feat(replay): Attach an error cause to send exceptions (#7350)

Attach the original exception as a `cause` when we throw "Unable to send replay" exceptions so that we know what is causing issues with sending replays.

Author: billyvg

packages/replay/src/util/sendReplay.ts

@@ -41,7 +41,17 @@ export async function sendReplay(
     // If an error happened here, it's likely that uploading the attachment
     // failed, we'll can retry with the same events payload
     if (retryConfig.count >= RETRY_MAX_COUNT) {
-      throw new Error(`${UNABLE_TO_SEND_REPLAY} - max retries exceeded`);
+      const error = new Error(`${UNABLE_TO_SEND_REPLAY} - max retries exceeded`);
+
+      try {
+        // In case browsers don't allow this property to be writable
+        // @ts-ignore This needs lib es2022 and newer
+        error.cause = err;
+      } catch {
+        // nothing to do
+      }
+
+      throw error;
     }
 
     // will retry in intervals of 5, 10, 30

packages/replay/src/util/sendReplayRequest.ts

@@ -115,8 +115,17 @@ export async function sendReplayRequest({
 
   try {
     response = await transport.send(envelope);
-  } catch {
-    throw new Error(UNABLE_TO_SEND_REPLAY);
+  } catch (err) {
+    const error = new Error(UNABLE_TO_SEND_REPLAY);
+
+    try {
+      // In case browsers don't allow this property to be writable
+      // @ts-ignore This needs lib es2022 and newer
+      error.cause = err;
+    } catch {
+      // nothing to do
+    }
+    throw error;
   }
 
   // TODO (v8): we can remove this guard once transport.send's type signature doesn't include void anymore

packages/replay/test/integration/sendReplayEvent.test.ts

@@ -391,6 +391,11 @@ describe('Integration | sendReplayEvent', () => {
     expect(spyHandleException).toHaveBeenCalledTimes(5);
     expect(spyHandleException).toHaveBeenLastCalledWith(new Error('Unable to send Replay - max retries exceeded'));
 
+    const spyHandleExceptionCall = spyHandleException.mock.calls;
+    expect(spyHandleExceptionCall[spyHandleExceptionCall.length - 1][0].cause.message).toEqual(
+      'Something bad happened',
+    );
+
     // No activity has occurred, session's last activity should remain the same
     expect(replay.session?.lastActivity).toBe(BASE_TIMESTAMP);