Can I somehow do a synchronous HTTP request via NSURLSession in Swift
HttpSwiftHttprequestNsurlHttp Problem Overview
Can I somehow do a synchronous HTTP request via NSURLSession in Swift?
I can do an asynchronous request via the following code:
if let url = NSURL(string: "https://2ch.hk/b/threads.json") {
let task = NSURLSession.sharedSession().dataTaskWithURL(url) {
(data, response, error) in
var jsonError: NSError?
let jsonDict = NSJSONSerialization.JSONObjectWithData(data, options: nil, error: &jsonError) as [String: AnyObject]
if jsonError != nil {
return
}
// ...
}
task.resume()
}
But what about synchronous request?
Http Solutions
Solution 1 - Http
You can use this NSURLSession extension to add a synchronous method:
extension NSURLSession {
func synchronousDataTaskWithURL(url: NSURL) -> (NSData?, NSURLResponse?, NSError?) {
var data: NSData?, response: NSURLResponse?, error: NSError?
let semaphore = dispatch_semaphore_create(0)
dataTaskWithURL(url) {
data = $0; response = $1; error = $2
dispatch_semaphore_signal(semaphore)
}.resume()
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER)
return (data, response, error)
}
}
Update for Swift 3:
extension URLSession {
func synchronousDataTask(with url: URL) -> (Data?, URLResponse?, Error?) {
var data: Data?
var response: URLResponse?
var error: Error?
let semaphore = DispatchSemaphore(value: 0)
let dataTask = self.dataTask(with: url) {
data = $0
response = $1
error = $2
semaphore.signal()
}
dataTask.resume()
_ = semaphore.wait(timeout: .distantFuture)
return (data, response, error)
}
}
Solution 2 - Http
Apple thread discussing the same issue.
+ (NSData *)sendSynchronousRequest:(NSURLRequest *)request
returningResponse:(__autoreleasing NSURLResponse **)responsePtr
error:(__autoreleasing NSError **)errorPtr {
dispatch_semaphore_t sem;
__block NSData * result;
result = nil;
sem = dispatch_semaphore_create(0);
[[[NSURLSession sharedSession] dataTaskWithRequest:request
completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
if (errorPtr != NULL) {
*errorPtr = error;
}
if (responsePtr != NULL) {
*responsePtr = response;
}
if (error == nil) {
result = data;
}
dispatch_semaphore_signal(sem);
}] resume];
dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER);
return result;
}
> Answer by Quinn "The Eskimo!" Apple Developer Relations, Developer > Technical Support, Core OS/Hardware
Solution 3 - Http
Updated one of the answers to use a URLRequest instead, so we can use PUT etc instead.
extension URLSession {
func synchronousDataTask(urlrequest: URLRequest) -> (data: Data?, response: URLResponse?, error: Error?) {
var data: Data?
var response: URLResponse?
var error: Error?
let semaphore = DispatchSemaphore(value: 0)
let dataTask = self.dataTask(with: urlrequest) {
data = $0
response = $1
error = $2
semaphore.signal()
}
dataTask.resume()
_ = semaphore.wait(timeout: .distantFuture)
return (data, response, error)
}
}
I'm calling like this.
var request = URLRequest(url: url1)
request.httpBody = body
request.httpMethod = "PUT"
let (_, _, error) = URLSession.shared.synchronousDataTask(urlrequest: request)
if let error = error {
print("Synchronous task ended with error: \(error)")
}
else {
print("Synchronous task ended without errors.")
}
Solution 4 - Http
I want to offer a more modern solution using DispatchGroup.
Usage example 1:
var urlRequest = URLRequest(url: config.pullUpdatesURL)
urlRequest.httpMethod = "GET"
urlRequest.httpBody = requestData
urlRequest.addValue("application/json", forHTTPHeaderField: "Content-Type")
urlRequest.addValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
let (data, response, error) = URLSession.shared.syncRequest(with: urlRequest)
Usage example 2:
let url = URL(string: "https://www.google.com/")
let (data, response, error) = URLSession.shared.syncRequest(with: url)
Extension code:
extension URLSession {
func syncRequest(with url: URL) -> (Data?, URLResponse?, Error?) {
var data: Data?
var response: URLResponse?
var error: Error?
let dispatchGroup = DispatchGroup()
let task = dataTask(with: url) {
data = $0
response = $1
error = $2
dispatchGroup.leave()
}
dispatchGroup.enter()
task.resume()
dispatchGroup.wait()
return (data, response, error)
}
func syncRequest(with request: URLRequest) -> (Data?, URLResponse?, Error?) {
var data: Data?
var response: URLResponse?
var error: Error?
let dispatchGroup = DispatchGroup()
let task = dataTask(with: request) {
data = $0
response = $1
error = $2
dispatchGroup.leave()
}
dispatchGroup.enter()
task.resume()
dispatchGroup.wait()
return (data, response, error)
}
}
As a bonus, if you need to, you can easily implement a timeout. To do this, you need to use
func wait(timeout: DispatchTime) -> DispatchTimeoutResult instead of
func wait()
Solution 5 - Http
Be careful with synchronous requests because it can result in bad user experience but I know sometimes its necessary. For synchronous requests use NSURLConnection:
func synchronousRequest() -> NSDictionary {
//creating the request
let url: NSURL! = NSURL(string: "exampledomain/...")
var request = NSMutableURLRequest(URL: url)
request.HTTPMethod = "GET"
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
var error: NSError?
var response: NSURLResponse?
let urlData = NSURLConnection.sendSynchronousRequest(request, returningResponse: &response, error: &error)
error = nil
let resultDictionary: NSDictionary = NSJSONSerialization.JSONObjectWithData(urlData!, options: NSJSONReadingOptions.MutableContainers, error: &error) as! NSDictionary
return resultDictionary
}
Solution 6 - Http
Duplicated answer from https://stackoverflow.com/a/58392835/246776
If semaphore based approach doesn't work for you, try polling based approach.
var reply = Data()
/// We need to make a session object.
/// This is key to make this work. This won't work with shared session.
let conf = URLSessionConfiguration.ephemeral
let sess = URLSession(configuration: conf)
let task = sess.dataTask(with: u) { data, _, _ in
reply = data ?? Data()
}
task.resume()
while task.state != .completed {
Thread.sleep(forTimeInterval: 0.1)
}
FileHandle.standardOutput.write(reply)