consumer: return descriptive error when a nil state is passed into NewJSONFileStore

consumer/shard.go

@@ -2,6 +2,7 @@ package consumer
 
 import (
 	"context"
+	"reflect"
 	"sync"
 	"time"
 
@@ -244,7 +245,7 @@ func servePrimary(s *shard) (err error) {
 func waitAndTearDown(s *shard, done func()) {
 	s.wg.Wait()
 
-	if s.store != nil {
+	if s.store != nil && !reflect.ValueOf(s.store).IsNil() {
 		s.store.Destroy()
 	}
 	done()

consumer/shard_test.go

@@ -156,6 +156,19 @@ func TestShardAppNewStoreError(t *testing.T) {
 	tf.allocateShard(makeShard(shardA)) // Cleanup.
 }
 
+func TestShardAppNilJSONStore(t *testing.T) {
+	var tf, cleanup = newTestFixture(t)
+	defer cleanup()
+
+	tf.app.nilStore = true
+	tf.allocateShard(makeShard(shardA), localID)
+
+	assert.Equal(t, "completeRecovery: app.NewStore: state must not be nil",
+		expectStatusCode(t, tf.state, pc.ReplicaStatus_FAILED).Errors[0])
+
+	tf.allocateShard(makeShard(shardA)) // Cleanup.
+}
+
 func TestShardAppNewMessageFails(t *testing.T) {
 	var tf, cleanup = newTestFixture(t)
 	defer cleanup()

consumer/store_json_file.go

@@ -31,8 +31,11 @@ var _ Store = &JSONFileStore{} // JSONFileStore is-a Store.
 
 // NewJSONFileStore returns a new JSONFileStore. |state| is the runtime instance
 // of the Store's state, which is decoded into, encoded from, and retained
-// as JSONFileState.State.
+// as JSONFileState.State. |state| must not be nil.
 func NewJSONFileStore(rec *recoverylog.Recorder, state interface{}) (*JSONFileStore, error) {
+	if state == nil {
+		return nil, errors.New("state must not be nil")
+	}
 	var store = &JSONFileStore{
 		State:    state,
 		fs:       recoverylog.RecordedAferoFS{Recorder: rec, Fs: afero.NewOsFs()},

consumer/test_support_test.go

@@ -83,6 +83,7 @@ type testApplication struct {
 	finalizeErr          error         // Error returned by Application.FinalizeTxn().
 	startCommitErr       error         // Error returned by Store.StartCommit().
 	restoreCheckpointErr error         // Error returned by Store.RestoreCheckpoint().
+	nilStore             bool          // Whether the application initializes its store in Application.NewStore().
 	finishedCh           chan OpFuture // Signaled on FinishedTxn().
 	db                   *sql.DB       // "Remote" sqlite database.
 }
@@ -114,6 +115,8 @@ func (a *testApplication) NewStore(shard Shard, rec *recoverylog.Recorder) (Stor
 		return &errStore{app: a}, nil
 	} else if rec == nil {
 		return NewSQLStore(a.db), nil
+	} else if a.nilStore {
+		return NewJSONFileStore(rec, nil)
 	} else {
 		var state = make(map[string]string)
 		return NewJSONFileStore(rec, &state)