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@@ -22,22 +22,85 @@ import (
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"sync/atomic"
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"time"
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+ "golang.org/x/exp/slices"
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"tailscale.com/atomicfile"
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+ "tailscale.com/envknob"
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+ "tailscale.com/net/dns/recursive"
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"tailscale.com/net/netmon"
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"tailscale.com/net/netns"
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"tailscale.com/net/tlsdial"
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"tailscale.com/net/tshttpproxy"
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"tailscale.com/tailcfg"
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"tailscale.com/types/logger"
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+ "tailscale.com/util/clientmetric"
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"tailscale.com/util/slicesx"
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)
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+var disableRecursiveResolver = envknob.RegisterBool("TS_DNSFALLBACK_DISABLE_RECURSIVE_RESOLVER")
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+
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// MakeLookupFunc creates a function that can be used to resolve hostnames
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// (e.g. as a LookupIPFallback from dnscache.Resolver).
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// The netMon parameter is optional; if non-nil it's used to do faster interface lookups.
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func MakeLookupFunc(logf logger.Logf, netMon *netmon.Monitor) func(ctx context.Context, host string) ([]netip.Addr, error) {
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return func(ctx context.Context, host string) ([]netip.Addr, error) {
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- return lookup(ctx, host, logf, netMon)
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+ if disableRecursiveResolver() {
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+ return lookup(ctx, host, logf, netMon)
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+ }
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+
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+ addrsCh := make(chan []netip.Addr, 1)
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+
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+ // Run the recursive resolver in the background so we can
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+ // compare the results.
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+ go func() {
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+ logf := logger.WithPrefix(logf, "recursive: ")
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+
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+ // Ensure that we catch panics while we're testing this
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+ // code path; this should never panic, but we don't
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+ // want to take down the process by having the panic
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+ // propagate to the top of the goroutine's stack and
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+ // then terminate.
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+ defer func() {
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+ if r := recover(); r != nil {
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+ logf("bootstrap DNS: recovered panic: %v", r)
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+ metricRecursiveErrors.Add(1)
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+ }
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+ }()
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+
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+ resolver := recursive.Resolver{
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+ Dialer: netns.NewDialer(logf, netMon),
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+ Logf: logf,
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+ }
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+ addrs, minTTL, err := resolver.Resolve(ctx, host)
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+ if err != nil {
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+ logf("error using recursive resolver: %v", err)
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+ metricRecursiveErrors.Add(1)
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+ return
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+ }
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+ slices.SortFunc(addrs, func(a, b netip.Addr) bool { return a.Less(b) })
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+
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+ // Wait for a response from the main function
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+ oldAddrs := <-addrsCh
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+ slices.SortFunc(oldAddrs, func(a, b netip.Addr) bool { return a.Less(b) })
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+
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+ matches := slices.Equal(addrs, oldAddrs)
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+
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+ logf("bootstrap DNS comparison: matches=%v oldAddrs=%v addrs=%v minTTL=%v", matches, oldAddrs, addrs, minTTL)
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+
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+ if matches {
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+ metricRecursiveMatches.Add(1)
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+ } else {
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+ metricRecursiveMismatches.Add(1)
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+ }
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+ }()
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+
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+ addrs, err := lookup(ctx, host, logf, netMon)
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+ if err != nil {
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+ addrsCh <- nil
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+ return nil, err
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+ }
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+
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+ addrsCh <- slices.Clone(addrs)
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+ return addrs, nil
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}
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}
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@@ -254,3 +317,9 @@ func SetCachePath(path string, logf logger.Logf) {
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cachedDERPMap.Store(dm)
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logf("[v2] dnsfallback: SetCachePath loaded cached DERP map")
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}
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+
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+var (
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+ metricRecursiveMatches = clientmetric.NewCounter("dnsfallback_recursive_matches")
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+ metricRecursiveMismatches = clientmetric.NewCounter("dnsfallback_recursive_mismatches")
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+ metricRecursiveErrors = clientmetric.NewCounter("dnsfallback_recursive_errors")
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+)
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Andrew Dunham