Handling redirects correctly with NSURLConnection

Question

For the purposes of this, I'm going to pretend the original url is http://host/form and the new url is https://host/form. (Note that before I ship this, both URLs are going to be secure. However, the nonsecure-to-secure seems like a convenient redirect to test this on.)

I'm accessing a web API using NSURLConnection that redirects me. Basically, I want to take everything I just submitted to http://hostaform and re-submit it to https://host/form. I thought this would be the default behavior, but it looks like the body is being lost in the redirect.

So I think I need to handle the connection:willSendRequest:redirectResponse: event of the NSURLConnection's delegate and re-attach the body. The problem is this message seems woefully underdocumented. The only info I can find on this method is NSURLConnection Class Reference, which isn't very helpful. Among other things, it includes this:

redirectResponse: The URL response that caused the redirect. May be nil in cases where this method is not being sent as a result of involving the delegate in redirect processing.

I'm not sure what this means. Combined with an initial willSendRequest: invocation, I think this is means willSendRequest: is being sent even for my initial request, prior to the redirect response. Is that correct?

So I've added code to my delegate to retain the body an extra time, and added this willSendRequest: handler:

- (NSURLRequest *)connection: (NSURLConnection *)inConnection
       willSendRequest: (NSURLRequest *)inRequest
      redirectResponse: (NSURLResponse *)inRedirectResponse;
{
    if (inRedirectResponse) {
        NSMutableURLRequest *r = [[inRequest mutableCopy] autorelease];
        [r setURL: [inRedirectResponse URL]];
        [r setHTTPBody: body];
        return r;
    } else {
        return inRequest;
    }
}

It doesn't work. But I'm not even sure if this is the right approach. It seems excessively hackish to me. What should I be doing? Is this documented anywhere? I've found nothing useful in Apple's documentation or using Google so far.

(This is on the iPhone, although there doesn't seem to be much difference in these classes.)

Answer 1

I think I may have solved this. Instead of the willSendResponse: in the original question, I'm using this:

- (NSURLRequest *)connection: (NSURLConnection *)inConnection
             willSendRequest: (NSURLRequest *)inRequest
            redirectResponse: (NSURLResponse *)inRedirectResponse;
{
    if (inRedirectResponse) {
        NSMutableURLRequest *r = [[request mutableCopy] autorelease]; // original request
        [r setURL: [inRequest URL]];
        return r;
    } else {
        return inRequest;
    }
}

The idea here is that instead of cloning the new request and trying to shape it the same as the one Cocoa Touch sends me, I create a clone of the original request and change just the URL to match the request Cocoa Touch sent me.

(I'll accept this answer and close this question as soon as I'm able to.)

Answer 2

You should be checking the HTTP response status code sent by the server to determine whether to send a GET or repeat the POST. For 303 (or 302), send a GET request. For 307, repeat the POST.