eth: make transaction propagation paths in the network deterministic (#29034)

* eth: make transaction propagation paths in the network deterministic

* eth: avoid potential division by 0

* eth: make tx propagation dependent on local node id too

* eth: fix review comments

eth/backend.go

@@ -236,6 +236,7 @@ func New(stack *node.Node, config *ethconfig.Config) (*Ethereum, error) {
 	// Permit the downloader to use the trie cache allowance during fast sync
 	cacheLimit := cacheConfig.TrieCleanLimit + cacheConfig.TrieDirtyLimit + cacheConfig.SnapshotLimit
 	if eth.handler, err = newHandler(&handlerConfig{
+		NodeID:         eth.p2pServer.Self().ID(),
 		Database:       chainDb,
 		Chain:          eth.blockchain,
 		TxPool:         eth.txPool,

eth/handler.go

@@ -32,6 +32,7 @@ import (
 	"github.com/ethereum/go-ethereum/core/rawdb"
 	"github.com/ethereum/go-ethereum/core/txpool"
 	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/ethereum/go-ethereum/eth/downloader"
 	"github.com/ethereum/go-ethereum/eth/fetcher"
 	"github.com/ethereum/go-ethereum/eth/protocols/eth"
@@ -41,7 +42,9 @@ import (
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/metrics"
 	"github.com/ethereum/go-ethereum/p2p"
+	"github.com/ethereum/go-ethereum/p2p/enode"
 	"github.com/ethereum/go-ethereum/triedb/pathdb"
+	"golang.org/x/crypto/sha3"
 )
 
 const (
@@ -84,6 +87,7 @@ type txPool interface {
 // handlerConfig is the collection of initialization parameters to create a full
 // node network handler.
 type handlerConfig struct {
+	NodeID         enode.ID               // P2P node ID used for tx propagation topology
 	Database       ethdb.Database         // Database for direct sync insertions
 	Chain          *core.BlockChain       // Blockchain to serve data from
 	TxPool         txPool                 // Transaction pool to propagate from
@@ -96,6 +100,7 @@ type handlerConfig struct {
 }
 
 type handler struct {
+	nodeID     enode.ID
 	networkID  uint64
 	forkFilter forkid.Filter // Fork ID filter, constant across the lifetime of the node
 
@@ -137,6 +142,7 @@ func newHandler(config *handlerConfig) (*handler, error) {
 		config.EventMux = new(event.TypeMux) // Nicety initialization for tests
 	}
 	h := &handler{
+		nodeID:         config.NodeID,
 		networkID:      config.Network,
 		forkFilter:     forkid.NewFilter(config.Chain),
 		eventMux:       config.EventMux,
@@ -614,25 +620,54 @@ func (h *handler) BroadcastTransactions(txs types.Transactions) {
 		annos = make(map[*ethPeer][]common.Hash) // Set peer->hash to announce
 	)
 	// Broadcast transactions to a batch of peers not knowing about it
-	for _, tx := range txs {
+	direct := big.NewInt(int64(math.Sqrt(float64(h.peers.len())))) // Approximate number of peers to broadcast to
-		peers := h.peers.peersWithoutTransaction(tx.Hash())
+	if direct.BitLen() == 0 {
+		direct = big.NewInt(1)
+	}
+	total := new(big.Int).Exp(direct, big.NewInt(2), nil) // Stabilise total peer count a bit based on sqrt peers
 
-		var numDirect int
+	var (
+		signer = types.LatestSignerForChainID(h.chain.Config().ChainID) // Don't care about chain status, we just need *a* sender
+		hasher = sha3.NewLegacyKeccak256().(crypto.KeccakState)
+		hash   = make([]byte, 32)
+	)
+	for _, tx := range txs {
+		var maybeDirect bool
 		switch {
 		case tx.Type() == types.BlobTxType:
 			blobTxs++
 		case tx.Size() > txMaxBroadcastSize:
 			largeTxs++
 		default:
-			numDirect = int(math.Sqrt(float64(len(peers))))
+			maybeDirect = true
 		}
-		// Send the tx unconditionally to a subset of our peers
+		// Send the transaction (if it's small enough) directly to a subset of
-		for _, peer := range peers[:numDirect] {
+		// the peers that have not received it yet, ensuring that the flow of
-			txset[peer] = append(txset[peer], tx.Hash())
+		// transactions is groupped by account to (try and) avoid nonce gaps.
-		}
+		//
-		// For the remaining peers, send announcement only
+		// To do this, we hash the local enode IW with together with a peer's
-		for _, peer := range peers[numDirect:] {
+		// enode ID together with the transaction sender and broadcast if
-			annos[peer] = append(annos[peer], tx.Hash())
+		// `sha(self, peer, sender) mod peers < sqrt(peers)`.
+		for _, peer := range h.peers.peersWithoutTransaction(tx.Hash()) {
+			var broadcast bool
+			if maybeDirect {
+				hasher.Reset()
+				hasher.Write(h.nodeID.Bytes())
+				hasher.Write(peer.Node().ID().Bytes())
+
+				from, _ := types.Sender(signer, tx) // Ignore error, we only use the addr as a propagation target splitter
+				hasher.Write(from.Bytes())
+
+				hasher.Read(hash)
+				if new(big.Int).Mod(new(big.Int).SetBytes(hash), total).Cmp(direct) < 0 {
+					broadcast = true
+				}
+			}
+			if broadcast {
+				txset[peer] = append(txset[peer], tx.Hash())
+			} else {
+				annos[peer] = append(annos[peer], tx.Hash())
+			}
 		}
 	}
 	for peer, hashes := range txset {