Bad UTF16 character crashes in RenderText.cpp #12772
Description
Steps to Reproduce
If I try to display an invalid UTF16 character in a Text(), it causes a hard crash due to assertion failure in the engine's RenderText.cpp. The code is trying to display text which it shouldn't, but I wouldn't expect it to crash in the rendering engine.
This can easily happen if you take a substring which happens to slice an SMP UTF32 character in half, as shown below. It's especially dangerous if the app deals with arbitrary user text input.
Test case:
testWidgets('Bad string is bad', (WidgetTester tester) async {
// First half of this UTF32 code point is not a valid UTF16 code point.
String invalidString = '💩'.substring(0, 1); // or codeUnitAt(0)
print('Invalid String: $invalidString');
Text text = new Text(invalidString);
print('Invalid Text: $text');
// This crashes during rendering.
await tester.pumpWidget(
new Directionality(child: text, textDirection: TextDirection.ltr));
});Logs
Test output:
Running Flutter tests.
00:01 +0: widget tests - Bad string is bad
Invalid String: ???
Invalid Text: Text("???")
Shell: ASSERTION FAILED: m_text
Shell: ../../flutter/sky/engine/core/rendering/RenderText.cpp(71) : blink::RenderText::RenderText(PassRefPtr<WTF::StringImpl>)In contrast, a null string in Text fails at the Dart level:
Running Flutter tests.
00:01 +0: widget tests - Bad string is bad
Invalid String: null
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following assertion was thrown running a test:
'package:flutter/src/widgets/text.dart': Failed assertion: line 208 pos 15: 'data != null': is not
true.Flutter Doctor
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