fix(reviewers): support localStorage again

After the migration to use a server that can handle the backend POST requests, AnkiDroid moved from having a static base URL to a dynamic one because the server port could change.

This fixes the issue by using a default port number. That should work in 99% of the cases.

If by chance another app uses the same port, a free one will be used instead. I haven't tested, but this may happen with parallel builds of AnkiDroid running at the same time. Still, the only issue that would surge is that localStorage wouldn't work on one of open builds until the other one is closed

Author: BrayanDSO

AnkiDroid/src/main/java/com/ichi2/anki/AbstractFlashcardViewer.kt

@@ -128,6 +128,7 @@ import com.ichi2.anki.settings.Prefs
 import com.ichi2.anki.snackbar.BaseSnackbarBuilderProvider
 import com.ichi2.anki.snackbar.SnackbarBuilder
 import com.ichi2.anki.snackbar.showSnackbar
+import com.ichi2.anki.ui.windows.reviewer.ReviewerViewModel
 import com.ichi2.anki.utils.OnlyOnce.Method.ANSWER_CARD
 import com.ichi2.anki.utils.OnlyOnce.preventSimultaneousExecutions
 import com.ichi2.anki.utils.ext.showDialogFragment
@@ -163,6 +164,8 @@ import kotlinx.coroutines.runBlocking
 import timber.log.Timber
 import java.io.File
 import java.io.UnsupportedEncodingException
+import java.net.BindException
+import java.net.ServerSocket
 import java.net.URLDecoder
 import java.util.concurrent.locks.Lock
 import java.util.concurrent.locks.ReadWriteLock
@@ -273,7 +276,7 @@ abstract class AbstractFlashcardViewer :
     /** Handle joysticks/pedals */
     protected lateinit var motionEventHandler: MotionEventHandler
 
-    val server = AnkiServer(this).also { it.start() }
+    val server: AnkiServer
 
     @get:VisibleForTesting
     var cardContent: String? = null
@@ -367,6 +370,16 @@ abstract class AbstractFlashcardViewer :
     }
 
     init {
+        val port =
+            try {
+                ServerSocket(ReviewerViewModel.DEFAULT_PORT).use {
+                    it.reuseAddress = true
+                    it.localPort
+                }
+            } catch (_: BindException) {
+                0
+            }
+        server = AnkiServer(this, port).also { it.start() }
         ChangeManager.subscribe(this)
     }
 

AnkiDroid/src/main/java/com/ichi2/anki/pages/AnkiServer.kt

@@ -24,7 +24,8 @@ import java.io.ByteArrayInputStream
 
 open class AnkiServer(
     private val postHandler: PostRequestHandler,
-) : NanoHTTPD(LOCALHOST, 0) {
+    port: Int = 0,
+) : NanoHTTPD(LOCALHOST, port) {
     fun baseUrl(): String = "http://$LOCALHOST:$listeningPort/"
 
     // it's faster to serve local files without GZip. see 'page render' in logs

AnkiDroid/src/main/java/com/ichi2/anki/previewer/CardViewerViewModel.kt

@@ -67,8 +67,9 @@ abstract class CardViewerViewModel(
 
     @CallSuper
     override fun onCleared() {
-        super.onCleared()
         cardMediaPlayer.close()
+        server.stop()
+        super.onCleared()
     }
 
     /* *********************************************************************************************

AnkiDroid/src/main/java/com/ichi2/anki/ui/windows/reviewer/ReviewerViewModel.kt

@@ -68,6 +68,8 @@ import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.MutableSharedFlow
 import kotlinx.coroutines.flow.MutableStateFlow
 import timber.log.Timber
+import java.net.BindException
+import java.net.ServerSocket
 
 class ReviewerViewModel(
     cardMediaPlayer: CardMediaPlayer,
@@ -96,7 +98,7 @@ class ReviewerViewModel(
     val typeAnswerFlow = MutableStateFlow<TypeAnswer?>(null)
     val destinationFlow = MutableSharedFlow<Destination>()
 
-    override val server = AnkiServer(this).also { it.start() }
+    override val server: AnkiServer
     private val stateMutationKey = TimeManager.time.intTimeMS().toString()
     val statesMutationEval = MutableSharedFlow<String>()
 
@@ -124,6 +126,17 @@ class ReviewerViewModel(
         }
 
     init {
+        val port =
+            try {
+                ServerSocket(DEFAULT_PORT).use {
+                    it.reuseAddress = true
+                    it.localPort
+                }
+            } catch (_: BindException) {
+                0
+            }
+        server = AnkiServer(this, port).also { it.start() }
+
         keyMap.setProcessor(this)
         ChangeManager.subscribe(this)
         launchCatchingIO {
@@ -628,6 +641,13 @@ class ReviewerViewModel(
     }
 
     companion object {
+        /**
+         * Default port of the Reviewer's [AnkiServer].
+         * Using a static port makes the URL constant, and that
+         * makes possible to use JavaScript's `localStorage`.
+         */
+        const val DEFAULT_PORT = 64009
+
         fun factory(
             soundPlayer: CardMediaPlayer,
             keyMap: PeripheralKeymap<ReviewerBinding, ViewerAction>,