add retry policy (#22)

buildSrc/src/main/java/Dependencies.kt

@@ -10,7 +10,7 @@ object Versions {
  val compile_sdk = 30
 
  // SDK version
- val intsoftdev_stations_client_version = "0.50"
+ val intsoftdev_stations_client_version = "0.51"
 
  // kotlin core
  const val kotlin = "1.5.30"

sdknrstations/src/commonMain/kotlin/com.intsoftdev.nrstations/cache/DBWrapper.kt

@@ -10,6 +10,5 @@ internal interface DBWrapper {
  fun getStationLocation(stationId: String): StationEntity?
  fun insertVersion(version: VersionEntity)
  fun getVersion(): VersionEntity?
-
  fun isEmpty(): Boolean
 }

sdknrstations/src/commonMain/kotlin/com.intsoftdev.nrstations/common/RequestRetryPolicy.kt

@@ -0,0 +1,47 @@
+package com.intsoftdev.nrstations.common
+
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.retryWhen
+
+/**
+ * Retry policy with exponential backoff.
+ *
+ * delayFactor is used to multiply delayMillis to increase the delay for the next retry.
+ *
+ * For instance, given a policy with numRetries of 4, delayMillis of 400ms and delayFactor of 2:
+ * - first retry: effective delayMillis will be 400
+ * - second retry: effective delayMillis will be 800
+ * - third retry: effective delayMillis will be 1600
+ * - forth retry: effective delayMillis will be 3200
+ *
+ * If no exponential backoff is desired, set delayFactor to 1
+ */
+interface RequestRetryPolicy {
+ val numRetries: Long
+ val delayMillis: Long
+ val delayFactor: Long
+}
+
+data class DefaultRetryPolicy(
+ override val numRetries: Long = 4,
+ override val delayMillis: Long = 400,
+ override val delayFactor: Long = 2
+) : RequestRetryPolicy
+
+
+fun <T> Flow<T>.retryWithPolicy(
+ requestRetryPolicy: RequestRetryPolicy
+): Flow<T> {
+ var currentDelay = requestRetryPolicy.delayMillis
+ val delayFactor = requestRetryPolicy.delayFactor
+ return retryWhen { cause, attempt ->
+ if (attempt < requestRetryPolicy.numRetries) {
+ delay(currentDelay)
+ currentDelay *= delayFactor
+ return@retryWhen true
+ } else {
+ return@retryWhen false
+ }
+ }
+}

sdknrstations/src/commonMain/kotlin/com.intsoftdev.nrstations/data/DataModule.kt

@@ -1,3 +1,4 @@
+import com.intsoftdev.nrstations.common.DefaultRetryPolicy
 import com.intsoftdev.nrstations.data.StationsAPI
 import com.intsoftdev.nrstations.data.StationsProxy
 import com.intsoftdev.nrstations.data.StationsRepositoryImpl
@@ -31,7 +32,8 @@ internal val stationsDataModule = module {
  StationsRepositoryImpl(
  stationsProxyService = get(),
  stationsCache = get(),
- requestDispatcher = get(named("NRStationsCoroutineDispatcher"))
+ requestDispatcher = get(named("NRStationsCoroutineDispatcher")),
+ requestRetryPolicy = DefaultRetryPolicy()
  )
  }
 }

sdknrstations/src/commonMain/kotlin/com.intsoftdev.nrstations/data/StationsRepositoryImpl.kt

@@ -3,9 +3,11 @@ package com.intsoftdev.nrstations.data
 import io.github.aakira.napier.Napier
 import com.intsoftdev.nrstations.cache.CacheState
 import com.intsoftdev.nrstations.cache.StationsCache
+import com.intsoftdev.nrstations.common.RequestRetryPolicy
 import com.intsoftdev.nrstations.common.StationLocation
 import com.intsoftdev.nrstations.common.StationsResult
 import com.intsoftdev.nrstations.common.StationsResultState
+import com.intsoftdev.nrstations.common.retryWithPolicy
 import com.intsoftdev.nrstations.data.model.station.DataVersion
 import com.intsoftdev.nrstations.data.model.station.toStationLocation
 import com.intsoftdev.nrstations.data.model.station.toUpdateVersion
@@ -19,7 +21,8 @@ import kotlinx.coroutines.flow.flowOn
 internal class StationsRepositoryImpl(
  private val stationsProxyService: StationsAPI,
  private val stationsCache: StationsCache,
- private val requestDispatcher: CoroutineDispatcher
+ private val requestDispatcher: CoroutineDispatcher,
+ private val requestRetryPolicy: RequestRetryPolicy
 ) : StationsRepository {
 
  override fun getAllStations(): Flow<StationsResultState<StationsResult>> =
@@ -39,7 +42,7 @@ internal class StationsRepositoryImpl(
  )
  }
  }
- }.catch { throwable ->
+ }.retryWithPolicy(requestRetryPolicy).catch { throwable ->
  emit(StationsResultState.Failure(throwable))
  }.flowOn(requestDispatcher)