watchtower: add FetchSessionCommittedUpdates func to DB

In this commit, a new tower client db function is added that can be used
to fetch all the committed updates for a given session ID. This is done
in preparation for an upcoming commit where the CommittedUpdates will be
removed from the ClientSession struct.

watchtower/wtclient/interface.go

@@ -65,6 +65,11 @@ type DB interface {
 	ListClientSessions(*wtdb.TowerID, ...wtdb.ClientSessionListOption) (
 		map[wtdb.SessionID]*wtdb.ClientSession, error)
 
+	// FetchSessionCommittedUpdates retrieves the current set of un-acked
+	// updates of the given session.
+	FetchSessionCommittedUpdates(id *wtdb.SessionID) (
+		[]wtdb.CommittedUpdate, error)
+
 	// FetchChanSummaries loads a mapping from all registered channels to
 	// their channel summaries.
 	FetchChanSummaries() (wtdb.ChannelSummaries, error)

watchtower/wtdb/client_db.go

@@ -842,6 +842,36 @@ func listTowerSessions(id TowerID, sessionsBkt, towersBkt,
 	return clientSessions, nil
 }
 
+// FetchSessionCommittedUpdates retrieves the current set of un-acked updates
+// of the given session.
+func (c *ClientDB) FetchSessionCommittedUpdates(id *SessionID) (
+	[]CommittedUpdate, error) {
+
+	var committedUpdates []CommittedUpdate
+	err := kvdb.View(c.db, func(tx kvdb.RTx) error {
+		sessions := tx.ReadBucket(cSessionBkt)
+		if sessions == nil {
+			return ErrUninitializedDB
+		}
+
+		sessionBkt := sessions.NestedReadBucket(id[:])
+		if sessionBkt == nil {
+			return ErrClientSessionNotFound
+		}
+
+		var err error
+		committedUpdates, err = getClientSessionCommits(
+			sessionBkt, nil, nil,
+		)
+		return err
+	}, func() {})
+	if err != nil {
+		return nil, err
+	}
+
+	return committedUpdates, nil
+}
+
 // FetchChanSummaries loads a mapping from all registered channels to their
 // channel summaries.
 func (c *ClientDB) FetchChanSummaries() (ChannelSummaries, error) {

watchtower/wtdb/client_db_test.go

@@ -207,6 +207,20 @@ func (h *clientDBHarness) newTower() *wtdb.Tower {
 	}, nil)
 }
 
+func (h *clientDBHarness) fetchSessionCommittedUpdates(id *wtdb.SessionID,
+	expErr error) []wtdb.CommittedUpdate {
+
+	h.t.Helper()
+
+	updates, err := h.db.FetchSessionCommittedUpdates(id)
+	if err != expErr {
+		h.t.Fatalf("expected fetch session committed updates error: "+
+			"%v, got: %v", expErr, err)
+	}
+
+	return updates
+}
+
 // testCreateClientSession asserts various conditions regarding the creation of
 // a new ClientSession. The test asserts:
 //   - client sessions can only be created if a session key index is reserved.
@@ -506,6 +520,9 @@ func testCommitUpdate(h *clientDBHarness) {
 	// session, which should fail.
 	update1 := randCommittedUpdate(h.t, 1)
 	h.commitUpdate(&session.ID, update1, wtdb.ErrClientSessionNotFound)
+	h.fetchSessionCommittedUpdates(
+		&session.ID, wtdb.ErrClientSessionNotFound,
+	)
 
 	// Reserve a session key index and insert the session.
 	session.KeyIndex = h.nextKeyIndex(session.TowerID, blobType)
@@ -665,14 +682,14 @@ func (h *clientDBHarness) assertUpdates(id wtdb.SessionID,
 	_ = h.listSessions(
 		nil, wtdb.WithPerAckedUpdate(perAckedUpdate(ackedUpdates)),
 	)
-	dbSession := h.listSessions(nil)[id]
-	checkCommittedUpdates(h.t, dbSession, expectedPending)
+	committedUpates := h.fetchSessionCommittedUpdates(&id, nil)
+	checkCommittedUpdates(h.t, committedUpates, expectedPending)
 	checkAckedUpdates(h.t, ackedUpdates, expectedAcked)
 }
 
 // checkCommittedUpdates asserts that the CommittedUpdates on session match the
 // expUpdates provided.
-func checkCommittedUpdates(t *testing.T, session *wtdb.ClientSession,
+func checkCommittedUpdates(t *testing.T, actualUpdates,
 	expUpdates []wtdb.CommittedUpdate) {
 
 	t.Helper()
@@ -684,7 +701,7 @@ func checkCommittedUpdates(t *testing.T, session *wtdb.ClientSession,
 		expUpdates = make([]wtdb.CommittedUpdate, 0)
 	}
 
-	require.Equal(t, expUpdates, session.CommittedUpdates)
+	require.Equal(t, expUpdates, actualUpdates)
 }
 
 // checkAckedUpdates asserts that the AckedUpdates on a session match the

watchtower/wtmock/client_db.go

@@ -242,6 +242,22 @@ func (m *ClientDB) listClientSessions(tower *wtdb.TowerID,
 	return sessions, nil
 }
 
+// FetchSessionCommittedUpdates retrieves the current set of un-acked updates
+// of the given session.
+func (m *ClientDB) FetchSessionCommittedUpdates(id *wtdb.SessionID) (
+	[]wtdb.CommittedUpdate, error) {
+
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	sess, ok := m.activeSessions[*id]
+	if !ok {
+		return nil, wtdb.ErrClientSessionNotFound
+	}
+
+	return sess.CommittedUpdates, nil
+}
+
 // CreateClientSession records a newly negotiated client session in the set of
 // active sessions. The session can be identified by its SessionID.
 func (m *ClientDB) CreateClientSession(session *wtdb.ClientSession) error {