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fix: back off unroutable IPv6 DoH upstream health-check spam

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When IPv6 is available locally but the selected IPv6 DoH endpoint is
unroutable (e.g. dialing [2606:1a40::22]:443 returns "no route to host"
while IPv4 stays usable), ctrld re-bootstrapped and re-dialed the endpoint
every ~2s. A weekend soak produced ~46.7k "no route to host" lines, with
the dial/health-check loop dominating the log during bad windows.

Add bounded backoff/suppression for network-unreachable endpoints at two
levels:

- ParallelDialer (internal/net): track dial addresses that fail with
  ENETUNREACH/EHOSTUNREACH and skip them for an exponentially growing,
  bounded window (5s -> 60s). A successful dial clears the entry
  immediately, so recovery is preserved when the route returns. When every
  candidate is suppressed the dial fails fast and quietly instead of
  hammering known-unroutable addresses.

- Upstream recovery loop (cmd/cli): demote unreachable check failures to
  debug and back off the retry cadence (2s -> 60s) for an unreachable
  streak; any other failure resets to the base cadence.

The new IsUnreachable classifier lives in internal/net and is reused by
cmd/cli's errNetworkError, so the unreachable-errno matching has a single
definition. Note the explicit winsock constants (10051/10065) are required
on Windows: syscall.ENETUNREACH/EHOSTUNREACH are Go's portable "invented"
values and never equal the raw WSA codes a failing connect surfaces.

Suppression and backoff are always bounded, so IPv6 is never disabled until
restart and recovers on its own once the route is back. Split-stack
selection and the #549 macOS intercept recovery work are untouched.

Adds unit tests for the classifier, the dialer's suppression tracker, and
the recovery backoff schedule.
This commit is contained in:
Cuong Manh Le
2026-06-30 14:47:33 +07:00
parent 8948fa402b
commit ff14fc8ac9
8 changed files with 269 additions and 27 deletions
Download Patch File Download Diff File Expand all files Collapse all files
cmd/cli/dns_intercept_darwin.go
+2 -12
View File
@@ -1417,15 +1417,6 @@ func (p *prog) ensurePFAnchorActive() bool {
return true
}
func (p *prog) scheduleDNSAfterVPNSettleRefresh(reason string, delay time.Duration) {
time.AfterFunc(delay, func() {
if p.dnsInterceptState == nil {
return
}
p.refreshDNSAfterVPNSettle(reason)
})
}
func (p *prog) pfExecBackoffActive() bool {
until := p.pfExecBackoffUntil.Load()
if until == 0 {
@@ -1436,7 +1427,7 @@ func (p *prog) pfExecBackoffActive() bool {
p.pfExecBackoffUntil.CompareAndSwap(until, 0)
return false
}
mainLog.Load().Debug().Dur("remaining", remaining).Msg("DNS intercept watchdog: suppressed during pf exec backoff")
mainLog.Load().Debug().Msgf("DNS intercept watchdog: suppressed during pf exec backoff (remaining: %s)", remaining)
return true
}
@@ -1446,8 +1437,7 @@ func (p *prog) pfBackoffResourceExhaustion(err error, output []byte, operation s
}
until := time.Now().Add(pfExecFailureBackoff)
p.pfExecBackoffUntil.Store(until.UnixMilli())
mainLog.Load().Warn().Err(err).Dur("backoff", pfExecFailureBackoff).Str("operation", operation).
Msg("DNS intercept watchdog: backing off after local exec resource exhaustion")
mainLog.Load().Warn().Err(err).Msgf("DNS intercept watchdog: backing off after local exec resource exhaustion (operation: %s, backoff: %s)", operation, pfExecFailureBackoff)
return true
}