Avoid querying DNS seeds, if we have open connections.

The goal is to increase independence and privacy.

src/init.cpp

@@ -240,7 +240,8 @@ std::string HelpMessage(HelpMessageMode mode)
     strUsage += "  -connect=<ip>          " + _("Connect only to the specified node(s)") + "\n";
     strUsage += "  -discover              " + _("Discover own IP address (default: 1 when listening and no -externalip)") + "\n";
     strUsage += "  -dns                   " + _("Allow DNS lookups for -addnode, -seednode and -connect") + " " + _("(default: 1)") + "\n";
-    strUsage += "  -dnsseed               " + _("Find peers using DNS lookup (default: 1 unless -connect)") + "\n";
+    strUsage += "  -dnsseed               " + _("Query for peer addresses via DNS lookup, if low on addresses (default: 1 unless -connect)") + "\n";
+    strUsage += "  -forcednsseed          " + _("Always query for peer addresses via DNS lookup (default: 0)") + "\n";
     strUsage += "  -externalip=<ip>       " + _("Specify your own public address") + "\n";
     strUsage += "  -listen                " + _("Accept connections from outside (default: 1 if no -proxy or -connect)") + "\n";
     strUsage += "  -maxconnections=<n>    " + _("Maintain at most <n> connections to peers (default: 125)") + "\n";

src/net.cpp

@@ -1221,6 +1221,18 @@ void MapPort(bool)
 
 void ThreadDNSAddressSeed()
 {
+    // goal: only query DNS seeds if address need is acute
+    if ((addrman.size() > 0) &&
+        (!GetBoolArg("-forcednsseed", false))) {
+        MilliSleep(11 * 1000);
+
+        LOCK(cs_vNodes);
+        if (vNodes.size() >= 2) {
+            LogPrintf("P2P peers available. Skipped DNS seeding.\n");
+            return;
+        }
+    }
+
     const vector<CDNSSeedData> &vSeeds = Params().DNSSeeds();
     int found = 0;