pkg/metrics_store: Accept Writer instead of returning metrics on scrape

main.go

@@ -227,7 +227,7 @@ func serveMetrics(collectors []*kcollectors.Collector, host string, port int, en
 }
 
 type metricHandler struct {
-	c                  []*kcollectors.Collector
+	collectors         []*kcollectors.Collector
 	enableGZIPEncoding bool
 }
 
@@ -251,14 +251,8 @@ func (m *metricHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	for _, c := range m.c {
-		for _, m := range c.Collect() {
-			_, err := fmt.Fprint(writer, m)
-			if err != nil {
-				// TODO: Handle panic
-				panic(err)
-			}
-		}
+	for _, c := range m.collectors {
+		c.Collect(w)
 	}
 
 	// In case we gziped the response, we have to close the writer.

pkg/collectors/collectors.go

@@ -16,10 +16,12 @@ limitations under the License.
 
 package collectors
 
-import ()
+import (
+	"io"
+)
 
 type Store interface {
-	GetAll() []string
+	WriteAll(io.Writer)
 }
 
 // Collector represents a kube-state-metrics metric collector. It is stripped
@@ -33,6 +35,6 @@ func NewCollector(s Store) *Collector {
 }
 
 // Collect returns all metrics of the underlying store of the collector.
-func (c *Collector) Collect() []string {
-	return c.Store.GetAll()
+func (c *Collector) Collect(w io.Writer) {
+	c.Store.WriteAll(w)
 }

pkg/metrics_store/metrics_store.go

@@ -1,6 +1,7 @@
 package metricsstore
 
 import (
+	"io"
 	"sync"
 
 	"k8s.io/kube-state-metrics/pkg/metrics"
@@ -10,7 +11,7 @@ import (
 )
 
 var (
-	helpPrefix = "# HELP "
+	helpPrefix = []byte("# HELP ")
 )
 
 // MetricsStore implements the k8s.io/kubernetes/client-go/tools/cache.Store
@@ -117,22 +118,19 @@ func (s *MetricsStore) Resync() error {
 	return nil
 }
 
-// GetAll returns all metrics of the store, zipped with the help text of each
-// metric family.
-func (s *MetricsStore) GetAll() []string {
-	metrics := []string{}
-
+// WriteAll writes all metrics of the store into the given writer, zipped with the
+// help text of each metric family.
+func (s *MetricsStore) WriteAll(w io.Writer) {
 	s.mutex.RLock()
 	defer s.mutex.RUnlock()
 
 	for i, help := range s.helpTexts {
-		metrics = append(metrics, helpPrefix+help+"\n")
+		w.Write(append(helpPrefix, []byte(help)...))
+		w.Write([]byte{'\n'})
 		for _, metricsPerObject := range s.metrics {
 			for _, metric := range metricsPerObject[i] {
-				metrics = append(metrics, string(*metric))
+				w.Write([]byte(*metric))
 			}
 		}
 	}
-
-	return metrics
 }

pkg/metrics_store/metrics_store_test.go

@@ -44,22 +44,18 @@ func TestObjectsSameNameDifferentNamespaces(t *testing.T) {
 		}
 	}
 
-	metrics := ms.GetAll()
+	w := strings.Builder{}
+	ms.WriteAll(&w)
+	m := w.String()
 
-	// Expect 3 lines, HELP + 2 metrics
-	if len(metrics) != 3 {
-		t.Fatalf("expected 2 metrics but got %v", len(metrics))
+	// Expect 4 lines, HELP + 2 metrics + newline
+	if len(strings.Split(m, "\n")) != 4 {
+		t.Fatalf("expected 2 metrics but got %v", len(strings.Split(m, "\n")))
 	}
 
 	for _, id := range serviceIDS {
-		found := false
-		for _, m := range metrics {
-			if strings.Contains(m, fmt.Sprintf("uid=\"%v\"", id)) {
-				found = true
-			}
-		}
+		if !strings.Contains(m, fmt.Sprintf("uid=\"%v\"", id)) {
 
-		if !found {
 			t.Fatalf("expected to find metric with uid %v", id)
 		}
 	}

tests/lib/lib_test.go

@@ -38,13 +38,11 @@ func TestAsLibrary(t *testing.T) {
 	// Wait for informers to sync
 	time.Sleep(time.Second)
 
-	m := c.Collect()
+	w := strings.Builder{}
+	c.Collect(&w)
+	m := w.String()
 
-	if len(m) != 2 {
-		t.Fatalf("expected HELP line and one metric to be returned but got %v", len(m))
-	}
-
-	if !strings.Contains(string(m[1]), service.ObjectMeta.Name) {
+	if !strings.Contains(m, service.ObjectMeta.Name) {
 		t.Fatal("expected string to contain service name")
 	}
 }