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捕获 flutter app的崩溃日志并上报
source link: https://www.tuicool.com/articles/UvQFzyn
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flutter 的崩溃日志收集主要有两个方面：
- 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）
- 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：
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 print 、 timers 、 microtasks 还有最关键的 how uncaught errors are handled 未捕获异常的处理
runZoned(() {
Future.error("asynchronous error");
}, onError: (dynamic e, StackTrace stack) {
reportError(e, stack);
});
在 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。
FlutterError.onError = (FlutterErrorDetails details) {
reportError(details.exception, details.stack);
};
该 error 一般是由 Widget 在 build 的时候抛出，如下：
@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：
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 crashlytics 、 bugly 、 xCrash 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:
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：
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：
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：
flutter --version
输出如下：
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。
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：
-
将原始堆栈保存到 stack.txt 中，注意第一行要以
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***开头*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** 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] ...
-
执行ndk-stack命令
$ANDROID_NDK/ndk-stack -sym ~/Downloads/flutter-52c7a1e849/armeabi-v7a -dump stack.txt > re-stack.txt
打开文件 re-stack.txt 即可看到还原后的堆栈：
********** Crash dump: ********** #00 0x00016998 /system/lib/libc.so (__memcpy_base+104) [armeabi-v7a::2b2dac1c583b68da2f7c58e7ed352851] #01 0x00158aed /data/app/com.netease.cartoonreader-1/lib/arm/libflutter.so [armeabi-v7a::2c9d8634bdb07ea641970181b0b00b84] fml::WriteAtomically(fml::UniqueObject<int, fml::internal::os_unix::UniqueFDTraits> const&, char const*, fml::Mapping const&) /b/s/w/ir/k/src/out/android_release/../../flutter/fml/platform/posix/file_posix.cc:203:3 flutter::PersistentCacheStore(fml::RefPtr<fml::TaskRunner>, std::__1::shared_ptr<fml::UniqueObject<int, fml::internal::os_unix::UniqueFDTraits> >, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::unique_ptr<fml::Mapping, std::__1::default_delete<fml::Mapping> >)::$_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] ...
上传符号表 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：
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
本文完，如你更好的方案请不要犹豫快留言告诉我。
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