How to download several files with GAE Python

Question

I'd like to download several files with GAE Python code. My current code is like below

import webapp2, urllib
url1 = 'http://dummy/sample1.jpg'
url2 = 'http://dummy/sample2.jpg'

class DownloadHandler(webapp2.RequestHandler):
    def get(self):
        #image1
        self.response.headers['Content-Type'] = 'application/octet-stream'
        self.response.headers['Content-Disposition'] = 'attachment; filename="' + 'sample1.jpg' + '"'
        f = urllib.urlopen(url1)
        data = f.read()
        self.response.out.write(data)

        #image2
        self.response.headers['Content-Type'] = 'application/octet-stream'
        self.response.headers['Content-Disposition'] = 'attachment; filename="' + 'sample2.jpg' + '"'
        f = urllib.urlopen(url2)
        data = f.read()
        self.response.out.write(data)

app = webapp2.WSGIApplication([('/.*', DownloadHandler)], 
                              debug=True)

I expected to occur download dialogue twice with this code, but actually occurred once, and only sample2.jpg was downloaded. How can you handle download dialogue several times?

I'd actually like to realize some other functions adding above as well. To display progressing message on the browser such as
sample1.jpg was downloaded
sample2.jpg was downloaded
sample3.jpg was downloaded ...

And redirect to the other page after downloading files. When I wrote a code such as

self.redirect('/otherpage')

after

self.response.out.write(data)

Only redirect had happened and didn't occur download procedure.

Would you give me any ideas to solve it please. I'm using python2.7

Answer 1

Two things.

1. You cannot write two files in one response that has a Content-Type of application/octet-stream. To stuff multiple files in in the response, you would have to encode your response with multipart/form-data or multipart/mixed and hope that the client would understand that and parse it and show two download dialogues

2. Once you've already called self.response.out.write(…), you shouldn't be setting any more headers.

To me it seems that the most foolproof option would be to serve an HTML file that contains something like:

<script>
  window.open('/path/to/file/1.jpg');
  window.open('/path/to/file/1.jpg');
</script>

… and then handle those paths using different handlers.

Another option would be to zip the two files and serve the zipfile to the client, though it may or may not be preferable in your case.

Answer 2

I reached the goal what I wanted to do.

As user interaction, generating html sources include below

<script type="text/javascript">
    window.open("/download?url=http://dummy/sample1.jpg")
    window.open("/download?url=http://dummy/sample2.jpg")
</script>

then created new windows are handled with this code.

class DownloadHandler(webapp2.RequestHandler):
    def get(self):
        url = self.request.get('url')
        filename = str(os.path.basename(url))
        self.response.headers['Content-Type'] ='application/octet-stream'
        self.response.headers['Content-Disposition'] = 'attachment; filename="%s"' % (filename)

        data = urllib.urlopen(url).read()
        self.response.out.write(data)

app = webapp2.WSGIApplication([('/download', DownloadHandler)], debug=True)

Thank you, Attila.