watchtower/wtdb: add bolt db impl of Queue

This commit adds a new generic DiskQueueDB type which is an
bbolt implementation of the Queue interface.

watchtower/wtdb/queue_test.go

@@ -0,0 +1,110 @@
+package wtdb_test
+
+import (
+	"testing"
+
+	"github.com/lightningnetwork/lnd/kvdb"
+	"github.com/lightningnetwork/lnd/watchtower/wtdb"
+	"github.com/stretchr/testify/require"
+)
+
+// TestDiskQueue ensures that the ClientDBs disk queue methods behave as is
+// expected of a queue.
+func TestDiskQueue(t *testing.T) {
+	t.Parallel()
+
+	// Set up a temporary bolt backend.
+	dbCfg := &kvdb.BoltConfig{DBTimeout: kvdb.DefaultDBTimeout}
+	bdb, err := wtdb.NewBoltBackendCreator(
+		true, t.TempDir(), "wtclient.db",
+	)(dbCfg)
+	require.NoError(t, err)
+
+	// Construct the ClientDB.
+	db, err := wtdb.OpenClientDB(bdb)
+	require.NoError(t, err)
+	t.Cleanup(func() {
+		err = db.Close()
+		require.NoError(t, err)
+	})
+
+	namespace := []byte("test-namespace")
+	queue := db.GetDBQueue(namespace)
+
+	addTasksToTail := func(tasks ...*wtdb.BackupID) {
+		err := queue.Push(tasks...)
+		require.NoError(t, err)
+	}
+
+	addTasksToHead := func(tasks ...*wtdb.BackupID) {
+		err := queue.PushHead(tasks...)
+		require.NoError(t, err)
+	}
+
+	assertNumTasks := func(expNum int) {
+		num, err := queue.Len()
+		require.NoError(t, err)
+		require.EqualValues(t, expNum, num)
+	}
+
+	popAndAssert := func(expTasks ...*wtdb.BackupID) {
+		tasks, err := queue.PopUpTo(len(expTasks))
+		require.NoError(t, err)
+		require.EqualValues(t, expTasks, tasks)
+	}
+
+	// Create a few tasks that we use throughout the test.
+	task1 := &wtdb.BackupID{CommitHeight: 1}
+	task2 := &wtdb.BackupID{CommitHeight: 2}
+	task3 := &wtdb.BackupID{CommitHeight: 3}
+	task4 := &wtdb.BackupID{CommitHeight: 4}
+	task5 := &wtdb.BackupID{CommitHeight: 5}
+	task6 := &wtdb.BackupID{CommitHeight: 6}
+
+	// Namespace 1 should initially have no items.
+	assertNumTasks(0)
+
+	// Now add a few items to the tail of the queue.
+	addTasksToTail(task1, task2)
+
+	// Check that the number of tasks is now two.
+	assertNumTasks(2)
+
+	// Pop a task, check that it is task 1 and assert that the number of
+	// items left is now 1.
+	popAndAssert(task1)
+	assertNumTasks(1)
+
+	// Pop a task, check that it is task 2 and assert that the number of
+	// items left is now 0.
+	popAndAssert(task2)
+	assertNumTasks(0)
+
+	// Once again add a few tasks.
+	addTasksToTail(task3, task4)
+
+	// Now push some tasks to the head of the queue.
+	addTasksToHead(task6, task5)
+
+	// Ensure that both the disk queue lengths are added together when
+	// querying the length of the queue.
+	assertNumTasks(4)
+
+	// Ensure that the order that the tasks are popped is correct.
+	popAndAssert(task6, task5, task3, task4)
+
+	// We also want to test that the head queue works as expected and that.
+	// To do this, we first push 4, 5 and 6 to the queue.
+	addTasksToTail(task4, task5, task6)
+
+	// Now we push 1, 2 and 3 to the head.
+	addTasksToHead(task1, task2, task3)
+
+	// Now, only pop item 1 from the queue and then re-add it to the head.
+	popAndAssert(task1)
+	addTasksToHead(task1)
+
+	// This should not have changed the order of the tasks, they should
+	// still appear in the correct order.
+	popAndAssert(task1, task2, task3, task4, task5, task6)
+}