kotlin - How to call asynchronous request synchronously with a timeout value?

Question

I have to synchronously call an asynchronous api request. Since this api request takes long time to answer, I also want to set a timeout to fail the api-request and continue with null. Here's my code to call this api:

private suspend fun call(
    accessStage: AccessStage,
): Response? = withContext<Response?>(Dispatchers.IO) {

    return@withContext withTimeoutOrNull(1000) {

        suspendCoroutine<Response?> { continuation ->

            val request = External3rdPartyApi.newRequest(
                accessStage
            ) { response, throwable ->

                continuation.resume(response)
            }

            request.parameters = hashMapOf<String, String>().apply {
                put["token"] = External3rdPartyApi.TOKEN
                put["salt"] = External3rdPartyApi.calculateSalt(accessStage)
            }
            request.executeAsync()
        }
    }
}

I can't change how External3rdPartyApi works.

I think above code looks evil. Also, I read in another answer:

withTimeout { ... } is designed to cancel the ongoing operation on timeout, which is only possible if the operation in question is cancellable.

So, should I use suspendCancellableCoroutine instead of suspendCoroutine?

How can I write it in a better way?

Answer 1

Using suspendCoroutine is fine if you can't (or do not wanna) handle cancelation of the Coroutine. But because you have a timeout, you should consider using suspendCancellableCoroutine and handle the cancelation event to stop the work (in the third party function - if you can).

suspendCancellableCoroutine<T> { continuation ->
  continuation.invokeOnCancellation { throwable ->
    // now you could stop your (third party) work  
  }        
}

When your third party function throws an exception, you could try-catch it and finish your continuation using either resuming with the exception or return a null value (depends on your use case):

suspendCancellableCoroutine<T?> { continuation ->
  try {
    continuation.resume(thirdParty.call())
  } catch (e: Exception) {
    // resume with exception
    continuation.resumeWithException(e)
    // or just return null and swallow the exception
    continuation.resume(null)
  }   
}

Lets put all together

suspend fun call(): Response? = withContext(Dispatchers.IO) {
  return@withContext withTimeoutOrNull(1000L) {
    return@withTimeoutOrNull suspendCancellableCoroutine { continuation ->
      try {
        continuation.resume(External3rdPartyApi.newRequest(accessStage))
      } catch (e: Exception) {
        // resume with exception
        continuation.resumeWithException(e)
        
        // or just return null and swallow the exception
        continuation.resume(null)
      }
         
      // in case the coroutine gets cancelled - because of timeout or something else
      continuation.invokeOnCancellation {
        // stop all the work
      }
    }
  }
}