Fix polling behavior (#468)

There is a bug that we fetch from multiple sources.

Author: xinlili-statsig

src/main/kotlin/com/statsig/sdk/SpecUpdater.kt

@@ -241,6 +241,7 @@ internal class SpecUpdater(
                     if (config != null) {
                         logger.debug("[StatsigSpecUpdater] Successfully fetched config specs from source: $source")
                         emit(Pair(config, source))
+                        break
                     }
                 }
             }

src/test/java/com/statsig/sdk/StatsigPollingTest.kt

@@ -0,0 +1,101 @@
+package com.statsig.sdk
+import kotlinx.coroutines.runBlocking
+import okhttp3.mockwebserver.Dispatcher
+import okhttp3.mockwebserver.MockResponse
+import okhttp3.mockwebserver.MockWebServer
+import okhttp3.mockwebserver.RecordedRequest
+import org.junit.After
+import org.junit.Before
+import org.junit.Test
+
+class StatsigPollingTest {
+    private lateinit var statsig: StatsigServer
+    private lateinit var options: StatsigOptions
+    private val logLines: MutableList<String> = mutableListOf()
+
+    @Before
+    fun setUp() {
+        options =
+            StatsigOptions(
+                fallbackToStatsigAPI = true,
+                rulesetsSyncIntervalMs = 1000,
+                customLogger =
+                object : LoggerInterface {
+                    override fun error(message: String) {
+                    }
+
+                    override fun warn(message: String) {
+                    }
+
+                    override fun info(message: String) {
+                        logLines.add(message)
+                    }
+
+                    override fun debug(message: String) {
+                    }
+
+                    override fun setLogLevel(level: LogLevel) {
+                    }
+                },
+                logLevel = LogLevel.INFO,
+            )
+        statsig = StatsigServer.create()
+    }
+
+    @After
+    fun cleanup() {
+        logLines.clear()
+        statsig.shutdown()
+    }
+
+    fun setupWebServer(success: Boolean): MockWebServer {
+        val server = MockWebServer()
+        server.dispatcher =
+            object : Dispatcher() {
+                override fun dispatch(request: RecordedRequest): MockResponse {
+                    if ("/v1/download_config_specs" in request.path!!) {
+                        if (success) {
+                            val downloadConfigSpecsResponse =
+                                StatsigE2ETest::class.java.getResource("/download_config_specs.json")?.readText() ?: ""
+                            return MockResponse().setResponseCode(200).setBody(downloadConfigSpecsResponse)
+                        } else {
+                            return MockResponse().setResponseCode(500)
+                        }
+                    }
+
+                    return MockResponse().setResponseCode(202)
+                }
+            }
+        return server
+    }
+
+    @Test
+    fun testPollFromSources() {
+        val server = setupWebServer(true)
+        options.api = server.url("/v1").toString()
+        runBlocking {
+            statsig.initialize("secret-key", options)
+        }
+        val dcsRequestCount =
+            logLines
+                .filter {
+                    it.startsWith("[StatsigHTTPHelper]") && it.contains("v1/download_config_specs")
+                }.size
+        assert(dcsRequestCount == 1)
+    }
+
+    @Test
+    fun testFallbackOnPollFromSources() {
+        val server = setupWebServer(false)
+        options.api = server.url("/v1").toString()
+        runBlocking {
+            statsig.initialize("secret-key", options)
+        }
+        val dcsRequestCount =
+            logLines
+                .filter {
+                    it.startsWith("[StatsigHTTPHelper]") && it.contains("v1/download_config_specs")
+                }.size
+        assert(dcsRequestCount == 2)
+    }
+}