Don't automatically restore saved DNS settings when switching networks

smol tweaks to nameserver test queries

fix restoreDNS errors

add some debugging information

fix wront type in log msg

set send logs command timeout to 5 mins

when the runningIface is no longer up, attempt to find a new interface

prefer default route, ignore non physical interfaces

prefer default route, ignore non physical interfaces

add max context timeout on performLeakingQuery with more debug logs

resolver.go

@@ -147,16 +147,82 @@ var testNameServerFn = testNameserver
 
 // testPlainDnsNameserver sends a test query to DNS nameserver to check if the server is available.
 func testNameserver(addr string) bool {
-	msg := new(dns.Msg)
-	msg.SetQuestion("controld.com.", dns.TypeNS)
-	client := new(dns.Client)
-	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
-	defer cancel()
-	_, _, err := client.ExchangeContext(ctx, msg, net.JoinHostPort(addr, "53"))
-	if err != nil {
-		ProxyLogger.Load().Debug().Err(err).Msgf("failed to connect to OS nameserver: %s", addr)
+	// Skip link-local addresses without scope IDs and deprecated site-local addresses
+	if ip, err := netip.ParseAddr(addr); err == nil {
+		if ip.Is6() {
+			if ip.IsLinkLocalUnicast() && !strings.Contains(addr, "%") {
+				ProxyLogger.Load().Debug().
+					Str("nameserver", addr).
+					Msg("skipping link-local IPv6 address without scope ID")
+				return false
+			}
+			// Skip deprecated site-local addresses (fec0::/10)
+			if strings.HasPrefix(ip.String(), "fec0:") {
+				ProxyLogger.Load().Debug().
+					Str("nameserver", addr).
+					Msg("skipping deprecated site-local IPv6 address")
+				return false
+			}
+		}
 	}
-	return err == nil
+
+	ProxyLogger.Load().Debug().
+		Str("input_addr", addr).
+		Msg("testing nameserver")
+
+	// Handle both IPv4 and IPv6 addresses
+	serverAddr := addr
+	host, port, err := net.SplitHostPort(addr)
+	if err != nil {
+		// No port in address, add default port 53
+		serverAddr = net.JoinHostPort(addr, "53")
+	} else if port == "" {
+		// Has split markers but empty port
+		serverAddr = net.JoinHostPort(host, "53")
+	}
+
+	ProxyLogger.Load().Debug().
+		Str("server_addr", serverAddr).
+		Msg("using server address")
+
+	// Test domains that are likely to exist and respond quickly
+	testDomains := []struct {
+		name  string
+		qtype uint16
+	}{
+		{".", dns.TypeNS},            // Root NS query - should always work
+		{"controld.com.", dns.TypeA}, // Fallback to a reliable domain
+		{"google.com.", dns.TypeA},   // Fallback to a reliable domain
+	}
+
+	client := &dns.Client{
+		Timeout: 2 * time.Second,
+		Net:     "udp",
+	}
+
+	// Try each test query until one succeeds
+	for _, test := range testDomains {
+		msg := new(dns.Msg)
+		msg.SetQuestion(test.name, test.qtype)
+		msg.RecursionDesired = true
+
+		ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+		resp, _, err := client.ExchangeContext(ctx, msg, serverAddr)
+		cancel()
+
+		if err == nil && resp != nil {
+			return true
+		}
+
+		ProxyLogger.Load().Error().
+			Err(err).
+			Str("nameserver", serverAddr).
+			Str("test_domain", test.name).
+			Str("query_type", dns.TypeToString[test.qtype]).
+			Msg("DNS availability test failed")
+	}
+
+	return false
 }
 
 // Resolver is the interface that wraps the basic DNS operations.
@@ -222,7 +288,7 @@ func (o *osResolver) Resolve(ctx context.Context, msg *dns.Msg) (*dns.Msg, error
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 
-	dnsClient := &dns.Client{Net: "udp"}
+	dnsClient := &dns.Client{Net: "udp", Timeout: 2 * time.Second}
 	ch := make(chan *osResolverResult, numServers)
 	wg := &sync.WaitGroup{}
 	wg.Add(numServers)
@@ -264,11 +330,14 @@ func (o *osResolver) Resolve(ctx context.Context, msg *dns.Msg) (*dns.Msg, error
 		case res.answer != nil && res.answer.Rcode == dns.RcodeSuccess:
 			switch {
 			case res.server == controldPublicDnsWithPort:
-				controldSuccessAnswer = res.answer // only use ControlD answer as last one.
+				Log(ctx, ProxyLogger.Load().Debug(), "got ControlD answer from: %s", res.server)
+				controldSuccessAnswer = res.answer
 			case !res.lan && publicServerAnswer == nil:
-				publicServerAnswer = res.answer // use public DNS answer after LAN server..
+				Log(ctx, ProxyLogger.Load().Debug(), "got public answer from: %s", res.server)
+				publicServerAnswer = res.answer
 				publicServer = res.server
 			default:
+				Log(ctx, ProxyLogger.Load().Debug(), "got LAN answer from: %s", res.server)
 				cancel()
 				logAnswer(res.server)
 				return res.answer, nil
@@ -276,6 +345,8 @@ func (o *osResolver) Resolve(ctx context.Context, msg *dns.Msg) (*dns.Msg, error
 		case res.answer != nil:
 			nonSuccessAnswer = res.answer
 			nonSuccessServer = res.server
+			Log(ctx, ProxyLogger.Load().Debug(), "got non-success answer from: %s with code: %d",
+				res.server, res.answer.Rcode)
 		}
 		errs = append(errs, res.err)
 	}