eth: select sync peer randomly when td equal

eth/peerset.go

@@ -23,6 +23,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/cometbft/cometbft/libs/rand"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/eth/protocols/bsc"
@@ -539,22 +540,26 @@ func (ps *peerSet) peerWithHighestHead() *eth.Peer {
 		bestPeer      *eth.Peer
 		bestJustified *uint64
 		bestTd        *big.Int
+		randUint      = rand.Uint()
 	)
 	for _, p := range knowJustifiedPeers {
 		_, justifiedNumber, td := p.Head()
 		if bestPeer == nil {
 			bestPeer, bestJustified, bestTd = p.Peer, justifiedNumber, td
-		} else if *justifiedNumber > *bestJustified ||
-			(*justifiedNumber == *bestJustified && td.Cmp(bestTd) > 0) {
+		} else if *justifiedNumber > *bestJustified {
 			bestPeer, bestJustified = p.Peer, justifiedNumber
 			if td.Cmp(bestTd) > 0 {
 				bestTd = td // may be not equal `to bestPeer.td`
 			}
+		} else if *justifiedNumber == *bestJustified {
+			if td.Cmp(bestTd) > 0 || (td.Cmp(bestTd) == 0 && randUint%2 == 0) {
+				bestPeer, bestTd = p.Peer, td
+			}
 		}
 	}
 	// if some nodes does not have justified number, back to behavior without fast finality
 	for _, p := range notKnowJustifiedPeers {
-		if _, _, td := p.Head(); bestPeer == nil || td.Cmp(bestTd) > 0 {
+		if _, _, td := p.Head(); bestPeer == nil || td.Cmp(bestTd) > 0 || (td.Cmp(bestTd) == 0 && randUint%2 == 0) {
 			bestPeer, bestTd = p.Peer, td
 		}
 	}