fix: ignore errors that caused by gap to keep peer connection

eth/downloader/skeleton.go

@@ -27,6 +27,7 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/rawdb"
 	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/eth/etherror"
 	"github.com/ethereum/go-ethereum/eth/protocols/eth"
 	"github.com/ethereum/go-ethereum/ethdb"
 	"github.com/ethereum/go-ethereum/log"
@@ -73,6 +74,9 @@ var errTerminated = errors.New("terminated")
 // with a new header, but it does not link up to the existing sync.
 var errReorgDenied = errors.New("non-forced head reorg denied")
 
+// maxBlockNumGapTolerance is the max gap tolerance by peer
+var maxBlockNumGapTolerance = uint64(30)
+
 func init() {
 	// Tuning parameters is nice, but the scratch space must be assignable in
 	// full to peers. It's a useless cornercase to support a dangling half-group.
@@ -786,25 +790,29 @@ func (s *skeleton) executeTask(peer *peerConnection, req *headerRequest) {
 		case len(headers) == 0:
 			// No headers were delivered, reject the response and reschedule
 			peer.log.Debug("No headers delivered")
-			res.Done <- errors.New("no headers delivered")
+			res.Done <- etherror.ErrNoHeadersDelivered
 			s.scheduleRevertRequest(req)
 
 		case headers[0].Number.Uint64() != req.head:
 			// Header batch anchored at non-requested number
 			peer.log.Debug("Invalid header response head", "have", headers[0].Number, "want", req.head)
-			res.Done <- errors.New("invalid header batch anchor")
+			if req.head-headers[0].Number.Uint64() < maxBlockNumGapTolerance {
+				res.Done <- etherror.ErrHeaderBatchAnchorLow
+			} else {
+				res.Done <- etherror.ErrInvalidHeaderBatchAnchor
+			}
 			s.scheduleRevertRequest(req)
 
 		case req.head >= requestHeaders && len(headers) != requestHeaders:
 			// Invalid number of non-genesis headers delivered, reject the response and reschedule
 			peer.log.Debug("Invalid non-genesis header count", "have", len(headers), "want", requestHeaders)
-			res.Done <- errors.New("not enough non-genesis headers delivered")
+			res.Done <- etherror.ErrNotEnoughNonGenesisHeaders
 			s.scheduleRevertRequest(req)
 
 		case req.head < requestHeaders && uint64(len(headers)) != req.head:
 			// Invalid number of genesis headers delivered, reject the response and reschedule
 			peer.log.Debug("Invalid genesis header count", "have", len(headers), "want", headers[0].Number.Uint64())
-			res.Done <- errors.New("not enough genesis headers delivered")
+			res.Done <- etherror.ErrNotEnoughGenesisHeaders
 			s.scheduleRevertRequest(req)
 
 		default:
@@ -813,7 +821,7 @@ func (s *skeleton) executeTask(peer *peerConnection, req *headerRequest) {
 			for i := 0; i < len(headers)-1; i++ {
 				if headers[i].ParentHash != headers[i+1].Hash() {
 					peer.log.Debug("Invalid hash progression", "index", i, "wantparenthash", headers[i].ParentHash, "haveparenthash", headers[i+1].Hash())
-					res.Done <- errors.New("invalid hash progression")
+					res.Done <- etherror.ErrInvalidHashProgression
 					s.scheduleRevertRequest(req)
 					return
 				}

eth/etherror/errors.go

@@ -0,0 +1,12 @@
+package etherror
+
+import "errors"
+
+var (
+	ErrNoHeadersDelivered         = errors.New("no headers delivered")
+	ErrInvalidHeaderBatchAnchor   = errors.New("invalid header batch anchor")
+	ErrNotEnoughNonGenesisHeaders = errors.New("not enough non-genesis headers delivered")
+	ErrNotEnoughGenesisHeaders    = errors.New("not enough genesis headers delivered")
+	ErrInvalidHashProgression     = errors.New("invalid hash progression")
+	ErrHeaderBatchAnchorLow       = errors.New("header batch anchor is lower than requested")
+)

eth/protocols/eth/handler.go

@@ -17,13 +17,15 @@
 package eth
 
 import (
+	"errors"
 	"fmt"
 	"math/big"
 	"time"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/eth/etherror"
 	"github.com/ethereum/go-ethereum/metrics"
 	"github.com/ethereum/go-ethereum/p2p"
 	"github.com/ethereum/go-ethereum/p2p/enode"
@@ -153,7 +155,19 @@ func nodeInfo(chain *core.BlockChain, network uint64) *NodeInfo {
 // connection is torn down.
 func Handle(backend Backend, peer *Peer) error {
 	for {
-		if err := handleMessage(backend, peer); err != nil {
+		err := handleMessage(backend, peer)
+		switch {
+		// TODO: currently no headers not ignored as it may leads to a dead peer not removing as expected
+		/*
+			case errors.Is(err, etherror.ErrNoHeadersDelivered):
+				// ignore no headers delivered
+				peer.Log().Warn("Message handling failed with no headers")
+		*/
+		case errors.Is(err, etherror.ErrHeaderBatchAnchorLow):
+			// ignore lower header anchor within tolerance
+			peer.Log().Warn("Message handling failed with lower batch anchor")
+
+		case err != nil:
 			peer.Log().Debug("Message handling failed in `eth`", "err", err)
 			return err
 		}