Fix scan type for nullable digests and digest texts (#3993)

Author: fridgepoet

internal/component/database_observability/mysql/collector/locks.go

@@ -144,7 +144,7 @@ func (c *LockCollector) fetchLocks(ctx context.Context) error {
 
 	for rsdl.Next() {
 		var waitingTimerWait, waitingLockTime, blockingTimerWait, blockingLockTime float64
-		var waitingDigest, waitingDigestText, blockingDigest, blockingDigestText string
+		var waitingDigest, waitingDigestText, blockingDigest, blockingDigestText sql.NullString
 
 		err := rsdl.Scan(&waitingTimerWait, &waitingLockTime, &waitingDigest, &waitingDigestText,
 			&blockingTimerWait, &blockingLockTime, &blockingDigest, &blockingDigestText)
@@ -157,10 +157,10 @@ func (c *LockCollector) fetchLocks(ctx context.Context) error {
 		if waitingLockTime > secondsToPicoseconds(c.lockTimeThreshold.Seconds()) {
 			lockMsg := fmt.Sprintf(
 				`waiting_digest="%s" waiting_digest_text="%s" blocking_digest="%s" blocking_digest_text="%s" waiting_timer_wait="%fms" waiting_lock_time="%fms" blocking_timer_wait="%fms" blocking_lock_time="%fms"`,
-				waitingDigest,
-				waitingDigestText,
-				blockingDigest,
-				blockingDigestText,
+				waitingDigest.String,
+				waitingDigestText.String,
+				blockingDigest.String,
+				blockingDigestText.String,
 				picosecondsToMilliseconds(waitingTimerWait),
 				picosecondsToMilliseconds(waitingLockTime),
 				picosecondsToMilliseconds(blockingTimerWait),

internal/component/database_observability/mysql/collector/locks_test.go

@@ -188,6 +188,62 @@ func Test_QueryLocks(t *testing.T) {
 		assert.Equal(t, `level="info" waiting_digest="xyz789" waiting_digest_text="SELECT * FROM orders WHERE user_id = ?" blocking_digest="ghi012" blocking_digest_text="DELETE FROM sessions WHERE expired = ?" waiting_timer_wait="2500.000000ms" waiting_lock_time="2000.000000ms" blocking_timer_wait="3000.000000ms" blocking_lock_time="2700.000000ms"`, lokiEntries[1].Line)
 	})
 
+	t.Run("data lock with null digests and digest texts", func(t *testing.T) {
+		db, mock, err := sqlmock.New(sqlmock.QueryMatcherOption(sqlmock.QueryMatcherEqual))
+		require.NoError(t, err)
+		defer db.Close()
+
+		lokiClient := fake.NewClient(func() {})
+
+		collector, err := NewLock(LockArguments{
+			DB:              db,
+			InstanceKey:     "mysql-db",
+			CollectInterval: time.Second,
+			EntryHandler:    lokiClient,
+			Logger:          log.NewLogfmtLogger(os.Stderr),
+		})
+		require.NoError(t, err)
+		require.NotNil(t, collector)
+
+		mock.ExpectQuery(selectDataLocks).RowsWillBeClosed().WillReturnRows(
+			sqlmock.NewRows(
+				[]string{
+					"waitingTimerWait",
+					"waitingLockTime",
+					"waitingDigest",
+					"waitingDigestText",
+					"blockingTimerWait",
+					"blockingLockTime",
+					"blockingDigest",
+					"blockingDigestText",
+				},
+			).AddRow(
+				1500000000000,
+				1000000000000,
+				nil,
+				nil,
+				2000000000000,
+				1700000000000,
+				nil,
+				nil,
+			),
+		)
+
+		require.NoError(t, collector.Start(t.Context()))
+
+		require.Eventually(t, func() bool {
+			return len(lokiClient.Received()) == 1
+		}, 2*time.Second, 50*time.Millisecond)
+
+		collector.Stop()
+		lokiClient.Stop()
+
+		require.NoError(t, mock.ExpectationsWereMet())
+		lokiEntries := lokiClient.Received()
+		assert.Equal(t, model.LabelSet{"job": database_observability.JobName, "op": OP_DATA_LOCKS, "instance": "mysql-db"}, lokiEntries[0].Labels)
+		assert.Equal(t, `level="info" waiting_digest="" waiting_digest_text="" blocking_digest="" blocking_digest_text="" waiting_timer_wait="1500.000000ms" waiting_lock_time="1000.000000ms" blocking_timer_wait="2000.000000ms" blocking_lock_time="1700.000000ms"`, lokiEntries[0].Line)
+	})
+
 	t.Run("recoverable sql error in selectDataLocks result set", func(t *testing.T) {
 		db, mock, err := sqlmock.New(sqlmock.QueryMatcherOption(sqlmock.QueryMatcherEqual))
 		require.NoError(t, err)