Is data sent via HTTP POST when the Server does not exist?

Question

I work for a large-ish advertising company. We've created a very lightweight clone of the PayPal IPN so we can offer CC Processing services for our top advertisers.

Like the PP IPN, it's a simple RESTful interface.

I deliberately instructed our admin guys to configure the vhost for this web app to only respond to requests on port 443.

This particular question is beyond my HTTP Protocol knowledge:

This may vary from browser to browser, but when a user submits a form, and the ACTION for that form is, say http://www.somesite.com, if the browser cannot resolve that site, does the post payload ever get sent over the wire?

I know this is a bit esoteric and it's more of an implementation question than something that exists in the HTTP RFC (as far as I could tell). Any takers?

Answer 1

Before sending any data the browser needs to open a TCP connection to the target site. Since this connection to the target site cannot be opened in the first place, no data can be sent.

Update (Thanks for the hint in the comments): Use HTTP-Requests like POST to avoid sending data over the wire which could be intercepted by proxies before the existence of the target could be checked. With proxies the TCP-connection is always established successfully and the HTTP-request-header is sent to it. The POST-request contains the additional data in his request-body which should be sent only if the request header returns no error. Nevertheless, the implementation of proxies differ and I cannot guarantee that there is no proxy which returns an error if the target-site is non-existing. But in such a case I don't know any way where you could avoid sending the complete data over the wire...