middleware/metrics: export ListenAddr (#366)

ListenAddr is the address where the prometheus metric are exported.
This can be used in tests to listen on "localhost:0" and then later
retrieve the metrics from there. It makes the tests indepent on each
other.

middleware/metrics/metrics.go

@@ -61,6 +61,7 @@ func (m *Metrics) OnStartup() error {
 		}
 
 		m.ln = ln
+		ListenAddr = m.ln.Addr().String()
 
 		m.mux = http.NewServeMux()
 
@@ -97,3 +98,7 @@ func keys(m map[string]bool) []string {
 	}
 	return sx
 }
+
+// ListenAddr is assigned the address of the prometheus listener. Its use is mainly in tests where
+// we listen on "localhost:0" and need to retrieve the actual address.
+var ListenAddr string

middleware/metrics/metrics_test.go

@@ -13,7 +13,7 @@ import (
 )
 
 func TestMetrics(t *testing.T) {
-	met := &Metrics{Addr: Addr, zoneMap: make(map[string]bool)}
+	met := &Metrics{Addr: "localhost:0", zoneMap: make(map[string]bool)}
 	if err := met.OnStartup(); err != nil {
 		t.Fatalf("Failed to start metrics handler: %s", err)
 	}
@@ -71,7 +71,7 @@ func TestMetrics(t *testing.T) {
 			t.Fatalf("Test %d: Expected no error, but got %s", i, err)
 		}
 
-		result := mtest.Scrape(t, "http://"+Addr+"/metrics")
+		result := mtest.Scrape(t, "http://"+ListenAddr+"/metrics")
 
 		if tc.expectedValue != "" {
 			got, _ := mtest.MetricValue(tc.metric, result)

middleware/metrics/setup.go

@@ -38,7 +38,7 @@ func setup(c *caddy.Controller) error {
 
 func prometheusParse(c *caddy.Controller) (*Metrics, error) {
 	var (
-		met = &Metrics{Addr: Addr, zoneMap: make(map[string]bool)}
+		met = &Metrics{Addr: addr, zoneMap: make(map[string]bool)}
 		err error
 	)
 
@@ -88,4 +88,4 @@ func prometheusParse(c *caddy.Controller) (*Metrics, error) {
 var metricsOnce sync.Once
 
 // Addr is the address the where the metrics are exported by default.
-const Addr = "localhost:9153"
+const addr = "localhost:9153"

test/metrics_test.go

@@ -20,12 +20,12 @@ import (
 func TestMetricsServer(t *testing.T) {
 	corefile := `example.org:0 {
 	chaos CoreDNS-001 miek@miek.nl
-	prometheus
+	prometheus localhost:0
 }
 
 example.com:0 {
 	proxy . 8.8.4.4:53
-	prometheus
+	prometheus localhost:0
 }
 `
 	srv, err := CoreDNSServer(corefile)
@@ -40,7 +40,7 @@ func TestMetricsRefused(t *testing.T) {
 
 	corefile := `example.org:0 {
 	proxy . 8.8.8.8:53
-	prometheus
+	prometheus localhost:0
 }
 `
 	srv, err := CoreDNSServer(corefile)
@@ -58,7 +58,7 @@ func TestMetricsRefused(t *testing.T) {
 		t.Fatalf("Could not send message: %s", err)
 	}
 
-	data := mtest.Scrape(t, "http://"+metrics.Addr+"/metrics")
+	data := mtest.Scrape(t, "http://"+metrics.ListenAddr+"/metrics")
 	got, labels := mtest.MetricValue(metricName, data)
 
 	if got != "1" {
@@ -77,7 +77,7 @@ func TestMetricsCache(t *testing.T) {
 
 	corefile := `example.net:0 {
 	proxy . 8.8.8.8:53
-	prometheus
+	prometheus localhost:0
 	cache
 }
 `
@@ -96,7 +96,7 @@ func TestMetricsCache(t *testing.T) {
 		t.Fatalf("Could not send message: %s", err)
 	}
 
-	data := mtest.Scrape(t, "http://"+metrics.Addr+"/metrics")
+	data := mtest.Scrape(t, "http://"+metrics.ListenAddr+"/metrics")
 	// Get the value for the metrics where the one of the labels values matches "success"
 	got, _ := mtest.MetricValueLabel(metricName, cache.Success, data)
 
@@ -111,12 +111,11 @@ func TestMetricsAuto(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	// TODO(miek): Random port as string and use that later?
 	corefile := `org:0 {
 		auto {
 			directory ` + tmpdir + ` db\.(.*) {1} 1
 		}
-		prometheus
+		prometheus localhost:0
 	}
 `
 
@@ -149,7 +148,7 @@ func TestMetricsAuto(t *testing.T) {
 
 	metricName := "coredns_dns_request_count_total" //{zone, proto, family}
 
-	data := mtest.Scrape(t, "http://"+metrics.Addr+"/metrics")
+	data := mtest.Scrape(t, "http://"+metrics.ListenAddr+"/metrics")
 	// Get the value for the metrics where the one of the labels values matches "example.org."
 	got, _ := mtest.MetricValueLabel(metricName, "example.org.", data)
 
@@ -164,7 +163,7 @@ func TestMetricsAuto(t *testing.T) {
 		t.Fatalf("Could not send message: %s", err)
 	}
 
-	data = mtest.Scrape(t, "http://"+metrics.Addr+"/metrics")
+	data = mtest.Scrape(t, "http://"+metrics.ListenAddr+"/metrics")
 	got, _ = mtest.MetricValueLabel(metricName, "example.org.", data)
 
 	if got != "1" {