Debugging Facebook AppEngine application locally

There is a good discussion around "how to use Facebook log-in from Google App Engine", but there is one tricky issue dealing with Facebook's app-id/secret-key pair, which is generated for a specific URL.

If you hard-code the id/key pair for your applicatin's URL in your source code, you won't be able to debug it until you deploy. 

I've encountered this issue when I was developing fruence.com (groupware for Facebook users), and came up with a simple work around.

Here is the code (the actual app-id and secret-code are replaced by "{app-id}","{secret-code}" to hide them):

@memoize
def _facebook_ids(domain):
    dict = {
        "www.fruence.com": ("{app-id}","{secret-code}"),
        "un-url.appspot.com": ("{app-id}", "{secret-code}"),
        "staging.latest.un-url.appspot.com": ("{app-id}", "{secret-code}"),
        "localhost:8104": ("{app-id}", "{secret-code}"),
        "10.0.1.100:8104": ("{app-id}","{secret-code}"),
    }
    return dict[domain]

class User(db.Model):
    ...
    @classmethod
    def facebook_ids(cls, rh):
        url = rh.request.url
        (a, domain, b, c, d, e) = urlparse.urlparse(url)
        return _facebook_ids(domain)

    @classmethod
    def current_user(cls, rh):
        if not hasattr(rh, "current_user"):
            rh.current_user = None
            (id, secret) = cls.facebook_ids(rh)
            cookie = facebook.get_user_from_cookie(rh.request.cookies, id, secret)
            if cookie:
                ... 

Notice that I have generated five app-id/secret-key pairs, including staging environment and local environment (localhost as well as LAN), which allows me to debug my application in any environment.

To see this mechanism in action, access my app from both www.fruence.com and un-url.appspot.com. Each URL has an unique app-id/secret-key pair, but both are connected to the same version of the application. As a Facebook user, you need to "approve" each app separately because they are two different apps from Facebook's point of view (and cookies are associated with each domain), but my application recognize you correctly because the "current_user" is associated with facebook id. 

Notice that Facebook allows you to register local URLs like "http://localhost:8104". As far as I can tell, Facebook generates a unique app-id/secret-key pair for each registration, therefore, you don't need to worry about collision. 

Viva Google App Engine!

Comments

[Dirk Diggler]

An alternative approach is to temporarily map your domain to localhost using /etc/hosts. Add this line when debugging:

127.0.0.1 www.fruence.com

Comment it out with a leading # when you want to hit the live site.

[Amir]

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[Esbolat]

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