1# Subscribing to Address Sanitizer Events (ArkTS)
2
3## Available APIs
4
5For details about how to use the APIs (such as parameter usage constraints and value ranges), see [Application Event Logging](../reference/apis-performance-analysis-kit/js-apis-hiviewdfx-hiappevent.md).
6
7| API                                             | **Description**                                        |
8| --------------------------------------------------- | -------------------------------------------- |
9| addWatcher(watcher: Watcher): AppEventPackageHolder | Adds a watcher to subscribe to application events.|
10| removeWatcher(watcher: Watcher): void               | Removes a watcher to unsubscribe from application events.|
11
12## **How to Develop**
13
14The following describes how to subscribe to an address sanitizer event for an array bounds write.
15
161. Create a native C++ project. The directory structure is as follows:
17
18   ```yml
19   entry:
20     src:
21       main:
22         cpp:
23           - types:
24               libentry:
25                 - index.d.ts
26           - CMakeLists.txt
27           - napi_init.cpp
28         ets:
29           - entryability:
30               - EntryAbility.ets
31           - pages:
32               - Index.ets
33   ```
34
352. In the **entry/src/main/ets/entryability/EntryAbility.ets** file of the project, import the dependent modules.
36
37   ```ts
38   import { hiAppEvent, hilog } from '@kit.PerformanceAnalysisKit';
39   ```
40
413. In the **entry/src/main/ets/entryability/EntryAbility.ets** file of the project, add a watcher in **onCreate()** to subscribe to system events. The sample code is as follows:
42
43   ```ts
44   hiAppEvent.addWatcher({
45     // Set the watcher name. The system identifies different watchers based on their names.
46     name: "watcher",
47     // Add the system events to watch, for example, the address sanitizer event.
48     appEventFilters: [
49       {
50         domain: hiAppEvent.domain.OS,
51         names: [hiAppEvent.event.ADDRESS_SANITIZER]
52       }
53     ],
54     // Implement a callback for the registered system event so that you can apply custom processing to the event data obtained.
55     onReceive: (domain: string, appEventGroups: Array<hiAppEvent.AppEventGroup>) => {
56       hilog.info(0x0000, 'testTag', `HiAppEvent onReceive: domain=${domain}`);
57       for (const eventGroup of appEventGroups) {
58         // The event name uniquely identifies a system event.
59         hilog.info(0x0000, 'testTag', `HiAppEvent eventName=${eventGroup.name}`);
60         for (const eventInfo of eventGroup.appEventInfos) {
61           // Customize how to process the event data obtained, for example, print the event data in the log.
62           hilog.info(0x0000, 'testTag', `HiAppEvent eventInfo.domain=${eventInfo.domain}`);
63           hilog.info(0x0000, 'testTag', `HiAppEvent eventInfo.name=${eventInfo.name}`);
64           hilog.info(0x0000, 'testTag', `HiAppEvent eventInfo.eventType=${eventInfo.eventType}`);
65           hilog.info(0x0000, 'testTag', `HiAppEvent eventInfo.time=${eventInfo.params['time']}`);
66           hilog.info(0x0000, 'testTag', `HiAppEvent eventInfo.bundle_version=${eventInfo.params['bundle_version']}`);
67           hilog.info(0x0000, 'testTag', `HiAppEvent eventInfo.bundle_name=${eventInfo.params['bundle_name']}`);
68           hilog.info(0x0000, 'testTag', `HiAppEvent eventInfo.pid=${eventInfo.params['pid']}`);
69           hilog.info(0x0000, 'testTag', `HiAppEvent eventInfo.uid=${eventInfo.params['uid']}`);
70           hilog.info(0x0000, 'testTag', `HiAppEvent eventInfo.type=${eventInfo.params['type']}`);
71           hilog.info(0x0000, 'testTag', `HiAppEvent eventInfo.external_log=${JSON.stringify(eventInfo.params['external_log'])}`);
72           hilog.info(0x0000, 'testTag', `HiAppEvent eventInfo.log_over_limit=${eventInfo.params['log_over_limit']}`);
73         }
74       }
75     }
76   });
77   ```
78
794. Edit the **entry/src/main/cpp/types/libentry/index.d.ets** file. The sample code is as follows:
80
81   ```ts
82   export const test: () => void;
83   ```
84
855. In the **entry/src/main/cpp/napi_init.cpp** file, implement the array bounds write scenario and provide Node-API for the application layer code to call. The sample code is as follows:
86
87   ```c++
88   #include "napi/native_api.h"
89
90   static napi_value Test(napi_env env, napi_callback_info info)
91   {
92       int a[10];
93       // Construct the array bounds write.
94       a[10] = 1;
95       return {};
96   }
97
98   EXTERN_C_START
99   static napi_value Init(napi_env env, napi_value exports)
100   {
101       napi_property_descriptor desc[] = {
102           { "test", nullptr, Test, nullptr, nullptr, nullptr, napi_default, nullptr }
103       };
104       napi_define_properties(env, exports, sizeof(desc) / sizeof(desc[0]), desc);
105       return exports;
106   }
107   EXTERN_C_END
108
109   static napi_module demoModule = {
110       .nm_version = 1,
111       .nm_flags = 0,
112       .nm_filename = nullptr,
113       .nm_register_func = Init,
114       .nm_modname = "entry",
115       .nm_priv = ((void*)0),
116       .reserved = { 0 },
117   };
118
119   extern "C" __attribute__((constructor)) void RegisterEntryModule(void)
120   {
121       napi_module_register(&demoModule);
122   }
123   ```
124
1256. In the **entry/src/main/ets/pages/Index.ets** file, add a button to trigger the address sanitizer event.
126
127   ```ts
128   import testNapi from 'libentry.so'
129
130   @Entry
131   @Component
132   struct Index {
133     build() {
134       Row() {
135         Column() {
136           Button("address-sanitizer").onClick(() => {
137             testNapi.test();
138           })
139         }
140         .width('100%')
141       }
142       .height('100%')
143     }
144   }
145   ```
146
1477. In DevEco Studio, choose **entry**, click **Edit Configurations**, click **Diagnostics**, select **Address Sanitizer**, and click **OK**. Click the **Run** button to run the project. Then, click the **address-sanitizer** button to trigger an address sanitizer event. The application crashes. After restarting the application, you can view the following event information in the **Log** window.
148
149   ```text
150   HiAppEvent onReceive: domain=OS
151   HiAppEvent eventName=ADDRESS_SANITIZER
152   HiAppEvent eventInfo.domain=OS
153   HiAppEvent eventInfo.name=ADDRESS_SANITIZER
154   HiAppEvent eventInfo.eventType=1
155   HiAppEvent eventInfo.time=1713161197957
156   HiAppEvent eventInfo.bundle_version=1.0.0
157   HiAppEvent eventInfo.bundle_name=com.example.myapplication
158   HiAppEvent eventInfo.pid=12889
159   HiAppEvent eventInfo.uid=20020140
160   HiAppEvent eventInfo.type=stack-buffer-overflow
161   HiAppEvent eventInfo.external_log=["/data/storage/el2/log/hiappevent/ADDRESS_SANITIZER_1713161197960_12889.log"]
162   HiAppEvent eventInfo.log_over_limit=false
163   ```
164