Add ChipMdnsShutdown()

#### Problem

Issue project-chip#8001 MdnsAvahi destructor segfault; require separate shutdown

MdnsAvahi can cause a crash on exit due to a static instance running
code in its destructor after dependent components have shut down.

#### Change overview

- Add `ChipMdnsShutdown()`. This is a narrow fix, which does not attempt
  to address other potential problems with singleton mDNS state.
- Fix TestMdns to shut down cleanly.

#### Testing

- TestMdns and CI.

src/controller/java/MdnsImpl.cpp

@@ -47,6 +47,11 @@ CHIP_ERROR ChipMdnsInit(MdnsAsyncReturnCallback initCallback, MdnsAsyncReturnCal
     return CHIP_NO_ERROR;
 }
 
+CHIP_ERROR ChipMdnsShutdown()
+{
+    return CHIP_NO_ERROR;
+}
+
 CHIP_ERROR ChipMdnsPublishService(const MdnsService * service)
 {
     return CHIP_ERROR_NOT_IMPLEMENTED;

src/lib/mdns/platform/Mdns.h

@@ -107,7 +107,7 @@ using MdnsBrowseCallback = void (*)(void * context, MdnsService * services, size
 using MdnsAsyncReturnCallback = void (*)(void * context, CHIP_ERROR error);
 
 /**
- * This function intializes the mdns module
+ * This function initializes the mdns module
  *
  * @param[in] initCallback    The callback for notifying the initialization result.
  * @param[in] errorCallback   The callback for notifying internal errors.
@@ -119,6 +119,15 @@ using MdnsAsyncReturnCallback = void (*)(void * context, CHIP_ERROR error);
  */
 CHIP_ERROR ChipMdnsInit(MdnsAsyncReturnCallback initCallback, MdnsAsyncReturnCallback errorCallback, void * context);
 
+/**
+ * This function shuts down the mdns module
+ *
+ * @retval CHIP_NO_ERROR  The shutdown succeeds.
+ * @retval Error code     The shutdown fails
+ *
+ */
+CHIP_ERROR ChipMdnsShutdown();
+
 /**
  * This function publishes an service via mDNS.
  *

src/platform/Darwin/MdnsImpl.cpp

@@ -485,6 +485,11 @@ CHIP_ERROR ChipMdnsInit(MdnsAsyncReturnCallback successCallback, MdnsAsyncReturn
     return CHIP_NO_ERROR;
 }
 
+CHIP_ERROR ChipMdnsShutdown()
+{
+    return CHIP_NO_ERROR;
+}
+
 CHIP_ERROR ChipMdnsPublishService(const MdnsService * service)
 {
     VerifyOrReturnError(service != nullptr, CHIP_ERROR_INVALID_ARGUMENT);

src/platform/ESP32/MdnsImpl.cpp

@@ -55,6 +55,11 @@ CHIP_ERROR ChipMdnsInit(MdnsAsyncReturnCallback initCallback, MdnsAsyncReturnCal
     return error;
 }
 
+CHIP_ERROR ChipMdnsShutdown()
+{
+    return CHIP_NO_ERROR;
+}
+
 static const char * GetProtocolString(MdnsServiceProtocol protocol)
 {
     return protocol == MdnsServiceProtocol::kMdnsProtocolTcp ? "_tcp" : "_udp";

src/platform/Linux/MdnsImpl.cpp

@@ -338,6 +338,21 @@ CHIP_ERROR MdnsAvahi::Init(MdnsAsyncReturnCallback initCallback, MdnsAsyncReturn
     return error;
 }
 
+CHIP_ERROR MdnsAvahi::Shutdown()
+{
+    if (mGroup)
+    {
+        avahi_entry_group_free(mGroup);
+        mGroup = nullptr;
+    }
+    if (mClient)
+    {
+        avahi_client_free(mClient);
+        mClient = nullptr;
+    }
+    return CHIP_NO_ERROR;
+}
+
 CHIP_ERROR MdnsAvahi::SetHostname(const char * hostname)
 {
     CHIP_ERROR error = CHIP_NO_ERROR;
@@ -733,18 +748,6 @@ void MdnsAvahi::HandleResolve(AvahiServiceResolver * resolver, AvahiIfIndex inte
     chip::Platform::Delete(context);
 }
 
-MdnsAvahi::~MdnsAvahi()
-{
-    if (mGroup)
-    {
-        avahi_entry_group_free(mGroup);
-    }
-    if (mClient)
-    {
-        avahi_client_free(mClient);
-    }
-}
-
 void GetMdnsTimeout(timeval & timeout)
 {
     MdnsAvahi::GetInstance().GetPoller().GetTimeout(timeout);
@@ -760,6 +763,11 @@ CHIP_ERROR ChipMdnsInit(MdnsAsyncReturnCallback initCallback, MdnsAsyncReturnCal
     return MdnsAvahi::GetInstance().Init(initCallback, errorCallback, context);
 }
 
+CHIP_ERROR ChipMdnsShutdown()
+{
+    return MdnsAvahi::GetInstance().Shutdown();
+}
+
 CHIP_ERROR ChipMdnsPublishService(const MdnsService * service)
 {
     if (strcmp(service->mHostName, "") != 0)

src/platform/Linux/MdnsImpl.h

@@ -100,6 +100,7 @@ class MdnsAvahi
     MdnsAvahi & operator=(const MdnsAvahi &) = delete;
 
     CHIP_ERROR Init(MdnsAsyncReturnCallback initCallback, MdnsAsyncReturnCallback errorCallback, void * context);
+    CHIP_ERROR Shutdown();
     CHIP_ERROR SetHostname(const char * hostname);
     CHIP_ERROR PublishService(const MdnsService & service);
     CHIP_ERROR StopPublish();
@@ -112,8 +113,6 @@ class MdnsAvahi
 
     static MdnsAvahi & GetInstance() { return sInstance; }
 
-    ~MdnsAvahi();
-
 private:
     struct BrowseContext
     {

src/platform/OpenThread/MdnsImpl.cpp

@@ -32,6 +32,11 @@ CHIP_ERROR ChipMdnsInit(MdnsAsyncReturnCallback initCallback, MdnsAsyncReturnCal
     return CHIP_NO_ERROR;
 }
 
+CHIP_ERROR ChipMdnsShutdown()
+{
+    return CHIP_NO_ERROR;
+}
+
 const char * GetProtocolString(MdnsServiceProtocol protocol)
 {
     return protocol == MdnsServiceProtocol::kMdnsProtocolUdp ? "_udp" : "_tcp";

src/platform/tests/TestMdns.cpp

@@ -27,6 +27,8 @@ static void HandleResolve(void * context, MdnsService * result, CHIP_ERROR error
     NL_TEST_ASSERT(suite, strcmp(result->mTextEntries[0].mKey, "key") == 0);
     NL_TEST_ASSERT(suite, strcmp(reinterpret_cast<const char *>(result->mTextEntries[0].mData), "val") == 0);
 
+    chip::DeviceLayer::PlatformMgr().StopEventLoopTask();
+    chip::DeviceLayer::PlatformMgr().Shutdown();
     exit(0);
 }
 
@@ -103,7 +105,8 @@ int TestMdns()
     bool ready = false;
 
     std::condition_variable doneCondition;
-    bool done = false;
+    bool done     = false;
+    bool shutdown = false;
 
     int retVal = EXIT_FAILURE;
 
@@ -139,8 +142,10 @@ int TestMdns()
             // This will stop the event loop above, and wait till it has actually stopped
             // (i.e exited RunEventLoop()).
             //
+            chip::Mdns::ChipMdnsShutdown();
             chip::DeviceLayer::PlatformMgr().StopEventLoopTask();
             chip::DeviceLayer::PlatformMgr().Shutdown();
+            shutdown = true;
 
             doneCondition.wait_for(lock, std::chrono::seconds(1));
             if (!done)
@@ -150,6 +155,16 @@ int TestMdns()
             retVal = EXIT_FAILURE;
         }
     }
+    t.join();
+
+    if (!shutdown)
+    {
+        chip::Mdns::ChipMdnsShutdown();
+        chip::DeviceLayer::PlatformMgr().StopEventLoopTask();
+        chip::DeviceLayer::PlatformMgr().Shutdown();
+    }
+    chip::Platform::MemoryShutdown();
+
     return retVal;
 }