ios NSURLConnection 自定义响应解析

情况是这样的。

登陆请求到后端是acegi框架，响应返回的是302.重定向
NSURLConnection如何手动判断响应状态码？并按重定向uri再次发送请求

以下写法时，会自动发送302请求。但会以GET形式，并且将sessionid信息都放在uri里

var req = NSMutableURLRequest(URL: NSURL(string: "..."))

NSURLConnection.sendAsynchronousRequest(req, queue: NSOperationQueue.mainQueue()) { (response: NSURLResponse!, data: NSData!, error: NSError!) -> Void in
    println("do buz")
 }

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好吧。
挣扎了一下午。
手动搞出了这种临时解决方案：

class CMHTTP : NSObject, NSURLConnectionDataDelegate {
    func send() {
        let req = NSMutableURLRequest(URL: NSURL(string: "...")!)
        req.HTTPMethod = "POST"
        req.HTTPBody = NSString(string: "a=b&b=c").dataUsingEncoding(NSUTF8StringEncoding)

        let conn = NSURLConnection(request: req, delegate: self, startImmediately: false)

        conn?.start()
    }

    func connection(connection: NSURLConnection, willSendRequest request: NSURLRequest, redirectResponse response: NSURLResponse?) -> NSURLRequest? {
        if (true) { // 满足自已的条件，新建一个自定义的request
            return NSURLRequest(URL: NSURL(string: "...")!)
        }
        return request
    }



}

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这里面搞response，重定向会回调
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response