How can I connect through HTTP in Kotlin/Native iOS development? - ios

Question

I tried to get a web page in Kotlin/Native with iOS platform, but it didn't work.
Please tell me where is the problem.
I created the project with Gradle and build.gradle contains:
plugins {
id 'kotlin-multiplatform' version '1.3.21'
}
Here are the codes.
package sample
fun main(args: Array<String>) {
println(WebGateway.get("https://www.google.com/"))
}
package sample
import platform.Foundation.*
import platform.darwin.*
actual object WebGateway {
actual fun get(urlString: String): String {
val semaphore = dispatch_semaphore_create(0)
var components = NSURLComponents(urlString)
val url = components.URL
var result: String = ""
val config = NSURLSessionConfiguration.defaultSessionConfiguration()
config.waitsForConnectivity = true
config.timeoutIntervalForResource = 300.0
val session = NSURLSession.sessionWithConfiguration(
config, null, NSOperationQueue.mainQueue()
)
val task = session
.dataTaskWithURL(url!!) { nsData: NSData?, nsurlResponse: NSURLResponse?, nsError: NSError? ->
nsData?.run { result = toString() }
println(nsData)
dispatch_semaphore_signal(semaphore);
}
task.resume()
session.finishTasksAndInvalidate()
NSOperationQueue.mainQueue().waitUntilAllOperationsAreFinished()
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER)
return result
}
}
After building the application, main.kexe was created.
I expected the Google web page HTML is printed in standard output by executing the application.
But the actual is:
% ./main.kexe
It doesn't show anything.
The program stops at dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER).
After executing the application, task.state became NSURLSessionTaskStateCompleted, but the program doesn't show anything or finish.
When I changed the session to NSURLSession.sessionWithConfiguration(config), I got the following output.
% ./main.kexe
Uncaught Kotlin exception: kotlin.native.IncorrectDereferenceException: illegal attempt to access non-shared sample.WebGateway.$<anonymous>$FUNCTION_REFERENCE$0#f6f058e8 from other thread
at 0 main.kexe 0x000000010039c3c3 ThrowIllegalObjectSharingException + 595
at 1 main.kexe 0x00000001003b9d6d -[KotlinObjectHolder ref] + 141
at 2 main.kexe 0x00000001003c9524 platform_Foundation_kniBridge11046 + 148
at 3 main.kexe 0x00000001003ca18c __platform_Foundation_kniBridge11045_block_invoke + 108
at 4 CFNetwork 0x00007fff4cd80763 __75-[__NSURLSessionLocal taskForClass:request:uploadFile:bodyData:completion:]_block_invoke + 19
at 5 CFNetwork 0x00007fff4cd8016c __49-[__NSCFLocalSessionTask _task_onqueue_didFinish]_block_invoke + 172
at 6 Foundation 0x00007fff50243a47 __NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 7
at 7 Foundation 0x00007fff5024394e -[NSBlockOperation main] + 68
at 8 Foundation 0x00007fff50218f7a -[__NSOperationInternal _start:] + 686
at 9 Foundation 0x00007fff5024367f __NSOQSchedule_f + 227
at 10 libdispatch.dylib 0x00007fff7aef3d4f _dispatch_call_block_and_release + 12
at 11 libdispatch.dylib 0x00007fff7aef4dcb _dispatch_client_callout + 8
at 12 libdispatch.dylib 0x00007fff7aef75d8 _dispatch_continuation_pop + 427
at 13 libdispatch.dylib 0x00007fff7aef6c7a _dispatch_async_redirect_invoke + 718
at 14 libdispatch.dylib 0x00007fff7af02d1a _dispatch_root_queue_drain + 325
at 15 libdispatch.dylib 0x00007fff7af034b1 _dispatch_worker_thread2 + 90
at 16 libsystem_pthread.dylib 0x00007fff7b1346ee _pthread_wqthread + 619
at 17 libsystem_pthread.dylib 0x00007fff7b134415 start_wqthread + 13
zsh: abort ./main.kexe
When I changed session to NSURLSession.sharedSession(), the same error appeared.

Answer 1

Kotlin native expects the callback to be called on the main thread.
This is how the native HTTP request is implemented in Kotlin conf spinner app.
https://github.com/Kotlin/kotlinconf-spinner/blob/master/clients/ios/src/iosMain/kotlin/platformUtils.kt