fix golang lint errors in metricsreader test image

test/test_images/metricsreader/metricsreader.go

@@ -22,7 +22,7 @@ import (
 	"encoding/json"
 	"flag"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"log"
 	"net"
 	"net/http"
@@ -35,8 +35,8 @@ import (
 )
 
 const (
-	ACTIVATOR_METRIC_KEY = "activator_tls_connection_count"
-	QUEUE_METRIC_KEY     = "revision_tls_connection_count"
+	ActivatorMetricKey = "activator_tls_connection_count"
+	QueueMetricKey     = "revision_tls_connection_count"
 )
 
 type PostData struct {
@@ -51,12 +51,12 @@ type MetricsClient struct {
 func (mc *MetricsClient) GetMetricsData(source string) (map[string]*io_prometheus_client.MetricFamily, error) {
 	resp, err := mc.Get(fmt.Sprintf("http://%s/metrics", source))
 	if err != nil {
-		return nil, fmt.Errorf("error: couldn't call %s metrics endpoint: %s", source, err)
+		return nil, fmt.Errorf("error: couldn't call %s metrics endpoint: %w", source, err)
 	}
 	defer resp.Body.Close()
-	body, err := ioutil.ReadAll(resp.Body)
+	body, err := io.ReadAll(resp.Body)
 	if err != nil {
-		return nil, fmt.Errorf("error: couldn't read response body from %s metrics endpoint: %s", source, err)
+		return nil, fmt.Errorf("error: couldn't read response body from %s metrics endpoint: %w", source, err)
 	}
 	return parseMetricsData(body)
 }
@@ -91,7 +91,7 @@ func parseMetricsData(d []byte) (map[string]*io_prometheus_client.MetricFamily,
 	var parser expfmt.TextParser
 	mf, err := parser.TextToMetricFamilies(bytes.NewReader(d))
 	if err != nil {
-		return nil, fmt.Errorf("error: couldn't parse metrics output: %s", err)
+		return nil, fmt.Errorf("error: couldn't parse metrics output: %w", err)
 	}
 	return mf, nil
 }
@@ -128,16 +128,16 @@ func getMetrics(w http.ResponseWriter, r *http.Request) {
 			http.Error(w, err.Error(), http.StatusInternalServerError)
 		}
 
-		if m, ok := activatorData[ACTIVATOR_METRIC_KEY]; ok {
-			results[ACTIVATOR_METRIC_KEY] = int(*m.Metric[0].Counter.Value)
+		if m, ok := activatorData[ActivatorMetricKey]; ok {
+			results[ActivatorMetricKey] = int(*m.Metric[0].Counter.Value)
 		} else {
-			results[ACTIVATOR_METRIC_KEY] = 0
+			results[ActivatorMetricKey] = 0
 		}
 
-		if m, ok := queueData[QUEUE_METRIC_KEY]; ok {
-			results[QUEUE_METRIC_KEY] = int(*m.Metric[0].Counter.Value)
+		if m, ok := queueData[QueueMetricKey]; ok {
+			results[QueueMetricKey] = int(*m.Metric[0].Counter.Value)
 		} else {
-			results[QUEUE_METRIC_KEY] = 0
+			results[QueueMetricKey] = 0
 		}
 
 		jsonResponseData, err := json.Marshal(results)