[dns] #done dns server demo

Author: brewlin

cmd/application/dns/README.md

@@ -0,0 +1,26 @@
+[toc]
+# DNS ClIENT
+```
+> cd net-protocol/tool;
+> go build up.go
+> sudo ./up
+
+> cd net-protocol/cmd/application/dns
+> sudo go run dns_client.go
+```
+![](../../../resource/dns_client.png)
+
+
+# DNS SERVER
+启动 udp server,另起窗口发送dns查询并指定dnsserver
+```
+> cd net-protocol/tool;
+> go build up.go
+> sudo ./up
+
+> cd net-protocol/cmd/application/dns
+> sudo go run dns_server.go
+//另起ssh窗口 发送dns查询并指定自定义的dns server 192.168.1.1:53
+> nslookup www.baidu.com 192.168.1.1
+```
+![](../../../resource/dns_server.png)

cmd/application/dns/dns_server.go

@@ -0,0 +1,116 @@
+package main
+
+import (
+	"fmt"
+	"github.com/brewlin/net-protocol/config"
+	"github.com/brewlin/net-protocol/internal/endpoint"
+	"github.com/brewlin/net-protocol/pkg/buffer"
+	_ "github.com/brewlin/net-protocol/pkg/logging"
+	_ "github.com/brewlin/net-protocol/pkg/logging"
+	"github.com/brewlin/net-protocol/pkg/waiter"
+	"github.com/brewlin/net-protocol/protocol/header"
+	"github.com/brewlin/net-protocol/protocol/network/ipv4"
+	"github.com/brewlin/net-protocol/protocol/transport/udp"
+	"github.com/brewlin/net-protocol/protocol/transport/udp/client"
+	"github.com/brewlin/net-protocol/stack"
+	"log"
+	"strconv"
+	"strings"
+
+	tcpip "github.com/brewlin/net-protocol/protocol"
+)
+
+//当前demo作为一个dns代理，接受dns请求并转发后，解析响应做一些操作
+func main() {
+	s := endpoint.NewEndpoint()
+
+	udploop(s)
+
+}
+func udploop(s *stack.Stack) {
+	var wq waiter.Queue
+	//新建一个UDP端
+	ep, err := s.NewEndpoint(udp.ProtocolNumber, ipv4.ProtocolNumber, &wq)
+	if err != nil {
+		log.Fatal(err)
+	}
+	//绑定本地端口  53是dns默认端口
+	if err := ep.Bind(tcpip.FullAddress{1, config.LocalAddres, 53}, nil); err != nil {
+		log.Fatal("@main : bind failed :", err)
+	}
+	defer ep.Close()
+	//创建队列 通知 channel
+	waitEntry, notifych := waiter.NewChannelEntry(nil)
+	wq.EventRegister(&waitEntry, waiter.EventIn)
+	defer wq.EventUnregister(&waitEntry)
+
+	var saddr tcpip.FullAddress
+
+	for {
+		v, _, err := ep.Read(&saddr)
+		if err != nil {
+			if err == tcpip.ErrWouldBlock {
+				<-notifych
+				continue
+			}
+			fmt.Println(err)
+			return
+		}
+		//接收到代理请求
+		h := header.DNS(v)
+		fmt.Println("@main :接收到代理域名:", string(h[header.DOMAIN:header.DOMAIN+h.GetDomainLen()-1]))
+		go handle_proxy(v,ep,saddr)
+	}
+}
+//转发代理请求，并解析响应数据
+func handle_proxy(v buffer.View,ep tcpip.Endpoint,saddr tcpip.FullAddress){
+	cli := client.NewClient("8.8.8.8",53)
+	cli.Connect()
+	cli.Write(v)
+	defer cli.Close()
+
+	rsp,err := cli.Read()
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	//返回给客户端
+	_, _, err = ep.Write(tcpip.SlicePayload(rsp), tcpip.WriteOptions{To: &saddr})
+	if err != nil {
+		fmt.Println(err)
+	}
+	p := header.DNS(rsp)
+	answer := p.GetAnswer()
+
+	for i := 0; i < len(*answer) ; i++ {
+		switch (*answer)[i].Type {
+		case header.A:
+			fmt.Println("dns 目标IP（A):",parseAName((*answer)[i].RData))
+		case header.CNAME:
+			fmt.Println("dns 目标IP（alias):",parseCName((*answer)[i].RData))
+		}
+	}
+}
+func parseAName(rd []byte) string {
+	res := []string{}
+	for _,v := range rd {
+		res = append(res,strconv.Itoa(int(v)))
+	}
+	return strings.Join(res,".")
+}
+
+func parseCName(rd []byte) (res string) {
+	for{
+		l := int(rd[0])
+		if l >= len(rd){
+			res += ".com"
+			return
+		}
+		rd = rd[1:]
+		res += string(rd[0:l])
+		rd = rd[l:]
+		if len(rd) == 0 {
+			return
+		}
+	}
+}

protocol/header/dns.go

@@ -136,7 +136,7 @@ func (d DNS)setID(id uint16){
 	//set id
 	binary.BigEndian.PutUint16(d[ID:], id)
 }
-//setDomain
+//getDomain
 func (d *DNS)getDomain(domain string) []byte {
 	var (
 		buffer   bytes.Buffer