/
main.go
145 lines (133 loc) · 3.37 KB
/
main.go
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package main
import (
"flag"
"fmt"
"log"
"os"
"strings"
"sync"
"time"
"github.com/miekg/dns"
)
const (
queryAttempts = 5
queryTimeout = 1100 * time.Millisecond
)
var (
flListen = flag.String("listen", ":53", "Listen address")
flUpstream = flag.String("upstream", ":53", "Upstream DNS server")
)
var (
cache = map[string]*dns.Msg{}
cacheLock = sync.Mutex{}
dnsclient = dns.Client{
UDPSize: dns.MaxMsgSize,
ReadTimeout: queryTimeout,
SingleInflight: true,
}
)
var logFormatExample = `Log format example:
1EF9┐a19.ru. A IN # uncached query
AAB1┐a19.ru. A IN # concurrent query
152E┐a19.ru. A IN # concurrent query
1EF9└a19.ru. A IN = (A 78.47.223.116) # answer now cached
AAB1┴1EF9 # answer already cached
152E┴1EF9 # answer already cached
2899┐a29.ru. A IN # uncached query
2899·a29.ru. A IN: [1/5] read udp 127.0.0.1:50019->127.0.0.1:53: i/o timeout
# first attempt of five failed to return an answer
2899╳a29.ru. A IN: [5/5] read udp 127.0.0.1:50019->127.0.0.1:53: i/o timeout
# final attempt failed, we sent client servfail
`
func main() {
log.SetFlags(log.Flags() | log.Lmicroseconds)
flag.Usage = func() {
fmt.Fprintln(os.Stderr, "Arguments:")
flag.PrintDefaults()
fmt.Fprint(os.Stderr, logFormatExample)
}
flag.Parse()
dns.HandleFunc(".", serve)
server := dns.Server{Addr: *flListen, Net: "udp"}
err := server.ListenAndServe()
eexit(err)
}
func msgKey(m *dns.Msg) string {
t := ""
if t1, ok := dns.TypeToString[m.Question[0].Qtype]; ok {
t = t1
}
cl := ""
if cl1, ok := dns.ClassToString[m.Question[0].Qclass]; ok {
cl = cl1
}
return m.Question[0].Name + " " + t + " " + cl
}
func recordSummary(r dns.RR) string {
s := r.String()
parts := strings.Split(s, "\t")
nparts := len(parts)
if nparts < 2 {
return s
}
return "(" + strings.Join(parts[nparts-2:], " ") + ")"
}
func answersSummary(m *dns.Msg) string {
var answers []string
if m.Answer != nil {
for _, rr := range m.Answer {
answers = append(answers, recordSummary(rr))
}
}
return strings.Join(answers, " ")
}
func serve(w dns.ResponseWriter, req *dns.Msg) {
var resp dns.Msg
var err error
key := msgKey(req)
cacheLock.Lock()
cached, ok := cache[key]
// cached value will not change until return because of SingleInflight
cacheLock.Unlock()
if !ok {
log.Printf("%04X┐%s\n", req.Id, key)
for attempt := 1; attempt <= queryAttempts; attempt++ {
cached, _, err = dnsclient.Exchange(req, *flUpstream)
if err != nil {
cacheLock.Lock()
_, ok = cache[key]
cacheLock.Unlock()
if ok {
// concurrent exchange succeeded
err = nil
break
}
sep := "·"
if attempt == queryAttempts {
sep = "╳"
}
log.Printf("%04X%s%s: [%d/%d] %v\n", req.Id, sep, key,
attempt, queryAttempts, err)
}
}
if err != nil {
dns.HandleFailed(w, req)
return
}
cacheLock.Lock()
cached2, ok := cache[key]
if ok {
// concurrent exchange has already updated the cache
cached = cached2
log.Printf("%04X┴%04X\n", req.Id, cached.Id)
} else {
cache[key] = cached
log.Printf("%04X└%s = %s\n", req.Id, key, answersSummary(cached))
}
cacheLock.Unlock()
}
resp = *cached
resp.Id = req.Id
err = w.WriteMsg(&resp)
eprint(err)
}