feat: allow manual configuration of dns resolver

Author: encodeous

core/nylon.go

@@ -1,6 +1,7 @@
 package core
 
 import (
+	"context"
 	"net"
 	"time"
 
@@ -25,6 +26,27 @@ func (n *Nylon) Init(s *state.State) error {
 
 	s.Log.Debug("init nylon")
 
+	if len(s.DnsResolvers) != 0 {
+		s.Log.Debug("setting custom DNS resolvers", "resolvers", s.DnsResolvers)
+		net.DefaultResolver = &net.Resolver{
+			PreferGo: true,
+			Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
+				d := net.Dialer{
+					Timeout: time.Second * 10,
+				}
+				var err error
+				var conn net.Conn
+				for _, resolver := range s.DnsResolvers {
+					conn, err = d.DialContext(ctx, network, resolver)
+					if err == nil {
+						return conn, nil
+					}
+				}
+				return conn, err
+			},
+		}
+	}
+
 	// add neighbours
 	for _, peer := range s.GetPeers(s.Id) {
 		if !s.IsRouter(peer) {

example/sample-node.yaml

@@ -6,6 +6,7 @@ usesystemrouting: false # Default: false - if enabled, Nylon will use the system
 logpath: "" # Default: "" - If set, Nylon will log to this file
 interfacename: "" # Default: "" - If set, Nylon will use this interface name instead of the default "nylon" or utunx on macOS
 disablerouting: false # Default: false - If true, Nylon will not route traffic through this node
+dnsresolvers: [] # Default: [] - If set (e.g ["1.1.1.1:53"]), nylon will use these DNS resolvers for its own queries
 dist: # Optional: If set, Nylon will bootstrap central.yaml from this URL if it does not exist already
   url: https://static.example.com/network1.nybundle
   key: 7PaN6DmAayz4KnDnsXSXJH+Oy0TFGeoM4FEbQfLriVY=

state/config.go

@@ -74,6 +74,7 @@ type LocalCfg struct {
 	DisableRouting   bool
 	UseSystemRouting bool
 	NoNetConfigure   bool `yaml:",omitempty"`
+	DnsResolvers     []string
 	InterfaceName    string
 	LogPath          string
 }

state/validation.go

@@ -61,6 +61,13 @@ func NodeConfigValidator(node *LocalCfg) error {
 			return err
 		}
 	}
+	if len(node.DnsResolvers) != 0 {
+		for _, resolver := range node.DnsResolvers {
+			if _, err := netip.ParseAddrPort(resolver); err != nil {
+				return fmt.Errorf("dns resolver %s is not a valid ip:port: %v", resolver, err)
+			}
+		}
+	}
 	return nil
 }
 

state/validation_test.go

@@ -23,6 +23,33 @@ func TestNameValidator_Invalid(t *testing.T) {
 	assert.Error(t, NameValidator(strings.Repeat("a", 200)))
 }
 
+func TestNodeConfigValidator_DnsResolver(t *testing.T) {
+	assert.NoError(t, NodeConfigValidator(&LocalCfg{
+		Id:          "valid-node",
+		Port:        5,
+		Key:         [32]byte{1},
+		DnsResolver: "1.1.1.1:53",
+	}))
+	assert.Error(t, NodeConfigValidator(&LocalCfg{
+		Id:          "invalid-node",
+		Port:        5,
+		Key:         [32]byte{1},
+		DnsResolver: "google.com",
+	}))
+	assert.Error(t, NodeConfigValidator(&LocalCfg{
+		Id:          "invalid-node",
+		Port:        5,
+		Key:         [32]byte{1},
+		DnsResolver: "google.com:53",
+	}))
+	assert.Error(t, NodeConfigValidator(&LocalCfg{
+		Id:          "invalid-node",
+		Port:        5,
+		Key:         [32]byte{1},
+		DnsResolver: "1.1.1.1",
+	}))
+}
+
 func TestCentralConfigValidator_OverlappingService(t *testing.T) {
 	cfg := &CentralCfg{
 		Services: map[ServiceId]netip.Prefix{