Fix message ordering in paywall webview communication

CHANGELOG.md

@@ -4,6 +4,8 @@ The changelog for `Superwall`. Also see the [releases](https://github.com/superw
 
 ## Unreleased
 
+- Fix multi-page paywalls only reporting the entry page view. 
+- Fix an active paywall not being reopened after its webview process crashes and is recreated. Recovery cancels messages for the old webview and sends the open after the replacement loads, only if the same presentation is still active.
 - Fix prices not showing when product/offers are fetched from cache
 - Fix a JSON null in placement parameters or user attributes reaching audience filters as the text `"null"`, so a filter checking whether a field is null never matched.
 

superwall/src/main/java/com/superwall/sdk/paywall/view/PaywallView.kt

@@ -1007,6 +1007,7 @@ class PaywallView(
 
     private fun recreateWebview() {
         val oldWebView = webView
+        oldWebView.messageHandler.resetForWebViewReload()
         oldWebView.detach(this)
         oldWebView.destroyView()
         webView =
@@ -1015,7 +1016,6 @@ class PaywallView(
             })
         webView.attach(this)
         webView.delegate = this
-        webView.messageHandler.handle(PaywallMessage.PaywallOpen)
         loadWebView()
     }
 

superwall/src/main/java/com/superwall/sdk/paywall/view/webview/messaging/PaywallMessageHandler.kt

@@ -32,6 +32,9 @@ import com.superwall.sdk.storage.core_data.convertToJsonElement
 import com.superwall.sdk.utilities.withErrorTracking
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.currentCoroutineContext
+import kotlinx.coroutines.ensureActive
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.suspendCancellableCoroutine
 import kotlinx.coroutines.withContext
@@ -41,8 +44,6 @@ import kotlinx.serialization.json.Json
 import kotlinx.serialization.json.JsonObject
 import java.net.URI
 import java.util.Date
-import java.util.LinkedList
-import java.util.Queue
 import kotlin.coroutines.resume
 
 interface PaywallStateDelegate {
@@ -97,7 +98,84 @@ class PaywallMessageHandler(
     }
 
     var messageHandler: PaywallMessageHandlerDelegate? = null
-    private val queue: Queue<PaywallMessage> = LinkedList()
+
+    private data class PendingMessage(
+        val message: PaywallMessage,
+        val shouldSend: () -> Boolean = { true },
+    )
+
+    // Reserve the order synchronously; template construction can suspend before the
+    // main-thread evaluation. Never bypass an unfinished send: late templates reset
+    // the runtime even if an open has already arrived. Reload cancels obsolete work.
+    // Permission and callback replies remain independent.
+    private val outboundLock = Any()
+    private val queue = ArrayDeque<PendingMessage>()
+    private val outboundJobs = mutableSetOf<Job>()
+    private var lastOutbound: Job? = null
+
+    private fun enqueueOutbound(block: suspend () -> Unit) {
+        synchronized(outboundLock) {
+            val previous = lastOutbound
+            val job =
+                ioScope.launch {
+                    previous?.join()
+                    block()
+                }
+            lastOutbound = job
+            outboundJobs.add(job)
+            job.invokeOnCompletion {
+                synchronized(outboundLock) {
+                    outboundJobs.remove(job)
+                    if (lastOutbound === job) lastOutbound = null
+                }
+            }
+        }
+    }
+
+    // Called on main before replacing the WebView. Cancel work for the old document
+    // and only restore an open if that same presentation is still active at delivery.
+    internal fun resetForWebViewReload() {
+        synchronized(outboundLock) {
+            outboundJobs.toList().forEach { it.cancel() }
+            lastOutbound = null
+            queue.clear()
+            val state = messageHandler?.state
+            messageHandler?.updateState(PaywallViewState.Updates.SetPaywallJsVersion(null))
+            if (state?.isPresented == true && !state.closedForBackground) {
+                // SetLastOpen replaces this object for each new presentation.
+                val lastOpen = state.lastOpen
+                queue.addLast(
+                    PendingMessage(PaywallMessage.PaywallOpen) {
+                        val current = messageHandler?.state
+                        current?.isPresented == true && !current.closedForBackground && current.lastOpen === lastOpen
+                    },
+                )
+            }
+        }
+    }
+
+    private fun sendLifecycleMessage(pending: PendingMessage) {
+        synchronized(outboundLock) {
+            if (!isWebViewLoaded) {
+                queue.addLast(pending)
+            } else {
+                val paywall = messageHandler?.state?.paywall ?: return
+                enqueueOutbound {
+                    withContext(Dispatchers.Main) {
+                        if (pending.shouldSend()) {
+                            val eventName =
+                                if (pending.message is PaywallMessage.PaywallOpen) {
+                                    SuperwallEvents.PaywallOpen.rawName
+                                } else {
+                                    SuperwallEvents.PaywallClose.rawName
+                                }
+                            pass(eventName = eventName, paywall = paywall)
+                        }
+                    }
+                }
+            }
+        }
+    }
 
     @JavascriptInterface
     fun postMessage(message: String) {
@@ -140,19 +218,18 @@ class PaywallMessageHandler(
         ) { "!! PaywallMessageHandler: Paywall: $paywall, delegeate: $messageHandler" }
         when (message) {
             is PaywallMessage.TemplateParamsAndUserAttributes ->
-                ioScope.launch { passTemplatesToWebView(paywall) }
+                enqueueOutbound { passTemplatesToWebView(paywall) }
 
             is PaywallMessage.OnReady -> {
-                messageHandler?.updateState(
-                    PaywallViewState.Updates.SetPaywallJsVersion(message.paywallJsVersion),
-                )
-                val loadedAt = Date()
-                Logger.debug(
-                    LogLevel.debug,
-                    LogScope.superwallCore,
-                    "!! PaywallMessageHandler: Ready !!",
-                )
-                ioScope.launch { didLoadWebView(paywall, loadedAt) }
+                // Publishing readiness and reserving initialization must be atomic
+                // with lifecycle sends from other threads.
+                synchronized(outboundLock) {
+                    messageHandler?.updateState(
+                        PaywallViewState.Updates.SetPaywallJsVersion(message.paywallJsVersion),
+                    )
+                    val loadedAt = Date()
+                    enqueueOutbound { didLoadWebView(paywall, loadedAt) }
+                }
             }
 
             is PaywallMessage.Close -> {
@@ -177,49 +254,34 @@ class PaywallMessageHandler(
                     shouldDismiss = message.shouldDismiss,
                 )
 
-            is PaywallMessage.PaywallOpen -> {
-                if (messageHandler?.state?.paywall?.paywalljsVersion == null) {
-                    queue.offer(message)
-                } else {
-                    ioScope.launch {
-                        pass(eventName = SuperwallEvents.PaywallOpen.rawName, paywall = paywall)
-                    }
-                }
-            }
-
-            is PaywallMessage.PaywallClose -> {
-                if (messageHandler?.state?.paywall?.paywalljsVersion == null) {
-                    queue.offer(message)
-                } else {
-                    ioScope.launch {
-                        val eventName = SuperwallEvents.PaywallClose.rawName
-                        pass(eventName = eventName, paywall = paywall)
-                    }
-                }
+            is PaywallMessage.PaywallOpen,
+            is PaywallMessage.PaywallClose,
+            -> {
+                sendLifecycleMessage(PendingMessage(message))
             }
 
             is PaywallMessage.BackButtonPressed ->
-                ioScope.launch {
+                enqueueOutbound {
                     pass(eventName = "back_button_input", paywall = paywall)
                 }
 
             is PaywallMessage.Custom -> handleCustomEvent(message.data)
             is PaywallMessage.CustomPlacement -> handleCustomPlacement(message.name, message.params)
             is PaywallMessage.RestoreFailed ->
-                ioScope.launch {
+                enqueueOutbound {
                     pass(SuperwallEvents.RestoreFail.rawName, paywall)
                 }
 
             is PaywallMessage.RequestReview -> handleRequestReview(message)
 
             is PaywallMessage.TransactionStart -> {
-                ioScope.launch {
+                enqueueOutbound {
                     pass(eventName = SuperwallEvents.TransactionStart.rawName, paywall = paywall)
                 }
             }
 
             is PaywallMessage.TransactionAbandon -> {
-                ioScope.launch {
+                enqueueOutbound {
                     pass(eventName = SuperwallEvents.TransactionAbandon.rawName, paywall = paywall)
                 }
             }
@@ -229,7 +291,7 @@ class PaywallMessageHandler(
             }
 
             is PaywallMessage.TransactionComplete -> {
-                ioScope.launch {
+                enqueueOutbound {
                     pass(
                         SuperwallEvents.TransactionComplete.rawName,
                         paywall,
@@ -239,7 +301,7 @@ class PaywallMessageHandler(
             }
 
             is PaywallMessage.TrialStarted -> {
-                ioScope.launch {
+                enqueueOutbound {
                     pass(
                         eventName = SuperwallEvents.FreeTrialStart.rawName,
                         paywall = paywall,
@@ -376,6 +438,7 @@ class PaywallMessageHandler(
         )
 
         withContext(Dispatchers.Main) {
+            currentCoroutineContext().ensureActive()
             messageHandler?.evaluate(templateScript) { error ->
                 if (error != null) {
                     Logger.debug(
@@ -395,22 +458,24 @@ class PaywallMessageHandler(
         paywall: Paywall,
         loadedAt: Date,
     ) {
-        ioScope.launch {
-            val delegate = this@PaywallMessageHandler.messageHandler
-            if (delegate != null) {
-                delegate.updateState(PaywallViewState.Updates.WebLoadingEnded(loadedAt))
+        val delegate = this@PaywallMessageHandler.messageHandler
+        if (delegate != null) {
+            delegate.updateState(PaywallViewState.Updates.WebLoadingEnded(loadedAt))
 
-                val paywallInfo = delegate.state.info
+            val paywallInfo = delegate.state.info
+            // Tracking talks to the network, so it stays off the outbound queue - only
+            // the messages the webview receives need to keep their order.
+            ioScope.launch {
                 val trackedEvent =
                     InternalSuperwallEvent.PaywallWebviewLoad(
                         state = InternalSuperwallEvent.PaywallWebviewLoad.State.Complete(),
                         paywallInfo = paywallInfo,
                     )
                 track(trackedEvent)
-
-                val behavior = options.makeSuperwallOptions().eventTrackingBehavior
-                passEventTrackingBehaviorToWebView(behavior)
             }
+
+            val behavior = options.makeSuperwallOptions().eventTrackingBehavior
+            passEventTrackingBehaviorToWebView(behavior)
         }
 
         Logger.debug(
@@ -451,7 +516,11 @@ class PaywallMessageHandler(
             message = { "Posting Message" },
         )
 
-        mainScope.launch {
+        // Awaited rather than launched, so this send completes before anything queued
+        // behind it - a `paywall_open` that arrives while the templates are still
+        // building must not reach the webview first.
+        withContext(Dispatchers.Main) {
+            currentCoroutineContext().ensureActive()
             messageHandler?.evaluate(scriptSrc) { error ->
                 if (error != null) {
                     Logger.debug(
@@ -476,20 +545,22 @@ class PaywallMessageHandler(
         }
     }
 
+    private val isWebViewLoaded: Boolean
+        get() = messageHandler?.state?.paywall?.paywalljsVersion != null
+
     fun flushPendingMessages() {
-        ioScope.launch {
-            mainScope.launch {
-                flushPendingMessagesInternal()
-            }
+        mainScope.launch {
+            flushPendingMessagesInternal()
         }
     }
 
     private fun flushPendingMessagesInternal() {
-        if (queue.isEmpty()) return
-
-        val pending = queue.toList()
-        queue.clear()
-        pending.forEach { handle(it) }
+        synchronized(outboundLock) {
+            if (!isWebViewLoaded) return
+            while (queue.isNotEmpty()) {
+                sendLifecycleMessage(queue.removeFirst())
+            }
+        }
     }
 
     private fun openUrl(