NetDB: Ensure tunnel diversity in ISJ retries

by only using tunnels closest to the target for the first request.
This increases reliability by not reusing the same tunnels for all retries.

router/java/src/net/i2p/router/networkdb/kademlia/IterativeSearchJob.java

@@ -305,14 +305,18 @@ public class IterativeSearchJob extends FloodSearchJob {
                 }
                 _unheardFrom.add(peer);
             }
-            sendQuery(peer);
+            sendQuery(peer, done + pend);
         }
     }
 
     /**
      *  Send a DLM to the peer
+     *
+     *  @param peer who to send to
+     *  @param previouslyTried how many did we send to before this one?
+     *  @since 0.9.53 added previouslyTried param
      */
-    private void sendQuery(Hash peer) {
+    private void sendQuery(Hash peer, int previouslyTried) {
             final RouterContext ctx = getContext();
             TunnelManagerFacade tm = ctx.tunnelManager();
             RouterInfo ri = ctx.netDb().lookupRouterInfoLocally(peer);
@@ -335,9 +339,19 @@ public class IterativeSearchJob extends FloodSearchJob {
             boolean supportsRatchet = false;
             boolean supportsElGamal = true;
             if (_fromLocalDest != null) {
-                outTunnel = tm.selectOutboundTunnel(_fromLocalDest, peer);
-                if (outTunnel == null)
-                    outTunnel = tm.selectOutboundExploratoryTunnel(peer);
+                // For all tunnel selections, the first time we pick the tunnel with the far-end closest
+                // to the target. After that we pick a random tunnel, or else we'd pick the
+                // same tunnels every time.
+                if (previouslyTried <= 0)
+                    outTunnel = tm.selectOutboundTunnel(_fromLocalDest, peer);
+                else
+                    outTunnel = tm.selectOutboundTunnel(_fromLocalDest);
+                if (outTunnel == null) {
+                    if (previouslyTried <= 0)
+                        outTunnel = tm.selectOutboundExploratoryTunnel(peer);
+                    else
+                        outTunnel = tm.selectOutboundTunnel();
+                }
                 LeaseSetKeys lsk = ctx.keyManager().getKeys(_fromLocalDest);
                 supportsRatchet = lsk != null &&
                                   lsk.isSupported(EncType.ECIES_X25519) &&
@@ -347,15 +361,25 @@ public class IterativeSearchJob extends FloodSearchJob {
                                   lsk.isSupported(EncType.ELGAMAL_2048);
                 if (supportsElGamal || supportsRatchet) {
                     // garlic encrypt to dest SKM
-                    replyTunnel = tm.selectInboundTunnel(_fromLocalDest, peer);
+                    if (previouslyTried <= 0)
+                        replyTunnel = tm.selectInboundTunnel(_fromLocalDest, peer);
+                    else
+                        replyTunnel = tm.selectInboundTunnel(_fromLocalDest);
                     isClientReplyTunnel = replyTunnel != null;
-                    if (!isClientReplyTunnel)
-                        replyTunnel = tm.selectInboundExploratoryTunnel(peer);
+                    if (!isClientReplyTunnel) {
+                        if (previouslyTried <= 0)
+                            replyTunnel = tm.selectInboundExploratoryTunnel(peer);
+                        else
+                            replyTunnel = tm.selectInboundTunnel();
+                    }
                 } else {
                     // We don't have a way to request/get a ECIES-tagged reply,
                     // so send it to the router SKM
                     isClientReplyTunnel = false;
-                    replyTunnel = tm.selectInboundExploratoryTunnel(peer);
+                    if (previouslyTried <= 0)
+                        replyTunnel = tm.selectInboundExploratoryTunnel(peer);
+                    else
+                        replyTunnel = tm.selectInboundTunnel();
                 }
                 isDirect = false;
             } else if ((!_isLease) && ri != null && ctx.commSystem().isEstablished(peer)) {
@@ -370,8 +394,13 @@ public class IterativeSearchJob extends FloodSearchJob {
                 isDirect = true;
                 ctx.statManager().addRateData("netDb.RILookupDirect", 1);
             } else {
-                outTunnel = tm.selectOutboundExploratoryTunnel(peer);
-                replyTunnel = tm.selectInboundExploratoryTunnel(peer);
+                if (previouslyTried <= 0) {
+                    outTunnel = tm.selectOutboundExploratoryTunnel(peer);
+                    replyTunnel = tm.selectInboundExploratoryTunnel(peer);
+                } else {
+                    outTunnel = tm.selectOutboundTunnel();
+                    replyTunnel = tm.selectInboundTunnel();
+                }
                 isClientReplyTunnel = false;
                 isDirect = false;
                 ctx.statManager().addRateData("netDb.RILookupDirect", 0);