Return a value when atleast one of the metrics returns a value (#47)

* Return a value when atleast one of the metrics returns a value

Signed-off-by: Arjun Naik <arjun.rn@gmail.com>

* Added test for max weighted collector

Signed-off-by: Arjun Naik <arjun.rn@gmail.com>

pkg/collector/max_collector.go

@@ -2,8 +2,10 @@ package collector
 
 import (
 	"fmt"
-	"k8s.io/apimachinery/pkg/api/resource"
+	"strings"
 	"time"
+
+	"k8s.io/apimachinery/pkg/api/resource"
 )
 
 // MaxWeightedCollector is a simple aggregator collector that returns the maximum value
@@ -25,18 +27,29 @@ func NewMaxWeightedCollector(interval time.Duration, weight float64, collectors
 
 // GetMetrics gets metrics from all collectors and return the higest value.
 func (c *MaxWeightedCollector) GetMetrics() ([]CollectedMetric, error) {
+	errors := make([]error, 0)
 	collectedMetrics := make([]CollectedMetric, 0)
 	for _, collector := range c.collectors {
 		values, err := collector.GetMetrics()
 		if err != nil {
-			return nil, err
+			errors = append(errors, err)
+			continue
 		}
 		for _, v := range values {
 			collectedMetrics = append(collectedMetrics, v)
 		}
 	}
 	if len(collectedMetrics) == 0 {
-		return nil, fmt.Errorf("no metrics collected, cannot determine max")
+		if len(errors) == 0 {
+			return nil, fmt.Errorf("no metrics collected, cannot determine max")
+		} else {
+			errorStrings := make([]string, len(errors))
+			for i, e := range errors {
+				errorStrings[i] = e.Error()
+			}
+			allErrors := strings.Join(errorStrings, ",")
+			return nil, fmt.Errorf("could not determine maximum due to errors: %s", allErrors)
+		}
 	}
 	max := collectedMetrics[0]
 	for _, value := range collectedMetrics {

pkg/collector/max_collector_test.go

@@ -0,0 +1,76 @@
+package collector
+
+import (
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"k8s.io/apimachinery/pkg/api/resource"
+	"k8s.io/metrics/pkg/apis/custom_metrics"
+)
+
+type dummyCollector struct {
+	value int64
+}
+
+func (c dummyCollector) Interval() time.Duration {
+	return time.Second
+}
+
+func (c dummyCollector) GetMetrics() ([]CollectedMetric, error) {
+	if c.value > 0 {
+		quantity := resource.NewQuantity(c.value, resource.DecimalSI)
+		return []CollectedMetric{
+			{
+				Custom: custom_metrics.MetricValue{
+					Value: *quantity,
+				},
+			},
+		}, nil
+	} else {
+		return nil, fmt.Errorf("test error")
+	}
+}
+
+func TestMaxCollector(t *testing.T) {
+	for _, tc := range []struct {
+		name     string
+		values   []int64
+		expected int
+		weight   float64
+	}{
+		{
+			name:     "basic",
+			values:   []int64{100, 10, 9},
+			expected: 100,
+			weight:   1,
+		},
+		{
+			name:     "weighted",
+			values:   []int64{100, 10, 9},
+			expected: 20,
+			weight:   0.2,
+		},
+		{
+			name:     "with error",
+			values:   []int64{-1, 10, 9},
+			expected: 5,
+			weight:   0.5,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			collectors := make([]Collector, len(tc.values))
+			for i, v := range tc.values {
+				collectors[i] = dummyCollector{value: v}
+			}
+			wc := NewMaxWeightedCollector(time.Second, tc.weight, collectors...)
+			metrics, err := wc.GetMetrics()
+			require.NoError(t, err)
+			require.Len(t, metrics, 1)
+			require.EqualValues(t, tc.expected, metrics[0].Custom.Value.Value())
+
+		})
+
+	}
+}