fix(core): Fix error handling when sending envelopes (#17662)

I noticed that we actually handled errors in `sendEnvelope` incorrectly
- we would resolve this function with the rejection reason, if sending
fails. this does not match the type of `TransportMakeRequestResponse`,
you could actually get something like this out (and the tests actually
incorrectly tested this):

```js
// transport.send() rejects with "fetch does not exist"
const res = await client.sendEnvelope(envelope);
// res --> "fetch does not exist" (string)
```

This PR fixes this to instead resolve with an empty object (which
matches the expected return type).

Extracted this out of
#17641 because it is
actually a bug/fix.

Author: mydea

packages/core/src/client.ts

@@ -415,10 +415,9 @@ export abstract class Client<O extends ClientOptions = ClientOptions> {
       env = addItemToEnvelope(env, createAttachmentEnvelopeItem(attachment));
     }
 
-    const promise = this.sendEnvelope(env);
-    if (promise) {
-      promise.then(sendResponse => this.emit('afterSendEvent', event, sendResponse), null);
-    }
+    // sendEnvelope should not throw
+    // eslint-disable-next-line @typescript-eslint/no-floating-promises
+    this.sendEnvelope(env).then(sendResponse => this.emit('afterSendEvent', event, sendResponse));
   }
 
   /**
@@ -879,12 +878,11 @@ export abstract class Client<O extends ClientOptions = ClientOptions> {
     if (this._isEnabled() && this._transport) {
       return this._transport.send(envelope).then(null, reason => {
         DEBUG_BUILD && debug.error('Error while sending envelope:', reason);
-        return reason;
+        return {};
       });
     }
 
     DEBUG_BUILD && debug.error('Transport disabled');
-
     return resolvedSyncPromise({});
   }
 

packages/core/test/lib/client.test.ts

@@ -2268,7 +2268,7 @@ describe('Client', () => {
 
       expect(mockSend).toBeCalledTimes(1);
       expect(callback).toBeCalledTimes(1);
-      expect(callback).toBeCalledWith(errorEvent, 'send error');
+      expect(callback).toBeCalledWith(errorEvent, {});
     });
 
     it('passes the response to the hook', async () => {

packages/replay-internal/src/coreHandlers/handleAfterSendEvent.ts

@@ -14,11 +14,10 @@ export function handleAfterSendEvent(replay: ReplayContainer): AfterSendEventCal
       return;
     }
 
-    const statusCode = sendResponse?.statusCode;
+    const statusCode = sendResponse.statusCode;
 
     // We only want to do stuff on successful error sending, otherwise you get error replays without errors attached
-    // If not using the base transport, we allow `undefined` response (as a custom transport may not implement this correctly yet)
-    // If we do use the base transport, we skip if we encountered an non-OK status code
+    // We skip if we encountered an non-OK status code
     if (!statusCode || statusCode < 200 || statusCode >= 300) {
       return;
     }