144 lines
3.4 KiB
Go
144 lines
3.4 KiB
Go
// Copyright 2011 Miek Gieben. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// DNS resolver client: see RFC 1035.
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package dns
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import (
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"os"
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"net"
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"time"
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)
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type Resolver struct {
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Servers []string // servers to use
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Search []string // suffixes to append to local name
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Port string // what port to use
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Ndots int // number of dots in name to trigger absolute lookup -- TODO
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Timeout int // seconds before giving up on packet
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Attempts int // lost packets before giving up on server
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Tcp bool // use TCP
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Mangle func([]byte) []byte // mangle the packet
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Rtt map[string]int64 // Store round trip times
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Rrb int // Last used server (for round robin)
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}
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// Send a query to the nameserver using the res.
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func (res *Resolver) Query(q *Msg) (d *Msg, err os.Error) {
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return res.QueryTsig(q, nil)
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}
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// Send a query to the nameserver using res, but perform TSIG validation.
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func (res *Resolver) QueryTsig(q *Msg, tsig *Tsig) (d *Msg, err os.Error) {
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var c net.Conn
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var inb []byte
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in := new(Msg)
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port, err := check(res, q)
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if err != nil {
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return nil, err
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}
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sending, ok := q.Pack()
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if !ok {
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return nil, ErrPack
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}
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if res.Mangle != nil {
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sending = res.Mangle(sending)
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}
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for i := 0; i < len(res.Servers); i++ {
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d := new(Conn)
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server := res.Servers[i] + ":" + port
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t := time.Nanoseconds()
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if res.Tcp {
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c, err = net.Dial("tcp", "", server)
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if err != nil {
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continue
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}
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d.TCP = c.(*net.TCPConn)
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d.Addr = d.TCP.RemoteAddr()
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} else {
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c, err = net.Dial("udp", "", server)
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if err != nil {
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continue
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}
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d.UDP = c.(*net.UDPConn)
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d.Addr = d.UDP.RemoteAddr()
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}
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d.Tsig = tsig
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inb, err = d.Exchange(sending, false)
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if err != nil {
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continue
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}
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in.Unpack(inb) // Discard error.
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res.Rtt[server] = time.Nanoseconds() - t
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c.Close()
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break
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}
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if err != nil {
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return nil, err
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}
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return in, nil
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}
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// Perform an incoming Ixfr or Axfr. If the message q's question
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// section contains an AXFR type an Axfr is performed. If q's question
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// section contains an IXFR type an Ixfr is performed.
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func (res *Resolver) Xfr(q *Msg, m chan Xfr) {
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res.XfrTsig(q, nil, m)
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}
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// Perform an incoming Ixfr or Axfr with Tsig validation. If the message
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// q's question section contains an AXFR type an Axfr is performed. If q's question
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// section contains an IXFR type an Ixfr is performed.
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func (res *Resolver) XfrTsig(q *Msg, t *Tsig, m chan Xfr) {
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port, err := check(res, q)
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if err != nil {
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close(m)
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return
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}
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sending, ok := q.Pack()
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if !ok {
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close(m)
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return
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}
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// No defer close(m) as m is closed in d.XfrRead()
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Server:
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for i := 0; i < len(res.Servers); i++ {
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server := res.Servers[i] + ":" + port
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c, err := net.Dial("tcp", "", server)
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if err != nil {
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continue Server
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}
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d := new(Conn)
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d.TCP = c.(*net.TCPConn)
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d.Addr = d.TCP.RemoteAddr()
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d.Tsig = t
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_, err = d.Write(sending)
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if err != nil {
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continue Server
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}
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d.XfrRead(q, m) // check
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}
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return
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}
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func check(res *Resolver, q *Msg) (port string, err os.Error) {
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if res.Port == "" {
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port = "53"
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} else {
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port = res.Port
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}
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if res.Rtt == nil {
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res.Rtt = make(map[string]int64)
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}
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if q.Id == 0 {
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q.Id = Id()
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}
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return
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}
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