Combining timeout and retry of network request

• Composes higher-level functions retry() and with timeout().
• Demonstrates how simple and readable code written with Coroutines can be.
• The mock API first responds after the timeout and then returns an unsuccessful response. The third attempt is then successful.

class TimeoutAndRetryViewModel(
    private val api: MockApi = mockApi()
) : BaseViewModel<UiState>() {

    fun performNetworkRequest() {
        uiState.value = UiState.Loading
        val numberOfRetries = 2
        val timeout = 1000L

        val oreoVersionsDeferred = viewModelScope.async {
            retryWithTimeout(numberOfRetries, timeout) {
                api.getAndroidVersionFeatures(27)
            }
        }

        val pieVersionsDeferred = viewModelScope.async {
            retryWithTimeout(numberOfRetries, timeout) {
                api.getAndroidVersionFeatures(28)
            }
        }

        viewModelScope.launch {
            try {
                val versionFeatures = listOf(
                    oreoVersionsDeferred,
                    pieVersionsDeferred
                ).awaitAll()

                uiState.value = UiState.Success(versionFeatures)

            } catch (e: Exception) {
                Timber.e(e)
                uiState.value = UiState.Error("Network Request failed")
            }
        }
    }

    private suspend fun <T> retryWithTimeout(
        numberOfRetries: Int,
        timeout: Long,
        block: suspend () -> T
    ) = retry(numberOfRetries) {
        withTimeout(timeout) {
            block()
        }
    }

    private suspend fun <T> retry(
        numberOfRetries: Int,
        delayBetweenRetries: Long = 100,
        block: suspend () -> T
    ): T {
        repeat(numberOfRetries) {
            try {
                return block()
            } catch (exception: Exception) {
                Timber.e(exception)
            }
            delay(delayBetweenRetries)
        }
        return block() // last attempt
    }
}