eth: broadcast blocks to at least 4 peers (#17725)

eth/handler.go

@@ -49,6 +49,9 @@ const (
 	// txChanSize is the size of channel listening to NewTxsEvent.
 	// The number is referenced from the size of tx pool.
 	txChanSize = 4096
+
+	// minimim number of peers to broadcast new blocks to
+	minBroadcastPeers = 4
 )
 
 var (
@@ -705,7 +708,14 @@ func (pm *ProtocolManager) BroadcastBlock(block *types.Block, propagate bool) {
 			return
 		}
 		// Send the block to a subset of our peers
-		transfer := peers[:int(math.Sqrt(float64(len(peers))))]
+		transferLen := int(math.Sqrt(float64(len(peers))))
+		if transferLen < minBroadcastPeers {
+			transferLen = minBroadcastPeers
+		}
+		if transferLen > len(peers) {
+			transferLen = len(peers)
+		}
+		transfer := peers[:transferLen]
 		for _, peer := range transfer {
 			peer.AsyncSendNewBlock(block, td)
 		}

eth/handler_test.go

@@ -17,6 +17,7 @@
 package eth
 
 import (
+	"fmt"
 	"math"
 	"math/big"
 	"math/rand"
@@ -472,8 +473,11 @@ func testDAOChallenge(t *testing.T, localForked, remoteForked bool, timeout bool
 		config  = &params.ChainConfig{DAOForkBlock: big.NewInt(1), DAOForkSupport: localForked}
 		gspec   = &core.Genesis{Config: config}
 		genesis = gspec.MustCommit(db)
-		blockchain, _ = core.NewBlockChain(db, nil, config, pow, vm.Config{}, nil)
 	)
+	blockchain, err := core.NewBlockChain(db, nil, config, pow, vm.Config{}, nil)
+	if err != nil {
+		t.Fatalf("failed to create new blockchain: %v", err)
+	}
 	pm, err := NewProtocolManager(config, downloader.FullSync, DefaultConfig.NetworkId, evmux, new(testTxPool), pow, blockchain, db)
 	if err != nil {
 		t.Fatalf("failed to start test protocol manager: %v", err)
@@ -520,3 +524,90 @@ func testDAOChallenge(t *testing.T, localForked, remoteForked bool, timeout bool
 		}
 	}
 }
+
+func TestBroadcastBlock(t *testing.T) {
+	var tests = []struct {
+		totalPeers        int
+		broadcastExpected int
+	}{
+		{1, 1},
+		{2, 2},
+		{3, 3},
+		{4, 4},
+		{5, 4},
+		{9, 4},
+		{12, 4},
+		{16, 4},
+		{26, 5},
+		{100, 10},
+	}
+	for _, test := range tests {
+		testBroadcastBlock(t, test.totalPeers, test.broadcastExpected)
+	}
+}
+
+func testBroadcastBlock(t *testing.T, totalPeers, broadcastExpected int) {
+	var (
+		evmux   = new(event.TypeMux)
+		pow     = ethash.NewFaker()
+		db      = ethdb.NewMemDatabase()
+		config  = &params.ChainConfig{}
+		gspec   = &core.Genesis{Config: config}
+		genesis = gspec.MustCommit(db)
+	)
+	blockchain, err := core.NewBlockChain(db, nil, config, pow, vm.Config{}, nil)
+	if err != nil {
+		t.Fatalf("failed to create new blockchain: %v", err)
+	}
+	pm, err := NewProtocolManager(config, downloader.FullSync, DefaultConfig.NetworkId, evmux, new(testTxPool), pow, blockchain, db)
+	if err != nil {
+		t.Fatalf("failed to start test protocol manager: %v", err)
+	}
+	pm.Start(1000)
+	defer pm.Stop()
+	var peers []*testPeer
+	for i := 0; i < totalPeers; i++ {
+		peer, _ := newTestPeer(fmt.Sprintf("peer %d", i), eth63, pm, true)
+		defer peer.close()
+		peers = append(peers, peer)
+	}
+	chain, _ := core.GenerateChain(gspec.Config, genesis, ethash.NewFaker(), db, 1, func(i int, gen *core.BlockGen) {})
+	pm.BroadcastBlock(chain[0], true /*propagate*/)
+
+	errCh := make(chan error, totalPeers)
+	doneCh := make(chan struct{}, totalPeers)
+	for _, peer := range peers {
+		go func(p *testPeer) {
+			if err := p2p.ExpectMsg(p.app, NewBlockMsg, &newBlockData{Block: chain[0], TD: big.NewInt(131136)}); err != nil {
+				errCh <- err
+			} else {
+				doneCh <- struct{}{}
+			}
+		}(peer)
+	}
+	timeoutCh := time.NewTimer(time.Millisecond * 100).C
+	var receivedCount int
+outer:
+	for {
+		select {
+		case err = <-errCh:
+			break outer
+		case <-doneCh:
+			receivedCount++
+			if receivedCount == totalPeers {
+				break outer
+			}
+		case <-timeoutCh:
+			break outer
+		}
+	}
+	for _, peer := range peers {
+		peer.app.Close()
+	}
+	if err != nil {
+		t.Errorf("error matching block by peer: %v", err)
+	}
+	if receivedCount != broadcastExpected {
+		t.Errorf("block broadcast to %d peers, expected %d", receivedCount, broadcastExpected)
+	}
+}