file sharing app

That's the redirect I mentioned. I would strongly recommend looking at the Location header rather than trying to parse the returned HTML. The header should contain the same URL but not require any fragile parsing.

I don't have any direct experience with Corona SDK, but I'd agree that the network.request documentation makes it look like the default behavior is to follow redirects. I don't have any insight as to why that isn't working as expected.

Since it looks like you're getting the original response (before the redirect), I'd suggest using event.responseHeaders.Location to get the URL from the 302 response. Or ping the Corona folks to figure out why the automatic redirect following isn't working.