Return empty list instead of null for new UI-auth sessions (#406)

fixes #399

Signed-off-by: Anant Prakash <anantprakashjsr@gmail.com>

src/github.com/matrix-org/dendrite/clientapi/routing/register.go

@@ -50,9 +50,35 @@ const (
 	sessionIDLength   = 24
 )
 
+// sessionsDict keeps track of completed auth stages for each session.
+type sessionsDict struct {
+	sessions map[string][]authtypes.LoginType
+}
+
+// GetCompletedStages returns the completed stages for a session.
+func (d sessionsDict) GetCompletedStages(sessionID string) []authtypes.LoginType {
+	if completedStages, ok := d.sessions[sessionID]; ok {
+		return completedStages
+	}
+	// Ensure that a empty slice is returned and not nil. See #399.
+	return make([]authtypes.LoginType, 0)
+}
+
+// AAddCompletedStage records that a session has completed an auth stage.
+func (d *sessionsDict) AddCompletedStage(sessionID string, stage authtypes.LoginType) {
+	d.sessions[sessionID] = append(d.GetCompletedStages(sessionID), stage)
+}
+
+func newSessionsDict() *sessionsDict {
+	return &sessionsDict{
+		sessions: make(map[string][]authtypes.LoginType),
+	}
+}
+
 var (
 	// TODO: Remove old sessions. Need to do so on a session-specific timeout.
-	sessions           = make(map[string][]authtypes.LoginType) // Sessions and completed flow stages
+	// sessions stores the completed flow stages for all sessions. Referenced using their sessionID.
+	sessions           = newSessionsDict()
 	validUsernameRegex = regexp.MustCompile(`^[0-9a-z_\-./]+$`)
 )
 
@@ -112,7 +138,7 @@ func newUserInteractiveResponse(
 	params map[string]interface{},
 ) userInteractiveResponse {
 	return userInteractiveResponse{
-		fs, sessions[sessionID], params, sessionID,
+		fs, sessions.GetCompletedStages(sessionID), params, sessionID,
 	}
 }
 
@@ -433,7 +459,7 @@ func handleRegistrationFlow(
 		}
 
 		// Add Recaptcha to the list of completed registration stages
-		sessions[sessionID] = append(sessions[sessionID], authtypes.LoginTypeRecaptcha)
+		sessions.AddCompletedStage(sessionID, authtypes.LoginTypeRecaptcha)
 
 	case authtypes.LoginTypeSharedSecret:
 		// Check shared secret against config
@@ -446,7 +472,7 @@ func handleRegistrationFlow(
 		}
 
 		// Add SharedSecret to the list of completed registration stages
-		sessions[sessionID] = append(sessions[sessionID], authtypes.LoginTypeSharedSecret)
+		sessions.AddCompletedStage(sessionID, authtypes.LoginTypeSharedSecret)
 
 	case authtypes.LoginTypeApplicationService:
 		// Check Application Service register user request is valid.
@@ -466,7 +492,7 @@ func handleRegistrationFlow(
 	case authtypes.LoginTypeDummy:
 		// there is nothing to do
 		// Add Dummy to the list of completed registration stages
-		sessions[sessionID] = append(sessions[sessionID], authtypes.LoginTypeDummy)
+		sessions.AddCompletedStage(sessionID, authtypes.LoginTypeDummy)
 
 	default:
 		return util.JSONResponse{
@@ -478,7 +504,8 @@ func handleRegistrationFlow(
 	// Check if the user's registration flow has been completed successfully
 	// A response with current registration flow and remaining available methods
 	// will be returned if a flow has not been successfully completed yet
-	return checkAndCompleteFlow(sessions[sessionID], req, r, sessionID, cfg, accountDB, deviceDB)
+	return checkAndCompleteFlow(sessions.GetCompletedStages(sessionID),
+		req, r, sessionID, cfg, accountDB, deviceDB)
 }
 
 // checkAndCompleteFlow checks if a given registration flow is completed given

src/github.com/matrix-org/dendrite/clientapi/routing/register_test.go

@@ -132,3 +132,16 @@ func TestFlowCheckingExtraneousIncorrectInput(t *testing.T) {
 		t.Error("Incorrect registration flow verification: ", testFlow, ", from allowed flows: ", allowedFlows, ". Should be false.")
 	}
 }
+
+// Completed flows stages should always be a valid slice header.
+// TestEmptyCompletedFlows checks that sessionsDict returns a slice & not nil.
+func TestEmptyCompletedFlows(t *testing.T) {
+	fakeEmptySessions := newSessionsDict()
+	fakeSessionID := "aRandomSessionIDWhichDoesNotExist"
+	ret := fakeEmptySessions.GetCompletedStages(fakeSessionID)
+
+	// check for []
+	if ret == nil || len(ret) != 0 {
+		t.Error("Empty Completed Flow Stages should be a empty slice: returned ", ret, ". Should be []")
+	}
+}