How Can I Serve Static Files Efficiently in a Flask Application?

Serving Static Files in Flask

Serving static files is a common task in web development. Flask offers several methods for handling this, including using the built-in static folder route or the send_from_directory function.

Built-in Static Folder Route

Flask automatically creates a route for static files under the /static/ path. To serve static files from this route, simply place them in the static folder next to your Flask app module. You can then use url_for to link to the static files.

from flask import url_for

@app.route('/')
def home():
    return url_for('static', filename='css/style.css')

send_from_directory Function

The send_from_directory function allows you to serve files from any directory in your app. It takes two arguments: the base directory and the requested file path. It ensures that the requested path is contained within the base directory, preventing directory traversal attacks.

from flask import send_from_directory

@app.route('/reports/<path:path>')
def send_report(path):
    return send_from_directory('reports', path)

Note:

Do not use send_file or send_static_file with user-supplied paths, as this can expose you to vulnerabilities. Instead, use send_from_directory, which is designed to safely handle user-supplied paths.

Serving In-Memory Files

If you need to serve a file that is generated in memory without writing it to disk, you can use BytesIO to create an in-memory file object and pass it to send_file. You will also need to specify the file name, content type, and other attributes.

from io import BytesIO
import zipfile

@app.route('/download.zip')
def download_zip():
    buffer = BytesIO()
    zipfile.ZipFile(buffer, 'w').write('file.txt')
    buffer.seek(0)
    
    return send_file(buffer, 
                       mimetype='application/zip', 
                       as_attachment=True, 
                       attachment_filename='download.zip')

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