135 lines
3.0 KiB
Go
135 lines
3.0 KiB
Go
// Copyright 2009 The Go Authors. 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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// A dns resolver is to be run as a seperate goroutine.
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// For every reply the resolver answers by sending the
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// received packet back on the channel.
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package dns
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import (
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"os"
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"rand"
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"time"
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"net"
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)
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// For communicating with a resolver
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// A nil msg ends the resolver goroutine
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type DnsMsg struct {
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Dns *Msg
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Error os.Error
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}
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type Resolver struct {
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Servers []string // servers to use
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rtt []int // round trip times for each NS (TODO)
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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
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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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Rotate bool // round robin among servers
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Tcp bool // use TCP
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Mangle func([]byte) []byte // Mangle the packet
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}
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// Start a new querier as a goroutine, return
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// the communication channel
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func NewQuerier(res *Resolver) (ch chan DnsMsg) {
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ch = make(chan DnsMsg)
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go query(res, ch)
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return
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}
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// do it
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func query(res *Resolver, msg chan DnsMsg) {
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var c net.Conn
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var err os.Error
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var in *Msg
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for {
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select {
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case out := <-msg: //msg received
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if out.Dns == nil {
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// nil message, quit the goroutine
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return
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}
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var cerr os.Error
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// Set an id
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//if len(name) >= 256 {
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out.Dns.Id = uint16(rand.Int()) ^ uint16(time.Nanoseconds())
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sending, ok := out.Dns.Pack()
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if !ok {
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msg <- DnsMsg{nil, nil} // todo error
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}
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for i := 0; i < len(res.Servers); i++ {
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// server := res.Servers[i] + ":" + res.Port
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server := res.Servers[i] + ":53"
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if res.Tcp == true {
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c, cerr = net.Dial("tcp", "", server)
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} else {
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c, cerr = net.Dial("udp", "", server)
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}
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if cerr != nil {
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err = cerr
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continue
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}
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in, err = exchange(c, sending, res)
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// Check id in.id != out.id
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c.Close()
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if err != nil {
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continue
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}
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}
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if err != nil {
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msg <- DnsMsg{nil, err}
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} else {
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msg <- DnsMsg{in, nil}
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}
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}
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}
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return
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}
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// Use Pack to create a DNS question, from a msg
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// Send a request on the connection and hope for a reply.
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// Up to res.Attempts attempts.
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func exchange(c net.Conn, m []byte, r *Resolver) (*Msg, os.Error) {
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if r.Mangle != nil {
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m = r.Mangle(m)
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}
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for attempt := 0; attempt < r.Attempts; attempt++ {
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n, err := c.Write(m)
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if err != nil {
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return nil, err
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}
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c.SetReadTimeout(int64(r.Timeout) * 1e9) // nanoseconds
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// EDNS TODO
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buf := make([]byte, 2000) // More than enough.
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n, err = c.Read(buf)
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if err != nil {
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// More Go foo needed
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//if e, ok := err.(Error); ok && e.Timeout() {
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// continue
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//}
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return nil, err
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}
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buf = buf[0:n]
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in := new(Msg)
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if !in.Unpack(buf) {
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continue
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}
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return in, nil
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}
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return nil, nil // todo error
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}
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