Preinitialize workCancel function in case StopAndCancel called be…

…fore start (#557)

This one's related to #549. Although the most proximate problem in that
repro code is that there was no error check when calling `Start`, it did
reveal a legitimate problem in that the River client will panic in case
`StopAndCancel` is called before `Start` because `workCancel` was never
set.

Here, initialize `workCancel` in the client's constructor. During normal
operation this will be overwritten almost immediately on `Start` as the
client starts up, but in case `Start` was never called or didn't run
successfully, it provides a function for `StopAndCancel` to call so that
it doesn't panic.

Fixes #549.

CHANGELOG.md

@@ -12,6 +12,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - A new `river migrate-list` command is available which lists available migrations and which version a target database is migrated to. [PR #534](https://github.com/riverqueue/river/pull/534).
 - `river version` or `river --version` now prints River version information. [PR #537](https://github.com/riverqueue/river/pull/537).
 
+## Fixed
+
+- Fixed a panic that'd occur if `StopAndCancel` was invoked before a client was started. [PR #557](https://github.com/riverqueue/river/pull/557).
+
 ## [0.11.4] - 2024-08-20
 
 ### Fixed

client.go

@@ -491,6 +491,7 @@ func NewClient[TTx any](driver riverdriver.Driver[TTx], config *Config) (*Client
 		uniqueInserter: baseservice.Init(archetype, &dbunique.UniqueInserter{
 			AdvisoryLockPrefix: config.AdvisoryLockPrefix,
 		}),
+		workCancel: func(cause error) {}, // replaced on start, but here in case StopAndCancel is called before start up
 	}
 	client.queues = &QueueBundle{addProducer: client.addProducer}
 

client_test.go

@@ -1050,18 +1050,6 @@ func Test_Client_StopAndCancel(t *testing.T) {
 
 		client := runNewTestClient(ctx, t, config)
 
-		insertRes, err := client.Insert(ctx, &callbackArgs{}, nil)
-		require.NoError(t, err)
-
-		startedJobID := riversharedtest.WaitOrTimeout(t, jobStartedChan)
-		require.Equal(t, insertRes.Job.ID, startedJobID)
-
-		select {
-		case <-client.Stopped():
-			t.Fatal("expected client to not be stopped yet")
-		default:
-		}
-
 		return client, &testBundle{
 			jobDoneChan:    jobDoneChan,
 			jobStartedChan: jobStartedChan,
@@ -1071,17 +1059,40 @@ func Test_Client_StopAndCancel(t *testing.T) {
 	t.Run("OnItsOwn", func(t *testing.T) {
 		t.Parallel()
 
-		client, _ := setup(t)
+		client, bundle := setup(t)
+
+		startClient(ctx, t, client)
+
+		_, err := client.Insert(ctx, &callbackArgs{}, nil)
+		require.NoError(t, err)
+
+		riversharedtest.WaitOrTimeout(t, bundle.jobStartedChan)
 
 		require.NoError(t, client.StopAndCancel(ctx))
 		riversharedtest.WaitOrTimeout(t, client.Stopped())
 	})
 
+	t.Run("BeforeStart", func(t *testing.T) {
+		t.Parallel()
+
+		client, _ := setup(t)
+
+		require.NoError(t, client.StopAndCancel(ctx))
+		riversharedtest.WaitOrTimeout(t, client.Stopped()) // this works because Stopped is nil
+	})
+
 	t.Run("AfterStop", func(t *testing.T) {
 		t.Parallel()
 
 		client, bundle := setup(t)
 
+		startClient(ctx, t, client)
+
+		_, err := client.Insert(ctx, &callbackArgs{}, nil)
+		require.NoError(t, err)
+
+		riversharedtest.WaitOrTimeout(t, bundle.jobStartedChan)
+
 		go func() {
 			require.NoError(t, client.Stop(ctx))
 		}()