I am using kotlin coroutines for network request using extension method to call class in retrofit like this
public suspend fun <T : Any> Call<T>.await(): T {
return suspendCancellableCoroutine { continuation ->
enqueue(object : Callback<T> {
override fun onResponse(call: Call<T>?, response: Response<T?>) {
if (response.isSuccessful) {
val body = response.body()
if (body == null) {
continuation.resumeWithException(
NullPointerException("Response body is null")
)
} else {
continuation.resume(body)
}
} else {
continuation.resumeWithException(HttpException(response))
}
}
override fun onFailure(call: Call<T>, t: Throwable) {
// Don't bother with resuming the continuation if it is already cancelled.
if (continuation.isCancelled) return
continuation.resumeWithException(t)
}
})
registerOnCompletion(continuation)
}
}
then from calling side i am using above method like this
private fun getArticles() = launch(UI) {
loading.value = true
try {
val networkResult = api.getArticle().await()
articles.value = networkResult
}catch (e: Throwable){
e.printStackTrace()
message.value = e.message
}finally {
loading.value = false
}
}
i want to exponential retry this api call in some case i.e (IOException) how can i achieve it ??
I would suggest to write a helper higher-order function for your retry logic. You can use the following implementation for a start:
suspend fun <T> retryIO(
times: Int = Int.MAX_VALUE,
initialDelay: Long = 100, // 0.1 second
maxDelay: Long = 1000, // 1 second
factor: Double = 2.0,
block: suspend () -> T): T
{
var currentDelay = initialDelay
repeat(times - 1) {
try {
return block()
} catch (e: IOException) {
// you can log an error here and/or make a more finer-grained
// analysis of the cause to see if retry is needed
}
delay(currentDelay)
currentDelay = (currentDelay * factor).toLong().coerceAtMost(maxDelay)
}
return block() // last attempt
}
Using this function is very strightforward:
val networkResult = retryIO { api.getArticle().await() }
You can change retry parameters on case-by-case basis, for example:
val networkResult = retryIO(times = 3) { api.doSomething().await() }
You can also completely change the implementation of retryIO
to suit the needs of your application. For example, you can hard-code all the retry parameters, get rid of the limit on the number of retries, change defaults, etc.