Replace AppEngine Devserver With Spawning (BaseHTTPRequestHandler as WSGI)

Question

I'm looking to replace AppEngine's devserver with spawning. Spawning handles standard wsgi handlers, just like appengine, so running your app on it is easy.

But the devserver takes into account your app.yaml file that has url redirects etc. I've been going through the devserver code and it is pretty easy to get the BaseHTTPRequestHandler like this:

from google.appengine.tools.dev_appserver import CreateRequestHandler
dev = CreateRequestHandler(os.path.dirname(__file__), '', require_indexes=False, static_caching=True)

But the BaseHTTPRequestHandler is not a WSGI app, so my guess is I need to put something around it to make it work. Any hints?

Answer 1

I don't think you're going to be able to pull out a part of the dev_appserver and use it in a custom WSGI server quite so easily. The dev_appserver does a lot of 'magic', and it isn't really structured to be pulled out and used as a WSGI wrapper in another server (more's the pity).

You may want to check out TwistedAE, which is working on creating an alternate serving environment; if you really want to use spawning, you can probably use TwistedAE's work as a basis.

That said, if you do want to do it yourself, there's a couple of options:

1. You can write your own shim to interface WSGI with the class returned by CreateRequestHandler. In that case, you need to replicate the interface in BaseHTTPServer.BaseHTTPRequestHandler from the Python SDK. Converting WSGI to that, just so the dev_appserver code can convert it back seems a bit perverse, though.
2. You can rip out the code from the _HandleRequest method of DevAppServerRequestHandler, modify it to work with WSGI, and create a WSGI app from that (probably your best bet if you want to DIY).
3. You can start from scratch, which I believe is the approach taken by TwistedAE.

One thing to bear in mind whatever you do: App Engine explicitly expects a single-threaded environment for its apps. Don't use a multithreaded approach if you want apps to work the same locally as they do in production or on the dev_appserver!