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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)
}
}
})
s.leasesPath = "testdata/dnsmasq.leases.does.not.exists"
t.Run("without leases file", func(t *testing.T) {
metrics := fetchMetrics(t, s)
want := map[string]string{
"dnsmasq_leases": "0",
"dnsmasq_cachesize": "666",
"dnsmasq_hits": "4",
"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
}