From 46f81e2bae18d5ebc3fedb8d9099475477e1fbbc Mon Sep 17 00:00:00 2001
From: Copilot <198982749+Copilot@users.noreply.github.com>
Date: Wed, 5 Nov 2025 13:06:21 +0800
Subject: [PATCH] Fix isNetworkError to match MDN spec: readyState === 4 &&
 status === 0 (#6050)
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closes #4253

The `isNetworkError` function incorrectly classified XHR states as
network errors. Per MDN, a network error occurs when a request completes
(`readyState === 4`) but has no HTTP status (`status === 0`), indicating
network/CORS/file access failures.

## Changes

- **Logic fix**: Changed from `(xhr.readyState !== 0 && xhr.readyState
!== 4) || xhr.status === 0` to `xhr.readyState === 4 && xhr.status ===
0`
- **Test update**: Removed invalid test expecting `readyState: 2` to be
a network error; added test verifying incomplete requests return `false`

## Example

```typescript
// Before: incorrectly treated in-progress requests as network errors
isNetworkError({ readyState: 2, status: 0 })  // true ❌

// After: only completed requests with no status are network errors
isNetworkError({ readyState: 4, status: 0 })  // true ✓
isNetworkError({ readyState: 2, status: 0 })  // false ✓
```

<!-- START COPILOT CODING AGENT SUFFIX -->



<details>

<summary>Original prompt</summary>

> Update the isNetworkError function in
packages/@uppy/utils/src/isNetworkError.ts to correctly detect network
errors according to MDN documentation. The new logic should return true
only if xhr.readyState === 4 and xhr.status === 0. The updated
implementation should be:
>
> function isNetworkError(xhr?: XMLHttpRequest): boolean {
>   if (!xhr) return false
> // finished but status is 0 — usually indicates a network/CORS/file
error
>   return xhr.readyState === 4 && xhr.status === 0
> }
>
> export default isNetworkError
>
> No other logic changes are needed. If you find related commentary
(e.g., outdated comments), clarify as needed.


</details>

*This pull request was created as a result of the following prompt from
Copilot chat.*
> Update the isNetworkError function in
packages/@uppy/utils/src/isNetworkError.ts to correctly detect network
errors according to MDN documentation. The new logic should return true
only if xhr.readyState === 4 and xhr.status === 0. The updated
implementation should be:
>
> function isNetworkError(xhr?: XMLHttpRequest): boolean {
>   if (!xhr) return false
> // finished but status is 0 — usually indicates a network/CORS/file
error
>   return xhr.readyState === 4 && xhr.status === 0
> }
>
> export default isNetworkError
>
> No other logic changes are needed. If you find related commentary
(e.g., outdated comments), clarify as needed.

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---
 packages/@uppy/utils/src/isNetworkError.test.ts | 14 +++++++-------
 packages/@uppy/utils/src/isNetworkError.ts      |  7 +++----
 2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/packages/@uppy/utils/src/isNetworkError.test.ts b/packages/@uppy/utils/src/isNetworkError.test.ts
index bfe755d1a..a1a2e8868 100644
--- a/packages/@uppy/utils/src/isNetworkError.test.ts
+++ b/packages/@uppy/utils/src/isNetworkError.test.ts
@@ -9,12 +9,6 @@ describe('isNetworkError', () => {
       status: 0,
     } as any as XMLHttpRequest
 
-    const xhrNetworkError2Mock = {
-      readyState: 2,
-      responseText: '',
-      status: 300,
-    } as any as XMLHttpRequest
-
     const xhrRegularErrorMock = {
       readyState: 4,
       responseText: 'Failed',
@@ -27,9 +21,15 @@ describe('isNetworkError', () => {
       status: 200,
     } as any as XMLHttpRequest
 
+    const xhrIncompleteRequestMock = {
+      readyState: 2,
+      responseText: '',
+      status: 0,
+    } as any as XMLHttpRequest
+
     expect(isNetworkError(xhrNetworkErrorMock)).toEqual(true)
-    expect(isNetworkError(xhrNetworkError2Mock)).toEqual(true)
     expect(isNetworkError(xhrRegularErrorMock)).toEqual(false)
     expect(isNetworkError(xhrNetworkSuccessMock)).toEqual(false)
+    expect(isNetworkError(xhrIncompleteRequestMock)).toEqual(false)
   })
 })
diff --git a/packages/@uppy/utils/src/isNetworkError.ts b/packages/@uppy/utils/src/isNetworkError.ts
index bc806c203..9bce2e3fd 100644
--- a/packages/@uppy/utils/src/isNetworkError.ts
+++ b/packages/@uppy/utils/src/isNetworkError.ts
@@ -1,8 +1,7 @@
 function isNetworkError(xhr?: XMLHttpRequest): boolean {
-  if (!xhr) {
-    return false
-  }
-  return (xhr.readyState !== 0 && xhr.readyState !== 4) || xhr.status === 0
+  if (!xhr) return false
+  // finished but status is 0 — usually indicates a network/CORS/file error
+  return xhr.readyState === 4 && xhr.status === 0
 }
 
 export default isNetworkError