从 Python 中的 API 服务器重定向下载文件

Question

I have 2 server: one backend for API and another one as web-frontend. The backend is working and provides files:

#API class for the route in Flask
class DownloadDocument(Resource):

    def get(self):

        # accept the filename which must be downloaded in HTTP request.
        # That file is surely present in the directory

        filename = request.headers.get('x-filename')      
       
        return send_from_directory(app.config['UPLOAD_FOLDER'], filename, as_attachment=True)

The web-frontend is currently getting the file in this way:

@app.route('/get_doc/<filename>')
@login_required
def get_doc(filename):
      sending = {'x-filename': filename}
      response = requests.get('http://<<api_server>>', headers=sending)
      return response.content

The result is that when I click download in the webpage ( http://<<frontend>>/get_doc/20201116003_895083.jpg ), I see the file as text and not downloaded. For example, I see a big page full of that:

����]ExifII*����

I don't understand if the problem is in the frontend or in the backend. In the frontend, I tried with urllib.request.Request or requests.request . Any idea how to manage this kind of download? Probably is something related to mime interpretation, bytes download or buffer it locally. Of course, I don't want to download the file in the web-frontend storage. I want to redirect it to the visitor.

Here are the headers from GET:

{'Content-Disposition': 'attachment; filename=20201116003_895083.jpg', 'Content-Length': '574424', 'Content-Type': 'image/jpeg', 'Last-Modified': 'Tue, 01 Dec 2020 14:04:30 GMT', 'Cache-Control': 'public, max-age=43200', 'Expires': 'Thu, 03 Dec 2020 02:34:51 GMT', 'ETag': '"1606831470.89299-574424-736697678"', 'Date': 'Wed, 02 Dec 2020 14:34:51 GMT', 'Server': 'Werkzeug/1.0.1 Python/3.8.3'}

Answer 1

I'm not sure if this is a good way to architect your application. I think the Restful backend is intended to work with a Javascript frontend, rather than a separate Flask app which contacts the 'backend' with the requests library. I'm not sure how this would behave in a larger app. The requests documentation raises some prod considerations about timeouts for example. You may see some unforseen issues down the line when deploying this with a WSGI server. (imo)

However, with that considered, a quick fix for the actual issue would be to use the flask.send_file function to return the file. This accepts a file pointer as the first argument, so you'll need to use io.BytesIO to convert the bytes object:

from flask import send_file
from io import BytesIO

@app.route('/get_doc/<filename>')
@login_required
def get_doc(filename):
      sending = {'x-filename': filename}
      response = requests.get('http://<<api_server>>', headers=sending)
      return send_file(BytesIO(response.content), mimetype='image/jpeg'
          #as_attachment=True
          )

You also need to provide the mimetype argument, as usually send_file guesses the mimetype based on the extension when a string like 'file.jpg' is passed as the first arg. Obviously that can't be done in this case.

You can also pass as_attachment=True if you want the user to receive a download prompt, rather that viewing the image in-browser. This is all mentioned in thesend_file docs .

Again, this feels like a hack. Something seems off with using the requests library in this way. Perhaps other SO users will be able to comment further on this.