I'm trying to make a generic request handler class based on Moya and Object Mapper.
Basically I want a method that performs a request to a Moya Target and performs some basic handling on both sucess and failure cases:
my class would be something like this based on this answer:
class APIRequestHandler<T: Mappable> {
let provider = APIManager().getAPIProvider() // Moya provider
func performRequest(target: Target, completionHandler: (response: T?, error: StoreError?) -> Void) {
provider.request(target) { result in
switch result {
case let .Success(response):
switch response.statusCode {
case 200..<300:
do {
let json = try NSJSONSerialization.JSONObjectWithData(response.data, options: .MutableContainers)
let contractualDocument = Mapper<T>().map(json)
completionHandler(response: contractualDocument!, error: nil)
} catch _ {
// Unexpected error when the response can't be parsed
completionHandler(response: nil, error: StoreError.UnexpectedError)
}
case 500:
completionHandler(response: nil, error: StoreError.ServerError)
default:
completionHandler(response: nil, error: StoreError.HTTPError(statusCode: response.statusCode))
}
case .Failure(_):
completionHandler(response: nil, error: StoreError.NetworkError)
}
}
}
}
My question is if I can get the same results using generics at a function level instead of class level:
func performRequest<T: Mappable>(target: Target, completionHandler: (response: T?, error: StoreError?) -> Void) {
provider.request(target) { result in
switch result {
case let .Success(response):
// blah, blah
case .Failure(_):
// bleh, bleh
}
}
}
I've tried it and I get a build error on my code:
Generic parameter "T" could not be inferred
Related
I'm trying to migrate my project from Alamofire 4.9 to 5.3 and I'm having a hard time with error handling. I would like to use Decodable as much as possible, but my API endpoints return one JSON structure when everything goes well, and a different JSON structure when there is an error, the same for all errors across all endpoints. The corresponding Codable in my code is ApiError.
I would like to create a custom response serializer that can give me a Result<T, ApiError> instead of the default Result<T, AFError>. I found this article that seems to explain the general process but the code in there does not compile.
How can I create such a custom ResponseSerializer?
I ended up making it work with the following ResponseSerializer:
struct APIError: Error, Decodable {
let message: String
let code: String
let args: [String]
}
final class TwoDecodableResponseSerializer<T: Decodable>: ResponseSerializer {
lazy var decoder: JSONDecoder = {
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601
return decoder
}()
private lazy var successSerializer = DecodableResponseSerializer<T>(decoder: decoder)
private lazy var errorSerializer = DecodableResponseSerializer<APIError>(decoder: decoder)
public func serialize(request: URLRequest?, response: HTTPURLResponse?, data: Data?, error: Error?) throws -> Result<T, APIError> {
guard error == nil else { return .failure(APIError(message: "Unknown error", code: "unknown", args: [])) }
guard let response = response else { return .failure(APIError(message: "Empty response", code: "empty_response", args: [])) }
do {
if response.statusCode < 200 || response.statusCode >= 300 {
let result = try errorSerializer.serialize(request: request, response: response, data: data, error: nil)
return .failure(result)
} else {
let result = try successSerializer.serialize(request: request, response: response, data: data, error: nil)
return .success(result)
}
} catch(let err) {
return .failure(APIError(message: "Could not serialize body", code: "unserializable_body", args: [String(data: data!, encoding: .utf8)!, err.localizedDescription]))
}
}
}
extension DataRequest {
#discardableResult func responseTwoDecodable<T: Decodable>(queue: DispatchQueue = DispatchQueue.global(qos: .userInitiated), of t: T.Type, completionHandler: #escaping (Result<T, APIError>) -> Void) -> Self {
return response(queue: .main, responseSerializer: TwoDecodableResponseSerializer<T>()) { response in
switch response.result {
case .success(let result):
completionHandler(result)
case .failure(let error):
completionHandler(.failure(APIError(message: "Other error", code: "other", args: [error.localizedDescription])))
}
}
}
}
And with that, I can call my API like so:
AF.request(request).validate().responseTwoDecodable(of: [Item].self) { response in
switch response {
case .success(let items):
completion(.success(items))
case .failure(let error): //error is an APIError
log.error("Error while loading items: \(String(describing: error))")
completion(.failure(.couldNotLoad(underlyingError: error)))
}
}
I simply consider that any status code outside of the 200-299 range corresponds to an error.
ResponseSerializers have a single requirement. Largely you can just copy the existing serializers. For example, if you wanted to parse a CSV (with no response checking):
struct CommaDelimitedSerializer: ResponseSerializer {
func serialize(request: URLRequest?, response: HTTPURLResponse?, data: Data?, error: Error?) throws -> [String] {
// Call the existing StringResponseSerializer to get many behaviors automatically.
let string = try StringResponseSerializer().serialize(request: request,
response: response,
data: data,
error: error)
return Array(string.split(separator: ","))
}
}
You can read more in Alamofire's documentation.
I have this piece of code in my app:
func saveContact2(contact: String) throws {
let contactStore = CNContactStore()
contactStore.requestAccess(for: .contacts, completionHandler: {(granted, error) in
if granted && error == nil {
//...
} else {
if !granted {
throw contactErrors.contactAccessNotGranted(["Error","Access to Contacts is not granted."])
}
}
})
}
I'd like to throw all errors raising in closure to calling function.
Compiler shows error:
Invalid conversion from throwing function of type '(_, _) throws -> ()' to non-throwing function type '(Bool, Error?) -> Void'
Could anyone help me please with the right syntax?
You cannot throw errors from an #escaping closure that is called asynchronously. And this makes sense because your app has carried on with its execution and there’s no where to catch the error.
So, instead, adopt completion handler pattern yourself:
func saveContact2(_ contact: String, completion: #escaping: (Result<Bool, Error>) -> Void) {
let contactStore = CNContactStore()
contactStore.requestAccess(for: .contacts) { (granted, error) in
guard granted else {
completion(.failure(error!)
return
}
//...
completion(.success(true))
}
}
And then you’d call it like:
saveContact2(contactName) { result in
switch result {
case .failure:
// handler error here
case .success:
// handle confirmation of success here
}
}
If you’re using an old compiler that doesn’t have the Result type, it’s basically:
enum Result<Success, Failure> where Failure: Error {
case success(Success)
case failure(Failure)
}
I have a network layer working with generics and I'm using protocols so I can test it later. I have followed this tutorial https://medium.com/thecocoapps/network-layer-in-swift-4-0-972bf2ea5033
This is my Mock for testing:
import Foundation
#testable import TraktTest
class MockUrlSessionProvider: ProviderProtocol {
enum Mode {
case success
case empty
case fail
}
private var mode: Mode
init(mode: Mode) {
self.mode = mode
}
func request<T>(type: T.Type, service: ServiceProtocol, completion: #escaping (NetworkResponse<T>) -> Void) where T: Decodable {
switch mode {
case .success: completion(NetworkResponse.success(T))
case .empty: completion(.failure(.noData))
case .fail: completion(.failure(.unknown("Error")))
}
}
}
I'm getting the error: Cannot convert value of type 'NetworkResponse<T.Type>' to expected argument type 'NetworkResponse<_>' in this line: completion(NetworkResponse.success(T))
If I send this to my completion success it compile:
try? JSONDecoder().decode(T.self, from: data!)
(dummy data that I created using encode and my model), but crash when get to my model because is nil despite I had encoded using JSONEncoder() with a correct model.
I think it works, because is the same logic that I use in my class that implements ProviderProtocol in my app:
final class URLSessionProvider: ProviderProtocol {
private var session: URLSessionProtocol
init(session: URLSessionProtocol = URLSession.shared) {
self.session = session
}
func request<T>(type: T.Type, service: ServiceProtocol, completion: #escaping (NetworkResponse<T>) -> Void) where T: Decodable {
let request = URLRequest(service: service)
session.dataTask(request: request) { [weak self] data, response, error in
let httpResponse = response as? HTTPURLResponse
self?.handleDataResponse(data: data, response: httpResponse, error: error, completion: completion)
}.resume()
}
private func handleDataResponse<T: Decodable>(data: Data?, response: HTTPURLResponse?, error: Error?, completion: (NetworkResponse<T>) -> Void) {
guard error == nil else { return completion(.failure(.unknown(error?.localizedDescription ?? "Error"))) }
guard let response = response else { return completion(.failure(.unknown("no_response".localized()))) }
switch response.statusCode {
case 200...299:
guard let data = data, let model = try? JSONDecoder().decode(T.self, from: data) else { return completion(.failure(.noData)) }
completion(.success(model))
default: completion(.failure(.unknown("no_response".localized())))
}
}
}
URLSessionProtocol is just a protocol which has a method dataTask same as the one in URLSession.shared (receive a URLRequest and returns Data, Response and Error in a completion).
My Network responses are a couple of enums:
enum NetworkResponse<T> {
case success(T)
case failure(NetworkError)
}
enum NetworkError {
case unknown(String)
case noData
}
My provider protocol just have a function to make the request using generics:
protocol ProviderProtocol {
func request<T>(type: T.Type, service: ServiceProtocol, completion: #escaping(NetworkResponse<T>) -> Void) where T: Decodable
}
I don't think I need to use ServiceProtocol in my test because is to setup the request with endpoint, headers, body, id, etc. But this is the protocol I created:
typealias Headers = [String: String]
typealias Parameters = [String: Any]
protocol ServiceProtocol {
func baseURL() -> URL
var path: String? { get }
var id: String? { get }
var method: HTTPMethod { get }
var task: Task { get }
var headers: Headers? { get }
var parametersEncoding: ParametersEncoding { get }
}
enum HTTPMethod: String {
case get = "GET"
case post = "POST"
}
enum Task {
case requestPlain
case requestParameters(Parameters)
}
enum ParametersEncoding {
case url
case json
}
In my app, I have a class that implement ProviderProtocol and use a URLSession.shared to make the dataTask when some viewModel call the request with the appropiate model.
I'm use to make test with protocols and a specific model, but with generics is showing me that error. How can I achieve to have a mock provider using generics so I can test any viewModel who make a call to network using different kinds of models (stubs).
The error occurs because NetworkResponse expects an instance of T, while the mock tries to provide the actual T.
So, you need to somehow provide an instance, however this cannot be generated by the mock as it doesn't have enough information about how to construct an instance.
I recommend injecting the success value from the outside, when creating the mock. You can do this either by making the mock class generic, or by making the Mode enum generic. Below is a sample implementation for the latter:
class MockUrlSessionProvider: ProviderProtocol {
// making the enum generic, to support injecting the success value
enum Mode<T> {
case success(T)
case empty
case fail
}
// need to have this as `Any` to cover all possible T generic arguments
private var mode: Any
// however the initializer can be very specific
init<T>(mode: Mode<T>) {
self.mode = mode
}
func request<T>(type: T.Type, service: ServiceProtocol, completion: #escaping (NetworkResponse<T>) -> Void) where T: Decodable {
// if the mock was not properly configured, do nothing
guard let mode = mode as? Mode<T> else { return }
// alternatively you force cast and have the unit test crash, this should help catching early configuration issues
// let mode = mode as! Mode<T>
switch mode {
case let .success(value): completion(NetworkResponse.success(value))
case .empty: completion(.failure(.noData))
case .fail: completion(.failure(.unknown("Error")))
}
}
}
For my networking module, I have this protocol that I adopt for accessing different parts of the API:
protocol Router: URLRequestConvertible {
var baseUrl: URL { get }
var route: Route { get }
var method: HTTPMethod { get }
var headers: [String: String]? { get }
var encoding: ParameterEncoding? { get }
var responseResultType: Decodable.Type? { get }
}
I'm adopting this with enums that look like this:
enum TestRouter: Router {
case getTestData(byId: Int)
case updateTestData(byId: Int)
var route: Route {
switch self {
case .getTestData(let id): return Route(path: "/testData/\(id)")
case .updateTestData(let id): return Route(path: "/testDataOtherPath/\(id)")
}
}
var method: HTTPMethod {
switch self {
case .getTestData: return .get
case .updateTestData: return .put
}
}
var headers: [String : String]? {
return [:]
}
var encoding: ParameterEncoding? {
return URLEncoding.default
}
var responseResultType: Decodable.Type? {
switch self {
case .getTestData: return TestData.self
case .updateTestData: return ValidationResponse.self
}
}
}
I want to use Codable for decoding nested Api responses. Every response consists of a token and a result which content is depending on the request route.
For making the request I want to use the type specified in the responseResultType property in the enum above.
struct ApiResponse<Result: Decodable>: Decodable {
let token: String
let result: Result
}
extension Router {
func asURLRequest() throws -> URLRequest {
// Construct URL
var completeUrl = baseUrl.appendingPathComponent(route.path, isDirectory: false)
completeUrl = URL(string: completeUrl.absoluteString.removingPercentEncoding ?? "")!
// Create URL Request...
var urlRequest = URLRequest(url: completeUrl)
// ... with Method
urlRequest.httpMethod = method.rawValue
// Add headers
headers?.forEach { urlRequest.addValue($0.value, forHTTPHeaderField: $0.key) }
// Encode URL Request with the parameters
if encoding != nil {
return try encoding!.encode(urlRequest, with: route.parameters)
} else {
return urlRequest
}
}
func requestAndDecode(completion: #escaping (Result?) -> Void) {
NetworkAdapter.sessionManager.request(urlRequest).validate().responseData { response in
let responseObject = try? JSONDecoder().decode(ApiResponse<self.responseResultType!>, from: response.data!)
completion(responseObject.result)
}
}
}
But in my requestAndDecode method It throws an compiler error (Cannot invoke 'decode' with an argument list of type '(Any.Type, from: Data)'). I can't use ApiResponse<self.responseResultType!> like that.
I could make this function generic and call it like this:
TestRouter.getTestData(byId: 123).requestAndDecode(TestData.self, completion:)
but then I'd have to pass the response type everytime I want to use this endpoint.
What I want to achieve is that the extension function requestAndDecode takes it response type information from itself, the responseResultType property.
Is this possible?
Ignoring the actual error report you have a fundamental problem with requestAndDecode: it is a generic function whose type parameters are determined at the call site which is declared to return a value of type Result yet it attempts to return a value of type self.responseResultType whose value is an unknown type.
If Swift's type system supported this it would require runtime type checking, potential failure, and your code would have to handle that. E.g. you could pass TestData to requestAndDecode while responseResultType might be ValidationResponse...
Change the JSON call to:
JSONDecoder().decode(ApiResponse<Result>.self ...
and the types statically match (even though the actual type that Result is is unknown).
You need to rethink your design. HTH
Create a Generic function with Combine and AlomFire. You can use it for all method(get, post, put, delete)
func fatchData<T: Codable>(requestType: String, url: String, params: [String : Any]?, myType: T.Type, completion: #escaping (Result<T, Error>) -> Void) {
var method = HTTPMethod.get
switch requestType {
case "Get":
method = HTTPMethod.get
case "Post":
method = HTTPMethod.post
print("requestType \(requestType) \(method) ")
case "Put":
method = HTTPMethod.put
default:
method = HTTPMethod.delete
}
print("url \(url) \(method) \(AppConstant.headers) ")
task = AF.request(url, method: method, parameters: params, encoding: JSONEncoding.default, headers: AppConstant.headers)
.publishDecodable(type: myType.self)
.sink(receiveCompletion: { (completion) in
switch completion{
case .finished:
()
case .failure(let error):
// completion(.failure(error))
print("error \(error)")
}
}, receiveValue: {
[weak self ](response) in
print("response \(response)")
switch response.result{
case .success(let model):
completion(.success(model))
print("error success")
case .failure(let error):
completion(.failure(error))
print("error failure \(error.localizedDescription)")
}
}
)
}
I'm attempting to define a custom model serialization for Alamofire 4.0. So far I'm following the model presented used by responseJson and friends. Specifically, what I have so far is:
extension Alamofire.Request {
public static func serializeResponseModel<T:ModelObject>(response:HTTPURLResponse?, data:Data?, error:Error?) -> Alamofire.Result<T> {
switch serializeResponseJSON(options: [], response: response, data: data, error: error) {
case .success(let jsonObject):
do {
return .success(try T(json:jsonObject as! JSONObject))
}
catch {
return .failure(error)
}
case .failure(let error):
return .failure(error)
}
}
}
extension Alamofire.DataRequest {
public static func serializeResponseModel<T:ModelObject>() -> DataResponseSerializer<T> {
return DataResponseSerializer { _, response, data, error in
return Request.serializeResponseConcierge(response: response, data: data, error: error)
}
}
#discardableResult
public func responseModel<T:ModelObject>(queue: DispatchQueue? = nil, completionHandler: #escaping (DataResponse<T>) -> Void) -> Self
{
return response(
queue: queue,
responseSerializer: DataRequest.serializeResponseModel(),
completionHandler: completionHandler
)
}
}
Unfortunately, the framework is somewhat poorly implemented and the line return response( is finding the response property (defined in Request) and not the appropriate response method (defined in DataRequest), which leads to the compile error:
Cannot call value of non-function type 'HTTPURLResponse?'
What am I missing here that allows this to work in the responseJson case, but not in my case?
Apparently the problem arose from over-generalization, and the compiler not being able to generate an appropriate type for DataRequest.serializeResponseModel() When I changed responseModel to the following and specified the appropriate type, things work as expected:
#discardableResult
public func responseModel<T:ModelObject>(queue: DispatchQueue? = nil, completionHandler: #escaping (DataResponse<T>) -> Void) -> Self
{
return response(
queue: queue,
responseSerializer: DataRequest.modelResponseSerializer() as DataResponseSerializer<T>,
completionHandler: completionHandler
)
}