Adding more source for getting available DNS

On some platforms, the gateway may not be a usable DNS. So extending the
current approach to allow retrieving DNS from many sources.

config_internal_test.go

@@ -14,6 +14,7 @@ func TestUpstreamConfig_SetupBootstrapIP(t *testing.T) {
 	uc.Init()
 	uc.setupBootstrapIP(false)
 	if uc.BootstrapIP == "" {
+		t.Log(availableNameservers())
 		t.Fatal("could not bootstrap ip without bootstrap DNS")
 	}
 	t.Log(uc)

nameservers.go

@@ -0,0 +1,29 @@
+package ctrld
+
+import "net"
+
+type dnsFn func() []string
+
+func nameservers() []string {
+	var dns []string
+	seen := make(map[string]bool)
+	ch := make(chan []string)
+	fns := dnsFns()
+
+	for _, fn := range fns {
+		go func(fn dnsFn) {
+			ch <- fn()
+		}(fn)
+	}
+	for range fns {
+		for _, ns := range <-ch {
+			if seen[ns] {
+				continue
+			}
+			seen[ns] = true
+			dns = append(dns, net.JoinHostPort(ns, "53"))
+		}
+	}
+
+	return dns
+}

nameservers_bsd.go

@@ -4,14 +4,20 @@ package ctrld
 
 import (
 	"net"
+	"os/exec"
+	"runtime"
+	"strings"
 	"syscall"
 
 	"golang.org/x/net/route"
 )
 
-func osNameservers() []string {
+func dnsFns() []dnsFn {
+	return []dnsFn{dnsFromRIB, dnsFromIPConfig}
+}
+
+func dnsFromRIB() []string {
 	var dns []string
-	seen := make(map[string]bool)
 	rib, err := route.FetchRIB(syscall.AF_UNSPEC, route.RIBTypeRoute, 0)
 	if err != nil {
 		return nil
@@ -33,17 +39,28 @@ func osNameservers() []string {
 		if dst == nil || gw == nil {
 			continue
 		}
-		if gw.IsLoopback() || seen[gw.String()] {
+		if gw.IsLoopback() {
 			continue
 		}
 		if dst.Equal(net.IPv4zero) || dst.Equal(net.IPv6zero) {
-			seen[gw.String()] = true
+			dns = append(dns, gw.String())
-			dns = append(dns, net.JoinHostPort(gw.String(), "53"))
 		}
 	}
 	return dns
 }
 
+func dnsFromIPConfig() []string {
+	if runtime.GOOS != "darwin" {
+		return nil
+	}
+	cmd := exec.Command("ipconfig", "getoption", "", "domain_name_server")
+	out, _ := cmd.Output()
+	if ip := net.ParseIP(strings.TrimSpace(string(out))); ip != nil {
+		return []string{ip.String()}
+	}
+	return nil
+}
+
 func toNetIP(addr route.Addr) net.IP {
 	switch t := addr.(type) {
 	case *route.Inet4Addr:

nameservers_linux.go

@@ -6,6 +6,8 @@ import (
 	"encoding/hex"
 	"net"
 	"os"
+
+	"github.com/Control-D-Inc/ctrld/internal/dns/resolvconffile"
 )
 
 const (
@@ -13,13 +15,8 @@ const (
 	v6RouteFile = "/proc/net/ipv6_route"
 )
 
-func osNameservers() []string {
+func dnsFns() []dnsFn {
-	ns4 := dns4()
+	return []dnsFn{dns4, dns6, dnsFromSystemdResolver}
-	ns6 := dns6()
-	ns := make([]string, len(ns4)+len(ns6))
-	ns = append(ns, ns4...)
-	ns = append(ns, ns6...)
-	return ns
 }
 
 func dns4() []string {
@@ -53,7 +50,7 @@ func dns4() []string {
 			continue
 		}
 		seen[ip.String()] = true
-		dns = append(dns, net.JoinHostPort(ip.String(), "53"))
+		dns = append(dns, ip.String())
 	}
 	return dns
 }
@@ -82,7 +79,19 @@ func dns6() []string {
 		if ip.Equal(net.IPv6zero) {
 			continue
 		}
-		dns = append(dns, net.JoinHostPort(ip.String(), "53"))
+		dns = append(dns, ip.String())
 	}
 	return dns
 }
+
+func dnsFromSystemdResolver() []string {
+	c, err := resolvconffile.ParseFile("/run/systemd/resolve/resolv.conf")
+	if err != nil {
+		return nil
+	}
+	ns := make([]string, 0, len(c.Nameservers))
+	for _, nameserver := range c.Nameservers {
+		ns = append(ns, nameserver.String())
+	}
+	return ns
+}

nameservers_unix.go

@@ -1,7 +0,0 @@
-//go:build unix
-
-package ctrld
-
-func nameservers() []string {
-	return osNameservers()
-}

nameservers_windows.go

@@ -9,7 +9,11 @@ import (
 	"golang.org/x/sys/windows"
 )
 
-func nameservers() []string {
+func dnsFns() []dnsFn {
+	return []dnsFn{dnsFromAdapter}
+}
+
+func dnsFromAdapter() []string {
 	aas, err := winipcfg.GetAdaptersAddresses(syscall.AF_UNSPEC, winipcfg.GAAFlagIncludeGateways|winipcfg.GAAFlagIncludePrefix)
 	if err != nil {
 		return nil
@@ -42,7 +46,7 @@ func nameservers() []string {
 			return
 		}
 		seen[ip.String()] = true
-		ns = append(ns, net.JoinHostPort(ip.String(), "53"))
+		ns = append(ns, ip.String())
 	}
 	for _, aa := range aas {
 		for dns := aa.FirstDNSServerAddress; dns != nil; dns = dns.Next {