198 lines
4.9 KiB
Go
198 lines
4.9 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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package dns
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// Envelope is used when doing [IA]XFR with a remote server.
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type Envelope struct {
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RR []RR // The set of RRs in the answer section of the AXFR reply message.
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Error error // If something went wrong, this contains the error.
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}
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// TransferIn performs a [AI]XFR request (depends on the message's Qtype). It returns
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// a channel of *Envelope on which the replies from the server are sent. At the end of
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// the transfer the channel is closed.
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// The messages are TSIG checked if
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// needed, no other post-processing is performed. The caller must dissect the returned
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// messages.
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//
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// Basic use pattern for receiving an AXFR:
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//
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// // m contains the AXFR request
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// t, e := c.TransferIn(m, "127.0.0.1:53")
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// for r := range t {
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// // ... deal with r.RR or r.Error
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// }
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func (c *Client) TransferIn(q *Msg, a string) (chan *Envelope, error) {
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w := new(reply)
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w.client = c
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w.addr = a
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w.req = q
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if err := w.dial(); err != nil {
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return nil, err
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}
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if err := w.send(q); err != nil {
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return nil, err
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}
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e := make(chan *Envelope)
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switch q.Question[0].Qtype {
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case TypeAXFR:
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go w.axfrIn(q, e)
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return e, nil
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case TypeIXFR:
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go w.ixfrIn(q, e)
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return e, nil
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default:
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return nil, nil
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}
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panic("dns: not reached")
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}
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func (w *reply) axfrIn(q *Msg, c chan *Envelope) {
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first := true
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defer w.conn.Close()
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defer close(c)
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for {
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in, err := w.receive()
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if err != nil {
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c <- &Envelope{nil, err}
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return
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}
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if in.Id != q.Id {
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c <- &Envelope{in.Answer, ErrId}
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return
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}
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if first {
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if !checkXfrSOA(in, true) {
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c <- &Envelope{in.Answer, ErrSoa}
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return
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}
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first = !first
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}
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if !first {
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w.tsigTimersOnly = true // Subsequent envelopes use this.
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if checkXfrSOA(in, false) {
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c <- &Envelope{in.Answer, nil}
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return
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}
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c <- &Envelope{in.Answer, nil}
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}
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}
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panic("dns: not reached")
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}
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func (w *reply) ixfrIn(q *Msg, c chan *Envelope) {
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var serial uint32 // The first serial seen is the current server serial
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first := true
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defer w.conn.Close()
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defer close(c)
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for {
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in, err := w.receive()
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if err != nil {
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c <- &Envelope{in.Answer, err}
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return
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}
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if q.Id != in.Id {
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c <- &Envelope{in.Answer, ErrId}
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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 && checkXfrSOA(in, true) {
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c <- &Envelope{in.Answer, nil}
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return
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}
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// Check if the returned answer is ok
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if !checkXfrSOA(in, true) {
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c <- &Envelope{in.Answer, ErrSoa}
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return
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}
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// This serial is important
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serial = in.Answer[0].(*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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if !first {
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w.tsigTimersOnly = true
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// If the last record in the IXFR contains the servers' SOA, we should quit
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if v, ok := in.Answer[len(in.Answer)-1].(*SOA); ok {
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if v.Serial == serial {
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c <- &Envelope{in.Answer, nil}
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return
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}
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}
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c <- &Envelope{in.Answer, nil}
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}
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}
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panic("dns: not reached")
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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 checkXfrSOA(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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// TransferOut performs an outgoing [AI]XFR depending on the request message. The
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// caller is responsible for sending the correct sequence of RR sets through
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// the channel c. For reasons of symmetry Envelope is re-used.
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// Errors are signaled via the error pointer, when an error occurs the function
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// sets the error and returns (it does not close the channel).
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// TSIG and enveloping is handled by TransferOut.
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//
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// Basic use pattern for sending an AXFR:
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//
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// // q contains the AXFR request
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// c := make(chan *Envelope)
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// var e *error
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// err := TransferOut(w, q, c, e)
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// w.Hijack() // hijack the connection so that the package doesn't close it
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// for _, rrset := range rrsets { // rrsets is a []RR
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// c <- &{Envelope{RR: rrset}
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// if e != nil {
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// close(c)
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// break
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// }
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// }
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// // w.Close() // Don't! Let the client close the connection
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func TransferOut(w ResponseWriter, q *Msg, c chan *Envelope, e *error) error {
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switch q.Question[0].Qtype {
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case TypeAXFR, TypeIXFR:
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go xfrOut(w, q, c, e)
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return nil
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default:
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return nil
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}
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panic("dns: not reached")
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}
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// TODO(mg): count the RRs and the resulting size.
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func xfrOut(w ResponseWriter, req *Msg, c chan *Envelope, e *error) {
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rep := new(Msg)
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rep.SetReply(req)
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rep.Authoritative = true
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for x := range c {
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// assume it fits
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rep.Answer = append(rep.Answer, x.RR...)
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if err := w.WriteMsg(rep); e != nil {
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*e = err
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return
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}
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w.TsigTimersOnly(true)
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rep.Answer = nil
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}
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}
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