<https://stackoverflow.com/questions/46872242/how-...

# coroutines

[elizarov]

https://stackoverflow.com/questions/46872242/how-to-exponential-backoff-retry-on-kotlin-coroutines/46890009

[frogman544]

Thank you! I saw the answer, but I don’t know how to do this retry only if I get a HTTP error. How can I access the result of the call and only retry if the call fails?

[elizarov]

Write the logic to analyze what kind of error is that. That is what “make a more finer-grained analysis” placeholder for

[frogman544]

If i get an error for the call the execution does not go in the catch block.

[elizarov]

It should. Can you produce a self-contained piece of code that demonstrates the problem? In particular, your implementation of Call.await

[frogman544]

suspend fun <T> Call<T>.awaitResult(retries: Int = 2): Result<T> {
    return suspendCancellableCoroutine { continuation ->
        enqueue(object : Callback<T> {
            override fun onResponse(call: Call<T>?, response: Response<T>) {
                continuation.resume(
                        if (response.isSuccessful) {
                            Result.Ok(response.body(), response.raw())
                        } else {
                            Result.Error(HttpError(response), response.raw(), call)
                        }
                )
            }

            override fun onFailure(call: Call<T>, t: Throwable) {
                continuation.resume(Result.Exception(t))
            }
        })
    }
}

[frogman544]

This is my implementation and I wrap the actual call inside.

retry { actualCall.awaitResult }

[elizarov]

So, your awaitResult implementation never resumes with exception, so it is no surprise that try { … } catch inside retry is not doing anything

[elizarov]

You have two options here:
1. Either use an implementation of await that throws exceptions on error.
2. Or implement a version of retry that is specifically tailored to Resut<T> can can make decisions based on it

[frogman544]

Thank you for the answers!