all: workaround problem with EdgeOS dnsmasq config

cmd/ctrld/prog.go

@@ -16,6 +16,8 @@ import (
 	"github.com/Control-D-Inc/ctrld/internal/clientinfo"
 	"github.com/Control-D-Inc/ctrld/internal/dnscache"
 	"github.com/Control-D-Inc/ctrld/internal/router"
+	"github.com/Control-D-Inc/ctrld/internal/router/dnsmasq"
+	"github.com/Control-D-Inc/ctrld/internal/router/edgeos"
 	"github.com/Control-D-Inc/ctrld/internal/router/firewalla"
 )
 
@@ -243,19 +245,26 @@ func (p *prog) setDNS() {
 	}
 	logger.Debug().Msg("setting DNS for interface")
 	ns := lc.IP
-	ifaceName := defaultIfaceName()
-	isFirewalla := router.Name() == firewalla.Name
-	if isFirewalla {
-		// On Firewalla, the lo interface is excluded in all dnsmasq settings of all interfaces.
-		// Thus, we use "br0" as the nameserver in /etc/resolv.conf file.
-		ifaceName = "br0"
-		logger.Warn().Msg("using br0 interface IP address as DNS server")
-	}
 	if couldBeDirectListener(lc) {
 		// If ctrld is direct listener, use 127.0.0.1 as nameserver.
 		ns = "127.0.0.1"
 	} else if lc.Port != 53 {
-		logger.Warn().Msg("ctrld is not running on port 53, use default route interface as DNS server")
+		ifaceName := defaultIfaceName()
+		switch router.Name() {
+		case firewalla.Name:
+			// On Firewalla, the lo interface is excluded in all dnsmasq settings of all interfaces.
+			// Thus, we use "br0" as the nameserver in /etc/resolv.conf file.
+			ifaceName = "br0"
+			logger.Warn().Msg("using br0 interface IP address as DNS server")
+		case edgeos.Name:
+			// On EdgeOS, dnsmasq is run with "--local-service", so we need to get
+			// the proper interface from dnsmasq config.
+			if name, _ := dnsmasq.InterfaceNameFromConfig("/etc/dnsmasq.conf"); name != "" {
+				ifaceName = name
+				logger.Warn().Msgf("using %s interface IP address as DNS server", ifaceName)
+			}
+		}
+		logger.Warn().Msg("ctrld is not running on port 53, use interface %s IP as DNS server")
 		netIface, err := net.InterfaceByName(ifaceName)
 		if err != nil {
 			mainLog.Fatal().Err(err).Msg("failed to get default route interface")

cmd/ctrld/prog_linux.go

@@ -34,7 +34,6 @@ func setDependencies(svc *service.Config) {
 		svc.Dependencies = append(svc.Dependencies, "Wants=vyatta-dhcpd.service")
 		svc.Dependencies = append(svc.Dependencies, "After=vyatta-dhcpd.service")
 		svc.Dependencies = append(svc.Dependencies, "Wants=dnsmasq.service")
-		svc.Dependencies = append(svc.Dependencies, "After=dnsmasq.service")
 	}
 }
 

internal/router/dnsmasq/conf.go

@@ -0,0 +1,30 @@
+package dnsmasq
+
+import (
+	"bufio"
+	"bytes"
+	"errors"
+	"io"
+	"os"
+	"strings"
+)
+
+func InterfaceNameFromConfig(filename string) (string, error) {
+	buf, err := os.ReadFile(filename)
+	if err != nil {
+		return "", err
+	}
+	return interfaceNameFromReader(bytes.NewReader(buf))
+}
+
+func interfaceNameFromReader(r io.Reader) (string, error) {
+	scanner := bufio.NewScanner(r)
+	for scanner.Scan() {
+		line := scanner.Text()
+		after, found := strings.CutPrefix(line, "interface=")
+		if found {
+			return after, nil
+		}
+	}
+	return "", errors.New("not found")
+}

internal/router/dnsmasq/conf_test.go

@@ -0,0 +1,46 @@
+package dnsmasq
+
+import (
+	"strings"
+	"testing"
+)
+
+func Test_interfaceNameFromReader(t *testing.T) {
+	tests := []struct {
+		name      string
+		in        string
+		wantIface string
+	}{
+		{
+			"good",
+			`interface=lo`,
+			"lo",
+		},
+		{
+			"multiple",
+			`interface=lo
+interface=eth0
+`,
+			"lo",
+		},
+		{
+			"no iface",
+			`cache-size=100`,
+			"",
+		},
+	}
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			ifaceName, err := interfaceNameFromReader(strings.NewReader(tc.in))
+			if tc.wantIface != "" && err != nil {
+				t.Errorf("unexpected error: %v", err)
+				return
+			}
+			if tc.wantIface != ifaceName {
+				t.Errorf("mismatched, want: %q, got: %q", tc.wantIface, ifaceName)
+			}
+		})
+	}
+}