Blog - ShiftEleven » google

Problem with writing RESTful Google App Engine Code

K. Adam Christensen — Sat, 12 Apr 2008 23:57:07 +0000

So after I used middleware to make browsers work with RESTful URLs in GAE I started to write more than simple little methods and I’m trying to write a test application. Upon doing so, I ran into a defect with how request parameters are returned for a PUT request To be fair, this is more of a problem with webob than with GAE, but I hope that this gets fixed because my attempts at monkey patching the problem have not worked out too well.

Letting Browsers use all of the RESTful Methods in Google App Engine

K. Adam Christensen — Wed, 09 Apr 2008 02:45:05 +0000

So there was much talk and whathave you about Google’s new App Engine and after viewing the tutorials and reading the documentation, I thought it was pretty rad too. Because I was using rack for some previous stuff, WSGI felt right at home (probably because rack was modeled after WSGI). There was one thing that bothered me however. When writing a class using their webapp framework there isn’t any magic param name, like _method, that I could use to mock requests methods like DELETE and PUT since the browser doesn’t support those HTTP methods.

Well my friends, fear not. If you enjoy the sweet freedom of RESTful urls, I’m here to help. Since this is all built on top of WSGI, we can create a some new Middleware to sit before the application to resolve this little issue.

MockHTTPMethodMiddleware

from google.appengine.ext import webapp

class MockHTTPMethodMiddleware(object):
  def __init__(self, app):
    self.app = app

  def __call__(self, environ, start_response):
    method = webapp.Request(environ).get('_method')
    if method:
      environ['REQUEST_METHOD'] = method.upper()
    return self.app(environ, start_response)

The code is pretty simple. So when this middleware is called, it processes the environ into a Request object. From there, I just inspect the params for a key called _method. If that param exists, then it overwrites the REQUEST_METHOD and bam…we have mocked the HTTP method of our choosing.

Putting that code to good use

Let’s pretend that this is our class is something inane like this:

from google.appengine.ext import webapp

class MethodTest(webapp.RequestHandler):
  def get(self):
    self.response.headers["Content-Type"] = 'text/text'
    self.response.out.write("Get")

  def put(self):
    self.response.headers["Content-Type"] = 'text/text'
    self.response.out.write("Put")

So now when you are writing your main method that creates the WSGI application, you would write it something like:

import wsgiref.handlers

def main():
  app = webapp.WSGIApplication(
      [('/', MethodTest)],
      debug=True)
  wsgiref.handlers.CGIHandler().run(MockHTTPMethodMiddleware(app))

if __name__ == "__main__":
  main()

Notice that in the run method arguments, MockHTTPMethodMiddleware takes app as a parameter, thus MockHTTPMethodMiddleware will run before it runs app.

Conclusion

While there wasn’t support out of the box for mocking HTTP methods for browsers, with a little help from a WSGI Middleware class, it’s not too hard to add that functionality in, nor is it hard to add anything else you would want to use.

Google Image Labeler

K. Adam Christensen — Sat, 02 Sep 2006 04:04:37 +0000

Google has released another beta product called Google Image Labeler The premise is you and a random partner have 90 seconds to get a match on as many pictures as you can. A match is a label or tag that you give to the image is the same as one your partner has given. So it’s a little game you can play in your off-time, and if you sign in, you can use a display name.

This is just genius. By creating a game out of it, Google is having the users of the internet help them find better ways for users to search for images. The other brilliant part is that it only lasts 90 seconds, so you are forced to think quick, and thus you have more of a stream of conscious going on and you are less likly to filter your response.