I am trying to figure out the simplest way to make an HTTP request in Swift 4 from the command line. I have copied this code from the URLSession programming guide, and added a couple print statements. I can't figure out why the .dataTask is not executing.
print("Testing URLSession")
let sessionWithoutADelegate = URLSession(configuration: URLSessionConfiguration.default)
if let url = URL(string: "https://www.example.com/") {
print("Encoded url \(url)")
(sessionWithoutADelegate.dataTask(with: url) { (data, response, error) in
print("Executing dataTask")
if let error = error {
print("Error: \(error)")
} else if let response = response,
let data = data,
let string = String(data: data, encoding: .utf8) {
print("Response: \(response)")
print("DATA:\n\(string)\nEND DATA\n")
}
}).resume()
}
The objective is to retrieve data from a REST api, but I can't even make a simple GET request to work properly...
I finally figured out how to make it work using CFRunLoop:
let runLoop = CFRunLoopGetCurrent()
let task = session.dataTask(with: request) { (data, response, error) in
print("Retrieved data")
CFRunLoopStop(runLoop)
}
task.resume()
CFRunLoopRun()
print("done")
Related
I am obviously missing something very fundamental/naïve/etc., but for the life of me I cannot figure out how to make simple GET requests.
I'm trying to make an HTTP GET request with Swift 5. I've looked at these posts/articles: one, two, but I can't get print() statements to show anything. When I use breakpoints to debug, the entire section within the URLSession.shared.dataTask section is skipped.
I am looking at the following code (from the first link, above):
func HTTP_Request() {
let url = URL(string: "http://www.stackoverflow.com")!
let task = URLSession.shared.dataTask(with: url) {(data: Data?, response: URLResponse?, error: Error?) in
guard let data = data else { return }
print(String(data: data, encoding: .utf8)!)
}
task.resume()
}
HTTP_Request()
I am running this in a MacOS Command Line Project created through XCode.
I would greatly appreciate any help I can get on this, thank you.
Right now, if there is an error, you are going to silently fail. So add some error logging, e.g.,
func httpRequest() {
let url = URL(string: "https://www.stackoverflow.com")! // note, https, not http
let task = URLSession.shared.dataTask(with: url) { data, response, error in
guard
error == nil,
let data = data,
let string = String(data: data, encoding: .utf8)
else {
print(error ?? "Unknown error")
return
}
print(string)
}
task.resume()
}
That should at least give you some indication of the problem.
A few other considerations:
If command line app, you have to recognize that the app may quit before this asynchronous network request finishes. One would generally start up a RunLoop, looping with run(mode:before:) until the network request finishes, as advised in the run documentation.
For example, you might give that routine a completion handler that will be called on the main thread when it is done. Then you can use that:
func httpRequest(completion: #escaping () -> Void) {
let url = URL(string: "https://www.stackoverflow.com")! // note, https, not http
let task = URLSession.shared.dataTask(with: url) { data, response, error in
defer {
DispatchQueue.main.async {
completion()
}
}
guard
error == nil,
let data = data,
let string = String(data: data, encoding: .utf8)
else {
print(error ?? "Unknown error")
return
}
print(string)
}
task.resume()
}
var finished = false
httpRequest {
finished = true
}
while !finished {
RunLoop.current.run(mode: .default, before: .distantFuture)
}
In standard macOS apps, you have to enable outgoing (client) connections in the “App Sandbox” capabilities.
If playground, you have to set needsIndefiniteExecution.
By default, macOS and iOS apps disable http requests unless you enable "Allow Arbitrary Loads” in your Info.plist. That is not applicable to command line apps, but you should be aware of that should you try to do this in standard macOS/iOS apps.
In this case, you should just use https and avoid that consideration altogether.
Make sure the response get print before exiting the process, you could try to append
RunLoop.main.run()
or
sleep(UINT32_MAX)
in the end to make sure the main thread won't exit. If you want to print the response and exit the process immediately, suggest using DispatchSemaphore:
let semphare = DispatchSemaphore(value: 0)
func HTTP_Request() {
let url = URL(string: "http://www.stackoverflow.com")!
let task = URLSession.shared.dataTask(with: url) {(data: Data?, response: URLResponse?, error: Error?) in
guard let data = data else { return }
print(String(data: data, encoding: .utf8)!)
semphare.signal()
}
task.resume()
}
HTTP_Request()
_ = semphare.wait(timeout: .distantFuture)
This works for me many times I suggest you snippet for future uses!
let url = URL(string: "https://google.com")
let task = URLSession.shared.dataTask(with: ((url ?? URL(string: "https://google.com"))!)) { [self] (data, response, error) in
do {
let jsonResponse = try JSONSerialization.jsonObject(with: data!, options: [])
print(jsonResponse)
guard let newValue = jsonResponse as? [String:Any] else {
print("invalid format")
}
}
catch let error {
print("Error: \(error)")
}
task.resume()
}
I am new to swift and doing a project in swift 4.0 to acquire data form Fitbit API and got a Strange problem, my url task does not send any urlrequest any more but skip all the code until task.resume, and do not give anything back. Can anyone helps me plz. The code is shown below
import UIKit
class FitbitAPI{
static let sharedInstance : FitbitAPI = FitbitAPI()
var parsedJson : [Any]? = nil
func authorize(with token: String){
let accessToken = token
let baseURL = URL(string: "https://api.fitbit.com/1/user/-/activities/steps/date/today/1m.json")
let request = NSMutableURLRequest(url:baseURL!)
let bodydata = "access_token=\(String(describing: accessToken))"
request.httpMethod = "GET"
request.setValue("Bearer \(String(describing: accessToken))", forHTTPHeaderField: "Authorization")
request.httpBody = bodydata.data(using: String.Encoding.utf8)
let task = URLSession.shared.dataTask(with: request as URLRequest, completionHandler: {[weak self] (data, response, error) in
if let error = error {
print(error)
}
if let data = data, error == nil{
do {
self?.parsedJson = (try JSONSerialization.jsonObject(with: data, options: []) as? [Any] )
print(String(describing: self?.parsedJson))
}catch _{
print("Received not-well-formatted JSON")
}
}
if let response = response {
let httpResponse = response as! HTTPURLResponse
print("response code = \(httpResponse.statusCode)")
}
})
task.resume()
}
}
As #Larme implied in his comment, all of that code between the let task = line and the task.resume() line is a callback. Meaning it won't get called until the task completes. Put breakpoints inside of that callback (like on your if let error = error line), and see if they get hit.
ALso, your URL task is a local variable in this method. That means it's entirely possible that its getting released from memory right at the end of this method, before the callback can even be executed. You'll need a reference to the task outside of the method if you want to guarantee that it stays alive in memory long enough to hit the completion callback.
I am trying to write a basic function to make an HTTP Get request and parse the xml data that comes back. I already have completed the section for parsing XML from a local file, but i can't seem to get any data from the server. I tested this code below, but the completion block does not even run, for information to be passed back from the server. Any suggestions please.
func getDatafromURL (url: String) {
guard let urlforRequest = NSURL(string: url) else {
print("Error: cannot create URL")
return
}
let request = NSURLRequest(URL: urlforRequest)
let config = NSURLSessionConfiguration.defaultSessionConfiguration()
let session = NSURLSession(configuration: config)
let task = session.dataTaskWithRequest(request) { (data, response, error) -> Void in
print(response)
print(error)
}
task.resume()
}
I have been following this tutorial to learn Swift and I have a few questions on the way they do things.
Specifically here:
let paramString = "data=Hello"
request.HTTPBody = paramString.dataUsingEncoding(NSUTF8StringEncoding)
let task = session.dataTaskWithRequest(request) {
(data, response, error) in
guard let _:NSData = data, let _:NSURLResponse = response where error == nil else {
print("Error")
return
}
let dataString = NSString(data: data!, encoding: NSUTF8StringEncoding)
print(dataString)
}
Why is (data, response, error) in always used in NSURLSessions? What does this line of code mean? Also, why does he have a guard statement underneath?
The whole section of code is here:
func dataRequest() {
let urlToRequest: String = " http://www.kaleidosblog.com/tutorial/nsurlsession_tutorial.php"
let url: NSURL = NSURL(string: urlToRequest)!
let session = NSURLSession.sharedSession()
let request = NSMutableURLRequest(URL: url)
request.HTTPMethod = "POST"
request.cachePolicy = NSURLRequestCachePolicy.ReloadIgnoringCacheData
let paramString = "data=Hello"
request.HTTPBody = paramString.dataUsingEncoding(NSUTF8StringEncoding)
let task = session.dataTaskWithRequest(request) {
(data, response, error) in
guard let _:NSData = data, let _:NSURLResponse = response where error == nil else {
print("Error")
return
}
let dataString = NSString(data: data!, encoding: NSUTF8StringEncoding)
print(dataString)
}
task.resume()
}
With NSURLSession you make asynchronous calls, meaning that you make / start a network request and your program continues running - it doesn't stop waiting for response. Then, when your response is ready a completion block gets called / executed. So you need a way to access the data that's coming to you with this response. This data is accessible to you with (data, response, error) properties. This are just the names of those properties, so that you know how to use them. You could have different names, but it would be confusing to anyone else.
You use the guard statement because you can't be sure that you actually have the data or the response. It could be nil if an error occurred (timeout, ...). In such case (if there's an error) you just print "Error" to the console and call return, which makes you leave the completion block without executing the lines let dataString = NSString(data: data!, encoding: NSUTF8StringEncoding) and print(dataString). Of course, if you have the data and the response and error == nil you skip the else block of the guard statement and you just execute you last two lines of code in the block.
I've been scouring examples looking to pull some ideas together, I've come up with this although I'm not getting any output. It never enters the do which leads me to believe I have an issue with my call.
Can anyone shed some light on this for me or lead me to an appropriate location with more information on API calls in swift 2.0? Examples of this are quite sparse.
let url : String = "http://www.fantasyfootballnerd.com/service/nfl-teams/json/test/"
let request : NSMutableURLRequest = NSMutableURLRequest()
request.URL = NSURL(string: url)
request.HTTPMethod = "GET"
print("Start")
let session = NSURLSession.sharedSession()
session.dataTaskWithRequest(request) { (data, response, error) -> Void in
do {
let jsonResult: NSDictionary! = try NSJSONSerialization.JSONObjectWithData(data!, options:NSJSONReadingOptions.MutableContainers) as? NSDictionary
print("In method")
if (jsonResult != nil) {
// process jsonResult
print("Data added")
} else {
print("No Data")
// couldn't load JSON, look at error
}
}
catch {
print("Error Occured")
}
}
You're missing just one thing. You need to start the request:
// call this after you configure your session
session.dataTaskWithRequest(request) { (data, response, error) -> Void in
// process results
}.resume()