Clear attempted regions when a connect failover cycle ends

.changeset/clear-attempted-regions.md

@@ -0,0 +1,5 @@
+---
+"client-sdk-android": patch
+---
+
+Fix region failover being skipped on later connects after a failed attempt

livekit-android-sdk/src/main/java/io/livekit/android/room/Room.kt

@@ -549,22 +549,30 @@ constructor(
             var nextUrl: String? = regionUrl ?: url
             regionUrl = null
 
-            while (nextUrl != null) {
-                val connectUrl = nextUrl
-                nextUrl = null
-                try {
-                    engine.regionUrlProvider = regionUrlProvider
-                    engine.join(connectUrl, token, options, roomOptions)
-                } catch (e: Exception) {
-                    e.rethrowIfCancellationSignal()
-
-                    nextUrl = regionUrlProvider?.getNextBestRegionUrl()
-                    if (nextUrl != null) {
-                        LKLog.d(e) { "Connection to $connectUrl failed, retrying with another region: $nextUrl" }
-                    } else {
-                        throw e // rethrow since no more regions to try.
+            // Attempted regions are scoped to this failover cycle, since the provider is reused
+            // across connects. Captured locally as prepareConnection can replace the field.
+            val cycleRegionUrlProvider = regionUrlProvider
+
+            try {
+                while (nextUrl != null) {
+                    val connectUrl = nextUrl
+                    nextUrl = null
+                    try {
+                        engine.regionUrlProvider = cycleRegionUrlProvider
+                        engine.join(connectUrl, token, options, roomOptions)
+                    } catch (e: Exception) {
+                        e.rethrowIfCancellationSignal()
+
+                        nextUrl = cycleRegionUrlProvider?.getNextBestRegionUrl()
+                        if (nextUrl != null) {
+                            LKLog.d(e) { "Connection to $connectUrl failed, retrying with another region: $nextUrl" }
+                        } else {
+                            throw e // rethrow since no more regions to try.
+                        }
                     }
                 }
+            } finally {
+                cycleRegionUrlProvider?.clearAttemptedRegions()
             }
 
             ensureActive()

livekit-android-test/src/test/java/io/livekit/android/room/RegionUrlProviderTest.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024 LiveKit, Inc.
+ * Copyright 2024-2026 LiveKit, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -79,6 +79,29 @@ class RegionUrlProviderTest : BaseTest() {
         // Check that only one request was needed.
         assertEquals(1, server.requestCount)
     }
+
+    /**
+     * The attempted set scopes one failover cycle. Once it is cleared the whole region list is
+     * eligible again, so a region that failed transiently is retried on the next cycle rather
+     * than being skipped for the life of the provider.
+     */
+    @Test
+    fun clearAttemptedRegionsMakesEveryRegionEligibleAgain() = runTest {
+        server = MockWebServer()
+        server.enqueue(MockResponse().setBody(regionResponse))
+        val regionUrlProvider = RegionUrlProvider(server.url("").toUri(), "token", OkHttpClient.Builder().build(), Json { ignoreUnknownKeys = true })
+
+        assertEquals("https://regiona.livekit.cloud", regionUrlProvider.getNextBestRegionUrl())
+        assertEquals("https://regionb.livekit.cloud", regionUrlProvider.getNextBestRegionUrl())
+
+        regionUrlProvider.clearAttemptedRegions()
+
+        // Back to the best region, not the next unattempted one.
+        assertEquals("https://regiona.livekit.cloud", regionUrlProvider.getNextBestRegionUrl())
+
+        // Still served from the cached settings.
+        assertEquals(1, server.requestCount)
+    }
 }
 
 private val regionResponse = """{