Created
December 19, 2017 03:44
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对特定域名根据内网域名是否可以访问返回特定的ip
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package main | |
import ( | |
"log" | |
"net" | |
"os" | |
"os/signal" | |
"syscall" | |
"time" | |
"github.com/miekg/dns" | |
) | |
const customeDomain = "xd" | |
const customeAddr = "10.17.1.71:22" | |
const targetIP = "8.8.8.8" | |
func main() { | |
udpServer := &dns.Server{Addr: ":53", Net: "udp"} | |
tcpServer := &dns.Server{Addr: ":53", Net: "tcp"} | |
dns.HandleFunc(".", proxy) | |
go func() { | |
if err := udpServer.ListenAndServe(); err != nil { | |
log.Fatal(err) | |
} | |
}() | |
go func() { | |
if err := tcpServer.ListenAndServe(); err != nil { | |
log.Fatal(err) | |
} | |
}() | |
sigs := make(chan os.Signal, 1) | |
signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM) | |
<-sigs | |
udpServer.Shutdown() | |
tcpServer.Shutdown() | |
} | |
func checkAddr(addr string, wait time.Duration) bool { | |
d := net.Dialer{Timeout: wait} | |
conn, err := d.Dial("tcp", addr) | |
if err != nil { | |
return false | |
} | |
defer conn.Close() | |
return true | |
} | |
func proxy(writer dns.ResponseWriter, msg *dns.Msg) { | |
var ip string | |
domain := msg.Question[0].Name | |
if domain == customeDomain+"." { | |
if checkAddr(customeAddr, time.Second*1) { | |
a, _ := net.ResolveTCPAddr("tcp", customeAddr) | |
ip = a.IP.String() | |
} else { | |
ip = targetIP | |
} | |
m := new(dns.Msg) | |
m.SetReply(msg) | |
m.Authoritative = true | |
rr1 := new(dns.A) | |
rr1.Hdr = dns.RR_Header{Name: domain, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 1} | |
rr1.A = net.ParseIP(ip) | |
m.Answer = []dns.RR{rr1} | |
writer.WriteMsg(m) | |
return | |
} | |
c := &dns.Client{Net: "udp"} | |
resp, _, err := c.Exchange(msg, "223.5.5.5:53") | |
if err != nil { | |
dns.HandleFailed(writer, msg) | |
return | |
} | |
writer.WriteMsg(resp) | |
} |
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