Alamofire returns .Success on error HTTP status codes

Question

I have a pretty simple scenario that I'm struggling with. I'm using Alamofire to register a user on a rest API. The first call to register is successful and the user can log in. The second call, when trying to register with the same email address should result in a HTTP status code 409 from the server. Alamofire, however, returns a .Success with an empty request and response. I have tested this this API with postman and it correctly returns a 409.

Why is Alamofire not returning .Failure(error), where the error has status code info etc?

Here is the call I run with the same input each time.

Alamofire.request(.POST, "http://localhost:8883/api/0.1/parent", parameters: registrationModel.getParentCandidateDictionary(), encoding: .JSON).response(completionHandler: { (req, res, d, e) -> Void in
        print(req, res, d, e)
    })

Answer 1

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)
         }
     }

Answer 2

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.

Answer 3

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

Answer 4

Here is my code for AlamoFire error catching:

switch response.result {
                case .success(let value):
                    completion(.success(value))
                case .failure(var error):

                    var errorString: String?

                    if let data = response.data {
                        if let json = try? (JSONSerialization.jsonObject(with: data, options: []) as! [String: String]) {
                            errorString = json["error"]

                        }
                    }
                    let error = MyError(str: errorString!)
                    let x = error as Error
                    print(x.localizedDescription)
                    completion(.failure(x))

                }

and the MyError class difinition:

class MyError: NSObject, LocalizedError {
        var desc = ""
        init(str: String) {
            desc = str
        }
        override var description: String {
            get {
                return "MyError: \(desc)"
            }
        }
        //You need to implement `errorDescription`, not `localizedDescription`.
        var errorDescription: String? {
            get {
                return self.description
            }
        }
    }