determining URL that forwarded

I have a series of different domain names that I would like to all point (via URL forwarding from my domain host) to开发者_Go百科 a google app engine application that reads what the forwarding URL is. So if the domain typed in was original XYZ.com, then when I am forwarded to my application, I can return what that original domain name was. I'm using the python variant. How best can I do this without coding for each and every variant?

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Generally, the target of a 301/302 redirect can't determine what URL issued the redirect. If the user is redirected by client-side code, the referring page should be present in the "Referer" request header. For server-side redirects, I don't believe it's standard for user agents to populate (or override) the Referer header.

If you want to point multiple domains to your App Engine app, try configuring them as custom domains rather than forwards. With this route, the custom domain would stay in the user's address bar, and you can simply check the host header to see which custom domain the visitor is using.

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If by forwarding you mean HTTP redirection, you can check the Referer header.

If you mean DNS resolving (e.g. distinguishing between your application being invoked via your own domain and .appspot.com one), there is SERVER_NAME environment variable (os.environ["SERVER_NAME"]) that stores the domain (e.g. www.example.com) used to issue the request.

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If you are using a javascript redirect, that you can just check the referrer:

http://en.wikipedia.org/wiki/HTTP_referrer

but this is not a 100% solution.

If you have multiple domains parked on one appengine instance and you just want to know which one the user is viewing, you can check the host name in the request object.