From 3b8c698025f6c9df84fb637d74a8f1f2606d9c01 Mon Sep 17 00:00:00 2001
From: Mihail Stoykov <M.Stoikov@gmail.com>
Date: Thu, 6 Mar 2025 19:32:58 +0200
Subject: [PATCH] Fix race when getting body - fixes #4596

---
 .../k6/browser/browser/response_mapping.go    | 21 ++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/internal/js/modules/k6/browser/browser/response_mapping.go b/internal/js/modules/k6/browser/browser/response_mapping.go
index f74cf9f72fa..bc87b4c1c2d 100644
--- a/internal/js/modules/k6/browser/browser/response_mapping.go
+++ b/internal/js/modules/k6/browser/browser/response_mapping.go
@@ -12,6 +12,8 @@ func mapResponseEvent(vu moduleVU, event common.PageOnEvent) mapping {
 }
 
 // mapResponse to the JS module.
+//
+//nolint:funlen
 func mapResponse(vu moduleVU, r *common.Response) mapping {
 	if r == nil {
 		return nil
@@ -23,14 +25,23 @@ func mapResponse(vu moduleVU, r *common.Response) mapping {
 			})
 		},
 		"body": func() *sobek.Promise {
-			return k6ext.Promise(vu.Context(), func() (any, error) {
+			rt := vu.Runtime()
+			promise, res, rej := rt.NewPromise()
+			callback := vu.RegisterCallback()
+			go func() {
 				body, err := r.Body()
 				if err != nil {
-					return nil, err //nolint: wrapcheck
+					callback(func() error {
+						return rej(err)
+					})
+					return
 				}
-				buf := vu.Runtime().NewArrayBuffer(body)
-				return &buf, nil
-			})
+				callback(func() error {
+					buf := vu.Runtime().NewArrayBuffer(body)
+					return res(&buf)
+				})
+			}()
+			return promise
 		},
 		"frame": func() mapping {
 			return mapFrame(vu, r.Frame())