Handle direction: up

internal/mscs/msc2836/msc2836.go

@@ -322,10 +322,6 @@ func (rc *reqCtx) includeChildren(db Database, parentID string, limit int, recen
 func walkThread(
 	ctx context.Context, db Database, rc *reqCtx, included map[string]bool, limit int,
 ) ([]*gomatrixserverlib.HeaderedEvent, bool) {
-	if rc.req.Direction != "down" {
-		util.GetLogger(ctx).Error("not implemented: direction=up")
-		return nil, false
-	}
 	var result []*gomatrixserverlib.HeaderedEvent
 	eventWalker := walker{
 		ctx: ctx,
@@ -620,9 +616,9 @@ type walker struct {
 
 // WalkFrom the event ID given
 func (w *walker) WalkFrom(eventID string) (limited bool, err error) {
-	children, err := w.db.ChildrenForParent(w.ctx, eventID, constRelType, w.req.RecentFirst)
+	children, err := w.childrenForParent(eventID)
 	if err != nil {
-		util.GetLogger(w.ctx).WithError(err).Error("WalkFrom() ChildrenForParent failed, cannot walk")
+		util.GetLogger(w.ctx).WithError(err).Error("WalkFrom() childrenForParent failed, cannot walk")
 		return false, err
 	}
 	var next *walkInfo
@@ -634,9 +630,9 @@ func (w *walker) WalkFrom(eventID string) (limited bool, err error) {
 			return true, nil
 		}
 		// find the children's children
-		children, err = w.db.ChildrenForParent(w.ctx, next.EventID, constRelType, w.req.RecentFirst)
+		children, err = w.childrenForParent(next.EventID)
 		if err != nil {
-			util.GetLogger(w.ctx).WithError(err).Error("WalkFrom() ChildrenForParent failed, cannot walk")
+			util.GetLogger(w.ctx).WithError(err).Error("WalkFrom() childrenForParent failed, cannot walk")
 			return false, err
 		}
 		toWalk = w.addChildren(toWalk, children, next.Depth+1)
@@ -695,3 +691,20 @@ func (w *walker) nextChild(toWalk []walkInfo) (*walkInfo, []walkInfo) {
 	child, toWalk = toWalk[0], toWalk[1:]
 	return &child, toWalk
 }
+
+// childrenForParent returns the children events for this event ID, honouring the direction: up|down flags
+// meaning this can actually be returning the parent for the event instead of the children.
+func (w *walker) childrenForParent(eventID string) ([]eventInfo, error) {
+	if w.req.Direction == "down" {
+		return w.db.ChildrenForParent(w.ctx, eventID, constRelType, w.req.RecentFirst)
+	}
+	// find the event to pull out the parent
+	ei, err := w.db.ParentForChild(w.ctx, eventID, constRelType)
+	if err != nil {
+		return nil, err
+	}
+	if ei != nil {
+		return []eventInfo{*ei}, nil
+	}
+	return nil, nil
+}

internal/mscs/msc2836/msc2836_test.go

@@ -349,6 +349,24 @@ func TestMSC2836(t *testing.T) {
 		}))
 		assertContains(t, body, []string{eventB.EventID(), eventC.EventID(), eventD.EventID(), eventE.EventID(), eventF.EventID(), eventG.EventID(), eventH.EventID()})
 	})
+	t.Run("can navigate up the graph with direction: up", func(t *testing.T) {
+		//   A4
+		//   |
+		//   B3
+		//  / \
+		// C   D2
+		//    /| \
+		//   E F1 G
+		//   |
+		//   H
+		body := postRelationships(t, 200, "alice", newReq(t, map[string]interface{}{
+			"event_id":     eventF.EventID(),
+			"recent_first": false,
+			"depth_first":  true,
+			"direction":    "up",
+		}))
+		assertContains(t, body, []string{eventF.EventID(), eventD.EventID(), eventB.EventID(), eventA.EventID()})
+	})
 }
 
 // TODO: TestMSC2836TerminatesLoops (short and long)

internal/mscs/msc2836/storage.go

@@ -25,6 +25,10 @@ type Database interface {
 	// provided `relType`. The returned slice is sorted by origin_server_ts according to whether
 	// `recentFirst` is true or false.
 	ChildrenForParent(ctx context.Context, eventID, relType string, recentFirst bool) ([]eventInfo, error)
+	// ParentForChild returns the parent event for the given child `eventID`. The eventInfo should be nil if
+	// there is no parent for this child event, with no error. The parent eventInfo can be missing the
+	// timestamp if the event is not known to the server.
+	ParentForChild(ctx context.Context, eventID, relType string) (*eventInfo, error)
 }
 
 type DB struct {
@@ -34,6 +38,7 @@ type DB struct {
 	insertNodeStmt                         *sql.Stmt
 	selectChildrenForParentOldestFirstStmt *sql.Stmt
 	selectChildrenForParentRecentFirstStmt *sql.Stmt
+	selectParentForChildStmt               *sql.Stmt
 }
 
 // NewDatabase loads the database for msc2836
@@ -93,6 +98,11 @@ func newPostgresDatabase(dbOpts *config.DatabaseOptions) (Database, error) {
 	if d.selectChildrenForParentRecentFirstStmt, err = d.db.Prepare(selectChildrenQuery + "DESC"); err != nil {
 		return nil, err
 	}
+	if d.selectParentForChildStmt, err = d.db.Prepare(`
+		SELECT parent_event_id, parent_room_id FROM msc2836_edges WHERE child_event_id = $1 AND rel_type = $2
+	`); err != nil {
+		return nil, err
+	}
 	return &d, err
 }
 
@@ -145,6 +155,11 @@ func newSQLiteDatabase(dbOpts *config.DatabaseOptions) (Database, error) {
 	if d.selectChildrenForParentRecentFirstStmt, err = d.db.Prepare(selectChildrenQuery + "DESC"); err != nil {
 		return nil, err
 	}
+	if d.selectParentForChildStmt, err = d.db.Prepare(`
+		SELECT parent_event_id, parent_room_id FROM msc2836_edges WHERE child_event_id = $1 AND rel_type = $2
+	`); err != nil {
+		return nil, err
+	}
 	return &d, nil
 }
 
@@ -191,6 +206,17 @@ func (p *DB) ChildrenForParent(ctx context.Context, eventID, relType string, rec
 	return children, nil
 }
 
+func (p *DB) ParentForChild(ctx context.Context, eventID, relType string) (*eventInfo, error) {
+	var ei eventInfo
+	err := p.selectParentForChildStmt.QueryRowContext(ctx, eventID, relType).Scan(&ei.EventID, &ei.RoomID)
+	if err == sql.ErrNoRows {
+		return nil, nil
+	} else if err != nil {
+		return nil, err
+	}
+	return &ei, nil
+}
+
 func parentChildEventIDs(ev *gomatrixserverlib.HeaderedEvent) (parent, child, relType string) {
 	if ev == nil {
 		return