Add GetChange method to tree

commonspace/object/tree/objecttree/historytree.go

@@ -11,6 +11,7 @@ type HistoryTree interface {
 	Root() *Change
 	Heads() []string
 	IterateFrom(id string, convert ChangeConvertFunc, iterate ChangeIterateFunc) error
+	GetChange(string) (*Change, error)
 }
 
 type historyTree struct {

commonspace/object/tree/objecttree/mock_objecttree/mock_objecttree.go

@@ -125,6 +125,21 @@ func (mr *MockObjectTreeMockRecorder) Delete() *gomock.Call {
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Delete", reflect.TypeOf((*MockObjectTree)(nil).Delete))
 }
 
+// GetChange mocks base method.
+func (m *MockObjectTree) GetChange(arg0 string) (*objecttree.Change, error) {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "GetChange", arg0)
+	ret0, _ := ret[0].(*objecttree.Change)
+	ret1, _ := ret[1].(error)
+	return ret0, ret1
+}
+
+// GetChange indicates an expected call of GetChange.
+func (mr *MockObjectTreeMockRecorder) GetChange(arg0 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "GetChange", reflect.TypeOf((*MockObjectTree)(nil).GetChange), arg0)
+}
+
 // HasChanges mocks base method.
 func (m *MockObjectTree) HasChanges(arg0 ...string) bool {
 	m.ctrl.T.Helper()

commonspace/object/tree/objecttree/objecttree.go

@@ -23,6 +23,7 @@ type RWLocker interface {
 var (
 	ErrHasInvalidChanges = errors.New("the change is invalid")
 	ErrNoCommonSnapshot  = errors.New("trees doesn't have a common snapshot")
+	ErrNoChangeInTree    = errors.New("no such change in tree")
 )
 
 type AddResultSummary int
@@ -51,9 +52,11 @@ type ObjectTree interface {
 	UnmarshalledHeader() *Change
 	Heads() []string
 	Root() *Change
-	HasChanges(...string) bool
-	DebugDump(parser DescriptionParser) (string, error)
 
+	HasChanges(...string) bool
+	GetChange(string) (*Change, error)
+
+	DebugDump(parser DescriptionParser) (string, error)
 	IterateRoot(convert ChangeConvertFunc, iterate ChangeIterateFunc) error
 	IterateFrom(id string, convert ChangeConvertFunc, iterate ChangeIterateFunc) error
 
@@ -155,6 +158,13 @@ func (ot *objectTree) Storage() treestorage.TreeStorage {
 	return ot.treeStorage
 }
 
+func (ot *objectTree) GetChange(id string) (*Change, error) {
+	if ch, ok := ot.tree.attached[id]; ok {
+		return ch, nil
+	}
+	return nil, ErrNoChangeInTree
+}
+
 func (ot *objectTree) AddContent(ctx context.Context, content SignableChangeContent) (res AddResult, err error) {
 	payload, err := ot.prepareBuilderContent(content)
 	if err != nil {

commonspace/object/tree/synctree/mock_synctree/mock_synctree.go

@@ -250,6 +250,21 @@ func (mr *MockSyncTreeMockRecorder) Delete() *gomock.Call {
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Delete", reflect.TypeOf((*MockSyncTree)(nil).Delete))
 }
 
+// GetChange mocks base method.
+func (m *MockSyncTree) GetChange(arg0 string) (*objecttree.Change, error) {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "GetChange", arg0)
+	ret0, _ := ret[0].(*objecttree.Change)
+	ret1, _ := ret[1].(error)
+	return ret0, ret1
+}
+
+// GetChange indicates an expected call of GetChange.
+func (mr *MockSyncTreeMockRecorder) GetChange(arg0 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "GetChange", reflect.TypeOf((*MockSyncTree)(nil).GetChange), arg0)
+}
+
 // HandleMessage mocks base method.
 func (m *MockSyncTree) HandleMessage(arg0 context.Context, arg1 string, arg2 *spacesyncproto.ObjectSyncMessage) error {
 	m.ctrl.T.Helper()