fix: back off route applies when they keep knocking the VPN down - #107
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A GlobalProtect on-demand session entered a 51-minute resonance loop: every tunnel restore re-armed the settle-gated apply, every apply's route-change broadcasts starved the client's gateway-route read, and every resulting drop caused the restore that re-armed the next apply. 28 cycles, until the client's retry gave up and logged the user out of its gateway, which an on-demand session never recovers from on its own. The deferral collapse could not see this shape (every drop landed AFTER the apply, so deferrals stayed 0) and would only have poked faster. Count a strike when a detected VPN drop lands within 90s of our own kernel-write burst, stamped at the two batch funnels all writes go through. Each strike doubles the next post-reconnect settle delay (20s base, 240s cap), overriding the deferral collapse. Strikes decay as a whole 30 minutes after the last one; unrelated drops neither add nor clear, so a client also dropping on its own cannot reset the backoff mid-storm. Fixes #106
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Included review availability: Your plan provides up to 2 included reviews per hour; 0 remain after this review. 📝 WalkthroughWalkthroughChangesThe reconnect flow records route-write bursts, attributes qualifying VPN drops as apply-kill strikes, and applies exponential settle backoff. Strike expiry, delay caps, deferral override behavior, and attribution boundaries are covered by tests. Apply-kill backoff
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🔵 Low · up to The change spaces out route application after repeated VPN drops, but VPN-Only traffic may follow the physical default route for up to 240 seconds before routes are restored. This is a bounded merge-readiness risk that should be explicitly accepted by the owner. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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Inline comments:
In `@Sources/VPNBypassCore/RerouteDecider.swift`:
- Line 122: Update the reconnect backoff handling in RerouteDecider’s delay
calculation so VPN-Only traffic remains blocked throughout the delay after
disconnect; preserve the existing capped exponential backoff while ensuring
RouteManager does not permit physical-default routing before VPN routes are
restored.
In `@Sources/VPNBypassCore/RouteManager.swift`:
- Around line 94-96: Ensure every tracked kernel-write batch delete updates
lastKernelBurstAt by routing the direct HelperManager.shared.removeRoutesBatch
calls in removeAllRoutes and the DNS refresh paths through removeRoutesBatchVia,
or by timestamping the shared removal funnel; preserve the existing 90-second
attribution behavior.
- Around line 828-829: Update the strike-recording block using lastKernelBurstAt
and ReconnectSettle.isSuspectedApplyKill so the attributed burst is consumed
after the first drop, preventing subsequent drops during the settle wait from
reusing it; preserve attribution for a newer route-write burst.
- Line 2539: Update both tracked batch paths in RouteManager.swift: at lines
2539-2539, record lastKernelBurstAt before awaiting the delete batch, and at
lines 4496-4496, record it before awaiting the add batch. Keep the existing
non-empty destinations guard so only submitted batches update the timestamp.
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Sources/VPNBypassCore/RerouteDecider.swiftSources/VPNBypassCore/RouteManager.swiftTests/VPNBypassTests/ReconnectSettleTests.swift
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…er burst Review follow-ups: the four direct removeRoutesBatch calls (removeAllRoutes catch-alls + rest, both DNS-refresh removals) now go through removeRoutesBatchVia so every tracked delete stamps the attribution anchor; both funnels stamp BEFORE the await so a status check interleaving with an in-flight batch judges the drop against the right timestamp; and a strike consumes its burst so a re-drop during the settle wait cannot blame the same batch twice.
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The problem
A GlobalProtect on-demand session died for good after 51 minutes of flapping, and our own applies were driving the cycle. Every tunnel restore re-armed the settle-gated apply. Every apply's route-change broadcasts starved the client's gateway-route read (
pan_get_gateway: timeout, thenFailed to find route, thenProcDrv quit). Every drop caused the restore that re-armed the next apply. 28 cycles, most drops within 16 seconds of one of our batches, until the client's retry failed twice and it logged the user out of its gateway. An on-demand session never recovers from that on its own. Full anatomy in #106.The existing defenses each miss this shape:
WritePacerpaces the burst, but a degraded reader starves even on a paced burst. macOS flagged the client for breaking its 50% CPU limit mid-loop.One observation shaped the fix: the same client instance, 90 minutes idle after the logout, survived a bigger apply (381 adds + 329 deletes) without a blip. A settled client tolerates our applies. The bug is re-poking a struggling one every 2-3 minutes.
The fix
Apply-kill strikes with exponential backoff.
addRoutesBatchTracked,removeRoutesBatchVia) stamplastKernelBurstAt. Even a failed RTM write is broadcast to every routing socket, so a submitted batch counts whether or not it stuck.ReconnectSettle.isSuspectedApplyKill). The window covers the observed chain: batch, client read timeout within 16s, teardown, then up to ~30s for our status timer plus the 1.5s disconnect recheck.suspected apply-kill (strike N)on the drop,backed off — N suspected apply-killson the reconnect.Replayed against the incident timeline the loop breaks around strike 4: applies space out to 4-minute intervals, the client gets the calm windows it demonstrably recovers in, and the retry-exhaustion logout never fires.
Bypass mode keeps its routes across drops (they egress the local gateway), so waiting costs nothing there. A VPN-Only reconnect has no routes installed until the apply runs; the 240s ceiling bounds that window rather than letting the backoff grow unbounded.
Tests
Six new cases in
ReconnectSettleTestslock the contract: exponential growth and cap, backoff overriding the deferral collapse (the regression test for the incident), cold-base scaling, default-parameter compatibility for every existing call, the forward-only bounded attribution window, and whole-strike decay. Full suite: 1078 tests, 0 failures.Fixes #106
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