Verifying the file descriptor permissions before passing it to `libki…

…wix`.

* We have implemented a method to ensure that `libkiwix` can open the `file descriptor` successfully. This precautionary step helps us prevent runtime crashes triggered by `libkiwix` in case there is an issue accessing the `file descriptor` via its path.

app/src/main/java/org/kiwix/kiwixmobile/nav/destination/reader/KiwixReaderFragment.kt

@@ -239,21 +239,27 @@ class KiwixReaderFragment : CoreReaderFragment() {
       } else {
         zimReaderContainer?.zimFileReader?.let(::setUpBookmarks)
       }
-    } else if (zimFile != null &&
-      getAssetFileDescriptorFromUri(requireActivity(), zimFile.toUri()) != null
-    ) {
-      getAssetFileDescriptorFromUri(
-        requireActivity(),
-        zimFile.toUri()
-      )?.let { assetFileDescriptor ->
-        openZimFile(null, assetFileDescriptor = assetFileDescriptor, filePath = "$zimFile")
-      }
     } else {
-      getCurrentWebView()?.snack(R.string.zim_not_opened)
+      zimFile?.let {
+        getAssetFileDescriptorFromUri(
+          requireActivity(),
+          zimFile.toUri()
+        )?.let { assetFileDescriptor ->
+          openZimFile(null, assetFileDescriptor = assetFileDescriptor, filePath = "$zimFile")
+          Log.d(
+            TAG_KIWIX,
+            "Kiwix normal start, Opened last used zimFile: -> $zimFile"
+          )
+        } ?: run(KiwixReaderFragment::showUnableToOpenFileToast)
+      } ?: run(KiwixReaderFragment::showUnableToOpenFileToast)
     }
     restoreTabs(zimArticles, zimPositions, currentTab)
   }
 
+  private fun showUnableToOpenFileToast() {
+    getCurrentWebView()?.snack(R.string.zim_not_opened)
+  }
+
   @Suppress("UnsafeCallOnNullableType")
   override fun createWebView(attrs: AttributeSet?): ToolbarScrollingKiwixWebView {
     return ToolbarScrollingKiwixWebView(

core/src/main/java/org/kiwix/kiwixmobile/core/utils/files/FileUtils.kt

@@ -47,6 +47,7 @@ import org.kiwix.kiwixmobile.core.reader.ZimReaderContainer
 import org.kiwix.kiwixmobile.core.utils.SharedPreferenceUtil
 import java.io.BufferedReader
 import java.io.File
+import java.io.FileInputStream
 import java.io.FileNotFoundException
 import java.io.IOException
 
@@ -410,13 +411,22 @@ object FileUtils {
   fun getDemoFilePathForCustomApp(context: Context) =
     "${ContextCompat.getExternalFilesDirs(context, null)[0]}/demo.zim"
 
+  @SuppressLint("Recycle")
   @JvmStatic
   fun getAssetFileDescriptorFromUri(
     context: Context,
     uri: Uri
   ): AssetFileDescriptor? {
     return try {
-      context.contentResolver.openAssetFileDescriptor(uri, "r")
+      val assetFileDescriptor = context.contentResolver.openAssetFileDescriptor(uri, "r")
+      // Verify whether libkiwix can successfully open this file descriptor or not.
+      return if (
+        isFileDescriptorCanOpenWithLibkiwix(assetFileDescriptor?.parcelFileDescriptor?.fd)
+      ) {
+        assetFileDescriptor
+      } else {
+        null
+      }
     } catch (ignore: FileNotFoundException) {
       null
     } catch (ignore: Exception) {
@@ -427,4 +437,21 @@ object FileUtils {
       null
     }
   }
+
+  @JvmStatic
+  fun isFileDescriptorCanOpenWithLibkiwix(fdNumber: Int?): Boolean {
+    return try {
+      // Attempt to create a FileInputStream object using the specified path.
+      // Since libkiwix utilizes this path to create the archive object internally,
+      // it is crucial to verify if we can successfully read the file descriptor (fd)
+      // via the given file path before passing it to libkiwix.
+      // This precaution helps prevent runtime crashes.
+      // For more details, refer to https://github.com/kiwix/kiwix-android/pull/3636.
+      FileInputStream("dev/fd/$fdNumber")
+      true
+    } catch (ignore: Exception) {
+      ignore.printStackTrace()
+      false
+    }
+  }
 }