feat: Rework how we track sessions

packages/browser/src/sdk.ts

@@ -201,73 +201,14 @@ function startSessionTracking(): void {
 
   const hub = getCurrentHub();
 
-  /**
-   * We should be using `Promise.all([windowLoaded, firstContentfulPaint])` here,
-   * but, as always, it's not available in the IE10-11. Thanks IE.
-   */
-  let loadResolved = document.readyState === 'complete';
-  let fcpResolved = false;
-  const possiblyEndSession = (): void => {
-    if (fcpResolved && loadResolved) {
-      hub.endSession();
-    }
-  };
-  const resolveWindowLoaded = (): void => {
-    loadResolved = true;
-    possiblyEndSession();
-    window.removeEventListener('load', resolveWindowLoaded);
-  };
-
   hub.startSession();
-
-  if (!loadResolved) {
-    // IE doesn't support `{ once: true }` for event listeners, so we have to manually
-    // attach and then detach it once completed.
-    window.addEventListener('load', resolveWindowLoaded);
-  }
-
-  try {
-    const po = new PerformanceObserver((entryList, po) => {
-      entryList.getEntries().forEach(entry => {
-        if (entry.name === 'first-contentful-paint' && entry.startTime < firstHiddenTime) {
-          po.disconnect();
-          fcpResolved = true;
-          possiblyEndSession();
-        }
-      });
-    });
-
-    // There's no need to even attach this listener if `PerformanceObserver` constructor will fail,
-    // so we do it below here.
-    let firstHiddenTime = document.visibilityState === 'hidden' ? 0 : Infinity;
-    document.addEventListener(
-      'visibilitychange',
-      event => {
-        firstHiddenTime = Math.min(firstHiddenTime, event.timeStamp);
-      },
-      { once: true },
-    );
-
-    po.observe({
-      type: 'paint',
-      buffered: true,
-    });
-  } catch (e) {
-    fcpResolved = true;
-    possiblyEndSession();
-  }
+  hub.captureSession();
 
   // We want to create a session for every navigation as well
   addInstrumentationHandler({
     callback: () => {
-      if (
-        !getCurrentHub()
-          .getScope()
-          ?.getSession()
-      ) {
-        hub.startSession();
-        hub.endSession();
-      }
+      hub.startSession();
+      hub.captureSession();
     },
     type: 'history',
   });

packages/core/src/baseclient.ts

@@ -156,6 +156,8 @@ export abstract class BaseClient<B extends Backend, O extends Options> implement
       logger.warn('Discarded session because of missing release');
     } else {
       this._sendSession(session);
+      // After sending, we set init false to inidcate it's not the first occurence
+      session.update({ init: false });
     }
   }
 
@@ -252,6 +254,7 @@ export abstract class BaseClient<B extends Backend, O extends Options> implement
       userAgent,
       errors: session.errors + Number(errored || crashed),
     });
+    this.captureSession(session);
   }
 
   /** Deliver captured session to Sentry */

packages/hub/src/hub.ts

@@ -13,6 +13,7 @@ import {
   IntegrationClass,
   Primitive,
   SessionContext,
+  SessionStatus,
   Severity,
   Span,
   SpanContext,
@@ -360,10 +361,33 @@ export class Hub implements HubInterface {
   /**
    * @inheritDoc
    */
-  public startSession(context?: SessionContext): Session {
-    // End existing session if there's one
-    this.endSession();
+  public captureSession(endSession: boolean = false): void {
+    // both send the update and pull the session from the scope
+    if (endSession) {
+      return this.endSession();
+    }
+
+    // only send the update
+    this._sendSessionUpdate();
+  }
+
+  /**
+   * @inheritDoc
+   */
+  public endSession(): void {
+    this.getStackTop()
+      ?.scope?.getSession()
+      ?.close();
+    this._sendSessionUpdate();
+
+    // the session is over; take it off of the scope
+    this.getStackTop()?.scope?.setSession();
+  }
 
+  /**
+   * @inheritDoc
+   */
+  public startSession(context?: SessionContext): Session {
     const { scope, client } = this.getStackTop();
     const { release, environment } = (client && client.getOptions()) || {};
     const session = new Session({
@@ -372,26 +396,34 @@ export class Hub implements HubInterface {
       ...(scope && { user: scope.getUser() }),
       ...context,
     });
+
     if (scope) {
+      // End existing session if there's one
+      const currentSession = scope.getSession && scope.getSession();
+      if (currentSession && currentSession.status === SessionStatus.Ok) {
+        currentSession.update({ status: SessionStatus.Exited });
+      }
+      this.endSession();
+
+      // Afterwards we set the new session on the scope
       scope.setSession(session);
     }
+
     return session;
   }
 
   /**
-   * @inheritDoc
+   * Sends the current Session on the scope
    */
-  public endSession(): void {
+  private _sendSessionUpdate(): void {
     const { scope, client } = this.getStackTop();
     if (!scope) return;
 
     const session = scope.getSession && scope.getSession();
     if (session) {
-      session.close();
       if (client && client.captureSession) {
         client.captureSession(session);
       }
-      scope.setSession();
     }
   }
 

packages/hub/src/session.ts

@@ -16,6 +16,7 @@ export class Session implements SessionInterface {
   public status: SessionStatus = SessionStatus.Ok;
   public environment?: string;
   public ipAddress?: string;
+  public init: boolean = true;
 
   constructor(context?: Omit<SessionContext, 'started' | 'status'>) {
     if (context) {
@@ -42,6 +43,9 @@ export class Session implements SessionInterface {
       // Good enough uuid validation. — Kamil
       this.sid = context.sid.length === 32 ? context.sid : uuid4();
     }
+    if (context.init !== undefined) {
+      this.init = context.init;
+    }
     if (context.did) {
       this.did = `${context.did}`;
     }
@@ -103,7 +107,7 @@ export class Session implements SessionInterface {
   } {
     return dropUndefinedKeys({
       sid: `${this.sid}`,
-      init: true,
+      init: this.init,
       started: new Date(this.started).toISOString(),
       timestamp: new Date(this.timestamp).toISOString(),
       status: this.status,

packages/types/src/hub.ts

@@ -222,4 +222,10 @@ export interface Hub {
    * Ends the session that lives on the current scope and sends it to Sentry
    */
   endSession(): void;
+
+  /**
+   * Sends the current session on the scope to Sentry
+   * @param endSession If set the session will be marked as exited and removed from the scope
+   */
+  captureSession(endSession: boolean): void;
 }

packages/types/src/session.ts

@@ -35,6 +35,7 @@ export interface Session extends SessionContext {
 export interface SessionContext {
   sid?: string;
   did?: string;
+  init?: boolean;
   timestamp?: number;
   started?: number;
   duration?: number;