Alamofire 4 Swift 3 ParameterEncoding Custom

Question

I updated my project to Swift 3 and Alamofire 4. I was using custom Encoding, but it's changed to other encoding methods. I am not able to find the alternative/equivalent to this:

alamoFire.request(urlString, method: HTTPMethod.post, parameters: [:], encoding: .Custom({
        (convertible, params) in

        let mutableRequest = convertible.URLRequest.copy() as! NSMutableURLRequest
        let data = (body as NSString).data(using: String.Encoding.utf8)
        mutableRequest.httpBody = data
        return (mutableRequest, nil)

    }), headers: headers()).responseJSON { (responseObject) -> Void in

        switch responseObject.result {
        case .success(let JSON):
            success(responseObject: JSON)

        case .failure(let error):
            failure(error: responseObject)
        }
    }

I also tried by making URLRequest object and simple request its also giving me errors

var request = URLRequest(url: URL(string: urlString)!)
    let data = (body as NSString).data(using: String.Encoding.utf8.rawValue)
    request.httpBody = data
    request.httpMethod = "POST"
    request.allHTTPHeaderFields = headers()

    alamoFire.request(request).responseJSON { (responseObject) -> Void in

        switch responseObject.result {
        case .success(let JSON):
            success(JSON)

        case .failure(let error):
            failure(responseObject, error)
        }
    }

Do point me in some direction, how to attach httpbody with the Alamofire 4