Appengine serve gzipped files - google-app-engine

Question

I'm using AppEngine to store some pickled python objects in my app. I want to serve these to the user directly, and I'm simply using the X-AppEngine-Blobkey header to serve the files to the user with a file.pickle.gz filename. However, when I try to extract these on my computer (Mac OS) using a simple double click, the files are turned into file.pickle.gz.cpgz.
I thought it was my browser being sneaky and extracting them, but I don't think so, since
pickle.load('file.pickle.gz')
Doesn't work, and neither does
pickle.load('file.pickle.gz.cpgz')
To store the files, I use:
blobfile = files.blobstore.create(mime_type='application/gzip')
with files.open(blobfile, 'a') as f:
gz = gzip.GzipFile(fileobj=f,mode='wb')
gz.write(my_pickled_object)
gz.close()
files.finalize(blobfile)
I think I'm not understanding the way gzips work. Can someone explain?

Answer 1

Are you sure file.pickle.gz.cpgz is the result of your double-clicking on the file.pickle.gz file you downloaded? Usually ".cpgz" is a different kind of archive file.
I can get the code you posted to work in a development server without significant changes. Here's the code, if it helps:
#!/usr/bin/env python
from __future__ import with_statement
import gzip
import pickle
from google.appengine.api import files
from google.appengine.api import memcache
from google.appengine.ext import blobstore
from google.appengine.ext import webapp
from google.appengine.ext.webapp import blobstore_handlers
from google.appengine.ext.webapp import util
class MainHandler(webapp.RequestHandler):
def get(self):
self.response.out.write('Hello world! make get')
class MakeFileHandler(webapp.RequestHandler):
def get(self):
data = pickle.dumps({'a':1, 'b':True, 'c':None})
blobfile = files.blobstore.create(mime_type='application/gzip')
with files.open(blobfile, 'a') as f:
gz = gzip.GzipFile(fileobj=f,mode='wb')
gz.write(data)
gz.close()
files.finalize(blobfile)
memcache.set('filekey', files.blobstore.get_blob_key(blobfile))
self.redirect('/')
class GetFileHandler(blobstore_handlers.BlobstoreDownloadHandler):
def get(self):
blobkey = memcache.get('filekey')
if blobkey:
self.send_blob(blobkey)
else:
self.response.out.write('No data key set back')
def main():
application = webapp.WSGIApplication([('/', MainHandler),
('/make', MakeFileHandler),
('/get', GetFileHandler)],
debug=True)
util.run_wsgi_app(application)
if __name__ == '__main__':
main()
Click on "make", then click on "get". A file named "get.gz" is downloaded to your ~/Downloads/ folder (at least in Chrome). Double-click on it to produce a file named "get". Then:
% python
>>> import pickle
>>> pickle.load(open('get'))
{'a': 1, 'c': None, 'b': True}