Uploading files with flash

Now we render this page as the main page i. We need to specify a directory to the Flask app where the uploaded files would be stored. Above line creates a uploads folder in the same directory where the src code of the site is stored. We should also check for file extension that the user is uploading as there would be some specific type of file that the site can process. Also there is security issue if the user can upload any type of file. User might upload html file that can cause XSS cross site-scripting problems.

For this post, we only need pdf file extensions as this Flask app would remove watermark from pdf files created by CamScanner App Famous App for scanning documents through Mobile Camera.

Pdf files would have watermark at the bottom similar to what is shown in the image below :. Function checks the filename for allowed file extension and if file type is supported the function returns True otherwise it returns False.

We can add more extension types in allowed extensions set for supporting different type of file uploads. This feature was added in Flask 0. For more information on that consult the Werkzeug documentation on file handling. A while ago many developers had the idea to read the incoming file in small chunks and store the upload progress in the database to be able to poll the progress with JavaScript from the client.

The client asks the server every 5 seconds how much it has transmitted, but this is something it should already know. Now there are better solutions that work faster and are more reliable. There are JavaScript libraries like jQuery that have form plugins to ease the construction of progress bar.

Because the common pattern for file uploads exists almost unchanged in all applications dealing with uploads, there are also some Flask extensions that implement a full fledged upload mechanism that allows controlling which file extensions are allowed to be uploaded. Navigation index modules next previous Flask Documentation 2. Connection Reset Issue When using the local development server, you may get a connection reset error instead of a response.

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