compose: For uploads, use verbatim URL string from server

Fixes #1709.

Round-tripping through `Uri.parse` and `.toString()` had the effect
of percent-encoding any non-ASCII characters in the given URL string.
The server expects, reasonably enough, that the client will refer to
the upload using the same URL string the server provided at upload
time; so do that.

Author: gnprice

lib/widgets/compose_box.dart

@@ -359,9 +359,9 @@ class ComposeContentController extends ComposeController<ContentValidationError>
 
   /// Tells the controller that a file upload has ended, with success or error.
   ///
-  /// To indicate success, pass the URL to be used for the Markdown link.
+  /// To indicate success, pass the URL string to be used for the Markdown link.
   /// If `url` is null, failure is assumed.
-  void registerUploadEnd(int tag, Uri? url) {
+  void registerUploadEnd(int tag, String? url) {
     final val = _uploads[tag];
     assert(val != null, 'registerUploadEnd called twice for same tag');
     final (:filename, :placeholder) = val!;
@@ -372,7 +372,7 @@ class ComposeContentController extends ComposeController<ContentValidationError>
 
     value = value.replaced(
       replacementRange,
-      url == null ? '' : inlineLink(filename, url.toString()));
+      url == null ? '' : inlineLink(filename, url));
     _uploads.remove(tag);
     notifyListeners(); // _uploads change could affect validationErrors
   }
@@ -971,15 +971,15 @@ Future<void> _uploadFiles({
 
   for (final (tag, file) in uploadsInProgress) {
     final _File(:content, :length, :filename, :mimeType) = file;
-    Uri? url;
+    String? url;
     try {
       final result = await uploadFile(store.connection,
         content: content,
         length: length,
         filename: filename,
         contentType: mimeType,
       );
-      url = Uri.parse(result.url);
+      url = result.url;
     } catch (e) {
       if (!context.mounted) return;
       // TODO(#741): Specifically handle `413 Payload Too Large`

test/widgets/compose_box_test.dart

@@ -1168,6 +1168,34 @@ void main() {
     // target platform the test is simulating.
     // TODO(upstream): unskip after fix to https://github.com/flutter/flutter/issues/161073
     skip: Platform.isWindows);
+
+    testWidgets('use verbatim URL string from server, not re-encoded', (tester) async {
+      // Regression test for: https://github.com/zulip/zulip-flutter/issues/1709
+      TypingNotifier.debugEnable = false;
+      addTearDown(TypingNotifier.debugReset);
+
+      final channel = eg.stream();
+      final narrow = eg.topicNarrow(channel.streamId, 'a topic');
+      await prepareComposeBox(tester, narrow: narrow, streams: [channel]);
+
+      testBinding.pickFilesResult = FilePickerResult([PlatformFile(
+        readStream: Stream.fromIterable(['asdf'.codeUnits]),
+        path: '/some/path/한국어 파일.txt',
+        name: '한국어 파일.txt',
+        size: 4,
+      )]);
+      connection.prepare(json: UploadFileResult(url:
+        '/user_uploads/1/4e/m2A3MSqFnWRLUf9SaPzQ0Up_/한국어 파일.txt').toJson());
+      await tester.tap(find.byIcon(ZulipIcons.image));
+      await tester.pump();
+      check(controller!.content.text)
+        .equals('[Uploading 한국어 파일.txt…]()\n\n');
+
+      await tester.pump(Duration.zero);
+      check(controller!.content.text)
+        .equals('[한국어 파일.txt]('
+          '/user_uploads/1/4e/m2A3MSqFnWRLUf9SaPzQ0Up_/한국어 파일.txt)\n\n');
+    });
   });
 
   group('error banner', () {