Passing custom events over single instance IPC

vendor/DOtherSide/lib/include/DOtherSide/DOtherSide.h

@@ -983,8 +983,9 @@ DOS_API int DOS_CALL dos_qdeclarative_qmlregistersingletontype(const QmlRegister
 
 /// \brief Create a new SingleInstance class
 /// \param uniqueName The UTF-8 string for QLocalServer name
+/// \param eventStr A custom string to be passed to the already running instance if detected
 /// \note The returned SingleInstance should be freed using the dos_singleinstance_delete() function
-DOS_API DosSingleInstance *DOS_CALL dos_singleinstance_create(const char *uniqueName);
+DOS_API DosSingleInstance *DOS_CALL dos_singleinstance_create(const char *uniqueName, const char *eventStr);
 
 /// \brief Returns bool indicating whether this is the first instance or not
 /// \returns true if this is the first instance

vendor/DOtherSide/lib/include/DOtherSide/DOtherSideSingleInstance.h

@@ -10,13 +10,19 @@ class SingleInstance : public QObject
     Q_OBJECT
 
 public:
-    explicit SingleInstance(const QString &uniqueName, QObject *parent = nullptr);
+    // uniqueName - the name of named pipe
+    // eventStr - optional event to send if another instance is detected
+    explicit SingleInstance(const QString &uniqueName, const QString &eventStr, QObject *parent = nullptr);
     ~SingleInstance() override;
 
     bool isFirstInstance() const;
 
 signals:
     void secondInstanceDetected();
+    void eventReceived(const QString &eventStr);
+
+private slots:
+    void handleNewConnection();
 
 private:
     QLocalServer *m_localServer;

vendor/DOtherSide/lib/src/DOtherSide.cpp

@@ -1333,9 +1333,9 @@ char *dos_qurl_replaceHostAndAddPath(char* url, char* newScheme, char* newHost,
     return convert_to_cstring(newQurl.toString());
 }
 
-DosSingleInstance *dos_singleinstance_create(const char *uniqueName)
+DosSingleInstance *dos_singleinstance_create(const char *uniqueName, const char *eventStr)
 {
-    return new SingleInstance(QString::fromUtf8(uniqueName));
+    return new SingleInstance(QString::fromUtf8(uniqueName), QString::fromUtf8(eventStr));
 }
 
 void dos_singleinstance_delete(DosSingleInstance *vptr)

vendor/DOtherSide/lib/src/DOtherSideSingleInstance.cpp

@@ -3,7 +3,11 @@
 #include <QLocalServer>
 #include <QLocalSocket>
 
-SingleInstance::SingleInstance(const QString &uniqueName, QObject *parent)
+namespace {
+    const int ReadWriteTimeoutMs = 1000;
+}
+
+SingleInstance::SingleInstance(const QString &uniqueName, const QString &eventStr, QObject *parent)
     : QObject(parent)
     , m_localServer(new QLocalServer(this))
 {
@@ -19,7 +23,7 @@ SingleInstance::SingleInstance(const QString &uniqueName, QObject *parent)
     // the first instance start will be delayed by this timeout (ms) to ensure there are no other instances.
     // note: this is an ad-hoc timeout value selected based on prior experience.
     if (!localSocket.waitForConnected(100)) {
-        connect(m_localServer, &QLocalServer::newConnection, this, &SingleInstance::secondInstanceDetected);
+        connect(m_localServer, &QLocalServer::newConnection, this, &SingleInstance::handleNewConnection);
         // on *nix a crashed process will leave /tmp/xyz file preventing to start a new server.
         // therefore, if we were unable to connect, then we assume the server died and we need to clean up.
         // p.s. on Windows, this function does nothing.
@@ -27,6 +31,9 @@ SingleInstance::SingleInstance(const QString &uniqueName, QObject *parent)
         if (!m_localServer->listen(socketName)) {
             qWarning() << "QLocalServer::listen(" << socketName << ") failed";
         }
+    } else if (!eventStr.isEmpty()) {
+        localSocket.write(eventStr.toUtf8() + '\n');
+        localSocket.waitForBytesWritten(ReadWriteTimeoutMs);
     }
 }
 
@@ -41,3 +48,16 @@ bool SingleInstance::isFirstInstance() const
 {
     return m_localServer->isListening();
 }
+
+void SingleInstance::handleNewConnection()
+{
+    emit secondInstanceDetected();
+
+    auto socket = m_localServer->nextPendingConnection();
+    if (socket->waitForReadyRead(ReadWriteTimeoutMs) && socket->canReadLine()) {
+        auto event = socket->readLine();
+        emit eventReceived(QString::fromUtf8(event));
+    }
+
+    socket->deleteLater();
+}