I am building an app that will work with Plaid. Plaid provides a nice little LinkKit that I need to use to grab my link_token. I provide that link_token to authenticate to a bank. I have written a request using Alamofire to send the .post to get the new link_token when someone would want to add another account. My issue is when I decode the JSON to a struct that I have built I cant seem to use that stored link_token value.
Code to retrieve link_token
let parameters = PlaidAPIKeys(client_id: K.plaidCreds.client_id,
secret: K.plaidCreds.secret,
client_name: K.plaidCreds.client_name,
language: K.plaidCreds.language,
country_codes: [K.plaidCreds.country_codes],
user: [K.plaidCreds.client_user_id: K.plaidCreds.unique_user_id],
products: [K.plaidCreds.products])
func getLinkToken() {
let linkTokenRequest = AF.request(K.plaidCreds.plaidLinkTokenURL,
method: .post,
parameters: parameters,
encoder: JSONParameterEncoder.default).responseDecodable(of: GeneratedLinkToken.self) { response in
print(response)
}
}
Struct I have built:
struct GeneratedLinkToken: Decodable {
let expiration: String
let linkToken: String
let requestID: String
enum CodingKeys: String, CodingKey {
case expiration = "expiration"
case linkToken = "link_token"
case requestID = "request_id"
}
}
I have tested by calling the function getLinkToken() when pressing my add account or dummy button, I do get the data back that I am needing. Why wouldnt I be able to access GeneratedLinkToken.linkToken directly after the request?
You aren't able to access linkToken property like this: GeneratedLinkToken.linkToken, because linkToken is as instance property(read here)
If you want to get an instance after your request, you can do it like this:
func getLinkToken(completion: #escaping ((GeneratedLinkToken) -> Void)) {
let linkTokenRequest = AF.request(K.plaidCreds.plaidLinkTokenURL,
method: .post,
parameters: parameters,
encoder: JSONParameterEncoder.default).responseDecodable(of: GeneratedLinkToken.self) { response in
print(response)
// if response is an object of type GeneratedLinkToken
switch response.result {
case .success(let object):
completion(object)
case .failure(let error):
// hanlde error
}
}
}
Later you can call as:
getLinkToken { linkObject in
print("My tokne: \(linkObject.linkToken)")
}
I added completion(read here) to your method, since the request executing async, you can take a look at this Q/A: read here. I also suggest you, pass parameters as a parameter to this function, not declare it globally.
Related
I am trying to write a simple function handling authentication POST requests that return JWT tokens.
My LoopBack 4 API returns the token as a JSON packet in the following format:
{ "token": "my.jwt.token" }
In case of an error, the following gets returned instead:
{
"error": {
"statusCode": 401,
"name": "UnauthorizedError",
"message": "Invalid email or password."
}
}
As you can see, these types are completely different, they don't have any common properties.
I've defined the following Swift structures to represent them:
// Success
struct Token: Decodable {
let token: String
}
// Error
struct TokenError: Decodable {
let error: ApiError
}
struct ApiError: Decodable {
let statusCode: Int
let name: String
let message: String
}
The signature of the authentication request that returns Swift Generics:
#available(iOS 15.0.0, *)
func requestToken<T: Decodable>(_ user: String, _ password: String) async throws -> T
I've been trying to unit test this function but Swift requires me to declare the type of the result up front:
let result: Token = try await requestToken(login, password)
This works perfectly fine for the happy path but if the authentication is unsuccessful, a The data couldn’t be read because it is missing. error gets thrown. I can certainly do-catch it but I haven't been able to cast the result to my TokenError type in order to access its properties.
I have come across a few threads on StackOverflow where the general advice is to represent the success and error types by a common protocol but I've had no luck with that either due to a conflict with the Decodable protocol that the response types already conform to.
So the question is whether it is possible to work with both success and error result variables returned by my requestToken function.
The most natural way, IMO is to throw ApiErrors, so that they can be handled in the same way as other errors. That would look like this:
Mark ApiError as an Error type:
extension ApiError: Error {}
Now you can decode Token directly, and it will throw ApiError if there's an API error, or DecodingError if the data is corrupted. (Note the use of try? in the first decode and try in the else decode. This way it throws if the data can't be decoded at all.)
extension Token: Decodable {
enum CodingKeys: CodingKey {
case token
}
init(from decoder: Decoder) throws {
if let container = try? decoder.container(keyedBy: CodingKeys.self),
let token = try? container.decode(String.self, forKey: .token)
{
self.init(token: token)
} else {
throw try TokenError(from: decoder).error
}
}
}
// Usage if you want to handle ApiErrors specially
do {
try JSONDecoder().decode(Token.self, from: data)
} catch let error as ApiError {
// Handle ApiErrors
} catch let error {
// Handle other errors
}
Another approach is to keep ApiErrors separate from other errors, in which case there are three possible ways requestToken can return. It can return a Token, or it can return a TokenError, or it can throw a parsing error. Throwing an error is handled by throws. Token/TokenError require an "or" type, which is an enum. This could be done with a Result, but that might be a little confusing, since the routine also throws. Instead I'll be explicit.
enum TokenRequestResult {
case token(Token)
case error(ApiError)
}
Now you can make this Decodable by first trying to decode it as a Token, and if that fails, try decoding it as a TokenError and extracting the ApiError from that:
extension TokenRequestResult: Decodable {
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
if let token = try?
container.decode(Token.self) {
self = .token(token)
} else {
self = .error(try container.decode(TokenError.self).error)
}
}
}
To use this, you just need to switch:
let result = try JSONDecoder().decode(TokenRequestResult.self, from: token)
switch result {
case .token(let token): // use token
case .error(let error): // use error
}
My API returns this format, where data can contain all kinds of responses.
{
status: // http status
error?: // error handle
data?: // your response data
meta?: // meta data, eg. pagination
debug?: // debuging infos
}
I have made a Codable Response type with a generic for the optional data, of which we do not know the type.
struct MyResponse<T: Codable>: Codable {
let status: Int
let error: String?
let data: T?
let meta: Paging?
let debug: String?
}
I am now trying to write API convenience methods as concisely as possible. So I have a function to return a generic publisher that I can use for all these responses, i.e. one that pre-parses the response and catches any errors upfront.
First, I get a dataTaskPublisher that processes the parameter inputs, if any. Endpoint is just a convenience String enum for my endpoints, Method is similar. MyRequest returns a URLRequest with some necessary headers etc.
Notice the way I define the parameters: params: [String:T]. This is standard JSON so it could be strings, numbers etc.
It seems this T is the problem somehow..
static fileprivate func publisher<T: Encodable>(
_ path: Endpoint,
method: Method,
params: [String:T] = [:]) throws
-> URLSession.DataTaskPublisher
{
let url = API.baseURL.appendingPathComponent(path.rawValue)
var request = API.MyRequest(url: url)
if method == .POST && params.count > 0 {
request.httpMethod = method.rawValue
do {
let data = try JSONEncoder().encode(params)
request.httpBody = data
return URLSession.shared.dataTaskPublisher(for: request)
}
catch let err {
throw MyError.encoding(description: String(describing: err))
}
}
return URLSession.shared.dataTaskPublisher(for: request)
}
Next, I am parsing the response.
static func myPublisher<T: Encodable, R: Decodable>(
_ path: Endpoint,
method: Method = .GET,
params: [String:T] = [:])
-> AnyPublisher<MyResponse<R>, MyError>
{
do {
return try publisher(path, method: method, params: params)
.map(\.data)
.mapError { MyError.network(description: "\($0)")}
.decode(type: MyResponse<R>.self, decoder: self.agent.decoder)
.mapError { MyError.encoding(description: "\($0)")} //(2)
.tryMap {
if $0.status > 204 {
throw MyError.network(description: "\($0.status): \($0.error!)")
}
else {
return $0 // returns a MyResponse
}
}
.mapError { $0 as! MyError }
//(1)
.eraseToAnyPublisher()
}
catch let err {
return Fail<MyResponse<R>,MyError>(error: err as? MyError ??
MyError.undefined(description: "\(err)"))
.eraseToAnyPublisher()
}
}
Now I can write an endpoint method easily. Here are two examples.
static func documents() -> AnyPublisher<[Document], MyError> {
return myPublisher(.documents)
.map(\.data!)
.mapError { MyError.network(description: $0.errorDescription) }
.receive(on: DispatchQueue.main)
.eraseToAnyPublisher() as AnyPublisher<[Document], MyError>
}
and
static func user() -> AnyPublisher<User, MyError> {
return myPublisher(.user)
.map(\.data!)
.mapError { MyError.network(description: $0.errorDescription) }
.receive(on: DispatchQueue.main)
.eraseToAnyPublisher() as AnyPublisher<User, MyError>
}
All this is working well. Please note that each time, I have to specify my exact return type twice. I think I can live with that.
I should be able to simplify this so that I do not have to repeat the same three operators (map, mapError, receive) in exactly the same way each time.
But when I insert .map(\.data!) at the location //(1) above I get the error Generic parameter T could not be inferred. at the location //(2).
This is really confusing. Why does the generic type in the input parameters play any role here? This must be related to the call to the .decode operator just above, where the generic in question is called R, not T.
Can you explain this? How can I refactor these operators upstream?
This code has a number of small problems. You're right that one is [String: T]. That means that for a given set of parameters, all the values must be of the same type. That's not "JSON." This will accept a [String: String] or a [String: Int], but you can't have both Int and String values in the same dictionary if you do it this way. And it will also accept [String: Document], and it doesn't seem like you really want that.
I'd recommend switching this to just Encodable, which would allow you to pass structs if that were convenient, or Dictionaries if that were convenient:
func publisher<Params: Encodable>(
_ path: Endpoint,
method: Method,
params: Params?) throws
-> URLSession.DataTaskPublisher
func myPublisher<Params: Encodable, R: Decodable>(
_ path: Endpoint,
method: Method = .GET,
params: Params?)
-> AnyPublisher<MyResponse<R>, MyError>
Then modify your params.count to check for nil instead.
Note that I didn't make params = nil a default parameter. That's because this would recreate a second problem you have. T (and Params) can't be inferred in the default case. For = [:], what is T? Swift has to know, even though it's empty. So instead of a default, you use an overload:
func myPublisher<R: Decodable>(
_ path: Endpoint,
method: Method = .GET)
-> AnyPublisher<MyResponse<R>, MyError> {
let params: String? = nil // This should be `Never?`, see https://twitter.com/cocoaphony/status/1184470123899478017
return myPublisher(path, method: method, params: params)
}
Now, when you don't pass any parameters, Params automatically becomes String.
So now your code is fine, and you don't need the as at the end
func documents() -> AnyPublisher<[Document], MyError> {
myPublisher(.documents)
.map(\.data!)
.mapError { MyError.network(description: $0.errorDescription) }
.receive(on: DispatchQueue.main)
.eraseToAnyPublisher() // <== Removed `as ...`
}
Now, that .map(\.data!) makes me sad. If you get back corrupt data from the server, the app will crash. There are lots of good reasons to crash apps; bad server data is never one of them. But fixing that isn't really related to this question (and is a little bit complicated because Failure types other than Error make things hard currently), so I'll leave it for now. My general recommendation is to use Error as your Failure type, and allow unexpected errors to just bubble up rather than wrapping them in an .undefined case. If you need some catch-all "other" anyway, you might as well do that with types ("is") rather than an extra enum case (which just moves the "is" to a switch). At the very least, I would move the Error->MyError mapping as late as possible, which will make handling this much easier.
One more tweak to make later things a little more general, I suspect MyResponse only needs to be Decodable, not Encodable (the rest of this works either way, but it makes it a little more flexible):
struct MyResponse<T: Decodable>: Decodable { ... }
And to your original question of how to make this reusable, you can now pull out a generic function:
func fetch<DataType, Params>(_: DataType.Type,
from endpoint: Endpoint,
method: Method = .GET,
params: Params?) -> AnyPublisher<DataType, MyError>
where DataType: Decodable, Params: Encodable
{
myPublisher(endpoint, method: method, params: params)
.map(\.data!)
.mapError { MyError.network(description: $0.errorDescription) }
.receive(on: DispatchQueue.main)
.eraseToAnyPublisher()
}
// Overload to handle no parameters
func fetch<DataType>(_ dataType: DataType.Type,
from endpoint: Endpoint,
method: Method = .GET) -> AnyPublisher<DataType, MyError>
where DataType: Decodable
{
fetch(dataType, from: endpoint, method: method, params: nil as String?)
}
func documents() -> AnyPublisher<[Document], MyError> {
fetch([Document].self, from: .documents)
}
I made this request:
func AlamofireGetCode()
{
let username: String = searchTextField.text!
var url:String!
url = "https:// ... "
AF.request(url, method: .get, encoding: JSONEncoding.default)
.responseJSON { response in
switch response.result {
case .success:
debugPrint(response)
case .failure(let error):
fatalError("\(error)")
}
}
}
And I'm getting this response with different fields:
[Result]: success({
"incomplete_results" = 0;
items = (
{
"username" = " ... "
...
How do I get some specific field like "username" in Swift?
I would like to have all the username of all the user and store them, could you help me?
You need to provide a type to parse the JSON response into. Using a site like quicktype.io can generate one from your JSON, but any Decodable type will do. Then you can use Alamofire's responseDecodable handler to parse your response.
AF.request(url).responseDecodable(of: TypeToParse.self) { response in
debugPrint(response)
}
Paste your response in https://jsonparseronline.com/ to see the structure of the object. It will show you all the keys and values that you can access using subscripts.
Do somebody know how to achieve Template on Response but without extra casting? Now if I do so Xcode returns me error that I can't override T dynamically. But I really believe I on right way but missed something. No?
Now it's looks like: func didReciveResponse(request: Request, response: Response<Any>)
enum Response<T> {
case success(response: T)
case failured(error: Error)
}
func pseudoResponse() {
let time: Timeinterval = 3
// somehow cast T (compiler shows error that I can't do this)
let response = .success<Timeinterval>(time)
didReciveResponse(.time, response)
}
// delegate method
func didReciveResponse(request: Request, response: Response) {
switch request {
case .time:
switch response {
// response without additional casting (as?)
case .success(let value): time = value
}
}
}
As the compiler cannot infer the generic type you have to annotate the type in this case
func pseudoResponse() {
let time: TimeInterval = 3.0
let response : Response<TimeInterval> = .success(response: time)
didReciveResponse(request: .time, response: response)
}
and you have to specify the Response type in the delegate method
func didReciveResponse(request: Request, response: Response<TimeInterval>) { ...
However if you want to make didReciveResponse (actually didReceiveResponse) also generic you need to write
func didReciveResponse<T>(request: Request, response: Response<T>) {
I am trying to access my MAMP database webservice using Alamofire. Following is my code:
Following is my router to construct my URL:
enum Router: URLRequestConvertible {
static let baseURLString = "http://pushchat.local:44447/"
case PostJoinRequest(String,String,String,String,String)
var URLRequest: NSURLRequest {
let (path: String, parameters: [String: AnyObject]) = {
switch self {
case .PostJoinRequest (let addPath, let userID, let token, let nickName, let secretCode):
let params = ["cmd": "join", "user_id": "\(userID)", "token": "\(token)", "name": "\(nickName)", "code": "\(secretCode)"]
return (addPath, params)
}
}()
let URL = NSURL(string: Router.baseURLString)
let URLRequest = NSURLRequest(URL: URL!.URLByAppendingPathComponent(path))
let encoding = Alamofire.ParameterEncoding.URL
return encoding.encode(URLRequest, parameters: parameters).0
}
}
Following is my viewdidload code:
Alamofire.request(.POST,Router.PostJoinRequest("api.php","12345678901234","12345678901234","ABCDEF","TopSecret")).responseJSON()
{(request, response, JSON, error) in
println(JSON)
}
Following is the compile error:
Cannot invoke 'responseJSON' with an argument list of type '((,,,)->_)'
Following is the declaration from Almofire for your reference.
:param: method The HTTP method.
:param: URLString The URL string.
:param: parameters The parameters. `nil` by default.
:param: encoding The parameter encoding. `.URL` by default.
:returns: The created request.
*/
// public func request(method: Method, _ URLString: URLStringConvertible, parameters: [String: AnyObject]? = nil, encoding: ParameterEncoding = .URL) -> Request {
// return request(encoding.encode(URLRequest(method, URLString), parameters: parameters).0)
// }
Please let me know why am I facing this issue while chaining and what is it that I am not doing right?
Thanks for your help.
Dev
The compiler error message is really misleading – there is no problem with responseJSON but with request method itself.
In fact compiler does not like your second parameter. You are passing URLRequestConvertible but URLStringConvertible is expected (see the signature you posted).
Maybe you wanted to call another version of request method:
//:param: URLRequest The URL request
//:returns: The created request.
public func request(URLRequest: URLRequestConvertible) -> Request
In that case you have to adjust your Router class and set HTTP method into NSURLRequest created inside. For example:
let URLRequest = NSMutableURLRequest(URL: URL!.URLByAppendingPathComponent(path))
URLRequest.HTTPMethod = "POST"
Note you will also probably need to use another parameter/data encoding.