From 7d665a80bc470b0d569b0e0144b367feb9c209d7 Mon Sep 17 00:00:00 2001
From: Martin Holst Swende <martin@swende.se>
Date: Wed, 15 Jan 2020 11:44:59 +0100
Subject: [PATCH] eth/handler: don't enqueue known broadcasted blocks

---
 eth/handler.go      |  5 ++--
 eth/handler_test.go | 56 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/eth/handler.go b/eth/handler.go
index e18fa61241..2069e4b164 100644
--- a/eth/handler.go
+++ b/eth/handler.go
@@ -703,8 +703,9 @@ func (pm *ProtocolManager) handleMsg(p *peer) error {
 
 		// Mark the peer as owning the block and schedule it for import
 		p.MarkBlock(request.Block.Hash())
-		pm.fetcher.Enqueue(p.id, request.Block)
-
+		if !pm.blockchain.HasBlock(request.Block.Hash(), request.Block.NumberU64()) {
+			pm.fetcher.Enqueue(p.id, request.Block)
+		}
 		// Assuming the block is importable by the peer, but possibly not yet done so,
 		// calculate the head hash and TD that the peer truly must have.
 		var (
diff --git a/eth/handler_test.go b/eth/handler_test.go
index 893bfffa42..8e9bdee008 100644
--- a/eth/handler_test.go
+++ b/eth/handler_test.go
@@ -696,3 +696,59 @@ func TestBroadcastMalformedBlock(t *testing.T) {
 		}
 	}
 }
+
+// TestBroadcastBlockSpam Tests that how we handle if a peer broadcasts a canon
+// block (close to head) multiple times
+func TestBroadcastBlockSpam(t *testing.T) {
+	// Create a live node to test propagation with
+	var (
+		engine  = ethash.NewFaker()
+		db      = rawdb.NewMemoryDatabase()
+		config  = &params.ChainConfig{}
+		gspec   = &core.Genesis{Config: config}
+		genesis = gspec.MustCommit(db)
+	)
+	blockchain, err := core.NewBlockChain(db, nil, config, engine, vm.Config{}, nil)
+	if err != nil {
+		t.Fatalf("failed to create new blockchain: %v", err)
+	}
+	pm, err := NewProtocolManager(config, nil, downloader.FullSync, DefaultConfig.NetworkId, new(event.TypeMux), new(testTxPool), engine, blockchain, db, 1, nil)
+	if err != nil {
+		t.Fatalf("failed to start test protocol manager: %v", err)
+	}
+	pm.Start(2)
+	defer pm.Stop()
+	// Create two peers, one to send the block with and one to check
+	// propagation
+	source, _ := newTestPeer("source", eth63, pm, true)
+	defer source.close()
+
+	sink, _ := newTestPeer("sink", eth63, pm, true)
+	defer sink.close()
+
+	// Create a chain
+	chain, _ := core.GenerateChain(gspec.Config, genesis, ethash.NewFaker(), db, 2, func(i int, gen *core.BlockGen) {})
+
+	// Broadcast head N times
+	nBroadcasts := 10
+	for i := 0; i < nBroadcasts; i++ {
+		block := chain[0]
+		if err := p2p.Send(source.app, NewBlockMsg, []interface{}{block, big.NewInt(131136)}); err != nil {
+			t.Fatalf("failed to broadcast block: %v", err)
+		}
+	}
+	// Broadcast new head N times
+	for i := 0; i < nBroadcasts; i++ {
+		block := chain[1]
+		if err := p2p.Send(source.app, NewBlockMsg, []interface{}{block, big.NewInt(131137)}); err != nil {
+			t.Fatalf("failed to broadcast block: %v", err)
+		}
+	}
+	// Broadcast old block N times
+	for i := 0; i < nBroadcasts; i++ {
+		block := chain[0]
+		if err := p2p.Send(source.app, NewBlockMsg, []interface{}{block, big.NewInt(131136)}); err != nil {
+			t.Fatalf("failed to broadcast block: %v", err)
+		}
+	}
+}