pull cleanup work out into its own function

Author: lobsterkatie

packages/nextjs/src/utils/withSentry.ts

@@ -116,32 +116,41 @@ type WrappedResponseEndMethod = AugmentedNextApiResponse['end'];
 
 function wrapEndMethod(origEnd: ResponseEndMethod): WrappedResponseEndMethod {
   return async function newEnd(this: AugmentedNextApiResponse, ...args: unknown[]) {
-    const transaction = this.__sentryTransaction;
-
-    if (transaction) {
-      transaction.setHttpStatus(this.statusCode);
-
-      // Push `transaction.finish` to the next event loop so open spans have a better chance of finishing before the
-      // transaction closes, and make sure to wait until that's done before flushing events
-      const transactionFinished: Promise<void> = new Promise(resolve => {
-        setImmediate(() => {
-          transaction.finish();
-          resolve();
-        });
-      });
-      await transactionFinished;
-    }
-
-    // flush the event queue to ensure that events get sent to Sentry before the response is finished and the lambda
-    // ends
-    try {
-      logger.log('Flushing events...');
-      await flush(2000);
-      logger.log('Done flushing events');
-    } catch (e) {
-      logger.log(`Error while flushing events:\n${e}`);
-    }
+    await finishSentryProcessing(this);
 
     return origEnd.call(this, ...args);
   };
 }
+
+/**
+ * Close the open transaction (if any) and flush events to Sentry.
+ *
+ * @param res The outgoing response for this request, on which the transaction is stored
+ */
+async function finishSentryProcessing(res: AugmentedNextApiResponse): Promise<void> {
+  const { __sentryTransaction: transaction } = res;
+
+  if (transaction) {
+    transaction.setHttpStatus(res.statusCode);
+
+    // Push `transaction.finish` to the next event loop so open spans have a better chance of finishing before the
+    // transaction closes, and make sure to wait until that's done before flushing events
+    const transactionFinished: Promise<void> = new Promise(resolve => {
+      setImmediate(() => {
+        transaction.finish();
+        resolve();
+      });
+    });
+    await transactionFinished;
+  }
+
+  // Flush the event queue to ensure that events get sent to Sentry before the response is finished and the lambda
+  // ends. If there was an error, rethrow it so that the normal exception-handling mechanisms can apply.
+  try {
+    logger.log('Flushing events...');
+    await flush(2000);
+    logger.log('Done flushing events');
+  } catch (e) {
+    logger.log(`Error while flushing events:\n${e}`);
+  }
+}