Description

This PR fixes a JavaScript crash that occurs during large file uploads, particularly in Firefox when network instability (HTTP/3/QUIC resets) causes XHR responses to be empty or undefined.

The Problem

When uploading large files, FileSender uses Terasender workers to upload chunks in parallel. If a network error occurs (timeout, connection reset, HTTP/3 instability), the XHR responseText property may be undefined instead of a string.

The current code attempts to call .replace() directly on responseText:

var msg = xhr.responseText.replace(/^\s+/, '').replace(/\s+$/, '');

This causes a TypeError: Cannot read property 'replace' of undefined, which:

• Crashes the JavaScript execution
• Prevents the built-in retry mechanism from activating
• Results in a blank error screen for users

Affected files:

• www/js/client.js (line 227) - General API error handling
• www/js/terasender/terasender_worker.js (line 508) - Chunk upload error handling

The Solution

Added defensive null-checking before accessing responseText:

var msg = (xhr.responseText || '').replace(/^\s+/, '').replace(/\s+$/, '');

This ensures:

• If responseText exists → Works exactly as before
• If responseText is undefined/null → Uses empty string, preventing crash
• The existing retry mechanism can now activate properly

Impact

• Before fix: Network errors during upload → JS crash → Upload fails permanently
• After fix: Network errors during upload → Graceful handling → Retry mechanism activates

Files Modified

• www/js/client.js (line 227)
• www/js/terasender/terasender_worker.js (line 508)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature
• Enhancement

How Has This Been Tested?

Tested in production environment with Firefox where HTTP/3 network resets were causing upload failures on large files (500MB+). After applying the fix, uploads complete successfully with automatic retries when network hiccups occur.