Any I/O resource can be temporarily unavailable and cause requests to fail. Use this library to catch errors and retry, slowing down according to your chosen strategy. Add validation rules for the result and error types if needed.

kotlin-backoff is available on Maven Central.
Add the library as a dependency to your project:

dependencies {
    implementation("io.github.reugn:kotlin-backoff:0.4.0")
}

Below is a list of backoff strategies implemented. To create your own strategy, implement the Strategy interface.

A strategy in which the next delay interval is calculated using baseDelayMs * expBase.pow(attempt) where:

• baseDelayMs is the base delay in milliseconds.
• attempt is the number of unsuccessful attempts that have been made.
• expBase is the exponent base configured for the strategy.

The specified jitter¹ and scale factor² are applied to the calculated interval. The delay time cannot exceed the specified maximum delay in milliseconds.

A strategy in which the next delay interval is calculated using baseDelayMs * attempt.pow(exponent) where:

• baseDelayMs is the base delay in milliseconds.
• attempt is the number of unsuccessful attempts that have been made.
• exponent is the exponent configured for the strategy.

The specified jitter¹ and scale factor² are applied to the calculated interval. The delay time cannot exceed the specified maximum delay in milliseconds.

A strategy that returns the delay time as a fixed value determined by the attempt number.

A simple backoff strategy that constantly returns the same value. The specified jitter¹ is applied to the interval. No jitter by default.

¹ Jitter adds a retry randomization factor to reduce resource congestion. Specify 1.0 for full jitter, 0.0 for no jitter.

² The delay determined by the backoff strategy is multiplied by the scale factor. By default, the coefficient is 1.

First, create an instance of StrategyBackoff. Then perform the operation, which may fail, using the retry or withRetries methods.

private suspend fun urlAction(): String = withContext(Dispatchers.IO) {
    URL("http://worldclockapi.com/api/json/utc/now").readText()
}

@Test
fun `remote URL`() {
    val backoff = StrategyBackoff<String>(
        maxRetries = 3,
        strategy = ExponentialStrategy(),
        errorValidator = ::nonFatal,
        resultValidator = { s -> s.isNotEmpty() },
    )
    val result = runBlocking { backoff.withRetries(::urlAction) }

    assert(result.isOk())
    assertEquals(result.retries, 0)
}

For more examples, see the tests.

Licensed under the Apache 2.0 License.