Download file, parse it and serve in Flask

Question

I'm taking my first steps with Flask. I can successfuly download a file from a client and give it back with the code from here: http://flask.pocoo.org/docs/patterns/fileuploads/

But how to change it (eg. line after line) and then serve it to the client?

I can get the string with read() after:

if file and allowed_file(file.filename):

and then process it. So the question really is: how do I serve output string as a file?

I don't want to save it on a server's hdd at all (both original version and changed).

Answer 1

You can use make_response to create the response for your string and add Content-Disposition: attachment; filename=anyNameHere.txt to it before returning it:

@app.route("/transform-file", methods=["POST"])
def transform():
    # Check for valid file and assign it to `inbound_file`
    data = inbound_file.read()
    data = data.replace("A", "Z")
    response = make_response(data)
    response.headers["Content-Disposition"] = "attachment; filename=outbound.txt"
    return response

See also: The docs on streaming content