Limit the number of times we retry peer discovery interactions. (#908)

Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

ethereum/p2p/src/main/java/tech/pegasys/pantheon/ethereum/p2p/discovery/internal/PeerDiscoveryController.java

@@ -408,7 +408,7 @@ public class PeerDiscoveryController {
 
     // The filter condition will be updated as soon as the action is performed.
     final PeerInteractionState ping =
-        new PeerInteractionState(action, PacketType.PONG, (packet) -> false, true);
+        new PeerInteractionState(action, peer.getId(), PacketType.PONG, (packet) -> false, true);
     dispatchInteraction(peer, ping);
   }
 
@@ -441,7 +441,7 @@ public class PeerDiscoveryController {
           sendPacket(peer, PacketType.FIND_NEIGHBORS, data);
         };
     final PeerInteractionState interaction =
-        new PeerInteractionState(action, PacketType.NEIGHBORS, packet -> true, true);
+        new PeerInteractionState(action, peer.getId(), PacketType.NEIGHBORS, packet -> true, true);
     dispatchInteraction(peer, interaction);
   }
 
@@ -459,7 +459,7 @@ public class PeerDiscoveryController {
     if (previous != null) {
       previous.cancelTimers();
     }
-    state.execute(0);
+    state.execute(0, 0);
   }
 
   private void respondToPing(
@@ -499,11 +499,15 @@ public class PeerDiscoveryController {
 
   /** Holds the state machine data for a peer interaction. */
   private class PeerInteractionState implements Predicate<Packet> {
+
+    private static final int MAX_RETRIES = 5;
     /**
      * The action that led to the peer being in this state (e.g. sending a PING or NEIGHBORS
      * message), in case it needs to be retried.
      */
     private final Consumer<PeerInteractionState> action;
+
+    private final BytesValue peerId;
     /** The expected type of the message that will transition the peer out of this state. */
     private final PacketType expectedType;
     /** A custom filter to accept transitions out of this state. */
@@ -515,10 +519,12 @@ public class PeerDiscoveryController {
 
     PeerInteractionState(
         final Consumer<PeerInteractionState> action,
+        final BytesValue peerId,
         final PacketType expectedType,
         final Predicate<Packet> filter,
         final boolean retryable) {
       this.action = action;
+      this.peerId = peerId;
       this.expectedType = expectedType;
       this.filter = filter;
       this.retryable = retryable;
@@ -540,11 +546,15 @@ public class PeerDiscoveryController {
      * @param lastTimeout the previous timeout, or 0 if this is the first time the action is being
      *     executed.
      */
-    void execute(final long lastTimeout) {
+    void execute(final long lastTimeout, final int retryCount) {
       action.accept(this);
-      if (retryable) {
+      if (retryable && retryCount < MAX_RETRIES) {
         final long newTimeout = retryDelayFunction.apply(lastTimeout);
-        timerId = OptionalLong.of(timerUtil.setTimer(newTimeout, () -> execute(newTimeout)));
+        timerId =
+            OptionalLong.of(
+                timerUtil.setTimer(newTimeout, () -> execute(newTimeout, retryCount + 1)));
+      } else {
+        inflightInteractions.remove(peerId);
       }
     }
 

ethereum/p2p/src/test/java/tech/pegasys/pantheon/ethereum/p2p/discovery/internal/MockTimerUtil.java

@@ -50,8 +50,7 @@ public class MockTimerUtil implements TimerUtil {
 
   public void runTimerHandlers() {
     // Create a copy of the handlers to avoid concurrent modification as handlers run
-    List<TimerHandler> handlers = new ArrayList<>();
+    final List<TimerHandler> handlers = new ArrayList<>(timerHandlers.values());
-    timerHandlers.forEach((id, handler) -> handlers.add(handler));
     timerHandlers.clear();
 
     handlers.forEach(TimerHandler::handle);

ethereum/p2p/src/test/java/tech/pegasys/pantheon/ethereum/p2p/discovery/internal/PeerDiscoveryControllerTest.java

@@ -192,19 +192,54 @@ public class PeerDiscoveryControllerTest {
     controller.onMessage(packet, peers.get(0));
 
     // Invoke timers again
-    for (int i = 0; i < 4; i++) {
+    for (int i = 0; i < 2; i++) {
       timer.runTimerHandlers();
     }
 
     // Ensure we receive no more PING packets for peer[0].
     // Assert PING packet was sent for peer[0] 4 times.
     for (final DiscoveryPeer peer : peers) {
-      final int expectedCount = peer.equals(peers.get(0)) ? 4 : 8;
+      final int expectedCount = peer.equals(peers.get(0)) ? 4 : 6;
       verify(outboundMessageHandler, times(expectedCount))
           .send(eq(peer), matchPacketOfType(PacketType.PING));
     }
   }
 
+  @Test
+  public void shouldStopRetryingInteractionWhenLimitIsReached() {
+    // Create peers.
+    final List<SECP256K1.KeyPair> keyPairs = PeerDiscoveryTestHelper.generateKeyPairs(3);
+    final List<DiscoveryPeer> peers = helper.createDiscoveryPeers(keyPairs);
+
+    final MockTimerUtil timer = new MockTimerUtil();
+    final OutboundMessageHandler outboundMessageHandler = mock(OutboundMessageHandler.class);
+    controller =
+        getControllerBuilder()
+            .peers(peers)
+            .timerUtil(timer)
+            .outboundMessageHandler(outboundMessageHandler)
+            .build();
+
+    // Mock the creation of the PING packet, so that we can control the hash,
+    // which gets validated when receiving the PONG.
+    final PingPacketData mockPing =
+        PingPacketData.create(localPeer.getEndpoint(), peers.get(0).getEndpoint());
+    final Packet mockPacket = Packet.create(PacketType.PING, mockPing, keyPairs.get(0));
+    doReturn(mockPacket).when(controller).createPacket(eq(PacketType.PING), any());
+
+    controller.start();
+
+    // Invoke timers several times so that ping to peers should be resent
+    for (int i = 0; i < 10; i++) {
+      timer.runTimerHandlers();
+    }
+
+    // Assert PING packet was sent only 6 times (initial attempt plus 5 retries)
+    for (final DiscoveryPeer peer : peers) {
+      verify(outboundMessageHandler, times(6)).send(eq(peer), matchPacketOfType(PacketType.PING));
+    }
+  }
+
   @Test
   public void bootstrapPeersPongReceived_HashMatched() {
     // Create peers.