Alamofire returns .Success on error HTTP status codes

From the Alamofire manual:

Validation

By default, Alamofire treats any completed request to be successful, regardless of the content of the response. Calling validate before a response handler causes an error to be generated if the response had an unacceptable status code or MIME type.

You can manually validate the status code using the validate method, again, from the manual:

Alamofire.request(.GET, "https://httpbin.org/get", parameters: ["foo": "bar"])     .validate(statusCode: 200..<300)     .validate(contentType: ["application/json"])     .response { response in         print(response)     }

Or you can semi-automatically validate the status code and content-type using the validate with no arguments:

Alamofire.request(.GET, "https://httpbin.org/get", parameters: ["foo": "bar"])     .validate()     .responseJSON { response in         switch response.result {         case .success:             print("Validation Successful")         case .failure(let error):             print(error)         }     }

If using response, you can check the NSHTTPURLResponse parameter:

Alamofire.request(urlString, method: .post, parameters: registrationModel.getParentCandidateDictionary(), encoding: JSONEncoding.default)    .response { response in        if response.response?.statusCode == 409 {            // handle as appropriate        }}

By default, 4xx status codes aren't treated as errors, but you can use validate to treat it as an such and then fold it into your broader error handling:

Alamofire.request(urlString, method: .post, parameters: registrationModel.getParentCandidateDictionary(), encoding: JSONEncoding.default)    .validate()    .response() { response in        guard response.error == nil else {            // handle error (including validate error) here, e.g.            if response.response?.statusCode == 409 {                // handle 409 here            }            return        }        // handle success here}

Or, if using responseJSON:

Alamofire.request(urlString, method: .post, parameters: registrationModel.getParentCandidateDictionary(), encoding: JSONEncoding.default).validate().responseJSON() { response in    switch response.result {    case .failure:        // handle errors (including `validate` errors) here        if let statusCode = response.response?.statusCode {            if statusCode == 409 {                // handle 409 specific error here, if you want            }        }    case .success(let value):        // handle success here        print(value)    }}

The above is Alamofire 4.x. See previous rendition of this answer for earlier versions of Alamofire.

if you use validate() you'll loose the error message from server, if you want to keep it, see this answer https://stackoverflow.com/a/36333378/1261547