plugin/metrics: Added New func (#1309)

If external plugins wanted to extend metrics there was no way since
zoneNames couldn't be initialized. Now plugins can call New to get an
instance of Metrics that they can extend.

3 files changed, 10 insertions, 8 deletions

diff --git a/plugin/metrics/metrics.go b/plugin/metrics/metrics.go
index 0dabcdf96..df07da0ae 100644
--- a/plugin/metrics/metrics.go
+++ b/plugin/metrics/metrics.go
@@ -36,6 +36,11 @@ type Metrics struct {
 	zoneMu    sync.RWMutex
 }
 
+// New returns a new instance of Metrics with the given address
+func New(addr string) *Metrics {
+	return &Metrics{Addr: addr, zoneMap: make(map[string]bool)}
+}
+
 // AddZone adds zone z to m.
 func (m *Metrics) AddZone(z string) {
 	m.zoneMu.Lock()
diff --git a/plugin/metrics/metrics_test.go b/plugin/metrics/metrics_test.go
index 54e7859e8..f3e4ba3d8 100644
--- a/plugin/metrics/metrics_test.go
+++ b/plugin/metrics/metrics_test.go
@@ -13,7 +13,7 @@ import (
 )
 
 func TestMetrics(t *testing.T) {
-	met := &Metrics{Addr: "localhost:0", zoneMap: make(map[string]bool)}
+	met := New("localhost:0")
 	if err := met.OnStartup(); err != nil {
 		t.Fatalf("Failed to start metrics handler: %s", err)
 	}
diff --git a/plugin/metrics/setup.go b/plugin/metrics/setup.go
index eecfac62c..a0f68a53f 100644
--- a/plugin/metrics/setup.go
+++ b/plugin/metrics/setup.go
@@ -42,10 +42,7 @@ func setup(c *caddy.Controller) error {
 }
 
 func prometheusParse(c *caddy.Controller) (*Metrics, error) {
-	var (
-		met = &Metrics{Addr: addr, zoneMap: make(map[string]bool)}
-		err error
-	)
+	var met = New(defaultAddr)
 
 	defer func() {
 		uniqAddr.SetAddress(met.Addr)
@@ -73,7 +70,7 @@ func prometheusParse(c *caddy.Controller) (*Metrics, error) {
 			return met, c.ArgErr()
 		}
 	}
-	return met, err
+	return met, nil
 }
 
 var uniqAddr addrs
@@ -91,8 +88,8 @@ func (a *addrs) SetAddress(addr string) {
 	a.a[addr] = todo
 }
 
-// Addr is the address the where the metrics are exported by default.
-const addr = "localhost:9153"
+// defaultAddr is the address the where the metrics are exported by default.
+const defaultAddr = "localhost:9153"
 
 const (
 	todo = 1