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@ -10,6 +10,7 @@ import (
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"log"
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"net"
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"syscall"
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"time"
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"golang.org/x/net/route"
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"golang.org/x/sys/unix"
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@ -28,6 +29,34 @@ func DefaultRouteInterface() (string, error) {
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return iface.Name, nil
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}
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// fetchRoutingTable is a retry loop around route.FetchRIB, fetching NET_RT_DUMP2.
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//
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// The retry loop is due to a bug in the BSDs (or Go?). See
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// https://github.com/tailscale/tailscale/issues/1345
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func fetchRoutingTable() (rib []byte, err error) {
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fails := 0
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for {
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rib, err := route.FetchRIB(syscall.AF_UNSPEC, syscall.NET_RT_DUMP2, 0)
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if err == nil {
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return rib, nil
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}
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fails++
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if fails < 10 {
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// Empirically, 1 retry is enough. In a long
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// stress test while toggling wifi on & off, I
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// only saw a few occurrences of 2 and one 3.
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// So 10 should be more plenty.
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if fails > 5 {
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time.Sleep(5 * time.Millisecond)
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}
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continue
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}
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if err != nil {
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return nil, fmt.Errorf("route.FetchRIB: %w", err)
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}
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}
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}
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func DefaultRouteInterfaceIndex() (int, error) {
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// $ netstat -nr
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// Routing tables
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@ -43,7 +72,7 @@ func DefaultRouteInterfaceIndex() (int, error) {
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// c RTF_PRCLONING Protocol-specified generate new routes on use
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// I RTF_IFSCOPE Route is associated with an interface scope
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rib, err := route.FetchRIB(syscall.AF_UNSPEC, syscall.NET_RT_DUMP2, 0)
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rib, err := fetchRoutingTable()
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if err != nil {
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return 0, fmt.Errorf("route.FetchRIB: %w", err)
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}
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@ -83,7 +112,7 @@ func init() {
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}
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func likelyHomeRouterIPDarwinFetchRIB() (ret netaddr.IP, ok bool) {
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rib, err := route.FetchRIB(syscall.AF_UNSPEC, syscall.NET_RT_DUMP2, 0)
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rib, err := fetchRoutingTable()
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if err != nil {
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log.Printf("routerIP/FetchRIB: %v", err)
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return ret, false
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