compose box: On failed message send, show error dialog

Fixes: zulip#815

Author: chrisbobbe

lib/widgets/compose_box.dart

@@ -5,6 +5,7 @@ import 'package:flutter/services.dart';
 import 'package:flutter_gen/gen_l10n/zulip_localizations.dart';
 import 'package:image_picker/image_picker.dart';
 
+import '../api/exception.dart';
 import '../api/model/model.dart';
 import '../api/route/messages.dart';
 import '../model/compose.dart';
@@ -716,7 +717,7 @@ class _SendButtonState extends State<_SendButton> {
       || widget.contentController.hasValidationErrors.value;
   }
 
-  void _send() {
+  void _send() async {
     if (_hasValidationErrors) {
       final zulipLocalizations = ZulipLocalizations.of(context);
       List<String> validationErrorMessages = [
@@ -735,9 +736,26 @@ class _SendButtonState extends State<_SendButton> {
 
     final store = PerAccountStoreWidget.of(context);
     final content = widget.contentController.textNormalized;
-    store.sendMessage(destination: widget.getDestination(), content: content);
 
     widget.contentController.clear();
+
+    try {
+      // TODO(#720) await send request, putting input(s) and send button into a
+      //   disabled "working on it" state (allowing input text to be selected
+      //   for copying).
+      await store.sendMessage(destination: widget.getDestination(), content: content);
+    } on ApiRequestException catch (e) {
+      if (!mounted) return;
+      final zulipLocalizations = ZulipLocalizations.of(context);
+      final message = switch (e) {
+        ZulipApiException() => zulipLocalizations.errorServerMessage(e.message),
+        _ => e.message,
+      };
+      showErrorDialog(context: context,
+        title: zulipLocalizations.errorMessageNotSent,
+        message: message);
+      return;
+    }
   }
 
   @override

test/widgets/compose_box_test.dart

@@ -16,6 +16,7 @@ import '../example_data.dart' as eg;
 import '../flutter_checks.dart';
 import '../model/binding.dart';
 import '../stdlib_checks.dart';
+import 'dialog_checks.dart';
 
 void main() {
   TestZulipBinding.ensureInitialized();
@@ -219,5 +220,23 @@ void main() {
       final errorDialogs = tester.widgetList(find.byType(AlertDialog));
       check(errorDialogs).isEmpty();
     });
+
+    testWidgets('ZulipApiException', (tester) async {
+      await setupAndTapSend(tester, prepareResponse: (message) {
+        connection.prepare(
+          httpStatus: 400,
+          json: {
+            'result': 'error',
+            'code': 'BAD_REQUEST',
+            'msg': 'You do not have permission to initiate direct message conversations.',
+          });
+      });
+      final zulipLocalizations = GlobalLocalizations.zulipLocalizations;
+      await tester.tap(find.byWidget(checkErrorDialog(tester,
+        expectedTitle: zulipLocalizations.errorMessageNotSent,
+        expectedMessage: zulipLocalizations.errorServerMessage(
+          'You do not have permission to initiate direct message conversations.'),
+      )));
+    });
   });
 }