Flask download file

So they are not dynamically generated. KDawG I already tried to use flask. Add a comment. Active Oldest Votes. Error Improve this answer. Is used when a class is defined -- there is only a function here, and this isn't passed to the function, so its understandable that the reference to this doesn't make any sense here.

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Allowing users to download files from your website of application is an often required feature of any website or application and Flask provides us with some useful function to do so.

In this example, we're going to allow our users to download 3 types of files, images, CSV's and PDF's simply by accessing a route and providing a unique id to the resource. First up, we're going to need some imports from flask. Go ahead and import the following:. Before we jump in and create any routes, I want to quickly discuss variable rules which we've touched on before. Although not a necessity, Flask provides us with some useful converters to add an additional layer of validation to any values soming in via the URL.

Using any of the converters listed above will convert the incoming variable into it's related type. Like many other important application configuration variables, we're going to add 3 new entries to our app.

But before we do so, we're going to create some new directories and add some files for our users to download:. We're going to create 3 new entries in our app. Now that we've updated our app config, let's go ahead and create our routes I'd recommend using a config file for this which you can read more about here.

As we haven't set a variable rule, Flask will default to string and not allow any slashes. If you try a filename that doesn't exist, you'll get a Not Found error in your browser. You'll notice these 2 routes are very similar to the first, with the addition of the filename variable.

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. It returns the index. Uploaded file attached in the POST request can be referenced by request. We check the name of the uploaded file before we save it to server filesystem. This is done because there is a possibility that user might name the file which clashes with some system configuration file, In this case if uploaded filename is not changed then system file will be overwritten.

This vulnerability can be used by hackers to hack the server.