add: use /etc/resolv.conf for config by default

client.go

@@ -18,12 +18,13 @@ type HTTPClientSettings struct {
 	TempDir               string
 	DNSServer             string
 	SkipHTTPStatusCodes   []int
+	DNSServers            []string
 	DedupeOptions         DedupeOptions
-	TCPTimeout            time.Duration
-	TLSHandshakeTimeout   time.Duration
+	DialTimeout           time.Duration
 	ResponseHeaderTimeout time.Duration
 	DNSResolutionTimeout  time.Duration
-	DialTimeout           time.Duration
+	TLSHandshakeTimeout   time.Duration
+	TCPTimeout            time.Duration
 	MaxReadBeforeTruncate int
 	DecompressBody        bool
 	FollowRedirects       bool
@@ -169,7 +170,7 @@ func NewWARCWritingHTTPClient(HTTPClientSettings HTTPClientSettings) (httpClient
 	httpClient.TLSHandshakeTimeout = HTTPClientSettings.TLSHandshakeTimeout
 
 	// Configure custom dialer / transport
-	customDialer, err := newCustomDialer(httpClient, HTTPClientSettings.Proxy, HTTPClientSettings.DialTimeout, HTTPClientSettings.DNSResolutionTimeout, HTTPClientSettings.DNSServer, HTTPClientSettings.DisableIPv4, HTTPClientSettings.DisableIPv6)
+	customDialer, err := newCustomDialer(httpClient, HTTPClientSettings.Proxy, HTTPClientSettings.DialTimeout, HTTPClientSettings.DNSResolutionTimeout, HTTPClientSettings.DNSServers, HTTPClientSettings.DisableIPv4, HTTPClientSettings.DisableIPv6)
 	if err != nil {
 		return nil, err
 	}

dialer.go

@@ -25,24 +25,29 @@ import (
 type customDialer struct {
 	proxyDialer proxy.Dialer
 	client      *CustomHTTPClient
+	DNSConfig   *dns.ClientConfig
 	DNSClient   *dns.Client
 	net.Dialer
 	DNSServer   string
 	disableIPv4 bool
 	disableIPv6 bool
 }
 
-func newCustomDialer(httpClient *CustomHTTPClient, proxyURL string, DialTimeout, DNSResolutionTimeout time.Duration, DNSServer string, disableIPv4, disableIPv6 bool) (d *customDialer, err error) {
+func newCustomDialer(httpClient *CustomHTTPClient, proxyURL string, DialTimeout, DNSResolutionTimeout time.Duration, DNSServers []string, disableIPv4, disableIPv6 bool) (d *customDialer, err error) {
 	d = new(customDialer)
 
 	d.Timeout = DialTimeout
 	d.client = httpClient
 	d.disableIPv4 = disableIPv4
 	d.disableIPv6 = disableIPv6
 
-	d.DNSServer = DNSServer
-	if DNSServer == "" {
-		d.DNSServer = "1.1.1.1:53"
+	d.DNSConfig, err = dns.ClientConfigFromFile("/etc/resolv.conf")
+	if err != nil {
+		return nil, err
+	}
+
+	if len(DNSServers) > 0 {
+		d.DNSConfig.Servers = DNSServers
 	}
 
 	d.DNSClient = &dns.Client{

dns.go

@@ -11,7 +11,7 @@ func (d *customDialer) resolveDNS(address string) (net.IP, error) {
 	m := new(dns.Msg)
 	m.SetQuestion(dns.Fqdn(address), dns.TypeA)
 
-	r, _, err := d.DNSClient.Exchange(m, d.DNSServer)
+	r, _, err := d.DNSClient.Exchange(m, net.JoinHostPort(d.DNSConfig.Servers[0], d.DNSConfig.Port))
 	if err != nil {
 		return nil, err
 	}