I would like to implement a way to check if the network is weak or disconnected during network calls I perform using Alamofire 4.9 - the following is what I am currently attempting to do, but I have noticed that if the network it off it never jumps to this line:
URLError.Code.notConnectedToInternet
why does this occur, is there a better way of attempting this?
//Fetch new data
guard let url = URL(string: "test.com")
else { return }
var request = URLRequest(url: url)
request.httpMethod = "POST"
request.httpBody = "value1=test1&value2=test2".data(using: .utf8)
URLSession.shared.dataTask(with: request) { [self] data, _, error in
guard let data = data else { return }
do {
let decoder = JSONDecoder()
let res = try decoder.decode([Structure].self, from: data)
}
}
catch {
if let err = error as? URLError, err.code == URLError.Code.notConnectedToInternet {
// No internet
} else {
print(error)
}
}
}.resume()
There are a variety of errors that can be produced by poor or entirely broken connectivity. .notConnectedToInternet is simply one of them. There is no single, exhaustive list provided by Apple of which errors may be returned when there are connectivity issues, so you'll want to experiment and see what you can produce. Additionally, there are a variety of errors which you can probably throw into a "network connectivity" bucket, such as .dnsLookupFailed or .cannotConnectToHost. Ultimately it may not be worth it to differentiate different types of URLErrors.
By the way, you should use Alamofire 5 if you can, as Alamofire 4 is no longer supported.
Related
I'm beginner in SwiftUI and I'm not familiar with variable management.
I'd like to send a very simple post request like this one with SwiftUI:
let full_path : String = "https://www.example.com/get_answer?my_message=current temperature"
I've tried with this piece of code but it didn't work.
if (URL(string: full_path) != nil) {
let url = URL(string: full_path)!
var request = URLRequest(url: url)
request.httpMethod = "POST"
var decodedAnswer = String("")
do {
let task = URLSession.shared.dataTask(with: url) { data, response, error in
print(response)
decodedAnswer = String(decoding: response, as: UTF8.self)
}
}
I have the following error:
Value of optional type 'URLResponse?' must be unwrapped to a value of
type 'URLResponse'
I don't know how to get the response.
How can I get the response from a simple Post request in SwiftUI?
Multiple issues here.
You are trying to decode the URLResponse object, but what you want is the data object in the decoder.
You seem to not know about optionals. I would refer you to the basic Apple tutorials about this topic. You can find it with your favorite search engine.
You are in an async context here. Everything inside the url datasession closure will be execute after your network request returns. The code in your function will be completed by that moment and your var decodedAnswer will be out of scope. So move it out of the function in to the class/struct.
You probably want something like this:
This should be defined in class scope or you won´t be able to use it:
var decodedAnswer: String = ""
This should be in a function:
let full_path: String = "https://www.example.com/get_answer?my_message=current temperature"
if let url = URL(string: full_path) {
var request = URLRequest(url: url)
request.httpMethod = "POST"
do {
let task = URLSession.shared.dataTask(with: url) { data, response, error in
//This converts the optionals in to non optionals that could be used further on
//Be aware this will just return when something goes wrong
guard let data = data, let response = response, error == nil else{
print("Something went wrong: error: \(error?.localizedDescription ?? "unkown error")")
return
}
print(response)
decodedAnswer = String(decoding: data, as: UTF8.self)
}
task.resume()
}
}
I'm trying to make a fairly simple API call in Swift but, for some reason, my dataTask code is not running. I've made sure that the .resume() is there. This code has worked in the past but, something has changed recently and I don't know what it is. The only thing I can think of is the url. I've changed the ingredients but, when putting the url into a browser, it returns JSON data normally. When running this function, I get two "Outside URLSession.shared.dataTask....." messages in a row with nothing in between, indicating that the URLSession block of code isn't running. I'm a little new to APIs so, any help would be greatly appreciated. Please let me know if there's any more information I can provide. Also, I'm on an older MacBook and am using Swift5 if that makes a difference. Thanks!
let url: URL! = URL(string: "https://api.spoonacular.com/recipes/findByIngredients?ingredients=" + ingredientString + "&apiKey=aaabbbccc111222333")
print("URL: " + url.absoluteString)
let request = URLRequest(url: url)
// Make the API call
print("Outide URLSession.shared.dataTask.....")
let session = URLSession.shared.dataTask(with: request) { data, response, error in
print("Inside URLSession.shared.dataTask.....")
DispatchQueue.main.async {
print("Inside DispatchQueue.main.async....")
if data == nil {
print("No data recieved.")
}
print("data != nil.... Moving on to JSONDecoder....")
self.model = try! JSONDecoder().decode([RecipeSearchElement].self, from: data!)
}
}
session.resume()
print("Outside URLSession.shared.dataTask.....")
Unrelated to your immediate question at hand (which I answered elsewhere), I would advise a few changes to the routine:
One should not build a URL through string interpolation. Use URLComponents. If, for example, the query parameter included a space or other character not permitted in a URL, URLComponents will percent-encode it for you. If do not percent-encode it properly, the building of the URL will fail.
I would avoid try!, which will crash the app if the server response was not what you expected. One should use try within a do-catch block, so it handles errors gracefully and will tell you what is wrong if it failed.
I would recommend renaming the URLSessionDataTask to be task, or something like that, to avoid conflating “sessions” with the “tasks” running on that session.
I would not advise updating the model from the background queue of the URLSession. Fetch and parse the response in the background queue and update the model on the main queue.
Thus:
var components = URLComponents(string: "https://api.spoonacular.com/recipes/findByIngredients")
components?.queryItems = [
URLQueryItem(name: "ingredients", value: ingredientString),
URLQueryItem(name: "apiKey", value: "aaabbbccc111222333")
]
guard let url = components?.url else {
print("Unable to build URL")
return
}
// Make the API call
let task = URLSession.shared.dataTask(with: url) { data, _, error in
DispatchQueue.main.async {
guard error == nil, let data = data else {
print("No data received:", error ?? URLError(.badServerResponse))
return
}
do {
let model = try JSONDecoder().decode([RecipeSearchElement].self, from: data)
DispatchQueue.main.async {
self.model = model
}
} catch let parseError {
print("Parsing error:", parseError, String(describing: String(data: data, encoding: .utf8)))
}
}
}
task.resume()
In a more advanced observation, I would never have a network call update the model directly. I would leave that to the caller. For example, you could use a completion handler pattern:
#discardableResult
func fetchIngredients(
_ ingredientString: String,
completion: #escaping (Result<[RecipeSearchElement], Error>) -> Void
) -> URLSessionTask? {
var components = URLComponents(string: "https://api.spoonacular.com/recipes/findByIngredients")
components?.queryItems = [
URLQueryItem(name: "ingredients", value: ingredientString),
URLQueryItem(name: "apiKey", value: "aaabbbccc111222333")
]
guard let url = components?.url else {
completion(.failure(URLError(.badURL)))
return nil
}
// Make the API call
let task = URLSession.shared.dataTask(with: url) { data, _, error in
print("Inside URLSession.shared.dataTask.....")
DispatchQueue.main.async {
guard error == nil, let data = data else {
DispatchQueue.main.async {
completion(.failure(error ?? URLError(.badServerResponse)))
}
return
}
do {
let model = try JSONDecoder().decode([RecipeSearchElement].self, from: data)
DispatchQueue.main.async {
completion(.success(model))
}
} catch let parseError {
DispatchQueue.main.async {
completion(.failure(parseError))
}
}
}
}
task.resume()
return task
}
And then the caller could do:
fetchIngredients(ingredientString) { [weak self] result in
switch result {
case .failure(let error): print(error)
case .success(let elements): self?.model = elements
}
}
This has two benefits:
The caller now knows when the model is updated, so you can update your UI at the appropriate point in time (if you want).
It maintains a better separation of responsibilities, architecturally avoiding the tight coupling of the network layer with that of the view or view model (or presenter or controller) layers.
Note, I am also returning the URLSessionTask object in case the caller would like to cancel it at a later time, but I made it an #discardableResult so that you do not have to worry about that if you are not tackling cancelation at this point.
If you (a) are reaching the “outside” message, but not seeing the “inside” message; and (b) are absolutely positive that you are reaching the resume statement, it is one of a few possibilities:
The app may be terminating before the asynchronous request has time to finish. This can happen, for example, if this is a command-line app and you are allowing the app to quit before the asynchronous request has a chance to finish. If you want a command-line app to wait for a network request to finish, you might run a RunLoop that does not exit until the network request is done.
It can also happen if you use a playground and neglect to set needsIndefiniteExecution:
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true
For the sake of completeness, there are a few other, less common, possibilities:
You have some other network request whose completion handler is blocked/deadlocked, thereby preventing anything else from running on the URLSession dedicated, serial, queue.
You have thread explosion somewhere else in your code, exhausting the limited pool of worker threads, preventing other tasks/operations from being able to get an available worker thread.
After this code is ran I get some pretty strange messange on the command line. (However it happens in every application where I write URLSession datatask. (This is the simplest one that reproduce the problem)
Facts:{
iOS: 13.6 (though version does not matter, happened to me in every version.
Xcode: 11.6 (also does not matter at all)
}
func getTemperatureWarning(){
let url = URL(string: "https://urlhere:2222/getTemperatureWarning") // checking settings on server
var request = URLRequest(url: url!)
request.httpMethod = "GET"
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
_ = URLSession.shared.dataTask(with: request){data, response, error in
if error != nil || data == nil {
print("Client error!")
return
}
guard let response = response as? HTTPURLResponse, response.statusCode == 200 else {
fatalError("failed!")
}
do {
let json = try JSONDecoder().decode(TempWarning.self, from: data!)
print(json.value)
DispatchQueue.main.async {
// not yet implemented
}
} catch let error {
print(error)
}
}.resume()
}
CommandLine:
25
2020-07-23 11:54:28.859871+0200 cameden[36484:2032497] [] tcp_input [C2.1.1:3] flags=[R] seq=3143354417, ack=0, win=0 state=LAST_ACK rcv_nxt=3143354417, snd_una=3725130175 2020-07-23
11:54:28.860170+0200 cameden[36484:2032497] [] tcp_input [C2.1.1:3] flags=[R] seq=3143354417, ack=0, win=0 state=CLOSED rcv_nxt=3143354417, snd_una=3725130175
Anybody has any clue what is it about, or how can I dive more deep into it? Is it an error or something that helps me acknowledge there is no error?
25 at the begining is the answer from my python3 flask server. That is the value I'm looking for. After that number there is a two line message which I dont understand. It also happens when I try to access 3rd party servers like twitter API or whatever.
This question is related to: Swift Core Data Sync With Web Server.
I have followed the steps that have been mentioned in the question above however I am unable to apply the third step to my current project.
I currently have a class called Records
class Records {
static let shared = Records()
var records = [Record]()
let context = PersistenceServce.context
let request = NSFetchRequest<Record>(entityName: "Record")
func recordData() -> [Record] {
do {
records = try context.fetch(Record.fetchRequest())
}catch {
print("Error fetching data from CoreData")
}
return records
}
}
and here is how I display the data on my tableViewController.
func getData() {
records = Records.shared.recordData()
self.tableView.reloadData()
}
I do know how save data to a web server as this tutorial explains: https://www.simplifiedios.net/swift-php-mysql-tutorial/ as well as check for internet connection. However I am unsure how to apply it to the CoreData where there are multiple data involved.
If anyone could direct me to a solution or an explain how this can be achieved I'd very much appreciate it.
The question that you have linked is not trying to explain how to communicate with a web server. It is explaining how to store data in core data and tag/mark it in a way that you know which records have been sent to the web server or not.
So the Predicate will fetch all records that have not been sent to the web server and allow you to send them when you have an internet connection available.
Communicating with a web server can be a broad topic and will depend on your web server and API setup, so it is too much to explain here fully. I refer you to some free online resources that will help you understand networking in Swift.
Udacity - Networking with Swift
Ray Wenderlich - Alamofire Tutorial
Stack Overflow - Swift POST Request
Here is an example of a POST Request from the StackOverflow answer above
var request = URLRequest(url: URL(string: "http://test.tranzporthub.com/street45/customer_login.php")!)
request.httpMethod = "POST"
let postString = "user_id=chaitanya3191#gmail.com&password=123"
request.httpBody = postString.data(using: .utf8)
let task = URLSession.shared.dataTask(with: request) { data, response, error in
guard let data = data, error == nil else { // check for fundamental networking error
print("error=\(error)")
return
}
if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 { // check for http errors
print("statusCode should be 200, but is \(httpStatus.statusCode)")
print("response = \(response)")
}
let responseString = String(data: data, encoding: .utf8)
print("responseString = \(responseString)")
}
task.resume()
Using code similar to this, you should be able to send data to your web server, then your web server can do whatever it likes with it.
UPDATE:
To encode your parameters to JSON you can use the following code as a guide
var dictionary = [
"username": "Test User",
"password": "Password"
]
if let jsonData = try? JSONSerialization.data(withJSONObject: dictionary, options: []) {
// jsonData is a byte sequence, to view it you would need to convert to string
print(String(bytes: jsonData, encoding: String.Encoding.utf8))
}
Which would output:
Optional("{\"username\":\"Test User\",\"password\":\"Password\"}")
Note: you would send it as data, not the string version. so your code might look like this:
request.httpBody = jsonData
I'm trying to develop a download accelerator in Swift. It should get the file's size and divide it to n parts. Then it should download them at once by running multiple threads, and then merge the parts.
I read C# - Creating a Download Accelerator, unfortunately it doesn't help me.
I can do the multiple thread part easily by
DispatchQueue.main.async {
// The new thread
}
but the other part is harder. I usually download a file like this:
try Data(contentsOf: URL(string: assetsUrl!)!)
or I can do the thing that is explained in this answer
class Downloader {
class func load(url: URL, to localUrl: URL, completion: #escaping () -> ()) {
let sessionConfig = URLSessionConfiguration.default
let session = URLSession(configuration: sessionConfig)
let request = try! URLRequest(url: url, method: .get)
let task = session.downloadTask(with: request) { (tempLocalUrl, response, error) in
if let tempLocalUrl = tempLocalUrl, error == nil {
// Success
if let statusCode = (response as? HTTPURLResponse)?.statusCode {
print("Success: \(statusCode)")
}
do {
try FileManager.default.copyItem(at: tempLocalUrl, to: localUrl)
completion()
} catch (let writeError) {
print("error writing file \(localUrl) : \(writeError)")
}
} else {
print("Failure: %#", error?.localizedDescription);
}
}
task.resume()
}
}
But this is not C - it's very simplistic and doesn't accept many arguments. How can I make it get "first 200_000 bytes" from the server?
First of all, the server needs to implement HTTP range requests. If it doesn't, and you don't control the server, then you will not be able to do this.
If the server supports HTTP range requests, then you need to specify the range with request headers, as explained here: https://developer.mozilla.org/en-US/docs/Web/HTTP/Range_requests
The essentials are that you first send a HEAD request to figure out whether the server supports HTTP range requests. This is determined by whether the response includes the Accept-Ranges header, with a non-zero value.
If the server supports HTTP range requests, then you can make a request for the resource, with the Range header set for example to a value of bytes=0-1023 (depends which format the Accept-Ranges header specified, in this case bytes)