586 lines
12 KiB
Go
586 lines
12 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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const packErr = "Failed to pack message"
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const servErr = "No servers could be reached"
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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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// Basic usage pattern for setting up a resolver:
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//
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// res := new(Resolver)
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// res.Servers = []string{"127.0.0.1"} // set the nameserver
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//
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// m := new(Msg) // prepare a new message
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// m.MsgHdr.Recursion_desired = true // header bits
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// m.Question = make([]Question, 1) // 1 RR in question section
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// m.Question[0] = Question{"miek.nl", TypeSOA, ClassINET}
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// in, err := res.Query(m) // Ask the question
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//
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// Note that message id checking is left to the caller.
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func (res *Resolver) Query(q *Msg) (d *Msg, err os.Error) {
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// Check if there is a TSIG appended, if so, check it
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var (
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c net.Conn
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in *Msg
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port string
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)
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if len(res.Servers) == 0 {
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return nil, &Error{Error: "No servers defined"}
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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 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 q.Id == 0 {
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// No Id sed, set it
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q.Id = Id()
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}
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sending, ok := q.Pack()
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if !ok {
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return nil, &Error{Error: packErr}
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}
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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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t := time.Nanoseconds()
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if res.Tcp {
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c, err = net.Dial("tcp", "", server)
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} else {
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c, err = net.Dial("udp", "", server)
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}
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if err != nil {
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continue
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}
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if res.Tcp {
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in, err = exchangeTCP(c, sending, res, true)
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} else {
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in, err = exchangeUDP(c, sending, res, true)
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}
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res.Rtt[server] = time.Nanoseconds() - t
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// Check id in.id != out.id, should be checked in the client!
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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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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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// Xfr is used in communicating with *xfr functions.
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// This structure is returned on the channel.
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type Xfr struct {
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Add bool // true is to be added, otherwise false
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RR
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Err os.Error
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}
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// Start an IXFR, q should contain a *Msg with the question
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// for an IXFR: "miek.nl" ANY IXFR. RRs that should be added
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// have Xfr.Add set to true otherwise it is false.
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// Channel m is closed when the IXFR ends.
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func (res *Resolver) Ixfr(q *Msg, m chan Xfr) {
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// TSIG
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var port string
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var in *Msg
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var x Xfr
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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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defer close(m)
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sending, ok := q.Pack()
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if !ok {
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return
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}
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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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first := true
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var serial uint32 // The first serial seen is the current server serial
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defer c.Close()
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for {
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if first {
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in, err = exchangeTCP(c, sending, res, true)
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} else {
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in, err = exchangeTCP(c, sending, res, false)
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}
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if err != nil {
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// Failed to send, try the next
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c.Close()
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continue Server
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}
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if in.Id != q.Id {
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return
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}
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if first {
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// A single SOA RR signals "no changes"
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if len(in.Answer) == 1 && checkAxfrSOA(in, true) {
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return
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}
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// But still check if the returned answer is ok
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if !checkAxfrSOA(in, true) {
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c.Close()
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continue Server
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}
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// This serial is important
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serial = in.Answer[0].(*RR_SOA).Serial
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first = !first
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}
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// Now we need to check each message for SOA records, to see what we need to do
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x.Add = true
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if !first {
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for k, r := range in.Answer {
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// If the last record in the IXFR contains the servers' SOA, we should quit
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if r.Header().Rrtype == TypeSOA {
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switch {
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case r.(*RR_SOA).Serial == serial:
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if k == len(in.Answer)-1 {
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// last rr is SOA with correct serial
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//m <- r dont' send it
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return
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}
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x.Add = true
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if k != 0 {
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// Intermediate SOA
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continue
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}
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case r.(*RR_SOA).Serial != serial:
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x.Add = false
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continue // Don't need to see this SOA
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}
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}
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x.RR = r
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m <- x
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}
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}
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return
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}
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panic("not reached")
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return
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}
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return
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}
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// Start an AXFR, q should contain a message with the question
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// for an AXFR: "miek.nl" ANY AXFR. The closing SOA isn't
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// returned over the channel, so the caller will receive
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// the zone as-is. Xfr.Add is always true.
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// The channel is closed to signal the end of the AXFR.
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func (res *Resolver) AxfrTSIG(q *Msg, m chan Xfr, secret string) {
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var port string
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var in *Msg
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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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defer close(m)
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sending, ok := q.Pack()
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if !ok {
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return
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}
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var tsig bool
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// Check if there is a TSIG added to the request msg
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if len(q.Extra) > 0 {
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tsig = q.Extra[len(q.Extra)-1].Header().Rrtype == TypeTSIG
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}
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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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first := true
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defer c.Close() // TODO(mg): if not open?
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for {
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if first {
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in, err = exchangeTCP(c, sending, res, true)
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} else {
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in, err = exchangeTCP(c, sending, res, false)
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}
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if err != nil {
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// Failed to send, try the next
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c.Close()
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continue Server
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}
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if in.Id != q.Id {
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c.Close()
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return
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}
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if tsig && len(in.Extra) > 0 { // What if not included?
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t := in.Extra[len(in.Extra)-1]
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switch t.(type) {
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case *RR_TSIG:
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if t.(*RR_TSIG).Verify(in, secret) {
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println("Validates")
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} else {
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println("DOES NOT validates")
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}
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}
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}
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if first {
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if !checkAxfrSOA(in, true) {
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c.Close()
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continue Server
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}
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first = !first
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}
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if !first {
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if !checkAxfrSOA(in, false) {
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// Soa record not the last one
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sendFromMsg(in, m, false)
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continue
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} else {
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sendFromMsg(in, m, true)
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return
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}
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}
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}
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panic("not reached")
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return
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}
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return
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}
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// Start an AXFR, q should contain a message with the question
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// for an AXFR: "miek.nl" ANY AXFR. The closing SOA isn't
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// returned over the channel, so the caller will receive
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// the zone as-is. Xfr.Add is always true.
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// The channel is closed to signal the end of the AXFR.
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func (res *Resolver) Axfr(q *Msg, m chan Xfr) {
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var port string
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var in *Msg
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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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defer close(m)
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sending, ok := q.Pack()
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if !ok {
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return
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}
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/*
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// Need the secret!
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var tsig *RR_TSIG
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// Check if there is a TSIG added
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if len(q.Extra) > 0 {
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lastrr := q.Extra[len(q.Extra)-1]
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if lastrr.Header().Rrtype == TypeTSIG {
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tsig = lastrr.(*RR_TSIG)
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}
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}
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*/
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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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first := true
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defer c.Close() // TODO(mg): if not open?
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for {
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if first {
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in, err = exchangeTCP(c, sending, res, true)
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} else {
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in, err = exchangeTCP(c, sending, res, false)
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}
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if err != nil {
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// Failed to send, try the next
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c.Close()
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continue Server
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}
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if in.Id != q.Id {
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c.Close()
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return
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}
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if first {
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if !checkAxfrSOA(in, true) {
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c.Close()
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continue Server
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}
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first = !first
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}
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if !first {
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if !checkAxfrSOA(in, false) {
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// Soa record not the last one
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sendFromMsg(in, m, false)
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continue
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} else {
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sendFromMsg(in, m, true)
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return
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}
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}
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}
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panic("not reached")
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return
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}
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return
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}
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// Send a request on the connection and hope for a reply.
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// Up to res.Attempts attempts. If send is false, nothing
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// is send.
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func exchangeUDP(c net.Conn, m []byte, r *Resolver, send bool) (*Msg, os.Error) {
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var timeout int64
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var attempts int
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if r.Mangle != nil {
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m = r.Mangle(m)
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}
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if r.Timeout == 0 {
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timeout = 1
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} else {
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timeout = int64(r.Timeout)
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}
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if r.Attempts == 0 {
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attempts = 1
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} else {
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attempts = r.Attempts
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}
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for a := 0; a < attempts; a++ {
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if send {
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err := sendUDP(m, c)
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if err != nil {
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if e, ok := err.(net.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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}
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c.SetReadTimeout(timeout * 1e9) // nanoseconds
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buf, err := recvUDP(c)
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if err != nil {
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if e, ok := err.(net.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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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, &Error{Error: servErr}
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}
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// Up to res.Attempts attempts.
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func exchangeTCP(c net.Conn, m []byte, r *Resolver, send bool) (*Msg, os.Error) {
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var timeout int64
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var attempts int
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if r.Mangle != nil {
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m = r.Mangle(m)
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}
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if r.Timeout == 0 {
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timeout = 1
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} else {
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timeout = int64(r.Timeout)
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}
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if r.Attempts == 0 {
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attempts = 1
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} else {
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attempts = r.Attempts
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}
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for a := 0; a < attempts; a++ {
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// only send something when told so
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if send {
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err := sendTCP(m, c)
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if err != nil {
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if e, ok := err.(net.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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}
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c.SetReadTimeout(timeout * 1e9) // nanoseconds
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// The server replies with two bytes length
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buf, err := recvTCP(c)
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if err != nil {
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if e, ok := err.(net.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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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, &Error{Error: servErr}
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}
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func sendUDP(m []byte, c net.Conn) os.Error {
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_, err := c.Write(m)
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if err != nil {
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return err
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}
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return nil
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}
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func recvUDP(c net.Conn) ([]byte, os.Error) {
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m := make([]byte, DefaultMsgSize) // More than enough???
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n, err := c.Read(m)
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if err != nil {
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return nil, err
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}
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m = m[:n]
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return m, nil
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}
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func sendTCP(m []byte, c net.Conn) os.Error {
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l := make([]byte, 2)
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l[0] = byte(len(m) >> 8)
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l[1] = byte(len(m))
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// First we send the length
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_, err := c.Write(l)
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if err != nil {
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return err
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}
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// And the the message
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_, err = c.Write(m)
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if err != nil {
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return err
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}
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return nil
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}
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func recvTCP(c net.Conn) ([]byte, os.Error) {
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l := make([]byte, 2) // receiver length
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// The server replies with two bytes length
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_, err := c.Read(l)
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if err != nil {
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return nil, err
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}
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length := uint16(l[0])<<8 | uint16(l[1])
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if length == 0 {
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return nil, &Error{Error: "received nil msg length", Server: c.RemoteAddr().String()}
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}
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m := make([]byte, length)
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n, cerr := c.Read(m)
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if cerr != nil {
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return nil, cerr
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}
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i := n
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for i < int(length) {
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n, err = c.Read(m[i:])
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if err != nil {
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return nil, err
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}
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i += n
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}
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return m, nil
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}
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// Check if he SOA record exists in the Answer section of
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// the packet. If first is true the first RR must be a soa
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// if false, the last one should be a SOA
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func checkAxfrSOA(in *Msg, first bool) bool {
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if len(in.Answer) > 0 {
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if first {
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return in.Answer[0].Header().Rrtype == TypeSOA
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} else {
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return in.Answer[len(in.Answer)-1].Header().Rrtype == TypeSOA
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}
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}
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return false
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}
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// Send the answer section to the channel
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func sendFromMsg(in *Msg, c chan Xfr, nosoa bool) {
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x := Xfr{Add: true}
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for k, r := range in.Answer {
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if nosoa && k == len(in.Answer)-1 {
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continue
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}
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x.RR = r
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c <- x
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}
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}
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