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dns_gslb.go
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dns_gslb.go
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package main
import (
"fmt"
"io"
"log"
"math/rand"
"net"
"net/http"
"strconv"
"strings"
"github.com/miekg/dns"
)
// NOTRACE is a shared trace config (basically: "no trace") that has no need to share the audit trail.
// No trail = shared across all instances without regards to thread safety;
// and just slightly less malloc'ing on function invocation.
var NOTRACE = NewLookupTraceOff()
// findViewOnly will cache.
func findViewOnly(ipString string) (view string) {
ip, _, err := net.SplitHostPort(ipString)
if err == nil {
ipString = ip // With the :portnumber removed.
}
if val, ok := CacheView.Get(ipString); ok {
return val
}
view, _, _ = findView(ipString) // view,asn,ispname
if view != "" {
CacheView.Set(ipString, view)
}
return view
}
// findView will (for a given IP string) return the "view" (ie, "comcast" or "default",
// the asn number (as a string), and the ISP info (as a string).
// This is not cached.
func findView(ipString string) (view string, asnString string, ispString string) {
//fmt.Printf("findView(%s)\n", ipString)
ip, _, err := net.SplitHostPort(ipString)
if err == nil {
ipString = ip // With the :portnumber removed.
}
var asn uint32
asn, ispString = GlobalMaxMind().LookupAsnPlusName(ipString) // AS number and ISP text Name
asnString = strconv.FormatUint(uint64(asn), 10)
statsMaxMind.Increment(asnString) // Keep track of queries from various service providers.
view = "default" // Default view name. May override based on ASN or Resolver
I := GlobalViewData() // Get and keep a stable (threadsafe) handle
if found, ok := I.GetSectionNameValueString("default", asnString); ok {
view = found
}
if found, ok := I.GetSectionNameValueString("default", ipString); ok {
view = found
}
return view, asnString, ispString
}
// ourNewRR combined dns.NewRR with a local cache.
func ourNewRR(s string) (dns.RR, error) {
// If needed, calculate and cache.
// ALWAYS return a deep copy - and leave
// the original pristine in the cache.
// This is critical to avoid leaking
// old queries to new (related to
// the vixie 0x20 hack)
if found, ok := CacheRR.Get(s); ok {
deep := dns.Copy(found)
return deep, nil
}
// Even a fresh instance will be deep copied.
parsed, err := dns.NewRR(s)
if err == nil {
CacheRR.Set(s, parsed)
}
deep := dns.Copy(parsed)
return deep, err
}
// handleReflectIP responds with the caller's IP address,
// in the form of A/AAAA as well as TXT
func handleGSLB(w dns.ResponseWriter, r *dns.Msg) {
// TODO Pack our own reply.
// TODO cache said reply.
// TODO serve from cache (with fixed msg.Id) when possible.
qname := r.Question[0].Name // This is OUR name; so use it in our response
ipString := w.RemoteAddr().String() // The user is from where?. dns.go only gives us strings.
qtype := r.Question[0].Qtype // What are we asking for?
qtypeStr := qtypeToString(qtype) // What are we asking for? A STRING!
qnameLC := toLower(qname) // We will ask for lowercase everything internally.
wasLC := qname == qnameLC // We really care about the case that people us when asking.
view := findViewOnly(ipString) // Geo + Resolver -> which data name in zone.conf
QI := QueryInfo{qname: qname, view: view, qtype: qtypeStr}
// Hey. Maybe we can return cached data?
if wasLC {
if cached, ok := CacheMsgs.Get(QI); ok {
statsCache.Increment("gslb-hit")
j := rand.Intn(len(cached)) // We expect multiple possible results; answer one at random.
bits := int(cached[j].msg[2]) // We need to figure out how to set/clear the RD bit
if r.RecursionDesired {
bits = bits | 0x01 // Set RD
} else {
bits = bits &^ 0x01 // Clear RD
}
// Build new data packet, with the new 3 bytes based on the current
// caller; and the remaining bytes on the cached data.
newLeader := []byte{uint8(r.Id >> 8), uint8(r.Id & 0xff), uint8(bits)}
newData := append(newLeader, cached[j].msg[3:]...)
w.Write(newData)
// Don't forget the stats.
statsQuery.Increment(qtypeStr)
statsResponse.Increment(cached[j].rcodeStr)
return
}
}
m := new(dns.Msg)
m.SetReply(r)
m.Compress = true
// Reasons to refuse to answer, there are many.
if r.Question[0].Qclass != dns.ClassINET ||
r.Question[0].Qtype == dns.TypeAXFR ||
r.Question[0].Qtype == dns.TypeIXFR {
statsCache.Increment("gslb-refused")
m.Rcode = dns.RcodeRefused
statsMsg(r)
statsMsg(m)
w.WriteMsg(m)
return
}
// Go do real computational work to see what our records should say.
// LookupFrontEnd handles some level of caching even if the vixie hack is used
stuff := LookupFrontEnd(qnameLC, view, qtypeStr, 0, NOTRACE)
// Shuffle, to randomize answers, if we got more than one.
if len(stuff.Ans) > 1 {
n := len(stuff.Ans)
for i := n - 1; i > 0; i-- {
j := rand.Intn(i + 1)
stuff.Ans[i], stuff.Ans[j] = stuff.Ans[j], stuff.Ans[i]
}
}
// Copy the results to fully formed RRs and stuff them into our
// message.
for _, s := range stuff.Ans {
rr, err := ourNewRR(s)
if err == nil {
m.Answer = append(m.Answer, rr)
} else {
log.Printf("Problems parsing '%s': %v\n", s, err)
}
}
for _, s := range stuff.Auth {
rr, err := ourNewRR(s)
if err == nil {
m.Ns = append(m.Ns, rr)
} else {
log.Printf("Problems parsing '%s': %v\n", s, err)
}
}
for _, s := range stuff.Add {
rr, err := ourNewRR(s)
if err == nil {
m.Extra = append(m.Extra, rr)
} else {
log.Printf("Problems parsing '%s': %v\n", s, err)
}
}
m.Rcode = stuff.Rcode
m.Authoritative = stuff.Aa
if len(stuff.Ans) > 1 {
n := len(stuff.Ans)
for i := n - 1; i > 0; i-- {
j := rand.Intn(i + 1)
stuff.Ans[i], stuff.Ans[j] = stuff.Ans[j], stuff.Ans[i]
}
}
// Finish up.
if wasLC {
vixie0x20HackMsg(m) // Handle MixEdCase.org requests
}
// Save some stats
statsMsg(r)
statsMsg(m)
// Finally, pack, possibly cache, and write the dns response
data, err := m.Pack()
if err != nil {
// We had an error creating a DNS packet?
log.Printf("Error with m.Pack %v", err)
return
}
if wasLC == true {
// Hey, we can cache this.
// No MixEdCaSE
rcodeStr := rcodeToString(stuff.Rcode) // For stats
group := []MsgCacheRecord{} // Allocate a new set of pointers
group = append(group, freshMsgCacheRecord(data, rcodeStr))
// Calculate the remaining rotations
for i := 1; i < len(stuff.Ans); i++ { // We already did "0"
m.Answer = append(m.Answer[1:], m.Answer[0]) // One DNS RR rotation
data, err = m.Pack() // Re-pack the DNS data
if err == nil { // If no error..
group = append(group, freshMsgCacheRecord(data, rcodeStr))
}
}
statsCache.Increment("gslb-miss")
CacheMsgs.Set(QI, group)
} else {
statsCache.Increment("gslb-nocache")
}
w.Write(data)
}
func dupedata(b []byte) []byte {
n := make([]byte, len(b))
copy(n, b)
return n
}
func freshMsgCacheRecord(data []byte, rcodeStr string) (m MsgCacheRecord) {
m.msg = dupedata(data)
m.rcodeStr = rcodeStr
return m
}
func rcodeToString(rcode int) string {
if cl1, ok := dns.RcodeToString[rcode]; ok {
return cl1
}
return fmt.Sprintf("Rcode%v", rcode)
}
func qtypeToString(qtype uint16) string {
if cl1, ok := dns.TypeToString[qtype]; ok {
return cl1
}
return fmt.Sprintf("Qtype%v", qtype)
}
// WebHandleTrace serves /gslb/trace/HOSTNAME
func WebHandleTrace(w http.ResponseWriter, r *http.Request) {
trace := NewLookupTrace()
myHTTPGslbTrace(w, r, trace)
}
// WebHandleLookup serves /gslb/lookup/HOSTNAME
func WebHandleLookup(w http.ResponseWriter, r *http.Request) {
notrace := NewLookupTraceOff()
myHTTPGslbTrace(w, r, notrace)
}
// handleReflectIP responds with the caller's IP address,
// in the form of A/AAAA as well as TXT
func myHTTPGslbTrace(w http.ResponseWriter, r *http.Request, trace *LookupTrace) {
qname := "unspecified"
qtypeStr := "A"
view := "default"
// /gslb/trace/test-ipv6.com
// /gslb/trace/test-ipv6.com/A
// /gslb/trace/test-ipv6.com/A/comcast
words := strings.Split(r.RequestURI, "/")
if len(words) < 3 {
w.WriteHeader(http.StatusBadRequest)
return
}
for _, word := range words[3:] {
uc := toUpper(word)
lc := toLower(word)
// Easy one first. DNS types
if _, ok := dns.StringToType[uc]; ok {
qtypeStr = uc
continue
}
// "Views" - by IP address or AS number.
I := GlobalViewData()
if found, ok := I.GetSectionNameValueString("default", word); ok {
view = found
continue
}
if found, ok := I.GetSectionNameValueString("default", lc); ok {
view = found
continue
}
// Otherwise, is it a hostname or a view (by name)?
// Assumption: views don't use dots.
if strings.ContainsAny(word, ".") {
qname = word
} else {
view = word
}
}
qnameLC := toLower(qname)
trace.Addf(0, "Looking up qname=%s qtype=%s view=%s", qnameLC, qtypeStr, view)
trace.Addf(0, "")
stuff := LookupFrontEnd(qnameLC, view, qtypeStr, 0, trace)
w.Header().Set("Content-Type", "text/plain")
text := strings.Join(trace.trace, "")
io.WriteString(w, text)
io.WriteString(w, "\n")
io.WriteString(w, fmt.Sprintf("QNAME: %v\n", qnameLC))
io.WriteString(w, fmt.Sprintf("RCODE: %v AA: %v\n", rcodeToString(stuff.Rcode), stuff.Aa))
io.WriteString(w, "\n")
if len(stuff.Ans) > 0 {
io.WriteString(w, "Answers:\n")
for _, s := range stuff.Ans {
io.WriteString(w, " "+s+"\n")
}
}
if len(stuff.Auth) > 0 {
io.WriteString(w, "Auth:\n")
for _, s := range stuff.Auth {
io.WriteString(w, " "+s+"\n")
}
}
if len(stuff.Add) > 0 {
io.WriteString(w, "Additional:\n")
for _, s := range stuff.Add {
io.WriteString(w, " "+s+"\n")
}
}
}
func statsMsg(reply *dns.Msg) {
isResponse := reply.Response
qname := reply.Question[0].Name
qnameLC := toLower(qname)
RcodeStr := rcodeToString(reply.Rcode)
qtypeStr := qtypeToString(reply.Question[0].Qtype)
if isResponse {
statsResponse.Increment(RcodeStr)
/*
// TODO Find a cheap way to figure out if our response is
// a wildcard response, or a legit direct answer.
// Why? Wildcards will polute the scoreboard - badly.
// For now, skip storing names.
if reply.Rcode == dns.RcodeSuccess {
statsQname.Add(qnameLC, 1)
}
*/
// If we needed the Vixie 0x20 bit hack for entropy,
// make a note of it in the stats. Might be useful.
if qname != qnameLC {
statsResponse.Increment("0x20")
}
} else {
statsQuery.Increment(qtypeStr)
}
}
func vixie0x20HackMsg(reply *dns.Msg) (changed bool) {
// If qname is not entirely lowercase, then
// spend extra cycles to modify all the names
// to meet the 0x20 hack
qname := reply.Question[0].Name
qnameLC := toLower(qname)
if qnameLC == qname {
return changed // Do nothing.
}
// I want to try all three of r.Answer, r.Ns, and r.Extra
// preferably without function call overhead. This seems
// awkward.
try := append(reply.Answer, append(reply.Ns, reply.Extra...)...)
for _, ptr := range try {
// ptr RR
s := ptr.Header().Name
if strings.HasSuffix(s, qnameLC) {
keep := len(s) - len(qnameLC)
s2 := s[0:keep] + qname
ptr.Header().Name = s2 // Replace with new mixedcase name
changed = true
}
}
return changed
}
func init() {
http.HandleFunc("/gslb/trace/", WebHandleTrace)
http.HandleFunc("/gslb/lookup/", WebHandleLookup)
}