add mangler option to the resolver

Makefile

@@ -13,8 +13,14 @@ GOFILES=\
 
 include $(GOROOT)/src/Make.pkg
 
-restest: restest.go
+p: restest manglertest packtest
+
+# too lazy to lookup how this works again in Makefiles
+restest: restest.go $(GOFILES)
 	6g -I _obj restest.go && 6l -L _obj -o restest restest.6
 
-packtest: packtest.go
+manglertest: manglertest.go $(GOFILES)
+	6g -I _obj manglertest.go && 6l -L _obj -o manglertest manglertest.6
+
+packtest: packtest.go $(GOFILES)
 	6g -I _obj packtest.go && 6l -L _obj -o packtest packtest.6

manglertest.go

@@ -0,0 +1,54 @@
+package main
+
+import (
+	"dns"
+	"time"
+	"fmt"
+)
+
+const (
+	NLOOP = 5
+)
+
+func identity(msg []byte) []byte {
+	return msg
+}
+
+func byteflip(msg []byte) []byte {
+	msg[len(msg) - 1] = 0
+	msg[2] = 0		// See what happens
+	return msg
+}
+
+func bitflip(msg []byte) []byte {
+	return msg
+}
+
+func main() {
+	res := new(dns.Resolver)
+	ch  := dns.NewQuerier(res)
+
+	// configure the resolver
+	res.Servers = []string{"192.168.1.2"}
+	res.Timeout = 2
+	res.Attempts = 1
+	res.Mangle = byteflip
+
+	// Setup done, now for some real work
+	// Create a new message
+	m := new(dns.Msg)
+	m.MsgHdr.Recursion_desired = true //only set this bit
+	m.Question = make([]dns.Question, 1)
+
+		// ask something
+		m.Question[0] = dns.Question{"miek.nl", dns.TypeSOA, dns.ClassINET}
+		ch <- dns.DnsMsg{m, nil}
+
+		// wait for an reply
+		in := <-ch
+		fmt.Printf("%v\n", in.Dns)
+
+	ch <- dns.DnsMsg{nil, nil}
+
+	time.Sleep(1.0e9) // wait for Go routine to do something
+}

resolver.go

@@ -16,6 +16,8 @@ import (
 	"net"
 )
 
+// For communicating with a resolver
+// A nil msg ends the resolver goroutine
 type DnsMsg struct {
 	Dns *Msg
 	Error os.Error
@@ -30,9 +32,9 @@ type Resolver struct {
 	Timeout  int      // seconds before giving up on packet
 	Attempts int      // lost packets before giving up on server
 	Rotate   bool     // round robin among servers
+	Mangle	 func([]byte) []byte // Mangle the packet
 }
 
-
 // Start a new querier as a goroutine, return
 // the communication channel
 func NewQuerier(res *Resolver) (ch chan DnsMsg) {
@@ -72,7 +74,7 @@ func query(res *Resolver, msg chan DnsMsg) {
 					err = cerr
 					continue
 				}
-				in, err = exchange(c, sending, res.Attempts, res.Timeout)
+				in, err = exchange(c, sending, res)
 				// Check id in.id != out.id
 
 				c.Close()
@@ -94,14 +96,18 @@ func query(res *Resolver, msg chan DnsMsg) {
 
 // Send a request on the connection and hope for a reply.
 // Up to res.Attempts attempts.
-func exchange(c net.Conn, m []byte, attempts, timeout int) (*Msg, os.Error) {
-	for attempt := 0; attempt < attempts; attempt++ {
+func exchange(c net.Conn, m []byte, r *Resolver) (*Msg, os.Error) {
+	if r.Mangle != nil {
+		m = r.Mangle(m)
+	}
+
+	for attempt := 0; attempt < r.Attempts; attempt++ {
 		n, err := c.Write(m)
 		if err != nil {
 			return nil, err
 		}
 
-		c.SetReadTimeout(int64(timeout) * 1e9) // nanoseconds
+		c.SetReadTimeout(int64(r.Timeout) * 1e9) // nanoseconds
 		// EDNS TODO
 		buf := make([]byte, 2000) // More than enough.
 		n, err = c.Read(buf)