add custom dns addr flag (#399)

Fixes #354

Signed-off-by: titanventura <aswath7862001@gmail.com>

arguments.go

@@ -16,6 +16,7 @@ type arguments struct {
 	MaxConnections         int      `short:"c" long:"max-connections" value-name:"<count>" default:"512" description:"Maximum number of HTTP connections"`
 	MaxConnectionsPerHost  int      `long:"max-connections-per-host" value-name:"<count>" default:"512" description:"Maximum number of HTTP connections per host"`
 	MaxResponseBodySize    int      `long:"max-response-body-size" value-name:"<size>" default:"10000000" description:"Maximum response body size to read"`
+	CustomDnsAddr          string   `long:"custom-dns-addr" description:"Custom DNS server to be used for requests"`
 	RawExcludedPatterns    []string `short:"e" long:"exclude" value-name:"<pattern>..." description:"Exclude URLs matched with given regular expressions"`
 	RawIncludedPatterns    []string `short:"i" long:"include" value-name:"<pattern>..." description:"Include URLs matched with given regular expressions"`
 	FollowRobotsTxt        bool     `long:"follow-robots-txt" description:"Follow robots.txt when scraping pages"`

command.go

@@ -56,6 +56,7 @@ func (c *command) runWithError(ss []string) (bool, error) {
 						SkipTLSVerification:   args.SkipTLSVerification,
 						Timeout:               time.Duration(args.Timeout) * time.Second,
 						Header:                args.Header,
+						CustomDnsAddr:         args.CustomDnsAddr,
 					},
 				),
 				args.RateLimit,

fasthttp_http_client_factory.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"context"
 	"crypto/tls"
 	"net"
 
@@ -24,6 +25,23 @@ func (*fasthttpHttpClientFactory) Create(o httpClientOptions) httpClient {
 		d = fasthttpproxy.FasthttpHTTPDialerTimeout(o.Proxy, tcpTimeout)
 	}
 
+	if o.CustomDnsAddr != "" {
+		d = func(addr string) (net.Conn, error) {
+			dialer := fasthttp.TCPDialer{
+				Concurrency: 1000,
+				Resolver: &net.Resolver{
+					PreferGo:     true,
+					StrictErrors: false,
+					Dial: func(ctx context.Context, network string, address string) (net.Conn, error) {
+						internalDialer := net.Dialer{}
+						return internalDialer.DialContext(ctx, "udp", o.CustomDnsAddr)
+					},
+				},
+			}
+			return dialer.DialTimeout(addr, tcpTimeout)
+		}
+	}
+
 	return newFasthttpHttpClient(
 		&fasthttp.Client{
 			MaxConnsPerHost: o.MaxConnectionsPerHost,

fasthttp_http_client_factory_test.go

@@ -9,3 +9,7 @@ func TestFasthttpHttpClientFactoryCreate(t *testing.T) {
 func TestFasthttpHttpClientFactoryCreateWithProxy(t *testing.T) {
 	newFasthttpHttpClientFactory().Create(httpClientOptions{Proxy: "foo"})
 }
+
+func TestFasthttpHttpClientFactoryCreateWithCustomDnsResolver(t *testing.T) {
+	newFasthttpHttpClientFactory().Create(httpClientOptions{CustomDnsAddr: "1.1.1.1:53"})
+}

http_client_factory.go

@@ -13,6 +13,7 @@ type httpClientOptions struct {
 	SkipTLSVerification bool
 	Timeout             time.Duration
 	Header              http.Header
+	CustomDnsAddr       string
 }
 
 type httpClientFactory interface {