Merge pull request #7 from projectdiscovery/feature-adding-resolver-file

Adding resolver file support

fastdialer/dialer.go

@@ -24,7 +24,15 @@ type Dialer struct {
 
 // NewDialer instance
 func NewDialer(options Options) (*Dialer, error) {
-	dnsclient := retryabledns.New(options.BaseResolvers, options.MaxRetries)
+	var resolvers []string
+	// Add system resolvers as the first to be tried
+	if options.ResolversFile {
+		systemResolvers, err := loadResolverFile()
+		if err == nil && len(systemResolvers) > 0 {
+			resolvers = systemResolvers
+		}
+	}
+	resolvers = append(resolvers, options.BaseResolvers...)
 	hm, err := hybrid.New(hybrid.DefaultDiskOptions)
 	if err != nil {
 		return nil, err
@@ -45,7 +53,7 @@ func NewDialer(options Options) (*Dialer, error) {
 		// nolint:errcheck // if they cannot be loaded it's not a hard failure
 		loadHostsFile(hm)
 	}
-
+	dnsclient := retryabledns.New(resolvers, options.MaxRetries)
 	return &Dialer{dnsclient: dnsclient, hm: hm, dialerHistory: dialerHistory, dialer: dialer, options: &options}, nil
 }
 

fastdialer/hostsfile.go

@@ -28,7 +28,7 @@ func loadHostsFile(hm *hybrid.HybridMap) error {
 	dnsDatas := make(map[string]retryabledns.DNSData)
 	scanner := bufio.NewScanner(utfbom.SkipOnly(file))
 	for scanner.Scan() {
-		ip, hosts := HandleLine(scanner.Text())
+		ip, hosts := HandleHostLine(scanner.Text())
 		if ip == "" || len(hosts) == 0 {
 			continue
 		}
@@ -58,8 +58,8 @@ func loadHostsFile(hm *hybrid.HybridMap) error {
 
 const commentChar string = "#"
 
-// HandleLine a hosts file line
-func HandleLine(raw string) (ip string, hosts []string) {
+// HandleHostLine a hosts file line
+func HandleHostLine(raw string) (ip string, hosts []string) {
 	// ignore comment
 	if IsComment(raw) {
 		return

fastdialer/options.go

@@ -12,6 +12,7 @@ type Options struct {
 	BaseResolvers  []string
 	MaxRetries     int
 	HostsFile      bool
+	ResolversFile  bool
 	EnableFallback bool
 }
 
@@ -20,4 +21,5 @@ var DefaultOptions = Options{
 	BaseResolvers: DefaultResolvers,
 	MaxRetries:    5,
 	HostsFile:     true,
+	ResolversFile: true,
 }

fastdialer/resolverfile.go

@@ -0,0 +1,68 @@
+package fastdialer
+
+import (
+	"bufio"
+	"net"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/dimchansky/utfbom"
+)
+
+func loadResolverFile() ([]string, error) {
+	osResolversFilePath := os.ExpandEnv(filepath.FromSlash(ResolverFilePath))
+
+	if env, isset := os.LookupEnv("RESOLVERS_PATH"); isset && len(env) > 0 {
+		osResolversFilePath = os.ExpandEnv(filepath.FromSlash(env))
+	}
+
+	file, err := os.Open(osResolversFilePath)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+
+	var systemResolvers []string
+
+	scanner := bufio.NewScanner(utfbom.SkipOnly(file))
+	for scanner.Scan() {
+		resolverIP := HandleResolverLine(scanner.Text())
+		if resolverIP == "" {
+			continue
+		}
+		systemResolvers = append(systemResolvers, net.JoinHostPort(resolverIP, "53"))
+	}
+	return systemResolvers, nil
+}
+
+// HandleLine a resolver file line
+func HandleResolverLine(raw string) (ip string) {
+	// ignore comment
+	if IsComment(raw) {
+		return
+	}
+
+	// trim comment
+	if HasComment(raw) {
+		commentSplit := strings.Split(raw, commentChar)
+		raw = commentSplit[0]
+	}
+
+	fields := strings.Fields(raw)
+	if len(fields) == 0 {
+		return
+	}
+
+	nameserverPrefix := fields[0]
+	if nameserverPrefix != "nameserver" {
+		return
+	}
+
+	ip = fields[1]
+	if net.ParseIP(ip) == nil {
+		return
+	}
+
+	return ip
+}

fastdialer/resolverfile_unix.go

@@ -0,0 +1,6 @@
+// +build !windows
+
+package fastdialer
+
+// ResolverFilePath in unix file os
+const ResolverFilePath = "/etc/resolv.conf"

fastdialer/resolverfile_windows.go

@@ -0,0 +1,5 @@
+// +build windows
+package fastdialer
+
+// To be implemented
+const ResolverFilePath = ""

go.mod

@@ -7,8 +7,7 @@ require (
 	github.com/golang/snappy v0.0.2 // indirect
 	github.com/miekg/dns v1.1.38 // indirect
 	github.com/projectdiscovery/hmap v0.0.1
-	github.com/projectdiscovery/retryabledns v1.0.7
-	github.com/stretchr/testify v1.7.0 // indirect
+	github.com/projectdiscovery/retryabledns v1.0.8-0.20210226233812-ee2ecc9839d9
 	golang.org/x/crypto v0.0.0-20201221181555-eec23a3978ad // indirect
 	golang.org/x/net v0.0.0-20210119194325-5f4716e94777 // indirect
 	golang.org/x/sys v0.0.0-20210124154548-22da62e12c0c // indirect

go.sum

@@ -25,8 +25,8 @@ github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZb
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/projectdiscovery/hmap v0.0.1 h1:VAONbJw5jP+syI5smhsfkrq9XPGn4aiYy5pR6KR1wog=
 github.com/projectdiscovery/hmap v0.0.1/go.mod h1:VDEfgzkKQdq7iGTKz8Ooul0NuYHQ8qiDs6r8bPD1Sb0=
-github.com/projectdiscovery/retryabledns v1.0.7 h1:fwbwrl+0XmWRvwiNzm/YSBjmUh7KwIsryScUK9juOuA=
-github.com/projectdiscovery/retryabledns v1.0.7/go.mod h1:/UzJn4I+cPdQl6pKiiQfvVAT636YZvJQYZhYhGB0dUQ=
+github.com/projectdiscovery/retryabledns v1.0.8-0.20210226233812-ee2ecc9839d9 h1:uFBvyv0YJub1E8N6LJhWd+Gf4JLeQLgOuX6s7VuQYDI=
+github.com/projectdiscovery/retryabledns v1.0.8-0.20210226233812-ee2ecc9839d9/go.mod h1:4sMC8HZyF01HXukRleSQYwz4870bwgb4+hTSXTMrkf4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=