Alamofire: Network error vs invalid status code?

Question

Using Alamofire 4/Swift 3 how can you differentiate between a request that fails due to:

1. Network connectivity (host down, can't reach host) vs
2. Invalid server HTTP response code (ie: 499) which causes the Alamofire request to fail due to calling validate()?

Code:

    sessionManager.request(url, method: .post, parameters:dict, encoding: JSONEncoding.default)
        .validate() //Validate status code
        .responseData { response in

        if response.result.isFailure {
               //??NETWORK ERROR OR INVALID SERVER RESPONSE??
        }
    }

We want to handle each case differently. In the latter case we want to interrogate the response. (In the former we don't as there is no response).

Answer 1

Here's our current working solution:

sessionManager.request(url, method: .post, parameters:dict, encoding: JSONEncoding.default)
    .validate() //Validate status code
    .responseData { response in

    if response.result.isFailure {
        if let error = response.result.error as? AFError, error.responseCode == 499 {
            //INVALID SESSION RESPONSE
        } else {
            //NETWORK FAILURE
        }
    }
}

If result.error it is of type AFError you can use responseCode. From the AFError source comments:

/// Returns whether the `AFError` is a response validation error. When `true`, the `acceptableContentTypes`,
/// `responseContentType`, and `responseCode` properties will contain the associated values.
public var isResponseValidationError: Bool {
    if case .responseValidationFailed = self { return true }
    return false
}

Maybe there is a better way (?) but that seems to work...