How to Exponential Backoff retry on kotlin coroutines

Here's a more sophisticated and convenient version of my previous answer, hope it helps someone:

class RetryOperation internal constructor(
    private val retries: Int,
    private val initialIntervalMilli: Long = 1000,
    private val retryStrategy: RetryStrategy = RetryStrategy.LINEAR,
    private val retry: suspend RetryOperation.() -> Unit
) {
    var tryNumber: Int = 0
        internal set

    suspend fun operationFailed() {
        tryNumber++
        if (tryNumber < retries) {
            delay(calculateDelay(tryNumber, initialIntervalMilli, retryStrategy))
            retry.invoke(this)
        }
    }
}

enum class RetryStrategy {
    CONSTANT, LINEAR, EXPONENTIAL
}

suspend fun retryOperation(
    retries: Int = 100,
    initialDelay: Long = 0,
    initialIntervalMilli: Long = 1000,
    retryStrategy: RetryStrategy = RetryStrategy.LINEAR,
    operation: suspend RetryOperation.() -> Unit
) {
    val retryOperation = RetryOperation(
        retries,
        initialIntervalMilli,
        retryStrategy,
        operation,
    )

    delay(initialDelay)

    operation.invoke(retryOperation)
}

internal fun calculateDelay(tryNumber: Int, initialIntervalMilli: Long, retryStrategy: RetryStrategy): Long {
    return when (retryStrategy) {
        RetryStrategy.CONSTANT -> initialIntervalMilli
        RetryStrategy.LINEAR -> initialIntervalMilli * tryNumber
        RetryStrategy.EXPONENTIAL -> 2.0.pow(tryNumber).toLong()
    }
}

Usage:

coroutineScope.launch {
    retryOperation(3) {
        if (!tryStuff()) {
            Log.d(TAG, "Try number $tryNumber")
            operationFailed()
        }
    }
}

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.

Here an example with the Flow and the retryWhen function

RetryWhen Extension :

fun <T> Flow<T>.retryWhen(
    @FloatRange(from = 0.0) initialDelay: Float = RETRY_INITIAL_DELAY,
    @FloatRange(from = 1.0) retryFactor: Float = RETRY_FACTOR_DELAY,
    predicate: suspend FlowCollector<T>.(cause: Throwable, attempt: Long, delay: Long) -> Boolean
): Flow<T> = this.retryWhen { cause, attempt ->
    val retryDelay = initialDelay * retryFactor.pow(attempt.toFloat())
    predicate(cause, attempt, retryDelay.toLong())
}

Usage :

flow {
    ...
}.retryWhen { cause, attempt, delay ->
    delay(delay)
    ...
}