// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package resolver
import (
"fmt"
"html"
"net/http"
"strconv"
"sync"
"sync/atomic"
"time"
"tailscale.com/health"
)
func init() {
health.RegisterDebugHandler("dnsfwd", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
n, _ := strconv.Atoi(r.FormValue("n"))
if n <= 0 {
n = 100
} else if n > 10000 {
n = 10000
}
fl := fwdLogAtomic.Load()
if fl == nil || n != len(fl.ent) {
fl = &fwdLog{ent: make([]fwdLogEntry, n)}
fwdLogAtomic.Store(fl)
}
fl.ServeHTTP(w, r)
}))
}
var fwdLogAtomic atomic.Pointer[fwdLog]
type fwdLog struct {
mu sync.Mutex
pos int // ent[pos] is next entry
ent []fwdLogEntry
}
type fwdLogEntry struct {
Domain string
Time time.Time
}
func (fl *fwdLog) addName(name string) {
if fl == nil {
return
}
fl.mu.Lock()
defer fl.mu.Unlock()
if len(fl.ent) == 0 {
return
}
fl.ent[fl.pos] = fwdLogEntry{Domain: name, Time: time.Now()}
fl.pos++
if fl.pos == len(fl.ent) {
fl.pos = 0
}
}
func (fl *fwdLog) ServeHTTP(w http.ResponseWriter, r *http.Request) {
fl.mu.Lock()
defer fl.mu.Unlock()
fmt.Fprintf(w, "<html><h1>DNS forwards</h1>")
now := time.Now()
for i := 0; i < len(fl.ent); i++ {
ent := fl.ent[(i+fl.pos)%len(fl.ent)]
if ent.Domain == "" {
continue
}
fmt.Fprintf(w, "%v ago: %v<br>\n", now.Sub(ent.Time).Round(time.Second), html.EscapeString(ent.Domain))
}
}