[receiver/dockerstats] Fix leaking goroutines (open-telemetry#31668)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
The dockerstats receiver starts a go routine that isn't shutdown until
its context is done. This adds a shutdown method to trigger the end of
this running goroutine in a timely manner. This also enables goleak to
check for leaking goroutines on this receiver.

**Link to tracking Issue:** <Issue number if applicable>
open-telemetry#30438

**Testing:** <Describe what testing was performed and which tests were
added.>
All existing and added checks are passing.

.chloggen/goleak_dockerstatsreceiver.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: dockerstatsreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add shutdown method to fix leaking goroutines
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [30438]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

receiver/dockerstatsreceiver/factory.go

@@ -52,7 +52,7 @@ func createMetricsReceiver(
 	dockerConfig := config.(*Config)
 	dsr := newMetricsReceiver(params, dockerConfig)
 
-	scrp, err := scraperhelper.NewScraper(metadata.Type.String(), dsr.scrapeV2, scraperhelper.WithStart(dsr.start))
+	scrp, err := scraperhelper.NewScraper(metadata.Type.String(), dsr.scrapeV2, scraperhelper.WithStart(dsr.start), scraperhelper.WithShutdown(dsr.shutdown))
 	if err != nil {
 		return nil, err
 	}

receiver/dockerstatsreceiver/package_test.go

@@ -0,0 +1,14 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package dockerstatsreceiver
+
+import (
+	"testing"
+
+	"go.uber.org/goleak"
+)
+
+func TestMain(m *testing.M) {
+	goleak.VerifyTestMain(m)
+}

receiver/dockerstatsreceiver/receiver.go

@@ -40,6 +40,7 @@ type metricsReceiver struct {
 	settings receiver.CreateSettings
 	client   *docker.Client
 	mb       *metadata.MetricsBuilder
+	cancel   context.CancelFunc
 }
 
 func newMetricsReceiver(set receiver.CreateSettings, config *Config) *metricsReceiver {
@@ -65,7 +66,17 @@ func (r *metricsReceiver) start(ctx context.Context, _ component.Host) error {
 		return err
 	}
 
-	go r.client.ContainerEventLoop(ctx)
+	cctx, cancel := context.WithCancel(ctx)
+	r.cancel = cancel
+
+	go r.client.ContainerEventLoop(cctx)
+	return nil
+}
+
+func (r *metricsReceiver) shutdown(context.Context) error {
+	if r.cancel != nil {
+		r.cancel()
+	}
 	return nil
 }
 

receiver/dockerstatsreceiver/receiver_test.go

@@ -301,6 +301,7 @@ func TestScrapeV2(t *testing.T) {
 				receivertest.NewNopCreateSettings(), tc.cfgBuilder.withEndpoint(mockDockerEngine.URL).build())
 			err := receiver.start(context.Background(), componenttest.NewNopHost())
 			require.NoError(t, err)
+			defer func() { require.NoError(t, receiver.shutdown(context.Background())) }()
 
 			actualMetrics, err := receiver.scrapeV2(context.Background())
 			require.NoError(t, err)