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NextHopRouter: fix 49.7-day millis() rollover in retransmission timing #10227

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NextHopRouter: fix 49.7-day millis() rollover in retransmission timing #10227

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8e354a8
NextHopRouter: fix 49.7-day millis() rollover in retransmission timing
nightjoker7 Apr 21, 2026
1d97a29
Address Copilot review: use unsigned half-range for rollover-safe ret…
nightjoker7 Apr 23, 2026
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12 changes: 10 additions & 2 deletions src/mesh/NextHopRouter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -405,8 +405,16 @@ int32_t NextHopRouter::doRetransmissions()

bool stillValid = true; // assume we'll keep this record around

// FIXME, handle 51 day rolloever here!!!
if (p.nextTxMsec <= now) {
// Use unsigned half-range comparison so retransmission timing stays correct across the
// ~49.7 day millis() wraparound (previously this FIXME would stall all retx for the
// duration of the wrap or fire them all at once immediately after).
//
// Casting an unsigned difference to int32_t for a "time passed" test is
// implementation-defined in C++ when the value exceeds INT32_MAX. The unsigned
// half-range form below is fully well-defined: nextTxMsec is in the past (or is now)
// iff (now - nextTxMsec) has not wrapped past 2^31 ms. Anything further in the
// future wraps into the top half and reads as "not yet."
if ((uint32_t)(now - p.nextTxMsec) < 0x80000000u) {
if (p.numRetransmissions == 0) {
if (isFromUs(p.packet)) {
LOG_DEBUG("Reliable send failed, returning a nak for fr=0x%08x,to=0x%08x,id=0x%08x", p.packet->from,
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