add integration test (running against an actual dnsmasq)

.travis.yml

@@ -0,0 +1,22 @@
+# Use the (faster) container-based infrastructure, see also
+# http://docs.travis-ci.com/user/workers/container-based-infrastructure/
+sudo: false
+dist: trusty
+services:
+  - docker
+
+language: go
+go:
+  - "1.10"
+go_import_path: github.com/stapelberg/dnsmasq_exporter
+
+
+script:
+  # Check whether files are syntactically correct.
+  - "gofmt -l $(find . -name '*.go' | tr '\\n' ' ') >/dev/null"
+  # Check whether files were not gofmt'ed.
+  - "gosrc=$(find . -name '*.go' | tr '\\n' ' '); [ $(gofmt -l $gosrc 2>&- | wc -l) -eq 0 ] || (echo 'gofmt was not run on these files:'; gofmt -l $gosrc 2>&-; false)"
+  - go tool vet .
+  - go test -c
+  - docker build --pull --no-cache --rm -t=dns -f travis/Dockerfile .
+  - docker run -v $PWD:/usr/src:ro dns /bin/sh -c './dnsmasq_exporter.test -test.v'

dnsmasq.go

@@ -101,13 +101,14 @@ func init() {
 // be:
 //     dig +short chaos txt cachesize.bind
 
-func main() {
-	flag.Parse()
-	promHandler := promhttp.Handler()
-	dnsClient := &dns.Client{
-		SingleInflight: true,
-	}
-	http.HandleFunc("/metrics", func(w http.ResponseWriter, r *http.Request) {
+type server struct {
+	promHandler http.Handler
+	dnsClient   *dns.Client
+	dnsmasqAddr string
+	leasesPath  string
+}
+
+func (s *server) metrics(w http.ResponseWriter, r *http.Request) {
 	var eg errgroup.Group
 
 	eg.Go(func() error {
@@ -126,7 +127,7 @@ func main() {
 				dns.Question{"servers.bind.", dns.TypeTXT, dns.ClassCHAOS},
 			},
 		}
-			in, _, err := dnsClient.Exchange(msg, *dnsmasqAddr)
+		in, _, err := s.dnsClient.Exchange(msg, s.dnsmasqAddr)
 		if err != nil {
 			return err
 		}
@@ -157,7 +158,7 @@ func main() {
 	})
 
 	eg.Go(func() error {
-			f, err := os.Open(*leasesPath)
+		f, err := os.Open(s.leasesPath)
 		if err != nil {
 			return err
 		}
@@ -179,7 +180,19 @@ func main() {
 		return
 	}
 
-		promHandler.ServeHTTP(w, r)
-	})
+	s.promHandler.ServeHTTP(w, r)
+}
+
+func main() {
+	flag.Parse()
+	s := &server{
+		promHandler: promhttp.Handler(),
+		dnsClient: &dns.Client{
+			SingleInflight: true,
+		},
+		dnsmasqAddr: *dnsmasqAddr,
+		leasesPath:  *leasesPath,
+	}
+	http.HandleFunc("/metrics", s.metrics)
 	log.Fatal(http.ListenAndServe(*listen, nil))
 }

dnsmasq_test.go

@@ -0,0 +1,152 @@
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"os/exec"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/miekg/dns"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+func TestDnsmasqExporter(t *testing.T) {
+	// NOTE(stapelberg): dnsmasq disables DNS operation upon --port=0 (as
+	// opposed to picking a free port). Hence, we must pick one. This is
+	// inherently prone to race conditions: another process could grab the port
+	// between our ln.Close() and dnsmasq’s bind(). Ideally, dnsmasq would
+	// support grabbing a free port and announcing it, or inheriting a listening
+	// socket à la systemd socket activation.
+
+	ln, err := net.Listen("tcp", "localhost:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, port, err := net.SplitHostPort(ln.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	ln.Close()
+
+	dnsmasq := exec.Command(
+		"dnsmasq",
+		"--port="+port,
+		"--no-daemon",
+		"--cache-size=666",
+		"--bind-interfaces",
+		"--interface=lo")
+	dnsmasq.Stderr = os.Stderr
+	fmt.Printf("starting %v\n", dnsmasq.Args)
+	if err := dnsmasq.Start(); err != nil {
+		t.Fatal(err)
+	}
+	defer dnsmasq.Process.Kill()
+
+	// Wait until dnsmasq started up
+	resolver := &dns.Client{}
+	for {
+		// Cause a cache miss (dnsmasq must forward this query)
+		var m dns.Msg
+		m.SetQuestion("localhost.", dns.TypeA)
+		if _, _, err := resolver.Exchange(&m, "localhost:"+port); err == nil {
+			break
+		}
+		time.Sleep(10 * time.Millisecond) // do not hog the CPU
+	}
+
+	s := &server{
+		promHandler: promhttp.Handler(),
+		dnsClient: &dns.Client{
+			SingleInflight: true,
+		},
+		dnsmasqAddr: "localhost:" + port,
+		leasesPath:  "testdata/dnsmasq.leases",
+	}
+
+	t.Run("first", func(t *testing.T) {
+		metrics := fetchMetrics(t, s)
+		want := map[string]string{
+			"dnsmasq_leases":    "2",
+			"dnsmasq_cachesize": "666",
+			"dnsmasq_hits":      "1",
+			"dnsmasq_misses":    "0",
+		}
+		for key, val := range want {
+			if got, want := metrics[key], val; got != want {
+				t.Errorf("metric %q: got %q, want %q", key, got, want)
+			}
+		}
+	})
+
+	t.Run("second", func(t *testing.T) {
+		metrics := fetchMetrics(t, s)
+		want := map[string]string{
+			"dnsmasq_leases":    "2",
+			"dnsmasq_cachesize": "666",
+			"dnsmasq_hits":      "2",
+			"dnsmasq_misses":    "0",
+		}
+		for key, val := range want {
+			if got, want := metrics[key], val; got != want {
+				t.Errorf("metric %q: got %q, want %q", key, got, want)
+			}
+		}
+	})
+
+	// Cause a cache miss (dnsmasq must forward this query)
+	var m dns.Msg
+	m.SetQuestion("no.such.domain.invalid.", dns.TypeA)
+	if _, _, err := resolver.Exchange(&m, "localhost:"+port); err != nil {
+		t.Fatal(err)
+	}
+
+	t.Run("after query", func(t *testing.T) {
+		metrics := fetchMetrics(t, s)
+		want := map[string]string{
+			"dnsmasq_leases":    "2",
+			"dnsmasq_cachesize": "666",
+			"dnsmasq_hits":      "3",
+			"dnsmasq_misses":    "1",
+		}
+		for key, val := range want {
+			if got, want := metrics[key], val; got != want {
+				t.Errorf("metric %q: got %q, want %q", key, got, want)
+			}
+		}
+	})
+}
+
+func fetchMetrics(t *testing.T, s *server) map[string]string {
+	rec := httptest.NewRecorder()
+	s.metrics(rec, httptest.NewRequest("GET", "/metrics", nil))
+	resp := rec.Result()
+	if got, want := resp.StatusCode, http.StatusOK; got != want {
+		b, _ := ioutil.ReadAll(resp.Body)
+		t.Fatalf("unexpected HTTP status: got %v (%v), want %v", resp.Status, string(b), want)
+	}
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	metrics := make(map[string]string)
+	for _, line := range strings.Split(strings.TrimSpace(string(body)), "\n") {
+		if strings.HasPrefix(line, "#") {
+			continue
+		}
+		parts := strings.Split(line, " ")
+		if len(parts) < 2 {
+			continue
+		}
+		if !strings.HasPrefix(parts[0], "dnsmasq_") {
+			continue
+		}
+		metrics[parts[0]] = parts[1]
+	}
+	return metrics
+}

testdata/dnsmasq.leases

@@ -0,0 +1,2 @@
+lease1
+lease2

travis/Dockerfile

@@ -0,0 +1,18 @@
+# vim:ft=Dockerfile
+FROM debian:sid
+
+RUN echo force-unsafe-io > /etc/dpkg/dpkg.cfg.d/docker-apt-speedup
+# Paper over occasional network flakiness of some mirrors.
+RUN echo 'APT::Acquire::Retries "5";' > /etc/apt/apt.conf.d/80retry
+
+# NOTE: I tried exclusively using gce_debian_mirror.storage.googleapis.com
+# instead of httpredir.debian.org, but the results (Fetched 123 MB in 36s (3357
+# kB/s)) are not any better than httpredir.debian.org (Fetched 123 MB in 34s
+# (3608 kB/s)). Hence, let’s stick with httpredir.debian.org (default) for now.
+
+RUN apt-get update && \
+    DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
+    dnsmasq && \
+    rm -rf /var/lib/apt/lists/*
+
+WORKDIR /usr/src