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Fix uint64 underflow in getHeader msIntoSlot for requests arriving before slot start #906

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Fix uint64 underflow in getHeader msIntoSlot for requests arriving before slot start #906

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4e094f0
fix uint64 underflow in getHeader msIntoSlot
vsaraikin Jul 7, 2026
0677c95
make regression test robust to Unix() second truncation
vsaraikin Jul 8, 2026
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10 changes: 9 additions & 1 deletion server/get_header.go
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Original file line number Diff line number Diff line change
Expand Up @@ -62,7 +62,15 @@ func (m *BoostService) getHeader(log *logrus.Entry, slot phase0.Slot, pubkey, pa

// Log how late into the slot the request starts
slotStartTimestamp := m.genesisTime + uint64(slot)*config.SlotTimeSec
msIntoSlot := uint64(time.Now().UTC().UnixMilli()) - slotStartTimestamp*1000
// The request can arrive before the slot start (e.g. scheduling jitter
// between VC and BN), which would underflow the unsigned subtraction and
// trip the late-in-slot guard below. Clamp negative values to zero, i.e.
// treat an early request as arriving exactly at slot start.
msIntoSlotSigned := time.Now().UTC().UnixMilli() - int64(slotStartTimestamp*1000)
var msIntoSlot uint64
if msIntoSlotSigned > 0 {
msIntoSlot = uint64(msIntoSlotSigned)
}
log.WithFields(logrus.Fields{
"genesisTime": m.genesisTime,
"slotTimeSec": config.SlotTimeSec,
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16 changes: 16 additions & 0 deletions server/service_test.go
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Expand Up @@ -326,6 +326,22 @@ func TestGetHeader(t *testing.T) {
require.Equal(t, 1, backend.relays[0].GetRequestCount(path))
})

t.Run("Request arriving before slot start still queries relays", func(t *testing.T) {
header := make(http.Header)
header.Set(HeaderAccept, MediaTypeJSON)

backend := newTestBackend(t, 1, time.Second)
// setting genesisTime so slot 1 starts several seconds in the future,
// making msIntoSlot reliably negative regardless of the Unix()
// second-truncation. Without clamping, the unsigned subtraction wraps
// and the late-in-slot guard skips all relays.
backend.boost.genesisTime = uint64(time.Now().Unix()) - 7

rr := backend.request(t, http.MethodGet, path, header, nil)
require.Equal(t, http.StatusOK, rr.Code, rr.Body.String())
require.Equal(t, 1, backend.relays[0].GetRequestCount(path))
})

t.Run("Okay response from relay deneb", func(t *testing.T) {
header := make(http.Header)
header.Set(HeaderAccept, MediaTypeJSON)
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