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net/dns/resolver: count errors when racing DNS queries, fail earlier
If all N queries failed, we waited until context timeout (in 5 seconds) to return. This makes (*forwarder).forward fail fast when the network's unavailable. Change-Id: Ibbb3efea7ed34acd3f3b29b5fee00ba8c7492569 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
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e3a4952527
@ -615,6 +615,10 @@ func (f *forwarder) forwardWithDestChan(ctx context.Context, query packet, respo
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return err
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}
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// Guarantee that the ctx we use below is done when this function returns.
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ctx, cancel := context.WithCancel(ctx)
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defer cancel()
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// Drop DNS service discovery spam, primarily for battery life
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// on mobile. Things like Spotify on iOS generate this traffic,
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// when browsing for LAN devices. But even when filtering this
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@ -655,12 +659,8 @@ func (f *forwarder) forwardWithDestChan(ctx context.Context, query packet, respo
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}
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defer fq.closeOnCtxDone.Close()
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resc := make(chan []byte, 1)
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var (
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mu sync.Mutex
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firstErr error
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)
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resc := make(chan []byte, 1) // it's fine buffered or not
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errc := make(chan error, 1) // it's fine buffered or not too
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for i := range resolvers {
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go func(rr *resolverAndDelay) {
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if rr.startDelay > 0 {
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@ -674,39 +674,48 @@ func (f *forwarder) forwardWithDestChan(ctx context.Context, query packet, respo
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}
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resb, err := f.send(ctx, fq, *rr)
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if err != nil {
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mu.Lock()
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defer mu.Unlock()
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if firstErr == nil {
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firstErr = err
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select {
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case errc <- err:
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case <-ctx.Done():
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}
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return
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}
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select {
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case resc <- resb:
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default:
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case <-ctx.Done():
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}
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}(&resolvers[i])
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}
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select {
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case v := <-resc:
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var firstErr error
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var numErr int
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for {
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select {
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case v := <-resc:
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select {
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case <-ctx.Done():
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metricDNSFwdErrorContext.Add(1)
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return ctx.Err()
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case responseChan <- packet{v, query.addr}:
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metricDNSFwdSuccess.Add(1)
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return nil
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}
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case err := <-errc:
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if firstErr == nil {
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firstErr = err
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}
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numErr++
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if numErr == len(resolvers) {
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return firstErr
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}
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case <-ctx.Done():
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metricDNSFwdErrorContext.Add(1)
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if firstErr != nil {
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metricDNSFwdErrorContextGotError.Add(1)
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return firstErr
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}
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return ctx.Err()
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case responseChan <- packet{v, query.addr}:
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metricDNSFwdSuccess.Add(1)
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return nil
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}
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case <-ctx.Done():
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mu.Lock()
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defer mu.Unlock()
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metricDNSFwdErrorContext.Add(1)
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if firstErr != nil {
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metricDNSFwdErrorContextGotError.Add(1)
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return firstErr
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}
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return ctx.Err()
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}
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}
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