From f0a62914069b310f2a99102f870e5ff05e7f2501 Mon Sep 17 00:00:00 2001
From: Eri Bastos <bastos.eri@gmail.com>
Date: Sat, 18 Apr 2020 12:51:50 -0400
Subject: [PATCH] Replaced cached IP with remote resolver

---
 config_sample.json               |  1 +
 handler/google/google_handler.go | 17 +++++++----------
 settings.go                      | 13 +++++++------
 utils.go                         | 30 ++++++++++++++++++++++++++++++
 4 files changed, 45 insertions(+), 16 deletions(-)

diff --git a/config_sample.json b/config_sample.json
index c5fccac..e33bd03 100644
--- a/config_sample.json
+++ b/config_sample.json
@@ -22,6 +22,7 @@
   "ipv6_url": "https://api-ipv6.ip.sb/ip",
   "ip_type": "IPv4",
   "interval": 300,
+  "resolver": "8.8.8.8",
   "user_agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/38.0.2125.111 Safari/537.36",
   "ip_interface": "eth0",
   "socks5_proxy": "",
diff --git a/handler/google/google_handler.go b/handler/google/google_handler.go
index 083613f..e93b53c 100644
--- a/handler/google/google_handler.go
+++ b/handler/google/google_handler.go
@@ -37,24 +37,21 @@ func (handler *Handler) DomainLoop(domain *godns.Domain, panicChan chan<- godns.
 		}
 	}()
 
-	var lastIP string
-
 	for {
 		currentIP, err := godns.GetCurrentIP(handler.Configuration)
-
 		if err != nil {
 			log.Println("get_currentIP:", err)
 			continue
 		}
 		log.Println("currentIP is:", currentIP)
+		for _, subDomain := range domain.SubDomains {
+			hostname := subDomain + "." + domain.DomainName
+			lastIP := godns.ResolveDNS(hostname, handler.Configuration.Resolver)
+			//check against currently known IP, if no change, skip update
+			if currentIP == lastIP {
+				log.Printf("IP is the same as cached one. Skip update.\n")
+			} else {
 
-		//check against locally cached IP, if no change, skip update
-		if currentIP == lastIP {
-			log.Printf("IP is the same as cached one. Skip update.\n")
-		} else {
-			lastIP = currentIP
-
-			for _, subDomain := range domain.SubDomains {
 				log.Printf("%s.%s Start to update record IP...\n", subDomain, domain.DomainName)
 				handler.UpdateIP(domain.DomainName, subDomain, currentIP)
 
diff --git a/settings.go b/settings.go
index fbf945f..899d729 100644
--- a/settings.go
+++ b/settings.go
@@ -14,10 +14,10 @@ type Domain struct {
 
 // Notify struct for telegram notification
 type TelegramNotify struct {
-	Enabled      bool   `json:"enabled"`
-	BotApiKey    string `json:"bot_api_key"`
-	ChatId       string `json:"chat_id"`
-	MsgTemplate  string `json:"message_template"`
+	Enabled     bool   `json:"enabled"`
+	BotApiKey   string `json:"bot_api_key"`
+	ChatId      string `json:"chat_id"`
+	MsgTemplate string `json:"message_template"`
 }
 
 // Notify struct for SMTP notification
@@ -32,8 +32,8 @@ type MailNotify struct {
 
 // Notify struct
 type Notify struct {
-	Telegram    TelegramNotify `json:"telegram"`
-	Mail        MailNotify `json:"mail"`
+	Telegram TelegramNotify `json:"telegram"`
+	Mail     MailNotify     `json:"mail"`
 }
 
 // Settings struct
@@ -52,6 +52,7 @@ type Settings struct {
 	Notify      Notify   `json:"notify"`
 	IPInterface string   `json:"ip_interface"`
 	IPType      string   `json:"ip_type"`
+	Resolver    string   `json:"resolver"`
 }
 
 // LoadSettings -- Load settings from config file
diff --git a/utils.go b/utils.go
index 7330ec2..c094694 100644
--- a/utils.go
+++ b/utils.go
@@ -12,6 +12,7 @@ import (
 	"net/http"
 	"strings"
 
+	"github.com/bogdanovich/dns_resolver"
 	"golang.org/x/net/proxy"
 	gomail "gopkg.in/gomail.v2"
 )
@@ -346,3 +347,32 @@ func buildTemplate(currentIP, domain string, tplsrc string) string {
 
 	return tpl.String()
 }
+
+// ResolveDNS will query DNS for a given hostname.
+func ResolveDNS(hostname, resolver string) string {
+
+	// If no DNS server is set in config file, falls back to default resolver.
+	if resolver == "" {
+		dnsAdress, err := net.LookupHost(hostname)
+		if err != nil {
+			if strings.HasSuffix(err.Error(), "no such host") {
+				return "<nil>"
+			}
+			log.Fatalf(err.Error())
+		}
+		return dnsAdress[0]
+	}
+	res := dns_resolver.New([]string{resolver})
+	// In case of i/o timeout
+	res.RetryTimes = 5
+
+	ip, err := res.LookupHost(hostname)
+	if err != nil {
+		if strings.HasSuffix(err.Error(), "NXDOMAIN") {
+			return "<nil>"
+		}
+		log.Fatalf(err.Error())
+	}
+	return ip[0].String()
+
+}