How to write a Webapp2 Request Handler to Allow Client to Get Data after receiving Channel API message

Question

As a follow up to another question I asked, I have a basic question about the easiest way to get a webapp2 python server to provide json data that is too large (about 100 kb) to send as a Channel API message to a client .

The webapp2 server generates several data files over several minutes based on a client request, and I am thinking that I would like the Channel API to send messages with the url to the client when the data is ready, and the client (a GWT app) could perform a http GET request to get the data. Each data file is unique to the client and therefore the server will have to have a request handler that will give the appropriate data file for the client.

Can you write a request handler that can provide the correct data file directly from another request handler for that particular client when the request is called? Or Do I need to store the data using Cloud SQL or the Data Store first until the client asks for it? Here is some incomplete sample code of what I would like to do:

class MainPage(webapp2.RequestHandler):
def get(self):
    ## This opens the GWT app    

class Service_handler(webapp2.RequestHandler):
def get(self, parameters):
    ## This is called by the GWT app and generates the data to be 
    ## sent to the client. 
    ## A channel API message is sent to the client with the url 
    ## for each data file generated.

class kml_handler(webapp2.RequestHandler):
def get(self, client_id):
    ##  I would like to return the correct data here when it is 
    ##  called by the client.  Do I need to store the data in  
    ##  Cloud SQL or the Data Store and then retrieve it
    ##  or can this handler take the results directly from the 
    ##  Service_handler as soon as it is generated?

app = webapp2.WSGIApplication([
                            webapp2.Route(r'/', handler=MainPage),
                            webapp2.Route(r'/Service/', handler=Service_handler),
                            webapp2.Route(r'/_ah/channel/<connected>/', handler = connection_handler),
                            webapp2.Route(r'/kml/<client_id>', handler = kml_handler)
                            ],
                          debug=True)

Answer 1

You can write files to the blobstore and serve those files from the blobstore.

Here is an example: https://developers.google.com/appengine/docs/python/blobstore/overview#Complete_Sample_App