Broken File Uploads in Vibecoded Apps

Test uploads with various file types and sizes. Upload a valid small file first to confirm the basic flow works. Then test edge cases: very large files (50MB+), zero-byte empty files, files with special characters in the name, and files with double extensions like image.jpg.exe. Check whether the app validates file types and sizes before uploading.

Watch for missing progress feedback. During a large file upload, the user should see progress — a percentage, a progress bar, or at minimum a spinner. If the UI shows nothing and then suddenly succeeds or fails, the upload component lacks progress tracking. Also check if the uploaded file is actually accessible after upload by trying to download or preview it.

Upload files larger than any configured size limit and check for graceful error messages versus silent failures or crashes. Drag and drop files if the UI supports it, and compare behavior with the file picker button. AI tools often implement one method but not the other, or wire them to different handlers.

Test network interruption during upload. Start uploading a large file and disable your network midway. The app should show an error and allow the user to retry. Also test uploading multiple files simultaneously if the feature claims to support it — many vibecoded multi-upload implementations process files sequentially or drop files silently.

Validate file type and size on both the client and server side before processing. Show a clear progress indicator using the XMLHttpRequest progress event or the fetch API with ReadableStream. Implement chunked uploads for large files to handle network interruptions gracefully and allow resumable uploads.

Store files in a dedicated object storage service rather than the local filesystem. Generate unique filenames on the server to avoid conflicts and sanitize original filenames to prevent directory traversal attacks. Always confirm the file is retrievable after upload — a successful upload response means nothing if the file is not actually stored correctly.