Add dns forwarding server library

dnsforward/standalone/.gitignore

@@ -0,0 +1 @@
+/standalone

dnsforward/standalone/standalone.go

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+package main
+
+import (
+	"log"
+	"net"
+	"net/http"
+	_ "net/http/pprof"
+	"os"
+	"os/signal"
+	"runtime"
+	"syscall"
+	"time"
+
+	"github.com/AdguardTeam/AdGuardHome/dnsforward"
+)
+
+//
+// main function
+//
+func main() {
+	go func() {
+		log.Println(http.ListenAndServe("localhost:6060", nil))
+	}()
+	go func() {
+		for range time.Tick(time.Second) {
+			log.Printf("goroutines = %d", runtime.NumGoroutine())
+		}
+	}()
+	s := dnsforward.Server{}
+	err := s.Start(nil)
+	if err != nil {
+		panic(err)
+	}
+	time.Sleep(time.Second)
+	err = s.Stop()
+	if err != nil {
+		panic(err)
+	}
+	err = s.Start(&dnsforward.ServerConfig{UDPListenAddr: &net.UDPAddr{Port: 53535}})
+	if err != nil {
+		panic(err)
+	}
+	err = s.Reconfigure(dnsforward.ServerConfig{UDPListenAddr: &net.UDPAddr{Port: 53, IP: net.ParseIP("0.0.0.0")}})
+	if err != nil {
+		panic(err)
+	}
+	log.Printf("Now serving DNS")
+	signal_channel := make(chan os.Signal)
+	signal.Notify(signal_channel, syscall.SIGINT, syscall.SIGTERM)
+	<-signal_channel
+}