ref(replay): Make Session a POJO (#6417)

Author: mydea

packages/replay/MIGRATION.md

@@ -57,3 +57,8 @@ If you only imported from `@sentry/replay`, this will not affect you.
 
 It is highly unlikely to affect anybody, but the type `IEventBuffer` was renamed to `EventBuffer` for consistency.
 Unless you manually imported this and used it somewhere in your codebase, this will not affect you.
+
+## Session object is now a plain object (https://github.com/getsentry/sentry-javascript/pull/6417)
+
+The `Session` object exported from Replay is now a plain object, instead of a class.
+This should not affect you unless you specifically accessed this class & did custom things with it.

packages/replay/src/session/Session.ts

@@ -1,11 +1,10 @@
 import { uuid4 } from '@sentry/utils';
 
-import { SampleRates } from '../types';
 import { isSampled } from '../util/isSampled';
 
 type Sampled = false | 'session' | 'error';
 
-interface SessionObject {
+export interface Session {
   id: string;
 
   /**
@@ -24,59 +23,41 @@ interface SessionObject {
   segmentId: number;
 
   /**
-   * Is the session sampled? `null` if the sampled, otherwise, `session` or `error`
+   * The ID of the previous session.
+   * If this is empty, there was no previous session.
    */
-  sampled: Sampled;
-}
-
-export class Session {
-  /**
-   * Session ID
-   */
-  public readonly id: string;
-
-  /**
-   * Start time of current session
-   */
-  public started: number;
-
-  /**
-   * Last known activity of the session
-   */
-  public lastActivity: number;
-
-  /**
-   * Sequence ID specific to replay updates
-   */
-  public segmentId: number;
+  previousSessionId?: string;
 
   /**
-   * Previous session ID
+   * Is the session sampled? `false` if not sampled, otherwise, `session` or `error`
    */
-  public previousSessionId: string | undefined;
-
-  /**
-   * Is the Session sampled?
-   */
-  public readonly sampled: Sampled;
+  sampled: Sampled;
+}
 
-  public constructor(session: Partial<SessionObject> = {}, { sessionSampleRate, errorSampleRate }: SampleRates) {
-    const now = new Date().getTime();
-    this.id = session.id || uuid4();
-    this.started = session.started ?? now;
-    this.lastActivity = session.lastActivity ?? now;
-    this.segmentId = session.segmentId ?? 0;
-    this.sampled =
-      session.sampled ?? (isSampled(sessionSampleRate) ? 'session' : isSampled(errorSampleRate) ? 'error' : false);
-  }
+/**
+ * Get a session with defaults & applied sampling.
+ */
+export function makeSession(session: Partial<Session> & { sampled: Sampled }): Session {
+  const now = new Date().getTime();
+  const id = session.id || uuid4();
+  // Note that this means we cannot set a started/lastActivity of `0`, but this should not be relevant outside of tests.
+  const started = session.started || now;
+  const lastActivity = session.lastActivity || now;
+  const segmentId = session.segmentId || 0;
+  const sampled = session.sampled;
+
+  return {
+    id,
+    started,
+    lastActivity,
+    segmentId,
+    sampled,
+  };
+}
 
-  toJSON(): SessionObject {
-    return {
-      id: this.id,
-      started: this.started,
-      lastActivity: this.lastActivity,
-      segmentId: this.segmentId,
-      sampled: this.sampled,
-    } as SessionObject;
-  }
+/**
+ * Get the sampled status for a session based on sample rates & current sampled status.
+ */
+export function getSessionSampleType(sessionSampleRate: number, errorSampleRate: number): Sampled {
+  return isSampled(sessionSampleRate) ? 'session' : isSampled(errorSampleRate) ? 'error' : false;
 }

packages/replay/src/session/createSession.ts

@@ -2,17 +2,17 @@ import { logger } from '@sentry/utils';
 
 import { SessionOptions } from '../types';
 import { saveSession } from './saveSession';
-import { Session } from './Session';
+import { getSessionSampleType, makeSession, Session } from './Session';
 
 /**
  * Create a new session, which in its current implementation is a Sentry event
  * that all replays will be saved to as attachments. Currently, we only expect
  * one of these Sentry events per "replay session".
  */
 export function createSession({ sessionSampleRate, errorSampleRate, stickySession = false }: SessionOptions): Session {
-  const session = new Session(undefined, {
-    errorSampleRate,
-    sessionSampleRate,
+  const sampled = getSessionSampleType(sessionSampleRate, errorSampleRate);
+  const session = makeSession({
+    sampled,
   });
 
   __DEBUG_BUILD__ && logger.log(`[Replay] Creating new session: ${session.id}`);

packages/replay/src/session/fetchSession.ts

@@ -1,11 +1,10 @@
 import { REPLAY_SESSION_KEY, WINDOW } from '../constants';
-import { SampleRates } from '../types';
-import { Session } from './Session';
+import { makeSession, Session } from './Session';
 
 /**
  * Fetches a session from storage
  */
-export function fetchSession({ sessionSampleRate, errorSampleRate }: SampleRates): Session | null {
+export function fetchSession(): Session | null {
   const hasSessionStorage = 'sessionStorage' in WINDOW;
 
   if (!hasSessionStorage) {
@@ -20,9 +19,9 @@ export function fetchSession({ sessionSampleRate, errorSampleRate }: SampleRates
       return null;
     }
 
-    const sessionObj = JSON.parse(sessionStringFromStorage);
+    const sessionObj = JSON.parse(sessionStringFromStorage) as Session;
 
-    return new Session(sessionObj, { sessionSampleRate, errorSampleRate });
+    return makeSession(sessionObj);
   } catch {
     return null;
   }

packages/replay/src/session/getSession.ts

@@ -29,7 +29,7 @@ export function getSession({
   errorSampleRate,
 }: GetSessionParams): { type: 'new' | 'saved'; session: Session } {
   // If session exists and is passed, use it instead of always hitting session storage
-  const session = currentSession || (stickySession && fetchSession({ sessionSampleRate, errorSampleRate }));
+  const session = currentSession || (stickySession && fetchSession());
 
   if (session) {
     // If there is a session, check if it is valid (e.g. "last activity" time

packages/replay/test/unit/session/Session.test.ts

@@ -26,7 +26,7 @@ jest.mock('@sentry/utils', () => {
 import * as Sentry from '@sentry/browser';
 
 import { WINDOW } from '../../../src/constants';
-import { Session } from '../../../src/session/Session';
+import { getSessionSampleType, makeSession } from '../../../src/session/Session';
 
 type CaptureEventMockType = jest.MockedFunction<typeof Sentry.captureEvent>;
 
@@ -39,42 +39,33 @@ afterEach(() => {
 });
 
 it('does not sample', function () {
-  const newSession = new Session(undefined, {
-    sessionSampleRate: 0.0,
-    errorSampleRate: 0.0,
+  const newSession = makeSession({
+    sampled: getSessionSampleType(0, 0),
   });
 
   expect(newSession.sampled).toBe(false);
 });
 
 it('samples using `sessionSampleRate`', function () {
-  const newSession = new Session(undefined, {
-    sessionSampleRate: 1.0,
-    errorSampleRate: 0.0,
+  const newSession = makeSession({
+    sampled: getSessionSampleType(1.0, 0),
   });
 
   expect(newSession.sampled).toBe('session');
 });
 
 it('samples using `errorSampleRate`', function () {
-  const newSession = new Session(undefined, {
-    sessionSampleRate: 0,
-    errorSampleRate: 1.0,
+  const newSession = makeSession({
+    sampled: getSessionSampleType(0, 1),
   });
 
   expect(newSession.sampled).toBe('error');
 });
 
 it('does not run sampling function if existing session was sampled', function () {
-  const newSession = new Session(
-    {
-      sampled: 'session',
-    },
-    {
-      sessionSampleRate: 0,
-      errorSampleRate: 0,
-    },
-  );
+  const newSession = makeSession({
+    sampled: 'session',
+  });
 
   expect(newSession.sampled).toBe('session');
 });

packages/replay/test/unit/session/fetchSession.test.ts

@@ -15,34 +15,44 @@ afterEach(() => {
   WINDOW.sessionStorage.clear();
 });
 
-const SAMPLE_RATES = {
-  sessionSampleRate: 1.0,
-  errorSampleRate: 0.0,
-};
-
 it('fetches a valid and sampled session', function () {
   WINDOW.sessionStorage.setItem(
     REPLAY_SESSION_KEY,
-    '{"id":"fd09adfc4117477abc8de643e5a5798a","sampled": true,"started":1648827162630,"lastActivity":1648827162658}',
+    '{"id":"fd09adfc4117477abc8de643e5a5798a","sampled": "session","started":1648827162630,"lastActivity":1648827162658}',
+  );
+
+  expect(fetchSession()).toEqual({
+    id: 'fd09adfc4117477abc8de643e5a5798a',
+    lastActivity: 1648827162658,
+    segmentId: 0,
+    sampled: 'session',
+    started: 1648827162630,
+  });
+});
+
+it('fetches an unsampled session', function () {
+  WINDOW.sessionStorage.setItem(
+    REPLAY_SESSION_KEY,
+    '{"id":"fd09adfc4117477abc8de643e5a5798a","sampled": false,"started":1648827162630,"lastActivity":1648827162658}',
   );
 
-  expect(fetchSession(SAMPLE_RATES)?.toJSON()).toEqual({
+  expect(fetchSession()).toEqual({
     id: 'fd09adfc4117477abc8de643e5a5798a',
     lastActivity: 1648827162658,
     segmentId: 0,
-    sampled: true,
+    sampled: false,
     started: 1648827162630,
   });
 });
 
 it('fetches a session that does not exist', function () {
-  expect(fetchSession(SAMPLE_RATES)).toBe(null);
+  expect(fetchSession()).toBe(null);
 });
 
 it('fetches an invalid session', function () {
   WINDOW.sessionStorage.setItem(REPLAY_SESSION_KEY, '{"id":"fd09adfc4117477abc8de643e5a5798a",');
 
-  expect(fetchSession(SAMPLE_RATES)).toBe(null);
+  expect(fetchSession()).toBe(null);
 });
 
 it('safely attempts to fetch session when Session Storage is disabled', function () {
@@ -55,5 +65,5 @@ it('safely attempts to fetch session when Session Storage is disabled', function
     },
   });
 
-  expect(fetchSession(SAMPLE_RATES)).toEqual(null);
+  expect(fetchSession()).toEqual(null);
 });