Fix incoming [IA]xfr

Make the function return a new channel, which is closed at the
end of the transfer. This way you can just use 'range' to loop
over the records.

ex/axfr/axfr.go

@@ -30,17 +30,13 @@ func main() {
 		m.SetTsig(name, dns.HmacMD5, 300, m.MsgHdr.Id, time.Now().Unix())
 	}
 
-	if err := client.XfrReceive(m, *nameserver); err == nil {
-		for r := range client.ReplyChan {
-			if r.Error != nil {
-				if r.Error == dns.ErrXfrLast {
-					fmt.Printf("%v\n", r.Reply)
-				}
-				break
+	if t, e := client.XfrReceive(m, *nameserver); e == nil {
+		for r := range t {
+			if r.Error == nil {
+				fmt.Printf("%v\n", r.Reply)
 			}
-			fmt.Printf("%v\n", r.Reply)
 		}
 	} else {
-		fmt.Printf("Error %v\n", err)
+		fmt.Printf("Error %v\n", e)
 	}
 }

xfr.go

@@ -1,48 +1,59 @@
 package dns
 
 // XfrReceives requests an incoming Ixfr or Axfr. If the message q's question
-// section contains an AXFR type an Axfr is performed, if it is IXFR it does an Ixfr.
-// Each message will be send along the Client's reply channel as it is received. 
-// The last message send has Exchange.Error set to ErrXfrLast
-// to signal there is nothing more to come.
-func (c *Client) XfrReceive(q *Msg, a string) error {
+// section has type TypeAXFR an Axfr is performed, if it is TypeIXFR it does an Ixfr.
+// The [AI]xfr's records are returned on the channel. Note the with an IXFR the client
+// needs to determine if records are to be removed are added.
+// The channel is closed when the transfer is terminated.
+//
+// Basic use pattern for setting up a transfer:
+//
+//	t, _ := client.XfrReceive(m, "127.0.0.1:53")
+//	for r := range t {
+//		// 
+//	}
+func (c *Client) XfrReceive(q *Msg, a string) (chan *Exchange, error) {
 	w := new(reply)
 	w.client = c
 	w.addr = a
 	w.req = q
 	if err := w.Dial(); err != nil {
-		return err
+		return nil, err
 	}
 	if err := w.Send(q); err != nil {
-		return err
+		return nil, err
 	}
+	e := make(chan *Exchange)
 	switch q.Question[0].Qtype {
 	case TypeAXFR:
-		go w.axfrReceive()
+		go w.axfrReceive(e)
+		return e, nil
 	case TypeIXFR:
-		go w.ixfrReceive()
+		go w.ixfrReceive(e)
+		return e, nil
 	default:
-		return ErrXfrType
+		return nil, ErrXfrType
 	}
-	return nil
+	panic("not reached")
 }
 
-func (w *reply) axfrReceive() {
+func (w *reply) axfrReceive(c chan *Exchange) {
 	first := true
 	defer w.Close()
+	defer close(c)
 	for {
 		in, err := w.Receive()
 		if err != nil {
-			w.Client().ReplyChan <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), err}
+			c <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), err}
 			return
 		}
 		if w.req.Id != in.Id {
-			w.Client().ReplyChan <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), ErrId}
+			c <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), ErrId}
 			return
 		}
 		if first {
 			if !checkXfrSOA(in, true) {
-				w.Client().ReplyChan <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), ErrXfrSoa}
+				c <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), ErrXfrSoa}
 				return
 			}
 			first = !first
@@ -51,41 +62,40 @@ func (w *reply) axfrReceive() {
 		if !first {
 			w.tsigTimersOnly = true // Subsequent envelopes use this.
 			if checkXfrSOA(in, false) {
-				w.Client().ReplyChan <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), ErrXfrLast}
+				c <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), ErrXfrLast}
 				return
 			}
-			w.Client().ReplyChan <- &Exchange{Request: w.req, Reply: in, Rtt: w.rtt, RemoteAddr: w.conn.RemoteAddr(), Error: nil}
+			c <- &Exchange{Request: w.req, Reply: in, Rtt: w.rtt, RemoteAddr: w.conn.RemoteAddr(), Error: nil}
 		}
 	}
 	panic("not reached")
-	return
 }
 
-func (w *reply) ixfrReceive() {
+func (w *reply) ixfrReceive(c chan *Exchange) {
 	var serial uint32 // The first serial seen is the current server serial
 	first := true
 	defer w.Close()
+	defer close(c)
 	for {
 		in, err := w.Receive()
 		if err != nil {
-			w.Client().ReplyChan <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), err}
+			c <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), err}
 			return
 		}
 		if w.req.Id != in.Id {
-			w.Client().ReplyChan <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), ErrId}
+			c <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), ErrId}
 			return
 		}
-
 		if first {
 			// A single SOA RR signals "no changes"
 			if len(in.Answer) == 1 && checkXfrSOA(in, true) {
-				w.Client().ReplyChan <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), ErrXfrLast}
+				c <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), nil}
 				return
 			}
 
 			// Check if the returned answer is ok
 			if !checkXfrSOA(in, true) {
-				w.Client().ReplyChan <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), ErrXfrSoa}
+				c <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), ErrXfrSoa}
 				return
 			}
 			// This serial is important
@@ -99,15 +109,14 @@ func (w *reply) ixfrReceive() {
 			// If the last record in the IXFR contains the servers' SOA,  we should quit
 			if v, ok := in.Answer[len(in.Answer)-1].(*RR_SOA); ok {
 				if v.Serial == serial {
-					w.Client().ReplyChan <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), ErrXfrLast}
+					c <- &Exchange{w.req, in, w.rtt, w.conn.RemoteAddr(), nil}
 					return
 				}
 			}
-			w.Client().ReplyChan <- &Exchange{Request: w.req, Reply: in}
+			c <- &Exchange{Request: w.req, Reply: in}
 		}
 	}
 	panic("not reached")
-	return
 }
 
 // XfrSend performs an outgoing Ixfr or Axfr. The function is xfr agnostic, it is