From cfb942a7fa99a017aefb0eef023ae0573e3e6210 Mon Sep 17 00:00:00 2001
From: Ross Nicoll <jrn@jrn.me.uk>
Date: Fri, 25 Dec 2015 15:17:02 +0000
Subject: [PATCH] Rate limit peer discovery

This changes PeerGroup to consider a peer discovery that doesn't return
enough results as a failure, so it does exponential backoff. Otherwise
it discovers constantly on a network with less than the maximum peers
available.

Also added a second sanity check to ensure it's never done more than
once a second.
---
 core/src/main/java/org/bitcoinj/core/PeerGroup.java | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/core/src/main/java/org/bitcoinj/core/PeerGroup.java b/core/src/main/java/org/bitcoinj/core/PeerGroup.java
index 1857be9f..a7c03379 100644
--- a/core/src/main/java/org/bitcoinj/core/PeerGroup.java
+++ b/core/src/main/java/org/bitcoinj/core/PeerGroup.java
@@ -476,6 +476,7 @@ public class PeerGroup implements TransactionBroadcaster {
 
     private Runnable triggerConnectionsJob = new Runnable() {
         private boolean firstRun = true;
+        private final static long MIN_PEER_DISCOVERY_INTERVAL = 1000L;
 
         @Override
         public void run() {
@@ -525,7 +526,9 @@ public class PeerGroup implements TransactionBroadcaster {
             lock.lock();
             try {
                 if (doDiscovery) {
-                    if (discoverySuccess) {
+                    // Require that we have enough connections, to consider this
+                    // a success, or we just constantly test for new peers
+                    if (discoverySuccess && countConnectedAndPendingPeers() >= getMaxConnections()) {
                         groupBackoff.trackSuccess();
                     } else {
                         groupBackoff.trackFailure();
@@ -534,8 +537,10 @@ public class PeerGroup implements TransactionBroadcaster {
                 // Inactives is sorted by backoffMap time.
                 if (inactives.isEmpty()) {
                     if (countConnectedAndPendingPeers() < getMaxConnections()) {
-                        log.info("Peer discovery didn't provide us any more peers, will try again later.");
-                        executor.schedule(this, groupBackoff.getRetryTime() - now, TimeUnit.MILLISECONDS);
+                        long interval = Math.max(groupBackoff.getRetryTime() - now, MIN_PEER_DISCOVERY_INTERVAL);
+                        log.info("Peer discovery didn't provide us any more peers, will try again in "
+                            + interval + "ms.");
+                        executor.schedule(this, interval, TimeUnit.MILLISECONDS);
                     } else {
                         // We have enough peers and discovery provided no more, so just settle down. Most likely we
                         // were given a fixed set of addresses in some test scenario.