fix_emoji_crash #31468

dansunhappy · 2019-04-23T04:14:34Z

Description

fix in iOS paste emoji crash
1 Test code

import 'package:flutter/material.dart';

class MyTextField extends StatelessWidget {
//  MediaQuery
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: TextField(
          maxLines: null,
        ),
      ),
    );
  }
}

void main() async {
  runApp(MaterialApp(
    home: MyTextField(),
  ));
}

environment
device：iOS 12 ，iPhone
keyboard setting ： english & emoji
analyze

main() {
  String a='𐐷';
  print(a.codeUnits.map((v)=> v.toRadixString(16)));
  String b='宋';
  print(b.codeUnits.map((v)=> v.toRadixString(16)));
}

https://en.wikipedia.org/wiki/UTF-16 @dnfield one character may be two code units.
try this code,

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dnfield · 2019-04-23T17:45:28Z

I've tried this locally on an iPhone 8. I can't seem to get the cursor to land in the middle of an emoji as you're showing here. What version of Flutter are you using? I'm on master.

dnfield · 2019-04-23T17:48:07Z

Scratch that - I managed to reproduce it with some dragging around. With a rainbow flag emoji, there was no crash (but I did end up with a separate rainbow and flag character :D). With a two code point emoji (one of the smiley faces), it crashed.

dnfield · 2019-04-23T17:50:07Z

This actually is hitting on multiple bugs - /cc @justinmc @GaryQian @goderbauer who have all been involved in things related to this.

We shouldn't have the cursor be able to land in the middle of an emoji.
We shouldn't crash if the platform receives a message like this on iOS.

Right now I think a higher priority is to fix the crash on the engine side.

dnfield · 2019-04-23T17:55:43Z

packages/flutter/lib/src/services/text_editing.dart

    assert(isNormalized);
+    if(text.isNotEmpty && start > 0 && start < text.length ){
+      final int startCodeUnit = text.codeUnitAt(start);
+      if( startCodeUnit & 0x8C00 == 0x8C00 ){


What happens if we're in a multi-byte character that has more than two bytes? e.g. the rainbow flag emoji is four codepoints:

🏳 U+1F3F3 ️ U+FE0F ‍ U+200D 🌈 U+1F308

In testing this issue, I was able to successfully land inside those codepoints, type a character, and split the flag into a blank flag with a rainbow. I don't think this logic would fix that scenario.

main() { String a='🌈'; print(a.codeUnits.map((v)=> v.toRadixString(16))); }

result is (d83c, df08), two characters, same as '𐐷'.

flutter using UTF-16 to handle character,

You can read the wikipedia carefully, only 2 cases, one case is 2 bytes, and the other case is 4 bytes. In flutter, it is 1 character and 2 characters. There are no other situations.

https://en.wikipedia.org/wiki/UTF-16

I am so sorry, I'm wrong.

Multi-byte characters do exist, like :

👨‍👩‍👧 (U+1F468, U+200D, U+1F469, U+200D, U+1F467) 🇨🇳 (U+1F1E8, U+1F1F3)

Above code is not working.
I am try to find a new way.

dnfield · 2019-04-23T17:58:47Z

See #30851 (comment) for the iOS stack trace

dnfield · 2019-04-23T21:16:27Z

Crash is due to iOS not tolerating invalid UTF-8 code sequence when decoding or encoding JSON.

Looking to see if we can make platform side more resilient (Android already handles this better). We should definitely fix this on the framework side too.

dansunhappy · 2019-04-24T01:28:48Z

I've tried this locally on an iPhone 8. I can't seem to get the cursor to land in the middle of an emoji as you're showing here. What version of Flutter are you using? I'm on master.

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel dev, v1.4.18, on Mac OS X 10.14.4 18E226, locale zh-Hans-CN)

[✓] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
[✓] iOS toolchain - develop for iOS devices (Xcode 10.2)
[✓] Android Studio (version 3.3)
[!] IntelliJ IDEA Community Edition (version 2018.3.3)
✗ Flutter plugin not installed; this adds Flutter specific functionality.
✗ Dart plugin not installed; this adds Dart specific functionality.
[✓] Connected device (2 available)

songfei · 2019-04-24T02:11:05Z

“make sure the cursor be NOT able to land in the middle of an emoji.” is better，

dnfield · 2019-04-25T23:12:09Z

I'm going to close this in favor of flutter/engine#8747

Thanks for your help in diagnosing this issue!

fix_emoji_crash

1e77df5

googlebot added the cla: yes label Apr 23, 2019

dnfield added a: typography Text rendering, possibly libtxt platform-ios iOS applications specifically engine flutter/engine related. See also e: labels. f: inspector Part of widget inspector in framework. labels Apr 23, 2019

dnfield closed this Apr 23, 2019

dnfield reopened this Apr 23, 2019

dnfield reviewed Apr 23, 2019

View reviewed changes

This was referenced Apr 24, 2019

Caret is able to select within emoji characters on the second line of text with emojis #24802

Closed

Fix crash when cursor ends up at invalid position flutter/engine#8747

Merged

dnfield closed this Apr 25, 2019

github-actions bot locked as resolved and limited conversation to collaborators Aug 6, 2021

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dansunhappy commented Apr 23, 2019

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