[icd] Defer subscription resumption

On some platforms, DNS-SD initialization is asynchronous and
any attempt to communicate with a peer node before that is
completed must fail.

Introduce kServerReady event that is emitted when all async
initialization tasks are completed (currently, only DNS-SD)
and resume persistent subscriptions in response to that
event.

src/app/server/Server.cpp

@@ -28,6 +28,7 @@
 #if CONFIG_NETWORK_LAYER_BLE
 #include <ble/BLEEndPoint.h>
 #endif
+#include <dnssd/DnssdBuildConfig.h>
 #include <inet/IPAddress.h>
 #include <inet/InetError.h>
 #include <lib/core/CHIPPersistentStorageDelegate.h>
@@ -353,12 +354,18 @@ CHIP_ERROR Server::Init(const ServerInitParams & initParams)
         }
     }
 
-#if CHIP_CONFIG_PERSIST_SUBSCRIPTIONS
-    ResumeSubscriptions();
-#endif
-
+    PlatformMgr().AddEventHandler(OnPlatformEventWrapper, 0);
     PlatformMgr().HandleServerStarted();
 
+#if CHIP_DNSSD_PLATFORM
+    // Platform DNS-SD implementation uses kPlatformDnssdInitialized event to signal that it's ready.
+    mIsDnssdReady = false;
+#else
+    // Minimal mDNS implementation is initialized synchronously so mark it as ready.
+    mIsDnssdReady = true;
+    CheckServerReadyEvent();
+#endif
+
 exit:
     if (err != CHIP_NO_ERROR)
     {
@@ -372,6 +379,45 @@ CHIP_ERROR Server::Init(const ServerInitParams & initParams)
     return err;
 }
 
+void Server::OnPlatformEvent(const DeviceLayer::ChipDeviceEvent & event)
+{
+    switch (event.Type)
+    {
+    case DeviceEventType::kServerReady:
+#if CHIP_CONFIG_PERSIST_SUBSCRIPTIONS
+        ResumeSubscriptions();
+#endif
+        break;
+#if CHIP_DNSSD_PLATFORM
+    case DeviceEventType::kDnssdPlatformInitialized:
+        if (!mIsDnssdReady)
+        {
+            mIsDnssdReady = true;
+            CheckServerReadyEvent();
+        }
+        break;
+#endif
+    default:
+        break;
+    }
+}
+
+void Server::CheckServerReadyEvent()
+{
+    // Check if all asynchronously initialized components (currently, only DNS-SD) are ready, and
+    // emit the 'server ready' event if so.
+    if (mIsDnssdReady)
+    {
+        ChipDeviceEvent event = { .Type = DeviceEventType::kServerReady };
+        PlatformMgr().PostEventOrDie(&event);
+    }
+}
+
+void Server::OnPlatformEventWrapper(const DeviceLayer::ChipDeviceEvent * event, intptr_t)
+{
+    Server::GetInstance().OnPlatformEvent(*event);
+}
+
 void Server::RejoinExistingMulticastGroups()
 {
     ChipLogProgress(AppServer, "Joining Multicast groups");
@@ -423,6 +469,7 @@ void Server::ScheduleFactoryReset()
 
 void Server::Shutdown()
 {
+    PlatformMgr().RemoveEventHandler(OnPlatformEventWrapper, 0);
     mCASEServer.Shutdown();
     mCASESessionManager.Shutdown();
     app::DnssdServer::Instance().SetCommissioningModeProvider(nullptr);

src/app/server/Server.h

@@ -377,6 +377,10 @@ class Server
     static Server sServer;
 
     void InitFailSafe();
+    void OnPlatformEvent(const DeviceLayer::ChipDeviceEvent & event);
+    void CheckServerReadyEvent();
+
+    static void OnPlatformEventWrapper(const DeviceLayer::ChipDeviceEvent * event, intptr_t);
 
 #if CHIP_CONFIG_PERSIST_SUBSCRIPTIONS
     /**
@@ -561,6 +565,7 @@ class Server
     uint16_t mOperationalServicePort;
     uint16_t mUserDirectedCommissioningPort;
     Inet::InterfaceId mInterfaceId;
+    bool mIsDnssdReady = false;
 };
 
 } // namespace chip

src/include/platform/CHIPDeviceEvent.h

@@ -225,6 +225,15 @@ enum PublicEventTypes
      * Signals that the state of the OTA engine changed.
      */
     kOtaStateChanged,
+
+    /**
+     * Server initialization has completed.
+     *
+     * Signals that all server components have been initialized and the node is ready to establish
+     * connections with other nodes. This event can be used to trigger on-boot actions that require
+     * sending messages to other nodes.
+     */
+    kServerReady,
 };
 
 /**

src/lib/dnssd/BUILD.gn

@@ -14,14 +14,30 @@
 
 import("//build_overrides/chip.gni")
 import("//build_overrides/nlunit_test.gni")
+
+import("${chip_root}/build/chip/buildconfig_header.gni")
 import("${chip_root}/src/platform/device.gni")
 
 source_set("platform_header") {
   sources = [ "platform/Dnssd.h" ]
 }
 
+buildconfig_header("dnssd_buildconfig") {
+  header = "DnssdBuildConfig.h"
+  header_dir = "dnssd"
+
+  chip_dnssd_minimal = chip_mdns == "minimal"
+  chip_dnssd_platform = chip_mdns == "platform"
+
+  defines = [
+    "CHIP_DNSSD_MINIMAL=${chip_dnssd_minimal}",
+    "CHIP_DNSSD_PLATFORM=${chip_dnssd_platform}",
+  ]
+}
+
 static_library("dnssd") {
   public_deps = [
+    ":dnssd_buildconfig",
     ":platform_header",
     "${chip_root}/src/crypto",
     "${chip_root}/src/lib/core",