// interceptRequest gets called upon each DNS request, and we determine
// whether we want to deal with it or not
func interceptRequest(w dns.ResponseWriter, r *dns.Msg) {
m := r.Copy()
err := error(nil)
defer w.Close()
if len(r.Question) < 1 {
return
}
// Hijack the response to point to us instead
if matchesCriteria(r.Question[0].Name) {
fmt.Println("Matches!", r.Question[0].Name)
if !(inAddressCache(r.Question[0].Name)) {
updateAddressCache(r)
}
m = hijackResponse(r)
// Pass it upstream, return the answer
} else {
//fmt.Println("Passing on ", r.Question[0].Name)
m, err = upstreamLookup(r)
if err != nil {
fmt.Println("Error when passing request through upstream - network problem?")
// in this instance, our response (m) has no answer
}
}
w.WriteMsg(m)
}
func (h *handler) handleRecursive(w dns.ResponseWriter, req *dns.Msg) {
h.ns.debugf("recursive request: %+v", *req)
// Resolve unqualified names locally
if len(req.Question) == 1 {
hostname := dns.Fqdn(req.Question[0].Name)
if strings.Count(hostname, ".") == 1 {
h.handleLocal(w, req)
return
}
}
upstreamConfig, err := h.upstream.Config()
if err != nil {
h.ns.errorf("unable to read upstream config: %s", err)
}
for _, server := range upstreamConfig.Servers {
reqCopy := req.Copy()
reqCopy.Id = dns.Id()
response, _, err := h.client.Exchange(reqCopy, fmt.Sprintf("%s:%s", server, upstreamConfig.Port))
if (err != nil && err != dns.ErrTruncated) || response == nil {
h.ns.debugf("error trying %s: %v", server, err)
continue
}
response.Id = req.Id
if h.responseTooBig(req, response) {
response.Compress = true
}
h.respond(w, response)
return
}
h.respond(w, h.makeErrorResponse(req, dns.RcodeServerFailure))
}
// InsertMessage inserts a message in the Cache. We will cache it for ttl seconds, which
// should be a small (60...300) integer.
func (c *Cache) InsertMessage(s string, msg *dns.Msg) {
if c.capacity <= 0 {
return
}
c.Lock()
if _, ok := c.m[s]; !ok {
c.m[s] = &elem{time.Now().UTC().Add(c.ttl), msg.Copy()}
}
c.EvictRandom()
c.Unlock()
}
// set the reply for the entry
// returns True if the entry has changed the validUntil time
func (e *cacheEntry) setReply(reply *dns.Msg, ttl int, flags uint8, now time.Time) bool {
var prevValidUntil time.Time
if e.Status == stResolved {
if reply != nil {
Debug.Printf("[cache msgid %d] replacing response in cache", reply.MsgHdr.Id)
}
prevValidUntil = e.validUntil
}
// make sure we do not overwrite noLocalReplies entries
if flags&CacheNoLocalReplies != 0 {
if e.Flags&CacheNoLocalReplies != 0 {
return false
}
}
if ttl != nullTTL {
e.validUntil = now.Add(time.Second * time.Duration(ttl))
} else if reply != nil {
// calculate the validUntil from the reply TTL
var minTTL uint32 = math.MaxUint32
for _, rr := range reply.Answer {
ttl := rr.Header().Ttl
if ttl < minTTL {
minTTL = ttl // TODO: improve the minTTL calculation (maybe we should skip some RRs)
}
}
e.validUntil = now.Add(time.Second * time.Duration(minTTL))
} else {
Warning.Printf("[cache] no valid TTL could be calculated")
}
e.Status = stResolved
e.Flags = flags
e.putTime = now
if reply != nil {
e.reply = *reply.Copy()
e.ReplyLen = reply.Len()
}
return (prevValidUntil != e.validUntil)
}
// Add adds dns.Msg to the cache
func (c *Cache) Add(msg *mdns.Msg) {
c.Lock()
defer c.Unlock()
if len(c.m) >= c.capacity {
// pick a random key and remove it
for k := range c.m {
delete(c.m, k)
break
}
}
key := generateKey(msg.Question[0])
if _, ok := c.m[key]; !ok {
c.m[key] = &Item{
Expiration: time.Now().UTC().Add(c.ttl),
Msg: msg.Copy(),
}
}
}
// updateAddressCache updates the dns map of real names to ip addresses
// used to relay traffic to the intended destination.
func updateAddressCache(r *dns.Msg) {
u := r.Copy()
u, err := upstreamLookup(u)
if err != nil {
fmt.Println("Network error: Cannnot lookup upstream!", err.Error())
return
}
// find all A records, save the name and address, replace the address and ttl
names := []string{}
ip := ""
// grab all names (and IP from A record), for updating (sans dot at end)
for _, answer := range u.Answer {
names = append(names, answer.Header().Name)
if dns.TypeToString[answer.Header().Rrtype] == "A" {
found := addressRegex.FindString(answer.String())
if found != "" {
ip = found
} else {
panic(r.String())
}
}
}
if ip == "" {
fmt.Println("Cannot updated map, no IP found")
fmt.Println(u.String())
return
}
updateMutex.Lock()
// Update both with . at the end and without
for _, name := range names {
addressMap[strings.ToLower(name)] = ip
addressMap[strings.ToLower(name[:len(name)-1])] = ip
fmt.Println("Updated address map with ", name, ip)
}
updateMutex.Unlock()
}
// forwardSearch resolves a query by suffixing with search paths
func (s *server) forwardSearch(req *dns.Msg, tcp bool) (*dns.Msg, error) {
var r *dns.Msg
var nodata *dns.Msg // stores the copy of a NODATA reply
var searchName string // stores the current name suffixed with search domain
var err error
var didSearch bool
name := req.Question[0].Name // original qname
reqCopy := req.Copy()
for _, domain := range s.config.SearchDomains {
if strings.HasSuffix(name, domain) {
continue
}
searchName = strings.ToLower(appendDomain(name, domain))
reqCopy.Question[0] = dns.Question{searchName, reqCopy.Question[0].Qtype, reqCopy.Question[0].Qclass}
didSearch = true
r, err = s.forwardQuery(reqCopy, tcp)
if err != nil {
// No server currently available, give up
break
}
switch r.Rcode {
case dns.RcodeSuccess:
// In case of NO_DATA keep searching, otherwise a wildcard entry
// could keep us from finding the answer higher in the search list
if len(r.Answer) == 0 && !r.MsgHdr.Truncated {
nodata = r.Copy()
continue
}
case dns.RcodeNameError:
fallthrough
case dns.RcodeServerFailure:
// try next search element if any
continue
}
// anything else implies that we are done searching
break
}
if !didSearch {
m := new(dns.Msg)
m.SetRcode(req, dns.RcodeNameError)
return m, nil
}
if err == nil {
if r.Rcode == dns.RcodeSuccess {
if len(r.Answer) > 0 {
cname := new(dns.CNAME)
cname.Hdr = dns.RR_Header{Name: name, Rrtype: dns.TypeCNAME, Class: dns.ClassINET, Ttl: 360}
cname.Target = searchName
answers := []dns.RR{cname}
for _, rr := range r.Answer {
answers = append(answers, rr)
}
r.Answer = answers
}
// If we ever got a NODATA, return this instead of a negative result
} else if nodata != nil {
r = nodata
}
// Restore original question
r.Question[0] = req.Question[0]
}
if err != nil && nodata != nil {
r = nodata
r.Question[0] = req.Question[0]
err = nil
}
return r, err
}
