From 90873175eed4b2776b8ce32d4ade1b8cf4a69724 Mon Sep 17 00:00:00 2001
From: Cottand <nico.dc@outlook.com>
Date: Tue, 8 Oct 2024 23:07:50 +0100
Subject: [PATCH] add metric for tracking cache hits

---
 api.go                    |  3 ++-
 handler.go                | 10 ++++------
 internal/metric/metric.go | 13 ++++++++++++-
 3 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/api.go b/api.go
index dc20afb..ed6d6bc 100644
--- a/api.go
+++ b/api.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"bufio"
+	"errors"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"net"
 	"net/http"
@@ -234,7 +235,7 @@ func StartAPIServer(config *Config,
 		return nil, err
 	}
 	go func() {
-		if err := server.Serve(listener); err != http.ErrServerClosed {
+		if err := server.Serve(listener); !errors.Is(err, http.ErrServerClosed) {
 			logger.Fatal(err)
 		}
 	}()
diff --git a/handler.go b/handler.go
index 59ce753..8519894 100644
--- a/handler.go
+++ b/handler.go
@@ -147,7 +147,7 @@ func (h *EventLoop) responseFor(Net string, req *dns.Msg, _local net.Addr, _remo
 				msg := *mesg
 				msg.Id = req.Id
 
-				defer metric.ReportDNSRespond(remote, &msg, blocked)
+				defer metric.ReportDNSRespond(remote, &msg, blocked, true)
 				return &msg, true
 			}
 		}
@@ -190,7 +190,7 @@ func (h *EventLoop) responseFor(Net string, req *dns.Msg, _local net.Addr, _remo
 				}
 			}
 
-			defer metric.ReportDNSRespond(remote, m, true)
+			defer metric.ReportDNSRespond(remote, m, true, false)
 
 			logger.Noticef("%s found in blocklist\n", Q.Qname)
 
@@ -252,7 +252,7 @@ func (h *EventLoop) responseFor(Net string, req *dns.Msg, _local net.Addr, _remo
 		}
 	}
 
-	defer metric.ReportDNSRespond(remote, mesg, false)
+	defer metric.ReportDNSRespond(remote, mesg, false, false)
 
 	if IPQuery > 0 && len(mesg.Answer) > 0 {
 		if !lengActive && blacklisted {
@@ -270,9 +270,7 @@ func (h *EventLoop) responseFor(Net string, req *dns.Msg, _local net.Addr, _remo
 
 func (h *EventLoop) doRequest(Net string, w dns.ResponseWriter, req *dns.Msg) {
 	defer func(w dns.ResponseWriter) {
-		err := w.Close()
-		if err != nil {
-		}
+		_ = w.Close()
 	}(w)
 
 	resp, ok := h.responseFor(Net, req, w.LocalAddr(), w.RemoteAddr())
diff --git a/internal/metric/metric.go b/internal/metric/metric.go
index 01089f8..42611a8 100644
--- a/internal/metric/metric.go
+++ b/internal/metric/metric.go
@@ -36,6 +36,14 @@ var (
 			Help:      "Served DNS replies",
 		}, []string{"q_type", "remote_ip", "q_name", "rcode", "blocked"})
 
+	cachedResponseCounter = prometheus.NewCounter(
+		prometheus.CounterOpts{
+			Namespace: Namespace,
+			Name:      "request_cached",
+			Help:      "Cached DNS replies",
+		},
+	)
+
 	RequestUpstreamResolveCounter = prometheus.NewCounterVec(
 		prometheus.CounterOpts{
 			Namespace: Namespace,
@@ -130,7 +138,7 @@ func ReportDNSResponse(w dns.ResponseWriter, message *dns.Msg, blocked bool) {
 	}).Inc()
 }
 
-func ReportDNSRespond(remote net.IP, message *dns.Msg, blocked bool) {
+func ReportDNSRespond(remote net.IP, message *dns.Msg, blocked bool, cached bool) {
 	question := message.Question[0]
 	var remoteHost string
 	var qName string
@@ -148,4 +156,7 @@ func ReportDNSRespond(remote net.IP, message *dns.Msg, blocked bool) {
 		"rcode":     dns.RcodeToString[message.Rcode],
 		"blocked":   strconv.FormatBool(blocked),
 	}).Inc()
+	if cached {
+		cachedResponseCounter.Inc()
+	}
 }