func main() {
flag.Parse()
listenStr := fmt.Sprintf(":%d", *listenPort)
l.Info("Starting up, listening on %s", listenStr)
listenAddr, err := net.ResolveUDPAddr("udp", listenStr)
if err != nil {
l.Panic("ResolveUDPAddr failed: %v", err)
}
conn, err := net.ListenUDP("udp", listenAddr)
if err != nil {
l.Panic("listen failed: %v", err)
}
buf := make([]byte, constants.MAX_SIZE_UDP) // Upper limit as defined by RFC 1035 2.3.4
nc := cache.NewNameCache()
sq := queue.NewServerQueue(nc)
cq := queue.NewClientQueue(conn, nc, sq)
for {
nread, remoteAddr, err := conn.ReadFromUDP(buf)
if err != nil || nread < constants.FIX_SIZE_HEADER {
l.Debug("%v dropping malformed datagram. Size=%d, err=%v", remoteAddr, nread, err)
continue
}
p, err := packet.Parse(buf[0:nread])
if err != nil {
l.Debug("%v failed to parse datagram, err=%v", remoteAddr, err)
continue
}
if p.Header.Response == false && p.Header.Opcode == constants.OP_QUERY && p.Header.RecDesired {
// This is a query, requesting recursion
cq.AddClientRequest(p, remoteAddr)
} else if p.Header.Response == true && p.Header.Opcode == constants.OP_QUERY {
// A reply, try to put it into our cache
nc.Put(p, remoteAddr)
} else {
// DOES NOT COMPUTE.
l.Info("%v dropped packet", remoteAddr)
}
}
}
func (cq *Cq) advanceCache(q packet.QuestionFormat) *packet.ParsedPacket {
// our hardcoded, not so redundant slist
targetNS := "192.5.5.241:53"
targetXH := &packet.Namelabel{}
targetQT := q.Type
POP_LOOP:
for i := 0; ; i++ {
label := q.Name.PoppedLabel(i) // removes 'i' labels from the label list
nsrec, _ := cq.cache.Lookup(*label, constants.TYPE_NS)
if nsrec != nil { // we got an NS cache entry for this level
var candidate_cres *cache.CacheResult
var candidate_label packet.Namelabel
// loop trough all NS servers for this record
for _, candidate_data := range nsrec.ResourceRecord {
name, err := packet.ParseName(candidate_data.Data)
if err == nil {
l.Debug("NS %v handles %v", name, label)
cres, _ := cq.cache.Lookup(name, constants.TYPE_A)
if cres != nil {
candidate_cres = cres
} else {
candidate_label = name
}
}
}
// Fixme: We should try to resolve (yet unknown) nameservers
// even if we got a candidate_res as the one we are contacting
// might fail for some reason.
if candidate_cres == nil && candidate_label.Len() > 0 {
l.Debug("Looking up IP of known candidate: %v", candidate_label)
c := make(chan *lookupRes)
go cq.collapsedLookup(packet.QuestionFormat{Type: constants.TYPE_A, Class: constants.CLASS_IN, Name: candidate_label}, c)
lres := <-c
if lres != nil && lres.negative == false {
candidate_cres = lres.cres
}
}
if candidate_cres != nil {
l.Debug("We got an RR: %v", candidate_cres)
for _, v := range candidate_cres.ResourceRecord {
if v.Type != constants.TYPE_A {
l.Panic("Not an A type: %v", v)
}
targetNS = fmt.Sprintf("%d.%d.%d.%d:53", v.Data[0], v.Data[1], v.Data[2], v.Data[3])
targetXH = label
break POP_LOOP
}
}
}
if label.Len() == 1 {
break
}
}
pp := &packet.ParsedPacket{}
pp.Header.Id = uint16(rand.Uint32()) // will simply overflow
pp.Header.Opcode = constants.OP_QUERY
pp.Header.QuestionCount = 1
pp.Questions = []packet.QuestionFormat{{Name: q.Name, Class: constants.CLASS_IN, Type: targetQT}}
remoteNs, err := net.ResolveUDPAddr("udp", targetNS)
if err == nil {
l.Info("+ op=query, remote=%s, type=%d, id=%d, name=%v", targetNS, targetQT, pp.Header.Id, q.Name)
cq.conn.WriteToUDP(packet.Assemble(pp), remoteNs)
cq.sq.registerQuery(pp.Questions[0], remoteNs, targetXH)
}
return pp
}