Using the library when the JSON data can be successful or an error message

[ManjitBedi]

Hi,

I am currently writing some code where I am using the Networking library to fetch code from a server using an access token and other parameters. If there is a problem with the body data in the request, an error response will be returned as JSON.

How do I could something using Networking & Combine to handle the data that comes back that can be one of two different responses per se. I am using something like this at the moment:

    /// - Parameters: dictionary with access token etc
    func somePost(paramsIn: Params) -> AnyPublisher<Any, Error> {
        post("/endpoint", params: paramsIn)
    }

api.somePost(paramsIn: params).sink { result in
            switch result {
            case .finished:
                break
            case .failure(let err):
                completion(err)
            }
        } receiveValue: { [self] responseData in
            // check what the response data is.
            if let err = checkForErrorsInReponse(data: data as! [String : Any]) {
                completion(err)
            } else {
                // Check what's in the data
               processResponse((data: data as! [String : Any])
                completion(nil)
            }
        }
        .store(in: &cancellables)

This code is not going to work - well it requires a lot of boilderplate; the data in the closure is a Dictionary not JSON data. I did try changing the type of responseData to Any but in the debugger it is indicating that it is still a dictionary.

How. might I rewrite the code using a JSON publisher?

let jsonPublisher: AnyPublisher<Any, Error> = client.get("")

[s4cha]

Hi ManjitBedi, please excuse the delay. From what I see you are using AnyPublisher<Any, Error> which is the "json" one already.
As for handling errors, if the status code is not in the 200 range, the error is going to be in the failure block and not the receiveValue. You can have more info here https://github.com/freshOS/Networking#handling-errors.

In the failure block, in order to access the error JSON, you need to parse the Error into NetworkingError, then you will have access to status, code & jsonPayload.

Here is an example using the async await api of parsing the error JSON Payload and bridging it to a Domain Error.

public func validate(user: User, with token: String) async throws {
    do {
        return try await put("/users/\(user.id)/validate", body: .urlEncoded(["token": token]))
    } catch {
        if let e = error as? NetworkingError, let payload = e.jsonPayload, let jsonData = try? JSONSerialization.data(withJSONObject: payload, options: []) {
            let decoder = JSODecoder()
            let validationError = try? decoder.decode(ValidationErrorResponseJSON.self, from: jsonData)
            if validationError?.error == "EmailAlreadyValidated" {
                throw MyDomainError.emailAlreadyValidated
            }
        }
        throw MyDomainError.unknown
    }
}

Hope it helps :)

[ManjitBedi]

Thanks for the reply. Since then, I have seen elsewhere that you can set up an enum in a struct to then handle if the response from the server has an error like an expired token.

To reiterate

• a successful response is received but in the body of the response there is an error.
• the JSON decoding to a struct does not work currently as there can be two different types of payloads in the response for a success or server error of some kind specific to the back end

I don't know how I can code this up efficiently to handle the multiple payloads. For the moment, I am get the data from the response then decoding the JSON etc. It is creating more boiler plate code.