[BUG] Query parameter values containing special characters (&, =, +) are corrupted in production

[mary-ext]

Describe the bug

I've noticed that requests with a query parameter like ?input=%7B%22search%22%3A%22Blake+%26+Mortimer%22%7D would randomly fail, it seems that OpenNext might not be accounting for the URL already having decoded query parameters?

Steps to reproduce

1. Clone this repository: https://github.com/mary-ext/repro-opennext-cloudflare-qs
2. Run pnpm dev, click on test query
3. Run pnpm preview, click on test query

Expected behavior

Queries shouldn't throw an error

@opennextjs/cloudflare version

1.16.5

Wrangler version

4.67.0

next info output

Using vars defined in .dev.vars
/bin/sh: line 1: yarn: command not found

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP PREEMPT_DYNAMIC Mon, 16 Feb 2026 18:22:29 +0000
  Available memory (MB): 31160
  Available CPU cores: 16
Binaries:
  Node: 22.22.0
  npm: 10.9.4
  Yarn: N/A
  pnpm: 10.30.0
Relevant Packages:
  next: 16.1.6 // Latest available version is detected (16.1.6).
  eslint-config-next: N/A
  react: 19.2.4
  react-dom: 19.2.4
  typescript: 5.9.3
Next.js Config:
  output: N/A

(next info seems to hang)

Additional context

No response

[sommeeeer]

Thanks for the report. I think the reason for this is these lines in OpenNext.

This was enabled in Next 15.4+ I believe to fix a data request path issue for pages router. However, it breaks with an URL containing a query like in your reproduction. It seems that the spaces are preserved and the req.url gets modified to /api/echo?input={"search":"Blake & Mortimer"}. Thats not a valid req.url.

[mary-ext]

yeah, ended up writing this patch to get things going for the time being

diff --git a/dist/core/routing/util.js b/dist/core/routing/util.js
index 80f7d0aefa606f4d0cfc0be6cc3b9e2ba48f7947..dd73464325fedc7d2dee52b75734f68cee3f3f5d 100644
--- a/dist/core/routing/util.js
+++ b/dist/core/routing/util.js
@@ -118,16 +118,17 @@ export function convertRes(res) {
  * @__PURE__
  */
 export function convertToQueryString(query) {
-    const queryStrings = [];
+    const params = new URLSearchParams();
     Object.entries(query).forEach(([key, value]) => {
         if (Array.isArray(value)) {
-            value.forEach((entry) => queryStrings.push(`${key}=${entry}`));
+            value.forEach((entry) => params.append(key, entry));
         }
         else {
-            queryStrings.push(`${key}=${value}`);
+            params.append(key, value);
         }
     });
-    return queryStrings.length > 0 ? `?${queryStrings.join("&")}` : "";
+    const qs = params.toString();
+    return qs.length > 0 ? `?${qs}` : "";
 }
 /**
  * Given a raw query string, returns a record with key value-array pairs