[posix] allow custom implementation of otPlatInfraIfDiscoverNat64Prefix (#10566)

This commit moves the macro guard
`OPENTHREAD_POSIX_CONFIG_INFRA_IF_ENABLE` in the code so that it can
allow custom implementation of `otPlatInfraIfDiscoverNat64Prefix` when
`OPENTHREAD_POSIX_CONFIG_INFRA_IF_ENABLE` is disabled.

The use case is on Android platform. We'll not let `ot-daemon`
proactively discover the prefixes by DNS. Instead, System Server will
do the discovery of NAT64 prefix on AIL and it will notify `ot-daemon`
when the AIL NAT64 prefix is discovered/removed.

src/core/border_router/infra_if.cpp

@@ -115,7 +115,11 @@ Error InfraIf::DiscoverNat64Prefix(void) const
 {
     OT_ASSERT(mInitialized);
 
+#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE
     return otPlatInfraIfDiscoverNat64Prefix(mIfIndex);
+#else
+    return kErrorNotImplemented;
+#endif
 }
 
 void InfraIf::DiscoverNat64PrefixDone(uint32_t aIfIndex, const Ip6::Prefix &aPrefix)

src/posix/platform/infra_if.cpp

@@ -101,16 +101,12 @@ otError otPlatInfraIfSendIcmp6Nd(uint32_t            aInfraIfIndex,
 }
 #endif
 
+#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE && OPENTHREAD_POSIX_CONFIG_NAT64_AIL_PREFIX_ENABLE
 otError otPlatInfraIfDiscoverNat64Prefix(uint32_t aInfraIfIndex)
 {
-    OT_UNUSED_VARIABLE(aInfraIfIndex);
-
-#if OPENTHREAD_POSIX_CONFIG_NAT64_AIL_PREFIX_ENABLE
     return ot::Posix::InfraNetif::Get().DiscoverNat64Prefix(aInfraIfIndex);
-#else
-    return OT_ERROR_DROP;
-#endif
 }
+#endif
 
 bool otSysInfraIfIsRunning(void) { return ot::Posix::InfraNetif::Get().IsRunning(); }
 
@@ -667,12 +663,13 @@ exit:
 }
 #endif // OPENTHREAD_CONFIG_BORDER_ROUTING_ENABLE
 
-#if OPENTHREAD_POSIX_CONFIG_NAT64_AIL_PREFIX_ENABLE
+#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE && OPENTHREAD_POSIX_CONFIG_NAT64_AIL_PREFIX_ENABLE
 const char         InfraNetif::kWellKnownIpv4OnlyName[]   = "ipv4only.arpa";
 const otIp4Address InfraNetif::kWellKnownIpv4OnlyAddress1 = {{{192, 0, 0, 170}}};
 const otIp4Address InfraNetif::kWellKnownIpv4OnlyAddress2 = {{{192, 0, 0, 171}}};
 const uint8_t      InfraNetif::kValidNat64PrefixLength[]  = {96, 64, 56, 48, 40, 32};
 
+#ifdef __linux__
 void InfraNetif::DiscoverNat64PrefixDone(union sigval sv)
 {
     struct gaicb    *req = (struct gaicb *)sv.sival_ptr;
@@ -750,9 +747,11 @@ exit:
     freeaddrinfo((struct addrinfo *)req->ar_request);
     free(req);
 }
+#endif // #ifdef __linux__
 
 otError InfraNetif::DiscoverNat64Prefix(uint32_t aInfraIfIndex)
 {
+#ifdef __linux__
     otError          error   = OT_ERROR_NONE;
     struct addrinfo *hints   = nullptr;
     struct gaicb    *reqs[1] = {nullptr};
@@ -795,8 +794,13 @@ exit:
         free(reqs[0]);
     }
     return error;
+#else
+    OT_UNUSED_VARIABLE(aInfraIfIndex);
+
+    return OT_ERROR_NOT_IMPLEMENTED;
+#endif // #ifdef __linux__
 }
-#endif // OPENTHREAD_POSIX_CONFIG_NAT64_AIL_PREFIX_ENABLE
+#endif // OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE && OPENTHREAD_POSIX_CONFIG_NAT64_AIL_PREFIX_ENABLE
 
 #if OPENTHREAD_CONFIG_BORDER_ROUTING_ENABLE
 void InfraNetif::SetInfraNetifIcmp6SocketForBorderRouting(int aIcmp6Socket)

src/posix/platform/infra_if.hpp

@@ -174,6 +174,7 @@ public:
                         const uint8_t      *aBuffer,
                         uint16_t            aBufferLength);
 
+#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE && OPENTHREAD_POSIX_CONFIG_NAT64_AIL_PREFIX_ENABLE
     /**
      * Sends an asynchronous address lookup for the well-known host name "ipv4only.arpa"
      * to discover the NAT64 prefix.
@@ -185,6 +186,7 @@ public:
      *
      */
     otError DiscoverNat64Prefix(uint32_t aInfraIfIndex);
+#endif
 
     /**
      * Gets the infrastructure network interface name.
@@ -240,12 +242,18 @@ private:
     MulticastRoutingManager mMulticastRoutingManager;
 #endif
 
+    bool HasLinkLocalAddress(void) const;
+
 #ifdef __linux__
     void ReceiveNetLinkMessage(void);
 #endif
 
-    bool        HasLinkLocalAddress(void) const;
+#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE && OPENTHREAD_POSIX_CONFIG_NAT64_AIL_PREFIX_ENABLE
+#ifdef __linux__
     static void DiscoverNat64PrefixDone(union sigval sv);
+#endif // #ifdef __linux__
+#endif
+
 #if OPENTHREAD_CONFIG_BORDER_ROUTING_ENABLE
     void SetInfraNetifIcmp6SocketForBorderRouting(int aIcmp6Socket);
     void ReceiveIcmp6Message(void);

tests/toranj/openthread-core-toranj-config-posix.h

@@ -65,6 +65,8 @@
 
 #define OPENTHREAD_POSIX_CONFIG_SPINEL_HDLC_INTERFACE_ENABLE 1
 
+#define OPENTHREAD_POSIX_CONFIG_NAT64_AIL_PREFIX_ENABLE 1
+
 // Disabled explicitly on posix `toranj` to validate the build with this config
 #define OPENTHREAD_CONFIG_BORDER_ROUTING_USE_HEAP_ENABLE 0