flutter 的崩溃日志收集主要有两个方面:

  1. flutter dart 代码的异常(包含app和framework代码两种情况,一般不会引起闪退,你猜为什么)
  2. flutter engine 的崩溃日志(一般会闪退)

Flutter App 代码异常捕获

人写的代码是无数异常交织起来的偶然产物,代码发生异常才是正常情况。

除了在关键的地方加上 try-catch 让它们变成已知异常之外,抓到未知异常才是真本事。

比如下面的一段代码中的try-catch是无效的:

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try {
Future.error("asynchronous surprise");
} catch (e){
print(e)
}

好在,Dart 有一个 Zone 的概念,有点类似sandbox的意思。不同的 Zone 代码上下文是不同的互不影响,Zone 还可以创建新的子Zone。Zone 可以重新定义自己的printtimersmicrotasks还有最关键的how uncaught errors are handled 未捕获异常的处理

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runZoned(() {
Future.error("asynchronous error");
}, onError: (dynamic e, StackTrace stack) {
reportError(e, stack);
});

reportError 里即可以进行上报处理(详见后面介绍)。

Flutter framework 异常捕获

注册 FlutterError.onError 回调,用于收集 Flutter framework 外抛的异常。

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FlutterError.onError = (FlutterErrorDetails details) {
reportError(details.exception, details.stack);
};

该 error 一般是由 Widgetbuild 的时候抛出,如下:

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@override
void performRebuild() {
Widget built;
try {
built = build();
} catch (e, stack) {
built = ErrorWidget.builder(_debugReportException(ErrorDescription("building $this"), e, stack));
} finally {
_dirty = false;
}
try {
_child = updateChild(_child, built, slot);
} catch (e, stack) {
built = ErrorWidget.builder(_debugReportException(ErrorDescription("building $this"), e, stack));
_child = updateChild(null, built, slot);
}
}

该代码有删减,具体请参看framework.dart源码。其中的_debugReportException 就是 FlutterError 的调用点:

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FlutterErrorDetails _debugReportException(
DiagnosticsNode context,
dynamic exception,
StackTrace stack, {
InformationCollector informationCollector,
}) {
final FlutterErrorDetails details = FlutterErrorDetails(
exception: exception,
stack: stack,
library: 'widgets library',
context: context,
informationCollector: informationCollector,
);
FlutterError.reportError(details);
return details;
}

Flutter engine 异常捕获

flutter engine 部分的异常,以Android 为例,主要为 libfutter.so发生的错误。

这部份可以直接交给native崩溃收集sdk来处理,比如 firebase crashlyticsbuglyxCrash 等等

reportError 堆栈上报

线上app 出现异常虽然捕获了,但只是打印出来是没办法解决问题,还需要把他上报到开发者能看到的地方。

上面提到了许多崩溃收集的sdk,以 bugly 为例,它支持自定义异常上报,我们只需将 dart 异常及堆栈通过 MethodChannel传递给 bugly sdk 即可。

Dart:

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var channel = new MethodChannel("crash_handler");

Future<void> reportError(dynamic exception, StackTrace stack) async {
try {
return channel.invokeMethod("report_error", <String, dynamic>{
"type": exception.runtimeType.toString(), // exception type
"message": exception.toString(), // message
"stack": stack.toString(), // stacktrace
});
} catch(ignored) {
}
}

Android Java代码如下:

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public class CrashHandler implements MethodCallHandler {
@Override
public void onMethodCall(MethodCall call, Result result) {
switch (call.method) {
case "report_error":
postFlutterExcetion(call.argument("type"), call.argument("message"), call.argument("stack"))
result.success(true);
break;
default:
result.notImplemented();
}
}

static void postFlutterExcetion(String excpetionType, String excpetionMessage, String stack) {
if (!CrashModule.hasInitialized()) return;
CrashReport.postException(4, excpetionType, excpetionMessage, stack, null);
}
}

// ...

MethodChannel(flutterView, "crash_handler").setMethodCallHandler(new CrashHandler())

iOS 类似的注册一个MethodChannel并在handleMethodCall中调用 Bugly 的reportExceptionWithCategory即可。

其它的sdk类似处理,此处略过不表。

堆栈还原

收集到异常之后,需要查符合表还原堆栈。下面以Android 端 bugly 收集到堆栈为一例:

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1 #00 pc 00016998 /system/lib/libc.so (__memcpy_base+104) [armeabi-v7a::2b2dac1c583b68da2f7c58e7ed352851]
2 #01 pc 00158aed /data/app/com.netease.cartoonreader-1/lib/arm/libflutter.so [armeabi-v7a::2c9d8634bdb07ea641970181b0b00b84]
3 #02 pc 00138041 /data/app/com.netease.cartoonreader-1/lib/arm/libflutter.so [armeabi-v7a::2c9d8634bdb07ea641970181b0b00b84]
4 #03 pc 00139461 /data/app/com.netease.cartoonreader-1/lib/arm/libflutter.so [armeabi-v7a::2c9d8634bdb07ea641970181b0b00b84]
5 #04 pc 00013057 /system/lib/libutils.so (_ZN7android6Looper9pollInnerEi+530) [armeabi-v7a::ac423f49f579c99cfababb65014363e9]
6 #05 pc 00013127 /system/lib/libutils.so (_ZN7android6Looper8pollOnceEiPiS1_PPv+130) [armeabi-v7a::ac423f49f579c99cfababb65014363e9]
7 #06 pc 00007889 /system/lib/libandroid.so (ALooper_pollOnce+64) [armeabi-v7a::954c216fdf1faa9aa08f41bc27503a87]
8 #07 pc 001394fb /data/app/com.netease.cartoonreader-1/lib/arm/libflutter.so [armeabi-v7a::2c9d8634bdb07ea641970181b0b00b84]
9 #08 pc 001371eb /data/app/com.netease.cartoonreader-1/lib/arm/libflutter.so [armeabi-v7a::2c9d8634bdb07ea641970181b0b00b84]
10 #09 pc 00138441 /data/app/com.netease.cartoonreader-1/lib/arm/libflutter.so [armeabi-v7a::2c9d8634bdb07ea641970181b0b00b84]
11 #10 pc 0004185b /system/lib/libc.so (_ZL15__pthread_startPv+30) [armeabi-v7a::2b2dac1c583b68da2f7c58e7ed352851]
12 #11 pc 000192a5 /system/lib/libc.so (__start_thread+6) [armeabi-v7a::2b2dac1c583b68da2f7c58e7ed352851]
13 java:
14 [Failed to get Java stack]

首先需要确认该 flutter engine 所属版本号,在命令行执行:

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flutter --version

输出如下:

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Flutter 1.5.4-hotfix.2 • channel stable • https://github.com/flutter/flutter.git
Framework • revision 7a4c33425d (9 weeks ago) • 2019-04-29 11:05:24 -0700
Engine • revision 52c7a1e849
Tools • Dart 2.3.0 (build 2.3.0-dev.0.5 a1668566e5)

可以看到 Engine 的 revision 为 52c7a1e849

其次,在 flutter infra 上找到对应cpu abi 的 symbols.zip 并下载 :https://console.cloud.google.com/storage/browser/flutter_infra/flutter/52c7a1e849a170be4b2b2fe34142ca2c0a6fea1f/android-arm-release

解压后,可以得到带有符合信息的 debug so 文件—— libflutter.so,并将其放到文件夹 armeabi-v7a 下。如需要x86等的符号信息,类似操作。

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mkdir -p ~/Downloads/flutter-52c7a1e849/armeabi-v7a
unzip symbols.zip -d ~/Downloads/flutter-52c7a1e849/armeabi-v7a

使用 ndk-stack 手动还原堆栈:

  1. 将原始堆栈保存到 stack.txt 中,注意第一行要以 *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** 开头

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    *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
    1 #00 pc 00016998 /system/lib/libc.so (__memcpy_base+104) [armeabi-v7a::2b2dac1c583b68da2f7c58e7ed352851]
    2 #01 pc 00158aed /data/app/com.netease.cartoonreader-1/lib/arm/libflutter.so [armeabi-v7a::2c9d8634bdb07ea641970181b0b00b84]
    3 #02 pc 00138041 /data/app/com.netease.cartoonreader-1/lib/arm/libflutter.so [armeabi-v7a::2c9d8634bdb07ea641970181b0b00b84]
    4 #03 pc 00139461 /data/app/com.netease.cartoonreader-1/lib/arm/libflutter.so [armeabi-v7a::2c9d8634bdb07ea641970181b0b00b84]
    5 #04 pc 00013057 /system/lib/libutils.so (_ZN7android6Looper9pollInnerEi+530) [armeabi-v7a::ac423f49f579c99cfababb65014363e9]
    ...
  2. 执行ndk-stack命令

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    $ANDROID_NDK/ndk-stack -sym ~/Downloads/flutter-52c7a1e849/armeabi-v7a -dump stack.txt > re-stack.txt

打开文件 re-stack.txt 即可看到还原后的堆栈:

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********** Crash dump: **********
#00 0x00016998 /system/lib/libc.so (__memcpy_base+104) [armeabi-v7a::2b2dac1c583b68da2f7c58e7ed352851]
#01 0x00158aed /data/app/com.netease.cartoonreader-1/lib/arm/libflutter.so [armeabi-v7a::2c9d8634bdb07ea641970181b0b00b84]
fml::WriteAtomically(fml::UniqueObject<int, fml::internal::os_unix::UniqueFDTraits> const&, char const*, fml::Mapping const&)
/b/s/w/ir/k/src/out/android_release/../../flutter/fml/platform/posix/file_posix.cc:203:3
flutter::PersistentCacheStore(fml::RefPtr<fml::TaskRunner>, std::__1::shared_ptr<fml::UniqueObject<int, fml::internal::os_unix::UniqueFDTraits> >, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::unique_ptr<fml::Mapping, std::__1::default_delete<fml::Mapping> >)::$_0::operator()()
/b/s/w/ir/k/src/out/android_release/../../flutter/shell/common/persistent_cache.cc:114:0
auto fml::internal::CopyableLambda<flutter::PersistentCacheStore(fml::RefPtr<fml::TaskRunner>, std::__1::shared_ptr<fml::UniqueObject<int, fml::internal::os_unix::UniqueFDTraits> >, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::unique_ptr<fml::Mapping, std::__1::default_delete<fml::Mapping> >)::$_0>::operator()<>() const
/b/s/w/ir/k/src/out/android_release/../../flutter/fml/make_copyable.h:24:0
#02 0x00138041 /data/app/com.netease.cartoonreader-1/lib/arm/libflutter.so [armeabi-v7a::2c9d8634bdb07ea641970181b0b00b84]
fml::MessageLoopImpl::FlushTasks(fml::MessageLoopImpl::FlushType)
/b/s/w/ir/k/src/out/android_release/../../flutter/fml/message_loop_impl.cc:140:5
fml::MessageLoopImpl::RunExpiredTasksNow()
/b/s/w/ir/k/src/out/android_release/../../flutter/fml/message_loop_impl.cc:148:0
#03 0x00139461 /data/app/com.netease.cartoonreader-1/lib/arm/libflutter.so [armeabi-v7a::2c9d8634bdb07ea641970181b0b00b84]
fml::MessageLoopAndroid::OnEventFired()
/b/s/w/ir/k/src/out/android_release/../../flutter/fml/platform/android/message_loop_android.cc:92:5
fml::MessageLoopAndroid::MessageLoopAndroid()::$_0::operator()(int, int, void*) const
/b/s/w/ir/k/src/out/android_release/../../flutter/fml/platform/android/message_loop_android.cc:42:0
fml::MessageLoopAndroid::MessageLoopAndroid()::$_0::__invoke(int, int, void*)
/b/s/w/ir/k/src/out/android_release/../../flutter/fml/platform/android/message_loop_android.cc:40:0
#04 0x00013057 /system/lib/libutils.so (_ZN7android6Looper9pollInnerEi+530) [armeabi-v7a::ac423f49f579c99cfababb65014363e9]

...

bugly 自动还原堆栈

一个个崩溃堆栈手动还原多麻烦(噫 你怎么这么多崩溃),下载好 debug so 之后你也可以使用 bugly给的符号表上传工具上传到bugly上,文档见:https://bugly.qq.com/docs/user-guide/symbol-configuration-android/?v=20181014122344#_4

输出符号表:

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java -jar buglySymbolAndroid.jar -i ~/Downloads/flutter-52c7a1e849/armeabi-v7a

将符号表上传之后,bugly 会自动将堆栈还原,如下图所示
image2019-7-2_12-45-47.png

本文完,如你更好的方案请不要犹豫快留言告诉我。