refactor: improve Proxy signal subscription (#389)

This makes D-Bus proxy signal registration more flexible, more dynamic, and less error-prone since no `finishRegistration()` call is needed. A proxy can register to a signal at any time during its lifetime, and can unregister freely by simply destroying the associated slot.

tests/integrationtests/integrationtests-proxy.h

@@ -22,9 +22,6 @@ protected:
     integrationtests_proxy(sdbus::IProxy& proxy)
         : proxy_(&proxy)
     {
-        proxy_->uponSignal("simpleSignal").onInterface(INTERFACE_NAME).call([this](){ this->onSimpleSignal(); });
-        proxy_->uponSignal("signalWithMap").onInterface(INTERFACE_NAME).call([this](const std::map<int32_t, std::string>& aMap){ this->onSignalWithMap(aMap); });
-        proxy_->uponSignal("signalWithVariant").onInterface(INTERFACE_NAME).call([this](const sdbus::Variant& aVariant){ this->onSignalWithVariant(aVariant); });
     }
 
     integrationtests_proxy(const integrationtests_proxy&) = delete;
@@ -34,6 +31,13 @@ protected:
 
     ~integrationtests_proxy() = default;
 
+    void registerProxy()
+    {
+        simpleSignalSlot_ = proxy_->uponSignal("simpleSignal").onInterface(INTERFACE_NAME).call([this](){ this->onSimpleSignal(); }, sdbus::request_slot);
+        proxy_->uponSignal("signalWithMap").onInterface(INTERFACE_NAME).call([this](const std::map<int32_t, std::string>& aMap){ this->onSignalWithMap(aMap); });
+        proxy_->uponSignal("signalWithVariant").onInterface(INTERFACE_NAME).call([this](const sdbus::Variant& aVariant){ this->onSignalWithVariant(aVariant); });
+    }
+
     virtual void onSimpleSignal() = 0;
     virtual void onSignalWithMap(const std::map<int32_t, std::string>& aMap) = 0;
     virtual void onSignalWithVariant(const sdbus::Variant& aVariant) = 0;
@@ -176,13 +180,12 @@ public:
 
     void unregisterSimpleSignalHandler()
     {
-        proxy_->muteSignal("simpleSignal").onInterface(INTERFACE_NAME);
+        simpleSignalSlot_.reset();
     }
 
     void reRegisterSimpleSignalHandler()
     {
-        proxy_->uponSignal("simpleSignal").onInterface(INTERFACE_NAME).call([this](){ this->onSimpleSignal(); });
-        proxy_->finishRegistration();
+        simpleSignalSlot_ = proxy_->uponSignal("simpleSignal").onInterface(INTERFACE_NAME).call([this](){ this->onSimpleSignal(); }, sdbus::request_slot);
     }
 
 public:
@@ -213,6 +216,7 @@ public:
 
 private:
     sdbus::IProxy* proxy_;
+    sdbus::Slot simpleSignalSlot_;
 };
 
 }} // namespaces

tests/perftests/perftests-proxy.h

@@ -22,7 +22,6 @@ protected:
     perftests_proxy(sdbus::IProxy& proxy)
         : proxy_(&proxy)
     {
-        proxy_->uponSignal("dataSignal").onInterface(INTERFACE_NAME).call([this](const std::string& data){ this->onDataSignal(data); });
     }
 
     perftests_proxy(const perftests_proxy&) = delete;
@@ -32,6 +31,11 @@ protected:
 
     ~perftests_proxy() = default;
 
+    void registerProxy()
+    {
+        proxy_->uponSignal("dataSignal").onInterface(INTERFACE_NAME).call([this](const std::string& data){ this->onDataSignal(data); });
+    }
+
     virtual void onDataSignal(const std::string& data) = 0;
 
 public:

tests/stresstests/celsius-thermometer-proxy.h

@@ -33,6 +33,10 @@ protected:
 
     ~thermometer_proxy() = default;
 
+    void registerProxy()
+    {
+    }
+
 public:
     uint32_t getCurrentTemperature()
     {

tests/stresstests/concatenator-proxy.h

@@ -23,7 +23,6 @@ protected:
     concatenator_proxy(sdbus::IProxy& proxy)
         : proxy_(&proxy)
     {
-        proxy_->uponSignal("concatenatedSignal").onInterface(INTERFACE_NAME).call([this](const std::string& concatenatedString){ this->onConcatenatedSignal(concatenatedString); });
     }
 
     concatenator_proxy(const concatenator_proxy&) = delete;
@@ -33,6 +32,11 @@ protected:
 
     ~concatenator_proxy() = default;
 
+    void registerProxy()
+    {
+        proxy_->uponSignal("concatenatedSignal").onInterface(INTERFACE_NAME).call([this](const std::string& concatenatedString){ this->onConcatenatedSignal(concatenatedString); });
+    }
+
     virtual void onConcatenatedSignal(const std::string& concatenatedString) = 0;
 
     virtual void onConcatenateReply(const std::string& result, const sdbus::Error* error) = 0;

tests/stresstests/fahrenheit-thermometer-proxy.h

@@ -33,6 +33,10 @@ protected:
 
     ~thermometer_proxy() = default;
 
+    void registerProxy()
+    {
+    }
+
 public:
     uint32_t getCurrentTemperature()
     {
@@ -71,6 +75,10 @@ protected:
 
     ~factory_proxy() = default;
 
+    void registerProxy()
+    {
+    }
+
 public:
     sdbus::ObjectPath createDelegateObject()
     {