net: only enforce the services required to connect

also once half of all outgoing nodes have our preferred flags, require only
minimal flags from the rest.

src/net.cpp

@@ -1721,11 +1721,17 @@ void CConnman::ThreadOpenConnections()
         // Only connect out to one peer per network group (/16 for IPv4).
         // Do this here so we don't have to critsect vNodes inside mapAddresses critsect.
         int nOutbound = 0;
+        int nOutboundRelevant = 0;
         std::set<std::vector<unsigned char> > setConnected;
         {
             LOCK(cs_vNodes);
             BOOST_FOREACH(CNode* pnode, vNodes) {
                 if (!pnode->fInbound && !pnode->fAddnode) {
+
+                    // Count the peers that have all relevant services
+                    if (pnode->fSuccessfullyConnected && !pnode->fFeeler && ((pnode->nServices & nRelevantServices) == nRelevantServices)) {
+                        nOutboundRelevant++;
+                    }
                     // Netgroups for inbound and addnode peers are not excluded because our goal here
                     // is to not use multiple of our limited outbound slots on a single netgroup
                     // but inbound and addnode peers do not use our outbound slots.  Inbound peers
@@ -1789,14 +1795,27 @@ void CConnman::ThreadOpenConnections()
                 continue;
 
             // only consider nodes missing relevant services after 40 failed attempts and only if less than half the outbound are up.
-            if ((addr.nServices & nRelevantServices) != nRelevantServices && (nTries < 40 || nOutbound >= (nMaxOutbound >> 1)))
+            ServiceFlags nRequiredServices = nRelevantServices;
+            if (nTries >= 40 && nOutbound < (nMaxOutbound >> 1)) {
+                nRequiredServices = REQUIRED_SERVICES;
+            }
+
+            if ((addr.nServices & nRequiredServices) != nRequiredServices) {
                 continue;
+            }
 
             // do not allow non-default ports, unless after 50 invalid addresses selected already
             if (addr.GetPort() != Params().GetDefaultPort() && nTries < 50)
                 continue;
 
             addrConnect = addr;
+
+            // regardless of the services assumed to be available, only require the minimum if half or more outbound have relevant services
+            if (nOutboundRelevant >= (nMaxOutbound >> 1)) {
+                addrConnect.nServices = REQUIRED_SERVICES;
+            } else {
+                addrConnect.nServices = nRequiredServices;
+            }
             break;
         }