File size limits in Flask - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of setting file size limits in Flask?

Setting file size limits in Flask helps prevent users from uploading files that are too large, which can protect the server from running out of memory or disk space and improve security.

beginner

How do you set a maximum file size limit in a Flask application?

You set the maximum file size limit by configuring the Flask app with the key MAX_CONTENT_LENGTH. For example, app.config['MAX_CONTENT_LENGTH'] = 16 * 1024 * 1024 limits uploads to 16 megabytes.

intermediate

What happens if a user tries to upload a file larger than the limit set by MAX_CONTENT_LENGTH?

Flask automatically stops the upload and raises a RequestEntityTooLarge exception, which you can catch to show a friendly error message to the user.

intermediate

How can you handle the error when a file is too large in Flask?

You can use Flask's error handler decorator for <code>RequestEntityTooLarge</code> to catch the error and return a custom message or page. For example:<br><pre>from werkzeug.exceptions import RequestEntityTooLarge

@app.errorhandler(RequestEntityTooLarge)
def handle_file_too_large(e):
    return 'File is too large', 413</pre>

beginner

Why is it important to set file size limits on the server side even if the client limits file size?

Client-side limits can be bypassed by users or malicious actors. Server-side limits ensure the server is protected regardless of client behavior, making your app more secure and reliable.

Which Flask configuration key sets the maximum allowed size for uploaded files?

A MAX_FILE_SIZE

B MAX_CONTENT_LENGTH

C UPLOAD_LIMIT

D FILE_SIZE_MAX

The correct key is MAX_CONTENT_LENGTH to limit the size of incoming request data including file uploads.

What exception does Flask raise when a file exceeds the size limit?

A RequestEntityTooLarge

B FileSizeExceeded

C UploadLimitError

D FileTooBigException

Flask raises RequestEntityTooLarge when the uploaded file is bigger than MAX_CONTENT_LENGTH.

If you want to limit uploads to 5 megabytes, what value should you set for MAX_CONTENT_LENGTH?

A 5000

B 5 * 1000 * 1000

C 5 * 1024 * 1024

D 5

MAX_CONTENT_LENGTH expects bytes, so 5 megabytes is 5 * 1024 * 1024 bytes.

Why should you handle the RequestEntityTooLarge error in your Flask app?

A To restart the server

B To increase the file size limit automatically

C To allow the upload anyway

D To show a friendly message instead of a default error page

Handling the error lets you inform users nicely that their file is too big.

Which of these is NOT a reason to set file size limits on the server?

A Make uploads faster

B Improve security

C Prevent server overload

D Avoid running out of disk space

File size limits protect resources and security but do not directly make uploads faster.

Explain how to set and handle file size limits in a Flask application.

Think about configuration and error handling steps.

Why is server-side file size limiting important even if the client limits file size?

Consider trust and control between client and server.