[mdns] fix bug that avahi may publish redundant meshcop services (#1104)

Avahi may rename the meshcop service and publish it when there's a
name conflict. However, our current logic has a bug that it may
publish redundant meshcop services after some renaming.

For example there are two BRs on the infra link:
- BR1 starts. It publishes instance._meshcop._udp.
- BR2 starts. It publishes instance #1._meshcop._udp.
- BR1 stops. It unpublishes instance._meshcop._udp.
- BR2 wants to update the existing meshcop service. However, it
  actually publishes a new service instance._meshcop._udp. There are
  two meshcop services existing at the same time both published by
  BR2.

To fix this bug, we will keep track of the original name in the avahi
publisher. When we call PublishService, we should always pass in the
original name and let the publisher handle the renaming. In this way
we will be able to find the wanted service when updating it or
unpublishing it.

src/mdns/mdns.hpp

@@ -233,7 +233,9 @@ class Publisher
      *                          to provide specific host name. Otherwise, the caller MUST publish the host
      *                          with method PublishHost.
      * @param[in] aPort         The port number of this service.
-     * @param[in] aName         The name of this service.
+     * @param[in] aName         The name of this service. Note that the published service name may be different from the
+     *                          original name due to renaming. You should always pass in the original name here to make
+     *                          sure you are referring to the intended service.
      * @param[in] aType         The type of this service.
      * @param[in] aSubTypeList  A list of service subtypes.
      * @param[in] aTxtList      A list of TXT name/value pairs.
@@ -252,7 +254,9 @@ class Publisher
     /**
      * This method un-publishes a service.
      *
-     * @param[in] aName  The name of this service.
+     * @param[in] aName  The name of this service. Note that the published service name may be different from the
+     *                   original name due to renaming. You should always pass in the original name here to make
+     *                   sure you are referring to the intended service.
      * @param[in] aType  The type of this service.
      *
      * @retval OTBR_ERROR_NONE   Successfully un-published the service.

src/mdns/mdns_avahi.cpp

@@ -376,8 +376,8 @@ void PublisherAvahi::HandleGroupState(AvahiEntryGroup *aGroup, AvahiEntryGroupSt
             uint16_t port            = service.mPort;
 
             ResetGroup(service.mGroup);
-            alternativeName = avahi_alternative_service_name(service.mName.c_str());
-            service.mName   = alternativeName;
+            alternativeName      = avahi_alternative_service_name(service.mCurrentName.c_str());
+            service.mCurrentName = alternativeName;
             avahi_free(alternativeName);
             service.mPort = 0; // To mark the service as outdated
             PublishService(service.mHostName, port, service.mName, service.mType, service.mSubTypeList,
@@ -470,8 +470,9 @@ otbrError PublisherAvahi::CreateService(AvahiClient &       aClient,
     otbrError error = OTBR_ERROR_NONE;
     Service   newService;
 
-    newService.mName = aName;
-    newService.mType = aType;
+    newService.mName        = aName;
+    newService.mCurrentName = aName;
+    newService.mType        = aType;
     SuccessOrExit(error = CreateGroup(aClient, newService.mGroup));
 
     mServices.push_back(newService);
@@ -640,9 +641,11 @@ otbrError PublisherAvahi::PublishService(const std::string &aHostName,
     }
     else
     {
-        otbrLogInfo("Update service %s.%s for host %s", aName.c_str(), aType.c_str(), logHostName.c_str());
+        otbrLogInfo("Update service %s.%s for host %s", serviceIt->mCurrentName.c_str(), aType.c_str(),
+                    logHostName.c_str());
         avahiError = avahi_entry_group_update_service_txt_strlst(serviceIt->mGroup, AVAHI_IF_UNSPEC, AVAHI_PROTO_UNSPEC,
-                                                                 AvahiPublishFlags{}, aName.c_str(), aType.c_str(),
+                                                                 AvahiPublishFlags{}, serviceIt->mCurrentName.c_str(),
+                                                                 aType.c_str(),
                                                                  /* domain */ nullptr, head);
         if (avahiError == 0 && mServiceHandler != nullptr)
         {
@@ -653,23 +656,27 @@ otbrError PublisherAvahi::PublishService(const std::string &aHostName,
         ExitNow();
     }
 
-    otbrLogInfo("Create service %s.%s for host %s", aName.c_str(), aType.c_str(), logHostName.c_str());
-    avahiError = avahi_entry_group_add_service_strlst(serviceIt->mGroup, AVAHI_IF_UNSPEC, AVAHI_PROTO_UNSPEC,
-                                                      AvahiPublishFlags{}, aName.c_str(), aType.c_str(),
-                                                      /* domain */ nullptr, fullHostName.c_str(), aPort, head);
+    otbrLogInfo("Create service %s.%s for host %s", serviceIt->mCurrentName.c_str(), aType.c_str(),
+                logHostName.c_str());
+    avahiError =
+        avahi_entry_group_add_service_strlst(serviceIt->mGroup, AVAHI_IF_UNSPEC, AVAHI_PROTO_UNSPEC,
+                                             AvahiPublishFlags{}, serviceIt->mCurrentName.c_str(), aType.c_str(),
+                                             /* domain */ nullptr, fullHostName.c_str(), aPort, head);
     SuccessOrExit(avahiError);
 
     for (const std::string &subType : aSubTypeList)
     {
-        otbrLogInfo("Add subtype %s for service %s.%s", subType.c_str(), aName.c_str(), aType.c_str());
+        otbrLogInfo("Add subtype %s for service %s.%s", subType.c_str(), serviceIt->mCurrentName.c_str(),
+                    aType.c_str());
         std::string fullSubType = subType + "._sub." + aType;
-        avahiError = avahi_entry_group_add_service_subtype(serviceIt->mGroup, AVAHI_IF_UNSPEC, AVAHI_PROTO_UNSPEC,
-                                                           AvahiPublishFlags{}, aName.c_str(), aType.c_str(),
-                                                           /* domain */ nullptr, fullSubType.c_str());
+        avahiError =
+            avahi_entry_group_add_service_subtype(serviceIt->mGroup, AVAHI_IF_UNSPEC, AVAHI_PROTO_UNSPEC,
+                                                  AvahiPublishFlags{}, serviceIt->mCurrentName.c_str(), aType.c_str(),
+                                                  /* domain */ nullptr, fullSubType.c_str());
         SuccessOrExit(avahiError);
     }
 
-    otbrLogInfo("Commit service %s.%s", aName.c_str(), aType.c_str());
+    otbrLogInfo("Commit service %s.%s", serviceIt->mCurrentName.c_str(), aType.c_str());
     avahiError = avahi_entry_group_commit(serviceIt->mGroup);
     SuccessOrExit(avahiError);
 
@@ -707,7 +714,7 @@ otbrError PublisherAvahi::UnpublishService(const std::string &aName, const std::
     serviceIt = FindService(aName, aType);
     VerifyOrExit(serviceIt != mServices.end());
 
-    otbrLogInfo("Unpublish service %s.%s", aName.c_str(), aType.c_str());
+    otbrLogInfo("Unpublish service %s.%s", serviceIt->mCurrentName.c_str(), aType.c_str());
     error = FreeGroup(serviceIt->mGroup);
     mServices.erase(serviceIt);
 

src/mdns/mdns_avahi.hpp

@@ -211,6 +211,7 @@ class PublisherAvahi : public Publisher
     struct Service
     {
         std::string      mName;
+        std::string      mCurrentName; // The current instance name. May be different from mName due to renaming.
         std::string      mType;
         SubTypeList      mSubTypeList;
         std::string      mHostName;