[srp-server] allow any number of host addresses (use Heap::Array) (#7420)

This commit changes the `Srp::Server` definition to use `Heap::Array`
to store the list of IPv6 addresses associated with a given `Host`.
This makes the array length dynamic and removes the need for
specifying a hard limit on the number of addresses and allow us to
remove `OPENTHREAD_CONFIG_SRP_SERVER_MAX_ADDRESSES_NUM` config.

src/core/config/openthread-core-config-check.h

@@ -614,4 +614,9 @@
 #error "OPENTHREAD_CONFIG_LOG_PREPEND_REGION was removed and not longer supported"
 #endif
 
+#ifdef OPENTHREAD_CONFIG_SRP_SERVER_MAX_ADDRESSES_NUM
+#error "OPENTHREAD_CONFIG_SRP_SERVER_MAX_ADDRESSES_NUM was removed. "\
+       "SRP host uses dynamic heap array to store addresses so no need for config on max number of addresses".
+#endif
+
 #endif // OPENTHREAD_CORE_CONFIG_CHECK_H_

src/core/config/srp_server.h

@@ -109,14 +109,4 @@
 #define OPENTHREAD_CONFIG_SRP_SERVER_SERVICE_UPDATE_TIMEOUT ((4 * 250u) + 250u)
 #endif
 
-/**
- * @def OPENTHREAD_CONFIG_SRP_SERVER_MAX_ADDRESSES_NUM
- *
- * Specifies the maximum number of addresses the SRP server can handle for a host.
- *
- */
-#ifndef OPENTHREAD_CONFIG_SRP_SERVER_MAX_ADDRESSES_NUM
-#define OPENTHREAD_CONFIG_SRP_SERVER_MAX_ADDRESSES_NUM 2
-#endif
-
 #endif // CONFIG_SRP_SERVER_H_

src/core/net/srp_server.cpp

@@ -1797,7 +1797,7 @@ void Server::Host::FreeAllServices(void)
 
 void Server::Host::ClearResources(void)
 {
-    mAddresses.Clear();
+    mAddresses.Free();
 }
 
 Error Server::Host::MergeServicesAndResourcesFrom(Host &aHost)
@@ -1810,7 +1810,7 @@ Error Server::Host::MergeServicesAndResourcesFrom(Host &aHost)
 
     LogInfo("update host %s", GetFullName());
 
-    mAddresses  = aHost.mAddresses;
+    mAddresses.TakeFrom(static_cast<Heap::Array<Ip6::Address> &&>(aHost.mAddresses));
     mKeyRecord  = aHost.mKeyRecord;
     mLease      = aHost.mLease;
     mKeyLease   = aHost.mKeyLease;

src/core/net/srp_server.hpp

@@ -58,12 +58,14 @@
 #include "common/clearable.hpp"
 #include "common/heap.hpp"
 #include "common/heap_allocatable.hpp"
+#include "common/heap_array.hpp"
 #include "common/heap_data.hpp"
 #include "common/heap_string.hpp"
 #include "common/linked_list.hpp"
 #include "common/locator.hpp"
 #include "common/non_copyable.hpp"
 #include "common/notifier.hpp"
+#include "common/numeric_limits.hpp"
 #include "common/retain_ptr.hpp"
 #include "common/timer.hpp"
 #include "crypto/ecdsa.hpp"
@@ -432,8 +434,8 @@ public:
          */
         const Ip6::Address *GetAddresses(uint8_t &aAddressesNum) const
         {
-            aAddressesNum = mAddresses.GetLength();
-            return mAddresses.Front();
+            aAddressesNum = static_cast<uint8_t>(OT_MIN(mAddresses.GetLength(), NumericLimits<uint8_t>::kMax));
+            return mAddresses.AsCArray();
         }
 
         /**
@@ -512,8 +514,6 @@ public:
         bool Matches(const char *aFullName) const;
 
     private:
-        static constexpr uint16_t kMaxAddresses = OPENTHREAD_CONFIG_SRP_SERVER_MAX_ADDRESSES_NUM;
-
         Host(Instance &aInstance, TimeMilli aUpdateTime);
         ~Host(void);
 
@@ -537,9 +537,9 @@ public:
         Service *                             FindService(const char *aServiceName, const char *aInstanceName);
         const Service *                       FindService(const char *aServiceName, const char *aInstanceName) const;
 
-        Host *                             mNext;
-        Heap::String                       mFullName;
-        Array<Ip6::Address, kMaxAddresses> mAddresses;
+        Host *                    mNext;
+        Heap::String              mFullName;
+        Heap::Array<Ip6::Address> mAddresses;
 
         // TODO(wgtdkp): there is no necessary to save the entire resource
         // record, saving only the ECDSA-256 public key should be enough.