Make System::Layer mockable

#### Problem

System::Layer is now an abstract base class, but in normal builds is
still accessed through a static global variable.

#### Change overview

Replace the direct global access `DeviceLayer::SystemLayer` with
a function indirecting through a pointer. In the normal case, the
pointer is initialized by `InitChipStack()` with the global, but
it can be set with a mock implementation before that.

#### Testing

Added a unit test case to TestPlatformMgr.

examples/all-clusters-app/esp32/main/DeviceCallbacks.cpp

@@ -217,7 +217,7 @@ void IdentifyTimerHandler(Layer * systemLayer, void * appState)
 
     if (identifyTimerCount)
     {
-        SystemLayer.StartTimer(kIdentifyTimerDelayMS, IdentifyTimerHandler, appState);
+        systemLayer->StartTimer(kIdentifyTimerDelayMS, IdentifyTimerHandler, appState);
         // Decrement the timer count.
         identifyTimerCount--;
     }
@@ -235,8 +235,8 @@ void DeviceCallbacks::OnIdentifyPostAttributeChangeCallback(EndpointId endpointI
     // Also, we want timerCount to be odd number, so the ligth state ends in the same state it starts.
     identifyTimerCount = (*value) * 4;
 
-    SystemLayer.CancelTimer(IdentifyTimerHandler, this);
-    SystemLayer.StartTimer(kIdentifyTimerDelayMS, IdentifyTimerHandler, this);
+    DeviceLayer::SystemLayer().CancelTimer(IdentifyTimerHandler, this);
+    DeviceLayer::SystemLayer().StartTimer(kIdentifyTimerDelayMS, IdentifyTimerHandler, this);
 
 exit:
     return;

examples/chip-tool/commands/common/Command.cpp

@@ -423,7 +423,7 @@ static void OnResponseTimeout(chip::System::Layer *, void *)
 
 CHIP_ERROR Command::ScheduleWaitForResponse(uint16_t seconds)
 {
-    CHIP_ERROR err = chip::DeviceLayer::SystemLayer.StartTimer(seconds * 1000, OnResponseTimeout, this);
+    CHIP_ERROR err = chip::DeviceLayer::SystemLayer().StartTimer(seconds * 1000, OnResponseTimeout, this);
     if (err != CHIP_NO_ERROR)
     {
         ChipLogError(chipTool, "Failed to allocate timer %" CHIP_ERROR_FORMAT, err.Format());

examples/chip-tool/commands/tests/TestCommand.cpp

@@ -54,5 +54,5 @@ void TestCommand::OnWaitForMsFn(chip::System::Layer * systemLayer, void * contex
 
 CHIP_ERROR TestCommand::WaitForMs(uint32_t ms)
 {
-    return chip::DeviceLayer::SystemLayer.StartTimer(ms, OnWaitForMsFn, this);
+    return chip::DeviceLayer::SystemLayer().StartTimer(ms, OnWaitForMsFn, this);
 }

examples/lighting-app/qpg/src/AppTask.cpp

@@ -374,15 +374,15 @@ void AppTask::FunctionHandler(AppEvent * aEvent)
 
 void AppTask::CancelTimer()
 {
-    SystemLayer.CancelTimer(TimerEventHandler, this);
+    SystemLayer().CancelTimer(TimerEventHandler, this);
     mFunctionTimerActive = false;
 }
 
 void AppTask::StartTimer(uint32_t aTimeoutInMs)
 {
     CHIP_ERROR err;
 
-    err = SystemLayer.StartTimer(aTimeoutInMs, TimerEventHandler, this);
+    err = SystemLayer().StartTimer(aTimeoutInMs, TimerEventHandler, this);
     SuccessOrExit(err);
 
     mFunctionTimerActive = true;

examples/lock-app/qpg/src/AppTask.cpp

@@ -389,16 +389,16 @@ void AppTask::FunctionHandler(AppEvent * aEvent)
 
 void AppTask::CancelTimer()
 {
-    SystemLayer.CancelTimer(TimerEventHandler, this);
+    chip::DeviceLayer::SystemLayer().CancelTimer(TimerEventHandler, this);
     mFunctionTimerActive = false;
 }
 
 void AppTask::StartTimer(uint32_t aTimeoutInMs)
 {
     CHIP_ERROR err;
 
-    SystemLayer.CancelTimer(TimerEventHandler, this);
-    err = SystemLayer.StartTimer(aTimeoutInMs, TimerEventHandler, this);
+    chip::DeviceLayer::SystemLayer().CancelTimer(TimerEventHandler, this);
+    err = chip::DeviceLayer::SystemLayer().StartTimer(aTimeoutInMs, TimerEventHandler, this);
     SuccessOrExit(err);
 
     mFunctionTimerActive = true;

examples/minimal-mdns/client.cpp

@@ -326,9 +326,9 @@ int main(int argc, char ** args)
 
     BroadcastPacket(&mdnsServer);
 
-    CHIP_ERROR err = DeviceLayer::SystemLayer.StartTimer(
+    CHIP_ERROR err = DeviceLayer::SystemLayer().StartTimer(
         gOptions.runtimeMs,
-        [](System::Layer *, void *, CHIP_ERROR err) {
+        [](System::Layer *, void *) {
             DeviceLayer::PlatformMgr().StopEventLoopTask();
             DeviceLayer::PlatformMgr().Shutdown();
         },

examples/ota-provider-app/linux/main.cpp

@@ -139,7 +139,7 @@ int main(int argc, char * argv[])
 
     BitFlags<TransferControlFlags> bdxFlags;
     bdxFlags.Set(TransferControlFlags::kReceiverDrive);
-    err = bdxServer.PrepareForTransfer(&chip::DeviceLayer::SystemLayer, chip::bdx::TransferRole::kSender, bdxFlags,
+    err = bdxServer.PrepareForTransfer(&chip::DeviceLayer::SystemLayer(), chip::bdx::TransferRole::kSender, bdxFlags,
                                        kMaxBdxBlockSize, kBdxTimeoutMs, kBdxPollFreqMs);
     if (err != CHIP_NO_ERROR)
     {

examples/shell/shell_common/cmd_ping.cpp

@@ -151,7 +151,7 @@ Transport::PeerAddress GetEchoPeerAddress()
 
 void Shutdown()
 {
-    chip::DeviceLayer::SystemLayer.CancelTimer(EchoTimerHandler, NULL);
+    chip::DeviceLayer::SystemLayer().CancelTimer(EchoTimerHandler, NULL);
 #if INET_CONFIG_ENABLE_TCP_ENDPOINT
     if (gPingArguments.IsUsingTCP())
     {
@@ -212,7 +212,7 @@ CHIP_ERROR SendEchoRequest(streamer_t * stream)
     }
 
     gPingArguments.SetLastEchoTime(System::Clock::GetMonotonicMilliseconds());
-    SuccessOrExit(chip::DeviceLayer::SystemLayer.StartTimer(gPingArguments.GetEchoInterval(), EchoTimerHandler, NULL));
+    SuccessOrExit(chip::DeviceLayer::SystemLayer().StartTimer(gPingArguments.GetEchoInterval(), EchoTimerHandler, NULL));
 
     streamer_printf(stream, "\nSend echo request message with payload size: %d bytes to Node: %" PRIu64 "\n", payloadSize,
                     kTestDeviceNodeId);
@@ -226,7 +226,7 @@ CHIP_ERROR SendEchoRequest(streamer_t * stream)
     }
     else
     {
-        chip::DeviceLayer::SystemLayer.CancelTimer(EchoTimerHandler, NULL);
+        chip::DeviceLayer::SystemLayer().CancelTimer(EchoTimerHandler, NULL);
     }
 
 exit:
@@ -306,7 +306,7 @@ void StartPinging(streamer_t * stream, char * destination)
 #if INET_CONFIG_ENABLE_TCP_ENDPOINT
     if (gPingArguments.IsUsingTCP())
     {
-        err = gSessionManager.Init(&DeviceLayer::SystemLayer, &gTCPManager, &gFabrics, &gMessageCounterManager);
+        err = gSessionManager.Init(&DeviceLayer::SystemLayer(), &gTCPManager, &gFabrics, &gMessageCounterManager);
         SuccessOrExit(err);
 
         err = gExchangeManager.Init(&gSessionManager);
@@ -315,7 +315,7 @@ void StartPinging(streamer_t * stream, char * destination)
     else
 #endif
     {
-        err = gSessionManager.Init(&DeviceLayer::SystemLayer, &gUDPManager, &gFabrics, &gMessageCounterManager);
+        err = gSessionManager.Init(&DeviceLayer::SystemLayer(), &gUDPManager, &gFabrics, &gMessageCounterManager);
         SuccessOrExit(err);
 
         err = gExchangeManager.Init(&gSessionManager);

examples/shell/shell_common/cmd_send.cpp

@@ -227,15 +227,15 @@ void ProcessCommand(streamer_t * stream, char * destination)
     {
         peerAddress = Transport::PeerAddress::TCP(gDestAddr, gSendArguments.GetPort());
 
-        err = gSessionManager.Init(&DeviceLayer::SystemLayer, &gTCPManager, &fabrics, &gMessageCounterManager);
+        err = gSessionManager.Init(&DeviceLayer::SystemLayer(), &gTCPManager, &fabrics, &gMessageCounterManager);
         SuccessOrExit(err);
     }
     else
 #endif
     {
         peerAddress = Transport::PeerAddress::UDP(gDestAddr, gSendArguments.GetPort(), INET_NULL_INTERFACEID);
 
-        err = gSessionManager.Init(&DeviceLayer::SystemLayer, &gUDPManager, &fabrics, &gMessageCounterManager);
+        err = gSessionManager.Init(&DeviceLayer::SystemLayer(), &gUDPManager, &fabrics, &gMessageCounterManager);
         SuccessOrExit(err);
     }
 

examples/tv-casting-app/linux/main.cpp

@@ -73,7 +73,7 @@ void RequestUserDirectedCommissioning(System::SocketEvents events, intptr_t data
     int selectedCommissionerNumber = CHIP_DEVICE_CONFIG_MAX_DISCOVERED_NODES;
     scanf("%d", &selectedCommissionerNumber);
     printf("%d\n", selectedCommissionerNumber);
-    chip::DeviceLayer::SystemLayer.StopWatchingSocket(&token);
+    chip::DeviceLayer::SystemLayerSockets().StopWatchingSocket(&token);
 
     const Mdns::DiscoveredNodeData * selectedCommissioner =
         commissionableNodeController.GetDiscoveredCommissioner(selectedCommissionerNumber - 1);
@@ -105,9 +105,10 @@ void InitCommissioningFlow(intptr_t commandArg)
         int flags = fcntl(STDIN_FILENO, F_GETFL, 0);
         VerifyOrReturn(fcntl(0, F_SETFL, flags | O_NONBLOCK) == 0,
                        ChipLogError(Zcl, "Could not set non-blocking mode for user input!"));
-        ReturnOnFailure(chip::DeviceLayer::SystemLayer.StartWatchingSocket(STDIN_FILENO, &token));
-        ReturnOnFailure(chip::DeviceLayer::SystemLayer.SetCallback(token, RequestUserDirectedCommissioning, (intptr_t) NULL));
-        ReturnOnFailure(chip::DeviceLayer::SystemLayer.RequestCallbackOnPendingRead(token));
+        ReturnOnFailure(chip::DeviceLayer::SystemLayerSockets().StartWatchingSocket(STDIN_FILENO, &token));
+        ReturnOnFailure(
+            chip::DeviceLayer::SystemLayerSockets().SetCallback(token, RequestUserDirectedCommissioning, (intptr_t) NULL));
+        ReturnOnFailure(chip::DeviceLayer::SystemLayerSockets().RequestCallbackOnPendingRead(token));
     }
     else
     {
@@ -127,7 +128,7 @@ int main(int argc, char * argv[])
                       Mdns::DiscoveryFilter(Mdns::DiscoveryFilterType::kDeviceType, kTvDeviceType)));
 
     // Give commissioners some time to respond and then ScheduleWork to initiate commissioning
-    DeviceLayer::SystemLayer.StartTimer(
+    DeviceLayer::SystemLayer().StartTimer(
         commissionerDiscoveryTimeoutInMs,
         [](System::Layer *, void *) { chip::DeviceLayer::PlatformMgr().ScheduleWork(InitCommissioningFlow); }, nullptr);
 

src/app/server/Server.cpp

@@ -286,7 +286,7 @@ CHIP_ERROR OpenBasicCommissioningWindow(ResetFabrics resetFabrics, uint16_t comm
     if (commissioningTimeoutSeconds != kNoCommissioningTimeout)
     {
         ReturnErrorOnFailure(
-            DeviceLayer::SystemLayer.StartTimer(commissioningTimeoutSeconds * 1000, HandlePairingWindowTimeout, nullptr));
+            DeviceLayer::SystemLayer().StartTimer(commissioningTimeoutSeconds * 1000, HandlePairingWindowTimeout, nullptr));
     }
 
     return CHIP_NO_ERROR;
@@ -313,7 +313,7 @@ CHIP_ERROR OpenEnhancedCommissioningWindow(uint16_t commissioningTimeoutSeconds,
     if (commissioningTimeoutSeconds != kNoCommissioningTimeout)
     {
         ReturnErrorOnFailure(
-            DeviceLayer::SystemLayer.StartTimer(commissioningTimeoutSeconds * 1000, HandlePairingWindowTimeout, nullptr));
+            DeviceLayer::SystemLayer().StartTimer(commissioningTimeoutSeconds * 1000, HandlePairingWindowTimeout, nullptr));
     }
 
     return CHIP_NO_ERROR;
@@ -384,7 +384,7 @@ void InitServer(AppDelegate * delegate)
 
     SuccessOrExit(err);
 
-    err = gSessions.Init(&DeviceLayer::SystemLayer, &gTransports, &gFabrics, &gMessageCounterManager);
+    err = gSessions.Init(&DeviceLayer::SystemLayer(), &gTransports, &gFabrics, &gMessageCounterManager);
     SuccessOrExit(err);
 
     err = gExchangeMgr.Init(&gSessions);

src/app/tests/integration/chip_im_initiator.cpp

@@ -325,12 +325,12 @@ void CommandRequestTimerHandler(chip::System::Layer * systemLayer, void * appSta
         err = SendCommandRequest(commandSender);
         VerifyOrExit(err == CHIP_NO_ERROR, printf("Failed to send command request with error: %s\n", chip::ErrorStr(err)));
 
-        err = chip::DeviceLayer::SystemLayer.StartTimer(gMessageIntervalMsec, CommandRequestTimerHandler, NULL);
+        err = chip::DeviceLayer::SystemLayer().StartTimer(gMessageIntervalMsec, CommandRequestTimerHandler, NULL);
         VerifyOrExit(err == CHIP_NO_ERROR, printf("Failed to schedule timer with error: %s\n", chip::ErrorStr(err)));
     }
     else
     {
-        err = chip::DeviceLayer::SystemLayer.StartTimer(gMessageIntervalMsec, BadCommandRequestTimerHandler, NULL);
+        err = chip::DeviceLayer::SystemLayer().StartTimer(gMessageIntervalMsec, BadCommandRequestTimerHandler, NULL);
         VerifyOrExit(err == CHIP_NO_ERROR, printf("Failed to schedule timer with error: %s\n", chip::ErrorStr(err)));
     }
 
@@ -351,7 +351,7 @@ void BadCommandRequestTimerHandler(chip::System::Layer * systemLayer, void * app
     err = SendBadCommandRequest(commandSender);
     VerifyOrExit(err == CHIP_NO_ERROR, printf("Failed to send bad command request with error: %s\n", chip::ErrorStr(err)));
 
-    err = chip::DeviceLayer::SystemLayer.StartTimer(gMessageIntervalMsec, ReadRequestTimerHandler, NULL);
+    err = chip::DeviceLayer::SystemLayer().StartTimer(gMessageIntervalMsec, ReadRequestTimerHandler, NULL);
     VerifyOrExit(err == CHIP_NO_ERROR, printf("Failed to schedule timer with error: %s\n", chip::ErrorStr(err)));
 
 exit:
@@ -378,12 +378,12 @@ void ReadRequestTimerHandler(chip::System::Layer * systemLayer, void * appState)
         err = SendReadRequest();
         VerifyOrExit(err == CHIP_NO_ERROR, printf("Failed to send read request with error: %s\n", chip::ErrorStr(err)));
 
-        err = chip::DeviceLayer::SystemLayer.StartTimer(gMessageIntervalMsec, ReadRequestTimerHandler, NULL);
+        err = chip::DeviceLayer::SystemLayer().StartTimer(gMessageIntervalMsec, ReadRequestTimerHandler, NULL);
         VerifyOrExit(err == CHIP_NO_ERROR, printf("Failed to schedule timer with error: %s\n", chip::ErrorStr(err)));
     }
     else
     {
-        err = chip::DeviceLayer::SystemLayer.StartTimer(gMessageIntervalMsec, WriteRequestTimerHandler, NULL);
+        err = chip::DeviceLayer::SystemLayer().StartTimer(gMessageIntervalMsec, WriteRequestTimerHandler, NULL);
         VerifyOrExit(err == CHIP_NO_ERROR, printf("Failed to schedule timer with error: %s\n", chip::ErrorStr(err)));
     }
 
@@ -415,7 +415,7 @@ void WriteRequestTimerHandler(chip::System::Layer * systemLayer, void * appState
         err = SendWriteRequest(writeClient);
         VerifyOrExit(err == CHIP_NO_ERROR, printf("Failed to send write request with error: %s\n", chip::ErrorStr(err)));
 
-        err = chip::DeviceLayer::SystemLayer.StartTimer(gMessageIntervalMsec, WriteRequestTimerHandler, NULL);
+        err = chip::DeviceLayer::SystemLayer().StartTimer(gMessageIntervalMsec, WriteRequestTimerHandler, NULL);
         VerifyOrExit(err == CHIP_NO_ERROR, printf("Failed to schedule timer with error: %s\n", chip::ErrorStr(err)));
     }
     else
@@ -583,7 +583,7 @@ int main(int argc, char * argv[])
                                      .SetListenPort(IM_CLIENT_PORT));
     SuccessOrExit(err);
 
-    err = gSessionManager.Init(&chip::DeviceLayer::SystemLayer, &gTransportManager, &fabrics, &gMessageCounterManager);
+    err = gSessionManager.Init(&chip::DeviceLayer::SystemLayer(), &gTransportManager, &fabrics, &gMessageCounterManager);
     SuccessOrExit(err);
 
     err = gExchangeManager.Init(&gSessionManager);
@@ -599,7 +599,7 @@ int main(int argc, char * argv[])
     err = EstablishSecureSession();
     SuccessOrExit(err);
 
-    err = chip::DeviceLayer::SystemLayer.StartTimer(0, CommandRequestTimerHandler, NULL);
+    err = chip::DeviceLayer::SystemLayer().StartTimer(0, CommandRequestTimerHandler, NULL);
     SuccessOrExit(err);
 
     chip::DeviceLayer::PlatformMgr().RunEventLoop();

src/app/tests/integration/chip_im_responder.cpp

@@ -175,7 +175,7 @@ int main(int argc, char * argv[])
         chip::Transport::UdpListenParameters(&chip::DeviceLayer::InetLayer).SetAddressType(chip::Inet::kIPAddressType_IPv4));
     SuccessOrExit(err);
 
-    err = gSessionManager.Init(&chip::DeviceLayer::SystemLayer, &gTransportManager, &fabrics, &gMessageCounterManager);
+    err = gSessionManager.Init(&chip::DeviceLayer::SystemLayer(), &gTransportManager, &fabrics, &gMessageCounterManager);
     SuccessOrExit(err);
 
     err = gExchangeManager.Init(&gSessionManager);

src/app/util/af-event.cpp

@@ -148,7 +148,7 @@ EmberStatus emberEventControlSetDelayMS(EmberEventControl * control, uint32_t de
     {
         control->status = EMBER_EVENT_MS_TIME;
 #if !CHIP_DEVICE_LAYER_NONE
-        chip::DeviceLayer::SystemLayer.StartTimer(delayMs, EventControlHandler, control);
+        chip::DeviceLayer::SystemLayer().StartTimer(delayMs, EventControlHandler, control);
 #endif
     }
     else
@@ -164,7 +164,7 @@ void emberEventControlSetInactive(EmberEventControl * control)
     {
         control->status = EMBER_EVENT_INACTIVE;
 #if !CHIP_DEVICE_LAYER_NONE
-        chip::DeviceLayer::SystemLayer.CancelTimer(EventControlHandler, control);
+        chip::DeviceLayer::SystemLayer().CancelTimer(EventControlHandler, control);
 #endif
     }
 }
@@ -178,7 +178,7 @@ void emberEventControlSetActive(EmberEventControl * control)
 {
     control->status = EMBER_EVENT_ZERO_DELAY;
 #if !CHIP_DEVICE_LAYER_NONE
-    chip::DeviceLayer::SystemLayer.ScheduleWork(EventControlHandler, control);
+    chip::DeviceLayer::SystemLayer().ScheduleWork(EventControlHandler, control);
 #endif
 }
 

src/controller/CHIPDeviceController.cpp

@@ -128,7 +128,7 @@ CHIP_ERROR DeviceController::Init(ControllerInitParams params)
 #if CONFIG_DEVICE_LAYER
         ReturnErrorOnFailure(DeviceLayer::PlatformMgr().InitChipStack());
 
-        mSystemLayer = &DeviceLayer::SystemLayer;
+        mSystemLayer = &DeviceLayer::SystemLayer();
         mInetLayer   = &DeviceLayer::InetLayer;
 #endif // CONFIG_DEVICE_LAYER
     }

src/controller/python/chip/internal/CommissionerImpl.cpp

@@ -98,7 +98,7 @@ extern "C" chip::Controller::DeviceCommissioner * pychip_internal_Commissioner_N
         chip::Controller::CommissionerInitParams params;
 
         params.storageDelegate = &gServerStorage;
-        params.systemLayer     = &chip::DeviceLayer::SystemLayer;
+        params.systemLayer     = &chip::DeviceLayer::SystemLayer();
         params.inetLayer       = &chip::DeviceLayer::InetLayer;
         params.pairingDelegate = &gPairingDelegate;
 

src/include/platform/CHIPDeviceLayer.h

@@ -45,9 +45,28 @@ namespace chip {
 namespace DeviceLayer {
 
 struct ChipDeviceEvent;
-extern chip::System::LayerImpl SystemLayer;
 extern Inet::InetLayer InetLayer;
 
+inline chip::System::Layer & SystemLayer()
+{
+    extern chip::System::Layer * globalSystemLayer;
+    return *globalSystemLayer;
+}
+
+#if CHIP_SYSTEM_CONFIG_USE_SOCKETS
+inline chip::System::LayerSockets & SystemLayerSockets()
+{
+    extern chip::System::Layer * globalSystemLayer;
+    return *static_cast<chip::System::LayerSockets *>(globalSystemLayer);
+}
+#endif // CHIP_SYSTEM_CONFIG_USE_SOCKETS
+
+inline void SetSystemLayerForTesting(System::Layer * layer)
+{
+    extern chip::System::Layer * globalSystemLayer;
+    globalSystemLayer = layer;
+}
+
 } // namespace DeviceLayer
 } // namespace chip