golang实现简单DNS服务器
package main
import (
"fmt"
"net"
"golang.org/x/net/dns/dnsmessage"
)
func main() {
conn, err := net.ListenUDP("udp", &net.UDPAddr{Port: 53})
if err != nil {
panic(err)
}
defer conn.Close()
fmt.Println("Listing ...")
for {
buf := make([]byte, 512)
_, addr, _ := conn.ReadFromUDP(buf)
var msg dnsmessage.Message
if err := msg.Unpack(buf); err != nil {
fmt.Println(err)
continue
}
go ServerDNS(addr, conn, msg)
}
}
// address books
var (
addressBookOfA = map[string][4]byte{
"www.baidu.com.": [4]byte{220, 181, 38, 150},
}
addressBookOfPTR = map[string]string{
"150.38.181.220.in-addr.arpa.": "www.baidu.com.",
}
)
// ServerDNS serve
func ServerDNS(addr *net.UDPAddr, conn *net.UDPConn, msg dnsmessage.Message) {
// query info
if len(msg.Questions) < 1 {
return
}
question := msg.Questions[0]
var (
queryTypeStr = question.Type.String()
queryNameStr = question.Name.String()
queryType = question.Type
queryName, _ = dnsmessage.NewName(queryNameStr)
)
fmt.Printf("[%s] queryName: [%s]n", queryTypeStr, queryNameStr)
// find record
var resource dnsmessage.Resource
switch queryType {
case dnsmessage.TypeA:
if rst, ok := addressBookOfA[queryNameStr]; ok {
resource = NewAResource(queryName, rst)
} else {
fmt.Printf("not fount A record queryName: [%s] n", queryNameStr)
Response(addr, conn, msg)
return
}
case dnsmessage.TypePTR:
if rst, ok := addressBookOfPTR[queryName.String()]; ok {
resource = NewPTRResource(queryName, rst)
} else {
fmt.Printf("not fount PTR record queryName: [%s] n", queryNameStr)
Response(addr, conn, msg)
return
}
default:
fmt.Printf("not support dns queryType: [%s] n", queryTypeStr)
return
}
// send response
msg.Response = true
msg.Answers = append(msg.Answers, resource)
Response(addr, conn, msg)
}
// Response return
func Response(addr *net.UDPAddr, conn *net.UDPConn, msg dnsmessage.Message) {
packed, err := msg.Pack()
if err != nil {
fmt.Println(err)
return
}
if _, err := conn.WriteToUDP(packed, addr); err != nil {
fmt.Println(err)
}
}
// NewAResource A record
func NewAResource(query dnsmessage.Name, a [4]byte) dnsmessage.Resource {
return dnsmessage.Resource{
Header: dnsmessage.ResourceHeader{
Name: query,
Class: dnsmessage.ClassINET,
TTL: 600,
},
Body: &dnsmessage.AResource{
A: a,
},
}
}
// NewPTRResource PTR record
func NewPTRResource(query dnsmessage.Name, ptr string) dnsmessage.Resource {
name, _ := dnsmessage.NewName(ptr)
return dnsmessage.Resource{
Header: dnsmessage.ResourceHeader{
Name: query,
Class: dnsmessage.ClassINET,
},
Body: &dnsmessage.PTRResource{
PTR: name,
},
}
}