Use fallback API hosts when receiving server down response

purchases/src/main/kotlin/com/revenuecat/purchases/common/AppConfig.kt

@@ -50,6 +50,11 @@ internal class AppConfig(
     val baseURL: URL = proxyURL?.also {
         log(LogIntent.INFO, ConfigureStrings.CONFIGURING_PURCHASES_PROXY_URL_SET)
     } ?: URL("https://api.revenuecat.com/")
+    val fallbackBaseURLs: List<URL> = if (proxyURL != null) {
+        emptyList()
+    } else {
+        listOf(URL("https://api-production.8-lives-cat.io/"))
+    }
     val customEntitlementComputation: Boolean
         get() = dangerousSettings.customEntitlementComputation
 

purchases/src/main/kotlin/com/revenuecat/purchases/common/Backend.kt

@@ -166,6 +166,7 @@ internal class Backend(
                     body = null,
                     postFieldsToSign = null,
                     backendHelper.authenticationHeaders,
+                    fallbackBaseURLs = appConfig.fallbackBaseURLs,
                 )
             }
 
@@ -272,6 +273,7 @@ internal class Backend(
                     body,
                     postFieldsToSign,
                     backendHelper.authenticationHeaders + extraHeaders,
+                    fallbackBaseURLs = appConfig.fallbackBaseURLs,
                 )
             }
 
@@ -338,6 +340,7 @@ internal class Backend(
                     body = null,
                     postFieldsToSign = null,
                     backendHelper.authenticationHeaders,
+                    fallbackBaseURLs = appConfig.fallbackBaseURLs,
                 )
             }
 
@@ -402,6 +405,7 @@ internal class Backend(
                     body,
                     postFieldsToSign,
                     backendHelper.authenticationHeaders,
+                    fallbackBaseURLs = appConfig.fallbackBaseURLs,
                 )
             }
 
@@ -455,6 +459,7 @@ internal class Backend(
                     body,
                     postFieldsToSign = null,
                     backendHelper.authenticationHeaders,
+                    fallbackBaseURLs = appConfig.fallbackBaseURLs,
                 )
             }
 
@@ -516,6 +521,7 @@ internal class Backend(
                     body,
                     postFieldsToSign = null,
                     backendHelper.authenticationHeaders,
+                    fallbackBaseURLs = appConfig.fallbackBaseURLs,
                 )
             }
 
@@ -564,6 +570,7 @@ internal class Backend(
                     body = null,
                     postFieldsToSign = null,
                     backendHelper.authenticationHeaders,
+                    fallbackBaseURLs = appConfig.fallbackBaseURLs,
                 )
             }
 
@@ -617,6 +624,7 @@ internal class Backend(
                     body = null,
                     postFieldsToSign = null,
                     backendHelper.authenticationHeaders,
+                    fallbackBaseURLs = appConfig.fallbackBaseURLs,
                 )
             }
 
@@ -677,6 +685,7 @@ internal class Backend(
                     body,
                     postFieldsToSign = null,
                     backendHelper.authenticationHeaders,
+                    fallbackBaseURLs = appConfig.fallbackBaseURLs,
                 )
             }
 

purchases/src/main/kotlin/com/revenuecat/purchases/common/BackendHelper.kt

@@ -32,6 +32,7 @@ internal class BackendHelper(
                         body,
                         postFieldsToSign,
                         authenticationHeaders,
+                        fallbackBaseURLs = appConfig.fallbackBaseURLs,
                     )
                 }
 

purchases/src/main/kotlin/com/revenuecat/purchases/common/HTTPClient.kt

@@ -99,7 +99,7 @@ internal class HTTPClient(
      * @throws JSONException Thrown for any JSON errors, not thrown for returned HTTP error codes
      * @throws IOException Thrown for any unexpected errors, not thrown for returned HTTP error codes
      */
-    @Suppress("LongParameterList")
+    @Suppress("LongParameterList", "LongMethod")
     @Throws(JSONException::class, IOException::class)
     fun performRequest(
         baseURL: URL,
@@ -108,6 +108,8 @@ internal class HTTPClient(
         postFieldsToSign: List<Pair<String, String>>?,
         requestHeaders: Map<String, String>,
         refreshETag: Boolean = false,
+        fallbackBaseURLs: List<URL> = emptyList(),
+        fallbackURLIndex: Int = 0,
     ): HTTPResult {
         if (appConfig.forceServerErrors) {
             warnLog("Forcing server error for request to ${endpoint.getPath()}")
@@ -136,7 +138,36 @@ internal class HTTPClient(
         }
         if (callResult == null) {
             log(LogIntent.WARNING, NetworkStrings.ETAG_RETRYING_CALL)
-            callResult = performRequest(baseURL, endpoint, body, postFieldsToSign, requestHeaders, refreshETag = true)
+            callResult = performRequest(
+                baseURL,
+                endpoint,
+                body,
+                postFieldsToSign,
+                requestHeaders,
+                refreshETag = true,
+                fallbackBaseURLs,
+                fallbackURLIndex,
+            )
+        } else if (RCHTTPStatusCodes.isServerError(callResult.responseCode) &&
+            endpoint.supportsFallbackBaseURLs &&
+            fallbackURLIndex in fallbackBaseURLs.indices
+        ) {
+            // Handle server errors with fallback URLs
+            val fallbackBaseURL = fallbackBaseURLs[fallbackURLIndex]
+            log(
+                LogIntent.DEBUG,
+                NetworkStrings.RETRYING_CALL_WITH_FALLBACK_URL.format(endpoint.getPath(), fallbackBaseURL),
+            )
+            callResult = performRequest(
+                fallbackBaseURL,
+                endpoint,
+                body,
+                postFieldsToSign,
+                requestHeaders,
+                refreshETag,
+                fallbackBaseURLs,
+                fallbackURLIndex + 1,
+            )
         }
         return callResult
     }

purchases/src/main/kotlin/com/revenuecat/purchases/common/networking/Endpoint.kt

@@ -84,4 +84,24 @@ internal sealed class Endpoint(val pathTemplate: String, val name: String) {
             ->
                 false
         }
+
+    val supportsFallbackBaseURLs: Boolean
+        get() = when (this) {
+            is GetOfferings,
+            GetProductEntitlementMapping,
+            ->
+                true
+
+            is LogIn,
+            PostReceipt,
+            PostRedeemWebPurchase,
+            is GetAmazonReceipt,
+            is PostAttributes,
+            PostDiagnostics,
+            PostPaywallEvents,
+            is GetCustomerInfo,
+            is GetCustomerCenterConfig,
+            ->
+                false
+        }
 }

purchases/src/main/kotlin/com/revenuecat/purchases/strings/NetworkStrings.kt

@@ -6,6 +6,7 @@ internal object NetworkStrings {
     const val HTTP_RESPONSE_PAYLOAD_NULL = "HTTP Response payload is null"
     const val ETAG_RETRYING_CALL = "We were expecting to be able to return a cached response, but we can't find it. " +
         "Retrying call with a new ETag"
+    const val RETRYING_CALL_WITH_FALLBACK_URL = "Retrying request %s using fallback URL %s"
     const val ETAG_CALL_ALREADY_RETRIED = "We can't find the cached response, but call has already been retried. " +
         "Returning result from backend: %s"
     const val SAME_CALL_SCHEDULED_WITHOUT_JITTER = "Request already scheduled without jitter delay, adding " +

purchases/src/test/java/com/revenuecat/purchases/amazon/AmazonBackendTest.kt

@@ -46,6 +46,7 @@ class AmazonBackendTest {
         mockClient = mockk()
         mockAppConfig = mockk<AppConfig>().apply {
             every { baseURL } returns [email protected]
+            every { fallbackBaseURLs } returns emptyList()
         }
         dispatcher = SyncDispatcher()
         backendHelper = BackendHelper(API_KEY, dispatcher, mockAppConfig, mockClient)

purchases/src/test/java/com/revenuecat/purchases/backend_integration_tests/BaseBackendIntegrationTest.kt

@@ -85,6 +85,7 @@ internal abstract class BaseBackendIntegrationTest {
             every { forceServerErrors } returns false
             every { forceSigningErrors } returns false
             every { isAppBackgrounded } returns false
+            every { fallbackBaseURLs } returns emptyList()
         }
         dispatcher = Dispatcher(Executors.newSingleThreadScheduledExecutor(), runningIntegrationTests = true)
         diagnosticsDispatcher = Dispatcher(Executors.newSingleThreadScheduledExecutor(), runningIntegrationTests = true)

purchases/src/test/java/com/revenuecat/purchases/common/AppConfigTest.kt

@@ -438,4 +438,36 @@ class AppConfigTest {
                 "showInAppMessagesAutomatically=false, " +
                 "baseURL=https://api.revenuecat.com/)")
     }
+
+    // region Fallback API host
+
+    @Test
+    fun `appConfig returns expected fallback URLs list when no proxy URL is set`() {
+        val appConfig = AppConfig(
+            context = mockk(relaxed = true),
+            purchasesAreCompletedBy = REVENUECAT,
+            showInAppMessagesAutomatically = false,
+            platformInfo = PlatformInfo(flavor = "native", version = "3.2.0"),
+            proxyURL = null,
+            store = Store.PLAY_STORE,
+            isDebugBuild = false,
+        )
+        assertThat(appConfig.fallbackBaseURLs).isEqualTo(listOf(URL("https://api-production.8-lives-cat.io/")))
+    }
+
+    @Test
+    fun `appConfig returns empty fallback URLs list when a proxy URL is set`() {
+        val appConfig = AppConfig(
+            context = mockk(relaxed = true),
+            purchasesAreCompletedBy = REVENUECAT,
+            showInAppMessagesAutomatically = false,
+            platformInfo = PlatformInfo(flavor = "native", version = "3.2.0"),
+            proxyURL = URL("https://proxy.com"),
+            store = Store.PLAY_STORE,
+            isDebugBuild = false,
+        )
+        assertThat(appConfig.fallbackBaseURLs).isEmpty()
+    }
+
+    // endregion Fallback API host
 }

purchases/src/test/java/com/revenuecat/purchases/common/BaseHTTPClientTest.kt

@@ -107,7 +107,8 @@ internal abstract class BaseHTTPClientTest {
         endpoint: Endpoint,
         expectedResult: HTTPResult,
         verificationResult: VerificationResult = VerificationResult.NOT_REQUESTED,
-        requestDateHeader: Date? = null
+        requestDateHeader: Date? = null,
+        server: MockWebServer = this.server,
     ) {
         every {
             mockETagManager.getHTTPResultFromCacheOrBackend(