feat: add flag push

build.gradle.kts

@@ -24,6 +24,7 @@ dependencies {
     testImplementation("io.mockk:mockk:${Versions.mockk}")
     implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:${Versions.serializationRuntime}")
     implementation("com.squareup.okhttp3:okhttp:${Versions.okhttp}")
+    implementation("com.squareup.okhttp3:okhttp-sse:${Versions.okhttpSse}")
     implementation("com.amplitude:evaluation-core:${Versions.evaluationCore}")
     implementation("com.amplitude:java-sdk:${Versions.amplitudeAnalytics}")
     implementation("org.json:json:${Versions.json}")

buildSrc/src/main/kotlin/Versions.kt

@@ -6,6 +6,7 @@ object Versions {
     const val serializationRuntime = "1.4.1"
     const val json = "20231013"
     const val okhttp = "4.12.0"
+    const val okhttpSse = "4.12.0" // Update this alongside okhttp. Note this library isn't stable and may contain breaking changes. Search uses of okhttp3.internal classes before updating.
     const val evaluationCore = "2.0.0-beta.2"
     const val amplitudeAnalytics = "1.12.0"
     const val mockk = "1.13.9"

src/main/kotlin/LocalEvaluationClient.kt

@@ -19,6 +19,8 @@ import com.amplitude.experiment.evaluation.EvaluationEngineImpl
 import com.amplitude.experiment.evaluation.EvaluationFlag
 import com.amplitude.experiment.evaluation.topologicalSort
 import com.amplitude.experiment.flag.DynamicFlagConfigApi
+import com.amplitude.experiment.flag.FlagConfigPoller
+import com.amplitude.experiment.flag.FlagConfigStreamApi
 import com.amplitude.experiment.flag.InMemoryFlagConfigStorage
 import com.amplitude.experiment.util.LocalEvaluationMetricsWrapper
 import com.amplitude.experiment.util.Logger
@@ -32,6 +34,10 @@ import com.amplitude.experiment.util.wrapMetrics
 import okhttp3.HttpUrl
 import okhttp3.HttpUrl.Companion.toHttpUrl
 import okhttp3.OkHttpClient
+import okhttp3.Request
+import okhttp3.sse.EventSource
+import okhttp3.sse.EventSourceListener
+import okhttp3.sse.EventSources
 
 class LocalEvaluationClient internal constructor(
     apiKey: String,
@@ -41,9 +47,13 @@ class LocalEvaluationClient internal constructor(
 ) {
     private val assignmentService: AssignmentService? = createAssignmentService(apiKey)
     private val serverUrl: HttpUrl = getServerUrl(config)
+    private val streamServerUrl: HttpUrl = getStreamServerUrl(config)
     private val evaluation: EvaluationEngine = EvaluationEngineImpl()
     private val metrics: LocalEvaluationMetrics = LocalEvaluationMetricsWrapper(config.metrics)
-    private val flagConfigApi = DynamicFlagConfigApi(apiKey, serverUrl, getProxyUrl(config), httpClient)
+    private val flagConfigApi = DynamicFlagConfigApi(apiKey, serverUrl, null, httpClient)
+    private val proxyUrl: HttpUrl? = getProxyUrl(config)
+    private val flagConfigProxyApi = if (proxyUrl == null) null else DynamicFlagConfigApi(apiKey, proxyUrl, null, httpClient)
+    private val flagConfigStreamApi = if (config.streamUpdates) FlagConfigStreamApi(apiKey, streamServerUrl, httpClient, config.streamFlagConnTimeoutMillis) else null
     private val flagConfigStorage = InMemoryFlagConfigStorage()
     private val cohortStorage = if (config.cohortSyncConfig == null) {
         null
@@ -60,6 +70,8 @@ class LocalEvaluationClient internal constructor(
     private val deploymentRunner = DeploymentRunner(
         config = config,
         flagConfigApi = flagConfigApi,
+        flagConfigProxyApi = flagConfigProxyApi,
+        flagConfigStreamApi = flagConfigStreamApi,
         flagConfigStorage = flagConfigStorage,
         cohortApi = cohortApi,
         cohortStorage = cohortStorage,
@@ -185,6 +197,17 @@ private fun getServerUrl(config: LocalEvaluationConfig): HttpUrl {
     }
 }
 
+private fun getStreamServerUrl(config: LocalEvaluationConfig): HttpUrl {
+    return if (config.streamServerUrl == LocalEvaluationConfig.Defaults.STREAM_SERVER_URL) {
+        when (config.serverZone) {
+            ServerZone.US -> US_STREAM_SERVER_URL.toHttpUrl()
+            ServerZone.EU -> EU_STREAM_SERVER_URL.toHttpUrl()
+        }
+    } else {
+        config.streamServerUrl.toHttpUrl()
+    }
+}
+
 private fun getProxyUrl(config: LocalEvaluationConfig): HttpUrl? {
     return config.evaluationProxyConfig?.proxyUrl?.toHttpUrl()
 }

src/main/kotlin/LocalEvaluationConfig.kt

@@ -22,6 +22,12 @@ class LocalEvaluationConfig internal constructor(
     @JvmField
     val flagConfigPollerRequestTimeoutMillis: Long = Defaults.FLAG_CONFIG_POLLER_REQUEST_TIMEOUT_MILLIS,
     @JvmField
+    val streamUpdates: Boolean = Defaults.STREAM_UPDATES,
+    @JvmField
+    val streamServerUrl: String = Defaults.STREAM_SERVER_URL,
+    @JvmField
+    val streamFlagConnTimeoutMillis: Long = Defaults.STREAM_FLAG_CONN_TIMEOUT_MILLIS,
+    @JvmField
     val assignmentConfiguration: AssignmentConfiguration? = Defaults.ASSIGNMENT_CONFIGURATION,
     @JvmField
     val cohortSyncConfig: CohortSyncConfig? = Defaults.COHORT_SYNC_CONFIGURATION,
@@ -76,6 +82,12 @@ class LocalEvaluationConfig internal constructor(
          */
         const val FLAG_CONFIG_POLLER_REQUEST_TIMEOUT_MILLIS = 10_000L
 
+        const val STREAM_UPDATES = false
+
+        const val STREAM_SERVER_URL = US_STREAM_SERVER_URL
+
+        const val STREAM_FLAG_CONN_TIMEOUT_MILLIS = 1_500L
+
         /**
          * null
          */
@@ -111,6 +123,9 @@ class LocalEvaluationConfig internal constructor(
         private var serverUrl = Defaults.SERVER_URL
         private var flagConfigPollerIntervalMillis = Defaults.FLAG_CONFIG_POLLER_INTERVAL_MILLIS
         private var flagConfigPollerRequestTimeoutMillis = Defaults.FLAG_CONFIG_POLLER_REQUEST_TIMEOUT_MILLIS
+        private var streamUpdates = Defaults.STREAM_UPDATES
+        private var streamServerUrl = Defaults.STREAM_SERVER_URL
+        private var streamFlagConnTimeoutMillis = Defaults.STREAM_FLAG_CONN_TIMEOUT_MILLIS
         private var assignmentConfiguration = Defaults.ASSIGNMENT_CONFIGURATION
         private var cohortSyncConfiguration = Defaults.COHORT_SYNC_CONFIGURATION
         private var evaluationProxyConfiguration = Defaults.EVALUATION_PROXY_CONFIGURATION
@@ -136,6 +151,18 @@ class LocalEvaluationConfig internal constructor(
             this.flagConfigPollerRequestTimeoutMillis = flagConfigPollerRequestTimeoutMillis
         }
 
+        fun streamUpdates(streamUpdates: Boolean) = apply {
+            this.streamUpdates = streamUpdates
+        }
+
+        fun streamServerUrl(streamServerUrl: String) = apply {
+            this.streamServerUrl = streamServerUrl
+        }
+
+        fun streamFlagConnTimeoutMillis(streamFlagConnTimeoutMillis: Long) = apply {
+            this.streamFlagConnTimeoutMillis = streamFlagConnTimeoutMillis
+        }
+
         fun enableAssignmentTracking(assignmentConfiguration: AssignmentConfiguration) = apply {
             this.assignmentConfiguration = assignmentConfiguration
         }
@@ -161,6 +188,9 @@ class LocalEvaluationConfig internal constructor(
                 serverZone = serverZone,
                 flagConfigPollerIntervalMillis = flagConfigPollerIntervalMillis,
                 flagConfigPollerRequestTimeoutMillis = flagConfigPollerRequestTimeoutMillis,
+                streamUpdates = streamUpdates,
+                streamServerUrl = streamServerUrl,
+                streamFlagConnTimeoutMillis = streamFlagConnTimeoutMillis,
                 assignmentConfiguration = assignmentConfiguration,
                 cohortSyncConfig = cohortSyncConfiguration,
                 evaluationProxyConfig = evaluationProxyConfiguration,
@@ -207,6 +237,8 @@ interface LocalEvaluationMetrics {
     fun onFlagConfigFetch()
     fun onFlagConfigFetchFailure(exception: Exception)
     fun onFlagConfigFetchOriginFallback(exception: Exception)
+    fun onFlagConfigStream()
+    fun onFlagConfigStreamFailure(exception: Exception?)
     fun onCohortDownload()
     fun onCohortDownloadFailure(exception: Exception)
     fun onCohortDownloadOriginFallback(exception: Exception)

src/main/kotlin/ServerZone.kt

@@ -2,6 +2,8 @@ package com.amplitude.experiment
 
 internal const val US_SERVER_URL = "https://api.lab.amplitude.com"
 internal const val EU_SERVER_URL = "https://api.lab.eu.amplitude.com"
+internal const val US_STREAM_SERVER_URL = "https://stream.lab.amplitude.com"
+internal const val EU_STREAM_SERVER_URL = "https://stream.lab.eu.amplitude.com"
 internal const val US_COHORT_SERVER_URL = "https://cohort-v2.lab.amplitude.com"
 internal const val EU_COHORT_SERVER_URL = "https://cohort-v2.lab.eu.amplitude.com"
 internal const val US_EVENT_SERVER_URL = "https://api2.amplitude.com/2/httpapi"

src/main/kotlin/deployment/DeploymentRunner.kt

@@ -2,22 +2,19 @@
 
 package com.amplitude.experiment.deployment
 
-import com.amplitude.experiment.ExperimentalApi
-import com.amplitude.experiment.LocalEvaluationConfig
-import com.amplitude.experiment.LocalEvaluationMetrics
+import com.amplitude.experiment.*
 import com.amplitude.experiment.cohort.CohortApi
 import com.amplitude.experiment.cohort.CohortLoader
 import com.amplitude.experiment.cohort.CohortStorage
+import com.amplitude.experiment.flag.*
 import com.amplitude.experiment.flag.FlagConfigApi
+import com.amplitude.experiment.flag.FlagConfigPoller
 import com.amplitude.experiment.flag.FlagConfigStorage
 import com.amplitude.experiment.util.LocalEvaluationMetricsWrapper
 import com.amplitude.experiment.util.Logger
 import com.amplitude.experiment.util.Once
 import com.amplitude.experiment.util.daemonFactory
 import com.amplitude.experiment.util.getAllCohortIds
-import com.amplitude.experiment.util.wrapMetrics
-import java.util.concurrent.CompletableFuture
-import java.util.concurrent.ConcurrentHashMap
 import java.util.concurrent.Executors
 import java.util.concurrent.TimeUnit
 
@@ -26,6 +23,8 @@ private const val MIN_COHORT_POLLING_INTERVAL = 60000L
 internal class DeploymentRunner(
     private val config: LocalEvaluationConfig,
     private val flagConfigApi: FlagConfigApi,
+    private val flagConfigProxyApi: FlagConfigApi? = null,
+    private val flagConfigStreamApi: FlagConfigStreamApi? = null,
     private val flagConfigStorage: FlagConfigStorage,
     cohortApi: CohortApi?,
     private val cohortStorage: CohortStorage?,
@@ -39,21 +38,29 @@ internal class DeploymentRunner(
         null
     }
     private val cohortPollingInterval: Long = getCohortPollingInterval()
+    // Fallback in this order: proxy, stream, poll.
+    private val amplitudeFlagConfigPoller = FlagConfigFallbackRetryWrapper(
+        FlagConfigPoller(flagConfigApi, flagConfigStorage, cohortLoader, cohortStorage, config, metrics),
+        null, config.flagConfigPollerIntervalMillis, 1000
+    )
+    private val amplitudeFlagConfigUpdater =
+        if (flagConfigStreamApi != null)
+            FlagConfigFallbackRetryWrapper(
+                FlagConfigStreamer(flagConfigStreamApi, flagConfigStorage, cohortLoader, cohortStorage, config, metrics),
+                amplitudeFlagConfigPoller,
+            )
+        else amplitudeFlagConfigPoller
+    private val flagConfigUpdater =
+        if (flagConfigProxyApi != null)
+            FlagConfigFallbackRetryWrapper(
+                FlagConfigPoller(flagConfigProxyApi, flagConfigStorage, cohortLoader, cohortStorage, config, metrics),
+                amplitudeFlagConfigPoller
+            )
+        else
+            amplitudeFlagConfigUpdater
 
     fun start() = lock.once {
-        refresh()
-        poller.scheduleWithFixedDelay(
-            {
-                try {
-                    refresh()
-                } catch (t: Throwable) {
-                    Logger.e("Refresh flag configs failed.", t)
-                }
-            },
-            config.flagConfigPollerIntervalMillis,
-            config.flagConfigPollerIntervalMillis,
-            TimeUnit.MILLISECONDS
-        )
+        flagConfigUpdater.start()
         if (cohortLoader != null) {
             poller.scheduleWithFixedDelay(
                 {
@@ -74,63 +81,7 @@ internal class DeploymentRunner(
 
     fun stop() {
         poller.shutdown()
-    }
-
-    fun refresh() {
-        Logger.d("Refreshing flag configs.")
-        // Get updated flags from the network.
-        val flagConfigs = wrapMetrics(
-            metric = metrics::onFlagConfigFetch,
-            failure = metrics::onFlagConfigFetchFailure,
-        ) {
-            flagConfigApi.getFlagConfigs()
-        }
-
-        // Remove flags that no longer exist.
-        val flagKeys = flagConfigs.map { it.key }.toSet()
-        flagConfigStorage.removeIf { !flagKeys.contains(it.key) }
-
-        // Get all flags from storage
-        val storageFlags = flagConfigStorage.getFlagConfigs()
-
-        // Load cohorts for each flag if applicable and put the flag in storage.
-        val futures = ConcurrentHashMap<String, CompletableFuture<*>>()
-        for (flagConfig in flagConfigs) {
-            if (cohortLoader == null) {
-                flagConfigStorage.putFlagConfig(flagConfig)
-                continue
-            }
-            val cohortIds = flagConfig.getAllCohortIds()
-            val storageCohortIds = storageFlags[flagConfig.key]?.getAllCohortIds() ?: emptySet()
-            val cohortsToLoad = cohortIds - storageCohortIds
-            if (cohortsToLoad.isEmpty()) {
-                flagConfigStorage.putFlagConfig(flagConfig)
-                continue
-            }
-            for (cohortId in cohortsToLoad) {
-                futures.putIfAbsent(
-                    cohortId,
-                    cohortLoader.loadCohort(cohortId).handle { _, exception ->
-                        if (exception != null) {
-                            Logger.e("Failed to load cohort $cohortId", exception)
-                        }
-                        flagConfigStorage.putFlagConfig(flagConfig)
-                    }
-                )
-            }
-        }
-        futures.values.forEach { it.join() }
-
-        // Delete unused cohorts
-        if (cohortStorage != null) {
-            val flagCohortIds = flagConfigStorage.getFlagConfigs().values.toList().getAllCohortIds()
-            val storageCohortIds = cohortStorage.getCohorts().keys
-            val deletedCohortIds = storageCohortIds - flagCohortIds
-            for (deletedCohortId in deletedCohortIds) {
-                cohortStorage.deleteCohort(deletedCohortId)
-            }
-        }
-        Logger.d("Refreshed ${flagConfigs.size} flag configs.")
+        flagConfigUpdater.shutdown()
     }
 
     private fun getCohortPollingInterval(): Long {