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eth/downloader: don't drop peer that is behind the requested head #33052

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eth/downloader: don't drop peer that is behind the requested head #33052

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fc96cfa
eth/downloader: don't drop peer if header is lagged
jsvisa Oct 29, 2025
8dce444
eth/downloader: update tests
jsvisa Oct 29, 2025
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10 changes: 8 additions & 2 deletions eth/downloader/skeleton.go
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Original file line number Diff line number Diff line change
Expand Up @@ -812,8 +812,14 @@ func (s *skeleton) executeTask(peer *peerConnection, req *headerRequest) {

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 peerHeader := headers[0].Number.Uint64(); peerHeader > req.head {
peer.log.Debug("Invalid header response head", "have", peerHeader, "want", req.head)
res.Done <- errors.New("invalid header batch anchor")
} else {
peer.log.Debug("Peer behind requested head, rescheduling", "have", peerHeader, "want", req.head)
// Do not penalize the peer if it is behind our requested head
res.Done <- nil
}
s.scheduleRevertRequest(req)

case req.head >= requestHeaders && len(headers) != requestHeaders:
Expand Down
8 changes: 4 additions & 4 deletions eth/downloader/skeleton_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -609,14 +609,14 @@ func TestSkeletonSyncRetrievals(t *testing.T) {
mid: skeletonExpect{
state: []*subchain{{Head: requestHeaders + 100, Tail: 100}},
serve: requestHeaders + 101 - 3, // len - head - genesis - missing
drop: 1, // penalize shortened header deliveries
drop: 0, // do not penalize in relaxed mode
},

newPeer: newSkeletonTestPeer("good-peer", chain),
end: skeletonExpect{
state: []*subchain{{Head: requestHeaders + 100, Tail: 1}},
serve: (requestHeaders + 101 - 3) + (100 - 1), // midserve + lenrest - genesis
drop: 1, // no new drops
drop: 0, // relaxed: no drops
},
},
// This test checks if a peer tries to withhold a header - *off* the sync
Expand Down Expand Up @@ -655,14 +655,14 @@ func TestSkeletonSyncRetrievals(t *testing.T) {
mid: skeletonExpect{
state: []*subchain{{Head: requestHeaders + 100, Tail: 100}},
serve: requestHeaders + 101 - 2, // len - head - genesis
drop: 1, // penalize invalid header sequences
drop: 0, // do not penalize in relaxed mode
},

newPeer: newSkeletonTestPeer("good-peer", chain),
end: skeletonExpect{
state: []*subchain{{Head: requestHeaders + 100, Tail: 1}},
serve: (requestHeaders + 101 - 2) + (100 - 1), // midserve + lenrest - genesis
drop: 1, // no new drops
drop: 0, // relaxed: no drops
},
},
// This test checks if a peer tries to duplicate a header - *off* the sync
Expand Down
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