[mdns] Fix Resolver initialization (#5347)

ChipMdnsInit() call has recently been moved to
ServiceAdvertiser::Start, hence the function is never called
on the mDNS resolver side. Call the initialization function
when necessary.

src/lib/mdns/Discovery_ImplPlatform.cpp

@@ -57,24 +57,28 @@ constexpr uint64_t kUndefinedNodeId = 0;
 namespace chip {
 namespace Mdns {
 
-DiscoveryImplPlatform::DiscoveryImplPlatform()
-{
-    mCommissionInstanceName = GetRandU64();
-}
+DiscoveryImplPlatform DiscoveryImplPlatform::sManager;
 
-CHIP_ERROR DiscoveryImplPlatform::Start(Inet::InetLayer * inetLayer, uint16_t port)
+DiscoveryImplPlatform::DiscoveryImplPlatform() = default;
+
+CHIP_ERROR DiscoveryImplPlatform::Init()
 {
-    CHIP_ERROR error = CHIP_NO_ERROR;
     if (!mMdnsInitialized)
     {
         ReturnErrorOnFailure(ChipMdnsInit(HandleMdnsInit, HandleMdnsError, this));
-        mMdnsInitialized = true;
-    }
-    else
-    {
-        error = ChipMdnsStopPublish();
+        mCommissionInstanceName = GetRandU64();
+        mMdnsInitialized        = true;
     }
 
+    return CHIP_NO_ERROR;
+}
+
+CHIP_ERROR DiscoveryImplPlatform::Start(Inet::InetLayer * inetLayer, uint16_t port)
+{
+    ReturnErrorOnFailure(Init());
+
+    CHIP_ERROR error = ChipMdnsStopPublish();
+
     if (error != CHIP_NO_ERROR)
     {
         ChipLogError(Discovery, "Failed to initialize platform mdns: %s", ErrorStr(error));
@@ -280,6 +284,8 @@ CHIP_ERROR DiscoveryImplPlatform::SetResolverDelegate(ResolverDelegate * delegat
 
 CHIP_ERROR DiscoveryImplPlatform::ResolveNodeId(uint64_t nodeId, uint64_t fabricId, Inet::IPAddressType type)
 {
+    ReturnErrorOnFailure(Init());
+
     MdnsService service;
 
     snprintf(service.mName, sizeof(service.mName), "%" PRIX64 "-%" PRIX64, nodeId, fabricId);
@@ -357,12 +363,6 @@ void DiscoveryImplPlatform::HandleNodeIdResolve(void * context, MdnsService * re
 
 DiscoveryImplPlatform & DiscoveryImplPlatform::GetInstance()
 {
-    // TODO: Clean Mdns initialization order
-    // Previously sManager was a global object, but DiscoveryImplPlatform constructor calls
-    // platform-specific ChipMdnsInit() which for Linux initializes MdnsAvahi global object
-    // and that may lead to improper initialization, since the order in which global objects'
-    // constructors are called is undefined.
-    static DiscoveryImplPlatform sManager;
     return sManager;
 }
 

src/lib/mdns/Discovery_ImplPlatform.h

@@ -30,6 +30,8 @@ namespace Mdns {
 class DiscoveryImplPlatform : public ServiceAdvertiser, public Resolver
 {
 public:
+    CHIP_ERROR Init();
+
     CHIP_ERROR Start(Inet::InetLayer * inetLayer, uint16_t port) override;
 
     /// Advertises the CHIP node as an operational node