share: Use filename to guess mimetype, in addition to the header bytes

Use the received file's name when trying to guess the mimetype in
addition to checking for magic header bytes, using `lookupMimeType`.

Author: rajveermalviya

android/app/src/main/kotlin/com/zulip/flutter/AndroidIntentEventListener.kt

@@ -94,7 +94,7 @@ fun getIntentSharedFile(context: Context, url: Uri): IntentSharedFile {
     cursor.moveToFirst()
     val nameIndex = cursor.getColumnIndex(OpenableColumns.DISPLAY_NAME)
     cursor.getString(nameIndex)
-  } ?: ("unknown." + (mimeType?.split('/')?.last() ?: "bin"))
+  }
 
   class ResolverFailedException(msg: String) : RuntimeException(msg)
 

android/app/src/main/kotlin/com/zulip/flutter/AndroidIntents.g.kt

@@ -48,14 +48,14 @@ private object AndroidIntentsPigeonUtils {
 
 /** Generated class from Pigeon that represents data sent in messages. */
 data class IntentSharedFile (
-  val name: String,
+  val name: String? = null,
   val mimeType: String? = null,
   val bytes: ByteArray
 )
  {
   companion object {
     fun fromList(pigeonVar_list: List<Any?>): IntentSharedFile {
-      val name = pigeonVar_list[0] as String
+      val name = pigeonVar_list[0] as String?
       val mimeType = pigeonVar_list[1] as String?
       val bytes = pigeonVar_list[2] as ByteArray
       return IntentSharedFile(name, mimeType, bytes)

lib/host/android_intents.g.dart

@@ -24,12 +24,12 @@ bool _deepEquals(Object? a, Object? b) {
 
 class IntentSharedFile {
   IntentSharedFile({
-    required this.name,
+    this.name,
     this.mimeType,
     required this.bytes,
   });
 
-  String name;
+  String? name;
 
   String? mimeType;
 
@@ -49,7 +49,7 @@ class IntentSharedFile {
   static IntentSharedFile decode(Object result) {
     result as List<Object?>;
     return IntentSharedFile(
-      name: result[0]! as String,
+      name: result[0] as String?,
       mimeType: result[1] as String?,
       bytes: result[2]! as Uint8List,
     );

lib/widgets/share.dart

@@ -79,19 +79,23 @@ class ShareService {
       // Try to guess the mimeType from file header magic-number.
       mimeType ??= lookupMimeType(
         // Seems like the path shouldn't be required; we still want to look for
-        // matches on `headerBytes`. Thankfully we can still do that, by calling
-        // lookupMimeType with the empty string as the path. That's a value that
-        // doesn't map to any particular type, so the path will be effectively
-        // ignored, as desired. Upstream comment:
+        // matches on `headerBytes` when we don't have a path/filename.
+        // Thankfully we can still do that, by calling lookupMimeType with the
+        // empty string as the path. That's a value that doesn't map to any
+        // particular type, so the path will be effectively ignored, as desired.
+        // Upstream comment:
         //   https://github.com/dart-lang/mime/issues/11#issuecomment-2246824452
-        '',
+        sharedFile.name ?? '',
         headerBytes: List.unmodifiable(
           sharedFile.bytes.take(defaultMagicNumbersMaxLength)));
 
+      final filename =
+        sharedFile.name ?? 'unknown.${mimeType?.split('/').last ?? 'bin'}';
+
       return FileToUpload(
         content: Stream.value(sharedFile.bytes),
         length: sharedFile.bytes.length,
-        filename: sharedFile.name,
+        filename: filename,
         mimeType: mimeType);
     });
 

pigeon/android_intents.dart

@@ -20,7 +20,7 @@ class IntentSharedFile {
     required this.bytes,
   });
 
-  final String name;
+  final String? name;
   final String? mimeType;
   final Uint8List bytes;
 }