prom: Fix leak when a call fails with the prometheus endpoint (#2456)

Author: vadmeste

restapi/admin_info.go

@@ -25,6 +25,7 @@ import (
 	"net/url"
 	"regexp"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/go-openapi/runtime/middleware"
@@ -977,20 +978,28 @@ func getUsageWidgetsForDeployment(ctx context.Context, prometheusURL string, mAd
 
 func unmarshalPrometheus(ctx context.Context, endpoint string, data interface{}) bool {
 	httpClnt := GetConsoleHTTPClient(endpoint)
-	resp, err := httpClnt.Get(endpoint)
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
+	if err != nil {
+		ErrorWithContext(ctx, fmt.Errorf("Unable to create the request to fetch labels from prometheus: %w", err))
+		return true
+	}
+
+	resp, err := httpClnt.Do(req)
 	if err != nil {
-		ErrorWithContext(ctx, fmt.Errorf("Unable to fetch labels from prometheus (%s)", resp.Status))
+		ErrorWithContext(ctx, fmt.Errorf("Unable to fetch labels from prometheus: %w", err))
 		return true
 	}
+
 	defer resp.Body.Close()
 
-	if resp.StatusCode != 200 {
-		ErrorWithContext(ctx, fmt.Errorf("Unexpected errors from prometheus (%s)", resp.Status))
+	if resp.StatusCode != http.StatusOK {
+		ErrorWithContext(ctx, fmt.Errorf("Unexpected status code from prometheus (%s)", resp.Status))
 		return true
 	}
 
 	if err = json.NewDecoder(resp.Body).Decode(data); err != nil {
-		ErrorWithContext(ctx, fmt.Errorf("Unexpected errors from prometheus (%s)", resp.Status))
+		ErrorWithContext(ctx, fmt.Errorf("Unexpected error from prometheus: %w", err))
 		return true
 	}
 
@@ -1081,10 +1090,17 @@ LabelsWaitLoop:
 			continue
 		}
 
-		targetResults := make(chan *models.ResultTarget)
+		var (
+			wg            sync.WaitGroup
+			targetResults = make([]*models.ResultTarget, len(m.Targets))
+		)
+
 		// for each target we will launch another goroutine to fetch the values
-		for _, target := range m.Targets {
-			go func(target Target, inStep *int32, inStart *int64, inEnd *int64) {
+		for idx, target := range m.Targets {
+			wg.Add(1)
+			go func(idx int, target Target, inStep *int32, inStart *int64, inEnd *int64) {
+				defer wg.Done()
+
 				apiType := "query_range"
 				now := time.Now()
 
@@ -1145,10 +1161,12 @@ LabelsWaitLoop:
 					})
 				}
 
-				targetResults <- &targetResult
-			}(target, step, start, end)
+				targetResults[idx] = &targetResult
+			}(idx, target, step, start, end)
 		}
 
+		wg.Wait()
+
 		wdgtResult := models.WidgetDetails{
 			ID:    m.ID,
 			Title: m.Title,
@@ -1161,15 +1179,10 @@ LabelsWaitLoop:
 				},
 			}
 		}
-		// count how many targets we have received
-		targetsReceived := 0
-
-		for res := range targetResults {
-			wdgtResult.Targets = append(wdgtResult.Targets, res)
-			targetsReceived++
-			// upon receiving the total number of targets needed, we can close the channel to not lock the goroutine
-			if targetsReceived >= len(m.Targets) {
-				close(targetResults)
+
+		for _, res := range targetResults {
+			if res != nil {
+				wdgtResult.Targets = append(wdgtResult.Targets, res)
 			}
 		}
 		return &wdgtResult, nil