a/src/lib/platform/EiScreen.h b/src/lib/platform/EiScreen.h
index 1ea378cdb..eed7739e7 100644
--- a/src/lib/platform/EiScreen.h
+++ b/src/lib/platform/EiScreen.h
@@ -96,9 +96,9 @@ private:
   void on_pointer_scroll_event(ei_event *event);
   void on_pointer_scroll_discrete_event(ei_event *event);
   void on_motion_event(ei_event *event);
-  void on_abs_motion_event(ei_event *event);
+  void on_abs_motion_event(ei_event *event) const;
   bool on_hotkey(KeyID key, bool is_press, KeyModifierMask mask);
-  void handle_ei_log_event(ei *ei, ei_log_priority priority, const char *message, ei_log_context *context);
+  void handle_ei_log_event(ei *ei, ei_log_priority priority, const char *message, ei_log_context *context) const;
   void handle_connected_to_eis_event(const Event &event, void *);
   void handle_portal_session_closed(const Event &event, void *);
 
diff --git a/src/lib/platform/PortalInputCapture.cpp b/src/lib/platform/PortalInputCapture.cpp
index 9744a8b45..5cb6b4b02 100644
--- a/src/lib/platform/PortalInputCapture.cpp
+++ b/src/lib/platform/PortalInputCapture.cpp
@@ -73,12 +73,12 @@ PortalInputCapture::~PortalInputCapture()
   g_object_unref(portal_);
 }
 
-gboolean PortalInputCapture::timeout_handler()
+gboolean PortalInputCapture::timeout_handler() const
 {
   return true; // keep re-triggering
 }
 
-int PortalInputCapture::fake_eis_fd()
+int PortalInputCapture::fake_eis_fd() const
 {
   auto path = std::getenv("LIBEI_SOCKET");
 
diff --git a/src/lib/platform/PortalInputCapture.h b/src/lib/platform/PortalInputCapture.h
index 67a8fbd57..b01cc51ab 100644
--- a/src/lib/platform/PortalInputCapture.h
+++ b/src/lib/platform/PortalInputCapture.h
@@ -34,7 +34,7 @@ public:
 
 private:
   void glib_thread(void *);
-  gboolean timeout_handler();
+  gboolean timeout_handler() const;
   gboolean init_input_capture_session();
   void cb_init_input_capture_session(GObject *object, GAsyncResult *res);
   void cb_set_pointer_barriers(GObject *object, GAsyncResult *res);
@@ -68,7 +68,7 @@ private:
     reinterpret_cast<PortalInputCapture *>(data)->cb_zones_changed(session, options);
   }
 
-  int fake_eis_fd();
+  int fake_eis_fd() const;
 
 private:
   EiScreen *screen_ = nullptr;
diff --git a/src/lib/platform/PortalRemoteDesktop.cpp b/src/lib/platform/PortalRemoteDesktop.cpp
index fc7120f1f..dee405681 100644
--- a/src/lib/platform/PortalRemoteDesktop.cpp
+++ b/src/lib/platform/PortalRemoteDesktop.cpp
@@ -49,7 +49,7 @@ PortalRemoteDesktop::~PortalRemoteDesktop()
   free(session_restore_token_);
 }
 
-gboolean PortalRemoteDesktop::timeout_handler()
+gboolean PortalRemoteDesktop::timeout_handler() const
 {
   return true; // keep re-triggering
 }
diff --git a/src/lib/platform/PortalRemoteDesktop.h b/src/lib/platform/PortalRemoteDesktop.h
index 0927916d5..b9c2c0d12 100644
--- a/src/lib/platform/PortalRemoteDesktop.h
+++ b/src/lib/platform/PortalRemoteDesktop.h
@@ -23,7 +23,7 @@ public:
 
 private:
   void glib_thread(void *);
-  gboolean timeout_handler();
+  gboolean timeout_handler() const;
   gboolean init_remote_desktop_session();
   void cb_init_remote_desktop_session(GObject *object, GAsyncResult *res);
   void cb_session_started(GObject *object, GAsyncResult *res);
diff --git a/src/lib/platform/XWindowsScreen.cpp b/src/lib/platform/XWindowsScreen.cpp
index cc15b7b4e..c3efc68b6 100644
--- a/src/lib/platform/XWindowsScreen.cpp
+++ b/src/lib/platform/XWindowsScreen.cpp
@@ -1642,7 +1642,7 @@ ClipboardID XWindowsScreen::getClipboardID(Atom selection) const
   return kClipboardEnd;
 }
 
-void XWindowsScreen::processClipboardRequest(Window requestor, Time time, Atom property)
+void XWindowsScreen::processClipboardRequest(Window requestor, Time time, Atom property) const
 {
   // check every clipboard until one returns success
   for (ClipboardID id = 0; id < kClipboardEnd; ++id) {
@@ -1652,7 +1652,7 @@ void XWindowsScreen::processClipboardRequest(Window requestor, Time time, Atom p
   }
 }
 
-void XWindowsScreen::destroyClipboardRequest(Window requestor)
+void XWindowsScreen::destroyClipboardRequest(Window requestor) const
 {
   // check every clipboard until one returns success
   for (ClipboardID id = 0; id < kClipboardEnd; ++id) {
diff --git a/src/lib/platform/XWindowsScreen.h b/src/lib/platform/XWindowsScreen.h
index 7b28c8442..a359c9dff 100644
--- a/src/lib/platform/XWindowsScreen.h
+++ b/src/lib/platform/XWindowsScreen.h
@@ -100,10 +100,10 @@ private:
   ClipboardID getClipboardID(Atom selection) const;
 
   // continue processing a selection request
-  void processClipboardRequest(Window window, Time time, Atom property);
+  void processClipboardRequest(Window window, Time time, Atom property) const;
 
   // terminate a selection request
-  void destroyClipboardRequest(Window window);
+  void destroyClipboardRequest(Window window) const;
 
   // X I/O error handler
   void onError();
diff --git a/src/lib/server/ClientProxy.cpp b/src/lib/server/ClientProxy.cpp
index bbbd62bf0..95abf236e 100644
--- a/src/lib/server/ClientProxy.cpp
+++ b/src/lib/server/ClientProxy.cpp
@@ -25,7 +25,7 @@ ClientProxy::~ClientProxy()
   delete m_stream;
 }
 
-void ClientProxy::close(const char *msg)
+void ClientProxy::close(const char *msg) const
 {
   LOG((CLOG_DEBUG1 "send close \"%s\" to \"%s\"", msg, getName().c_str()));
   ProtocolUtil::writef(getStream(), msg);
diff --git a/src/lib/server/ClientProxy.h b/src/lib/server/ClientProxy.h
index 44fa15029..d33463e33 100644
--- a/src/lib/server/ClientProxy.h
+++ b/src/lib/server/ClientProxy.h
@@ -37,7 +37,7 @@ public:
   /*!
   Ask the client to disconnect, using \p msg as the reason.
   */
-  void close(const char *msg);
+  void close(const char *msg) const;
 
   //@}
   //! @name accessors
diff --git a/src/lib/server/ClientProxy1_5.cpp b/src/lib/server/ClientProxy1_5.cpp
index 2ed05d990..0b4828b9f 100644
--- a/src/lib/server/ClientProxy1_5.cpp
+++ b/src/lib/server/ClientProxy1_5.cpp
@@ -49,12 +49,12 @@ bool ClientProxy1_5::parseMessage(const uint8_t *code)
   return true;
 }
 
-void ClientProxy1_5::fileChunkReceived()
+void ClientProxy1_5::fileChunkReceived() const
 {
   // do nothing
 }
 
-void ClientProxy1_5::dragInfoReceived()
+void ClientProxy1_5::dragInfoReceived() const
 {
   // do nothing
 }
diff --git a/src/lib/server/ClientProxy1_5.h b/src/lib/server/ClientProxy1_5.h
index b733d870e..7b25e7a52 100644
--- a/src/lib/server/ClientProxy1_5.h
+++ b/src/lib/server/ClientProxy1_5.h
@@ -29,8 +29,8 @@ public:
   void sendDragInfo(uint32_t fileCount, const char *info, size_t size) override;
   void fileChunkSending(uint8_t mark, char *data, size_t dataSize) override;
   bool parseMessage(const uint8_t *code) override;
-  void fileChunkReceived();
-  void dragInfoReceived();
+  void fileChunkReceived() const;
+  void dragInfoReceived() const;
 
 private:
   IEventQueue *m_events;
diff --git a/src/lib/server/Config.h b/src/lib/server/Config.h
index 91d1783fc..e17e2fc09 100644
--- a/src/lib/server/Config.h
+++ b/src/lib/server/Config.h
@@ -160,11 +160,11 @@ public:
       m_i = i.m_i;
       return *this;
     }
-    std::string operator*()
+    std::string operator*() const
     {
       return m_i->first;
     }
-    const std::string *operator->()
+    const std::string *operator->() const
     {
       return &(m_i->first);
     }