[net] Change AdvertiseLocal to GetLocalAddrForPeer

Gossiping addresses to peers is the responsibility of net processing.
Change AdvertiseLocal() in net to just return an (optional) address
for net processing to advertise. Update function name to reflect
new responsibility.

Author: jnewbery

src/net.cpp

@@ -201,8 +201,7 @@ bool IsPeerAddrLocalGood(CNode *pnode)
            IsReachable(addrLocal.GetNetwork());
 }
 
-// pushes our own address to a peer
-void AdvertiseLocal(CNode *pnode)
+Optional<CAddress> GetLocalAddrForPeer(CNode *pnode)
 {
     if (fListen && pnode->fSuccessfullyConnected)
     {
@@ -222,10 +221,12 @@ void AdvertiseLocal(CNode *pnode)
         }
         if (addrLocal.IsRoutable() || gArgs.GetBoolArg("-addrmantest", false))
         {
-            LogPrint(BCLog::NET, "AdvertiseLocal: advertising address %s\n", addrLocal.ToString());
-            pnode->PushAddress(addrLocal, rng);
+            LogPrint(BCLog::NET, "Advertising address %s to peer=%d\n", addrLocal.ToString(), pnode->GetId());
+            return addrLocal;
         }
     }
+    // Address is unroutable. Don't advertise.
+    return nullopt;
 }
 
 // learn a new local address

src/net.h

@@ -197,7 +197,8 @@ enum
 };
 
 bool IsPeerAddrLocalGood(CNode *pnode);
-void AdvertiseLocal(CNode *pnode);
+/** Returns a local address that we should advertise to this peer */
+Optional<CAddress> GetLocalAddrForPeer(CNode *pnode);
 
 /**
  * Mark a network as reachable or unreachable (no automatic connects to it)

src/net_processing.cpp

@@ -4426,7 +4426,10 @@ bool PeerManagerImpl::SendMessages(CNode* pto)
             if (pto->m_next_local_addr_send != 0us) {
                 pto->m_addr_known->reset();
             }
-            AdvertiseLocal(pto);
+            if (Optional<CAddress> local_addr = GetLocalAddrForPeer(pto)) {
+                FastRandomContext insecure_rand;
+                pto->PushAddress(*local_addr, insecure_rand);
+            }
             pto->m_next_local_addr_send = PoissonNextSend(current_time, AVG_LOCAL_ADDRESS_BROADCAST_INTERVAL);
         }
 

src/test/net_tests.cpp

@@ -691,7 +691,7 @@ BOOST_AUTO_TEST_CASE(ipv4_peer_with_ipv6_addrMe_test)
     pnode->SetAddrLocal(addrLocal);
 
     // before patch, this causes undefined behavior detectable with clang's -fsanitize=memory
-    AdvertiseLocal(&*pnode);
+    GetLocalAddrForPeer(&*pnode);
 
     // suppress no-checks-run warning; if this test fails, it's by triggering a sanitizer
     BOOST_CHECK(1);