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使用AppServiceExtensionAbility组件实现后台服务

概述​

从API version 20开始，支持开发者使用AppServiceExtensionAbility组件，为应用提供后台服务能力，其他三方应用可通过启动或连接该AppServiceExtensionAbility组件获取相应的服务。

例如，企业部署的数据防泄漏 (DLP) 软件需要能够长期无界面运行，持续监听文件操作、网络流量，并拦截违规行为，可以使用AppServiceExtensionAbility组件来实现其核心的后台监控服务。

本文将被启动或被连接的AppServiceExtensionAbility组件称为服务端，将启动或连接AppServiceExtensionAbility组件的应用组件（当前仅支持UIAbility）称为客户端。

约束与限制​

设备限制​

AppServiceExtensionAbility组件当前仅支持2in1设备。

规格限制​

  • 应用集成AppServiceExtensionAbility组件需要申请ACL权限（ohos.permission.SUPPORT_APP_SERVICE_EXTENSION）。该ACL权限当前只对企业普通应用开放申请。
  • AppServiceExtensionAbility组件内不支持调用window相关API。

运作机制​

开发者可以在UIAbility中以启动或连接的方式来拉起AppServiceExtensionAbility组件。

下表展示了拉起和连接的几种场景：

“客户端是否可信”为是时，表示客户端属于服务端所属应用或已配置在appIdentifierAllowList中。为否时，表示客户端不属于服务端所属应用且未配置在appIdentifierAllowList中。

客户端操作服务端状态客户端是否可信结果说明
startAppServiceExtensionAbility未启动是成功，服务端通过start方式启动，服务端状态变为已启动。
startAppServiceExtensionAbility未启动否失败，客户端不在允许列表中，无法调用启动服务。
startAppServiceExtensionAbility已启动是成功，服务端已经启动，start操作直接返回成功。
startAppServiceExtensionAbility已启动否失败，客户端不在允许列表中，无法调用启动服务。
connectAppServiceExtensionAbility未启动是成功，服务端通过connect方式启动，并建立连接。
connectAppServiceExtensionAbility未启动否失败，客户端不在允许列表中，无法启动服务端。
connectAppServiceExtensionAbility已启动是成功，服务端已启动，直接建立连接。
connectAppServiceExtensionAbility已启动否成功，服务端已启动，直接建立连接。

实现一个后台服务​

在DevEco Studio工程中手动新建一个AppServiceExtensionAbility组件，具体步骤如下：

  1. 在工程Module对应的ets目录下，右键选择“New > Directory”，新建一个目录并命名为myappserviceextability。

  2. 在myappserviceextability目录，右键选择“New > ArkTS File”，新建一个文件并命名为MyAppServiceExtAbility.ets。

    其目录结构如下所示：

    ├── ets
    │ ├── myappserviceextability
    │ │   ├── MyAppServiceExtAbility.ets
    └

  3. 在MyAppServiceExtAbility.ets文件中，增加导入AppServiceExtensionAbility的依赖包，自定义类继承AppServiceExtensionAbility组件并实现生命周期回调。

    import { AppServiceExtensionAbility, Want } from '@kit.AbilityKit';
    import { rpc } from '@kit.IPCKit';
    // ···
    import { hilog } from '@kit.PerformanceAnalysisKit';

    const TAG: string = '[MyAppServiceExtAbility]';
    const DOMAIN_NUMBER: number = 0xFF00;

    class StubTest extends rpc.RemoteObject {
      constructor(des: string) {
        super(des);
      }

      onRemoteMessageRequest(code: number,
        data: rpc.MessageSequence,
        reply: rpc.MessageSequence,
        options: rpc.MessageOption): boolean | Promise<boolean> {
        // 处理客户端发送的消息
        return true;
      }
    }

    export default class MyAppServiceExtAbility extends AppServiceExtensionAbility {
      onCreate(want: Want): void {
        let appServiceExtensionContext = this.context;
        hilog.info(DOMAIN_NUMBER, TAG, `onCreate, want: ${want.abilityName}`);
        // ···
      }

      onRequest(want: Want, startId: number): void {
        hilog.info(DOMAIN_NUMBER, TAG, `onRequest, want: ${want.abilityName}`);
      }

      onConnect(want: Want): rpc.RemoteObject {
        hilog.info(DOMAIN_NUMBER, TAG, `onConnect, want: ${want.abilityName}`);
        return new StubTest('test');
      }

      onDisconnect(want: Want): void {
        hilog.info(DOMAIN_NUMBER, TAG, `onDisconnect, want: ${want.abilityName}`);
      }

      onDestroy(): void {
        hilog.info(DOMAIN_NUMBER, TAG, 'onDestroy');
      }
    };

  4. 在工程Module对应的module.json5配置文件中注册AppServiceExtensionAbility组件，type标签需要设置为“appService”，srcEntry标签表示当前ExtensionAbility组件所对应的代码路径。

    {
      "module": {
        // ···
        "extensionAbilities": [
        // ···
          {
            "name": "MyAppServiceExtAbility",
            "description": "appService",
            "type": "appService",
            "exported": true,
            "srcEntry": "./ets/myappserviceextability/MyAppServiceExtAbility.ets",
            "appIdentifierAllowList": [
              // 此处填写允许启动该后台服务的客户端应用的appIdentifier列表
            ],
          }
        ]
      }
    }

启动一个后台服务​

应用通过startAppServiceExtensionAbility()方法启动一个后台服务，服务的onRequest()回调就会被调用，并在该回调方法中接收到调用者传递过来的Want对象。后台服务启动后，其生命周期独立于客户端，即使客户端已经销毁，该后台服务仍可继续运行。因此，后台服务需要在其工作完成时通过调用AppServiceExtensionContext的terminateSelf()来自行停止，或者由另一个组件调用stopAppServiceExtensionAbility()来将其停止。

AppServiceExtensionAbility组件以start方式启动，并且没有连接的时候，AppServiceExtensionAbility组件进程可能被挂起（请参考Background Tasks Kit简介）。

  • 在应用中启动一个新的AppServiceExtensionAbility组件。示例中的context的获取方式请参见获取UIAbility的上下文信息。

    import { common, Want } from '@kit.AbilityKit';
    import { hilog } from '@kit.PerformanceAnalysisKit';
    import { BusinessError } from '@kit.BasicServicesKit';

    const TAG: string = '[StartAppServiceExt]';
    const DOMAIN_NUMBER: number = 0xFF00;

    @Entry
    @Component
    struct StartAppServiceExt {
      build() {
        Column() {
        // ···
          List({ initialIndex: 0 }) {
            ListItem() {
              Row() {
                // ···
              }
            // ···
              .onClick(() => {
                let context = this.getUIContext().getHostContext() as common.UIAbilityContext; // UIAbilityContext
                let want: Want = {
                  deviceId: '',
                  bundleName: 'com.samples.appserviceextensionability',
                  abilityName: 'MyAppServiceExtAbility'
                };
                context.startAppServiceExtensionAbility(want).then(() => {
                  hilog.info(DOMAIN_NUMBER, TAG, 'Succeeded in starting AppServiceExtensionAbility.');
                  // 成功启动后台服务
                  this.getUIContext().getPromptAction().showToast({
                    message: 'SuccessfullyStartBackendService'
                  });
                }).catch((err: BusinessError) => {
                  hilog.error(DOMAIN_NUMBER, TAG,
                    `Failed to start AppServiceExtensionAbility. Code is ${err.code}, message is ${err.message}`);
                });
              })
            }

            // ···
          }
        // ···
        }

        // ···
      }
    }

  • 在应用中停止一个已启动的AppServiceExtensionAbility组件。

    import { common, Want } from '@kit.AbilityKit';
    import { hilog } from '@kit.PerformanceAnalysisKit';
    import { BusinessError } from '@kit.BasicServicesKit';

    const TAG: string = '[StopAppServiceExt]';
    const DOMAIN_NUMBER: number = 0xFF00;

    @Entry
    @Component
    struct StopAppServiceExt {
      build() {
        Column() {
        // ···
          List({ initialIndex: 0 }) {
            ListItem() {
              Row() {
                // ···
              }
            // ···
              .onClick(() => {
                let context = this.getUIContext().getHostContext() as common.UIAbilityContext; // UIAbilityContext
                let want: Want = {
                  deviceId: '',
                  bundleName: 'com.samples.appserviceextensionability',
                  abilityName: 'MyAppServiceExtAbility'
                };
                context.stopAppServiceExtensionAbility(want).then(() => {
                  hilog.info(DOMAIN_NUMBER, TAG, 'Succeeded in stopping AppServiceExtensionAbility.');
                  this.getUIContext().getPromptAction().showToast({
                    message: 'SuccessfullyStoppedAStartedBackendService'
                  });
                }).catch((err: BusinessError) => {
                  hilog.error(DOMAIN_NUMBER, TAG,
                    `Failed to stop AppServiceExtensionAbility. Code is ${err.code}, message is ${err.message}`);
                });
              })
            }

            // ···
          }

        // ···
        }

        // ···
      }
    }

  • 已启动的AppServiceExtensionAbility组件停止自身。

    import { AppServiceExtensionAbility, Want } from '@kit.AbilityKit';
    // ···
    import { BusinessError } from '@kit.BasicServicesKit';
    import { hilog } from '@kit.PerformanceAnalysisKit';

    const TAG: string = '[MyAppServiceExtAbility]';
    // ···

    export default class MyAppServiceExtAbility extends AppServiceExtensionAbility {
      onCreate(want: Want): void {
        // ···
        // 执行业务逻辑
        this.context.terminateSelf().then(() => {
          hilog.info(0x0000, TAG, '----------- terminateSelf succeed -----------');
        }).catch((error: BusinessError) => {
          hilog.error(0x0000, TAG, `terminateSelf failed, error.code: ${error.code}, error.message: ${error.message}`);
        });
      }

    // ···
    };

连接一个后台服务​

客户端连接服务端​

客户端可以通过connectAppServiceExtensionAbility()连接服务端（在Want对象中指定连接的目标服务），服务端的onConnect()就会被调用，并在该回调方法中接收到客户端传递过来的Want对象。

服务端的AppServiceExtensionAbility组件会在onConnect()中返回IRemoteObject对象给客户端ConnectOptions的onConnect()方法。开发者通过该IRemoteObject定义通信接口，实现客户端与服务端的RPC交互。多个客户端可以同时连接到同一个后台服务，客户端完成与服务端的交互后，客户端需要通过调用disconnectAppServiceExtensionAbility()来断开连接。如果所有连接到某个后台服务的客户端均已断开连接，则系统会销毁该服务。

  • 使用connectAppServiceExtensionAbility()建立与后台服务的连接。示例中的context的获取方式请参见获取UIAbility的上下文信息。

    import { common, Want } from '@kit.AbilityKit';
    import { rpc } from '@kit.IPCKit';
    import { hilog } from '@kit.PerformanceAnalysisKit';

    const TAG: string = '[ConnectAppServiceExt]';
    const DOMAIN_NUMBER: number = 0xFF00;

    let connectionId: number;
    let want: Want = {
      deviceId: '',
      bundleName: 'com.samples.appserviceextensionability',
      abilityName: 'MyAppServiceExtAbility'
    };

    let options: common.ConnectOptions = {
      onConnect(elementName, remote: rpc.IRemoteObject): void {
        hilog.info(DOMAIN_NUMBER, TAG, 'onConnect callback');
        if (remote === null) {
          hilog.info(DOMAIN_NUMBER, TAG, `onConnect remote is null`);
          return;
        }
        // 通过remote进行通信
      },
      onDisconnect(elementName): void {
        hilog.info(DOMAIN_NUMBER, TAG, 'onDisconnect callback');
      },
      onFailed(code: number): void {
        hilog.info(DOMAIN_NUMBER, TAG, 'onFailed callback', JSON.stringify(code));
      }
    };

    @Entry
    @Component
    struct ConnectAppServiceExt {
      build() {
        Column() {
        // ···
          List({ initialIndex: 0 }) {
            ListItem() {
              Row() {
                // ···
              }
            // ···
              .onClick(() => {
                let context = this.getUIContext().getHostContext() as common.UIAbilityContext; // UIAbilityContext
                // 建立连接后返回的Id需要保存下来，在解绑服务时需要作为参数传入
                connectionId = context.connectAppServiceExtensionAbility(want, options);
                // 成功连接后台服务
                this.getUIContext().getPromptAction().showToast({
                  message: 'SuccessfullyConnectBackendService'
                });
                hilog.info(DOMAIN_NUMBER, TAG, `connectionId is : ${connectionId}`);
              })
            }

            // ···
          }

        // ···
        }

        // ···
      }
    }

  • 使用disconnectAppServiceExtensionAbility()断开与后台服务的连接。

    import { common } from '@kit.AbilityKit';
    import { hilog } from '@kit.PerformanceAnalysisKit';
    import { BusinessError } from '@kit.BasicServicesKit';

    const TAG: string = '[DisConnectAppServiceExt]';
    const DOMAIN_NUMBER: number = 0xFF00;

    let connectionId: number;

    @Entry
    @Component
    struct DisConnectAppServiceExt {
      build() {
        Column() {
        // ···
          List({ initialIndex: 0 }) {
            ListItem() {
              Row() {
                // ···
              }
            // ···
              .onClick(() => {
                let context = this.getUIContext().getHostContext() as common.UIAbilityContext; // UIAbilityContext
                // connectionId为调用connectServiceExtensionAbility接口时的返回值，需开发者自行维护
                context.disconnectAppServiceExtensionAbility(connectionId).then(() => {
                  hilog.info(DOMAIN_NUMBER, TAG, 'disconnectAppServiceExtensionAbility success');
                  // 成功断连后台服务
                  this.getUIContext().getPromptAction().showToast({
                    message: 'SuccessfullyDisconnectBackendService'
                  });
                }).catch((error: BusinessError) => {
                  hilog.error(DOMAIN_NUMBER, TAG, 'disconnectAppServiceExtensionAbility failed');
                });
              })
            }

            // ···
          }

        // ···
        }

        // ···
      }
    }

客户端与服务端通信​

客户端在onConnect()中获取到rpc.IRemoteObject对象后便可与服务端进行通信。

客户端：使用sendMessageRequest接口向服务端发送消息。

import { common, Want } from '@kit.AbilityKit';
import { rpc } from '@kit.IPCKit';
import { hilog } from '@kit.PerformanceAnalysisKit';
import { BusinessError } from '@kit.BasicServicesKit';

const TAG: string = '[ClientServerExt]';
const DOMAIN_NUMBER: number = 0xFF00;
const REQUEST_CODE = 1;
let connectionId: number;
let want: Want = {
  deviceId: '',
  bundleName: 'com.samples.appserviceextensionability',
  abilityName: 'MyAppServiceExtAbility'
};
let options: common.ConnectOptions = {
  onConnect(elementName, remote): void {
    hilog.info(DOMAIN_NUMBER, TAG, 'onConnect callback');
    if (remote === null) {
      hilog.info(DOMAIN_NUMBER, TAG, `onConnect remote is null`);
      return;
    }
    let option = new rpc.MessageOption();
    let data = new rpc.MessageSequence();
    let reply = new rpc.MessageSequence();

    // 写入请求数据
    data.writeInt(1);
    data.writeInt(2);

    remote.sendMessageRequest(REQUEST_CODE, data, reply, option).then((ret: rpc.RequestResult) => {
      if (ret.errCode === 0) {
        hilog.info(DOMAIN_NUMBER, TAG, `sendRequest got result`);
        let sum = ret.reply.readInt();
        hilog.info(DOMAIN_NUMBER, TAG, `sendRequest success, sum:${sum}`);
      } else {
        hilog.error(DOMAIN_NUMBER, TAG, `sendRequest failed`);
      }
    }).catch((error: BusinessError) => {
      hilog.error(DOMAIN_NUMBER, TAG, `sendRequest failed, ${JSON.stringify(error)}`);
    });
  },
  onDisconnect(elementName): void {
    hilog.info(DOMAIN_NUMBER, TAG, 'onDisconnect callback');
  },
  onFailed(code): void {
    hilog.info(DOMAIN_NUMBER, TAG, 'onFailed callback');
  }
};

// 调用connectAppServiceExtensionAbility相关代码

@Entry
@Component
struct ClientServerExt {
  build() {
    Column() {
    // ···
      List({ initialIndex: 0 }) {
        ListItem() {
          Row() {
            // ···
          }
        // ···
          .onClick(() => {
            let context = this.getUIContext().getHostContext() as common.UIAbilityContext; // UIAbilityContext
            connectionId = context.connectAppServiceExtensionAbility(want, options);
            hilog.info(DOMAIN_NUMBER, TAG, `connectionId is : ${connectionId}`);
          })
        }
      }
    // ···
    }
  }
}

服务端：使用onRemoteMessageRequest接口接收客户端发送的消息。

import { AppServiceExtensionAbility, Want } from '@kit.AbilityKit';
import { rpc } from '@kit.IPCKit';
import { hilog } from '@kit.PerformanceAnalysisKit';

const TAG: string = '[MyAppServiceExtAbility]';
const DOMAIN_NUMBER: number = 0xFF00;

// 开发者需要在这个类型里对接口进行实现
class Stub extends rpc.RemoteObject {
  onRemoteMessageRequest(code: number,
    data: rpc.MessageSequence,
    reply: rpc.MessageSequence,
    options: rpc.MessageOption): boolean | Promise<boolean> {
    hilog.info(DOMAIN_NUMBER, TAG, 'onRemoteMessageRequest');
    let sum = data.readInt() + data.readInt();
    reply.writeInt(sum);
    return true;
  }
}

// 服务端实现
export default class MyAppServiceExtAbility extends AppServiceExtensionAbility {
  onCreate(want: Want): void {
    hilog.info(DOMAIN_NUMBER, TAG, 'MyAppServiceExtAbility onCreate');
  }

  onDestroy(): void {
    hilog.info(DOMAIN_NUMBER, TAG, 'MyAppServiceExtAbility onDestroy');
  }

  onConnect(want: Want): rpc.RemoteObject {
    hilog.info(DOMAIN_NUMBER, TAG, 'MyAppServiceExtAbility onConnect');
    return new Stub('test');
  }

  onDisconnect(): void {
    hilog.info(DOMAIN_NUMBER, TAG, 'MyAppServiceExtAbility onDisconnect');
  }
}

服务端对客户端身份校验​

部分开发者需要使用AppServiceExtensionAbility组件提供一些较为敏感的服务，可以通过如下方式对客户端身份进行校验。

通过callerTokenId对客户端进行鉴权

通过调用getCallingTokenId()接口获取客户端的tokenID，再调用verifyAccessTokenSync()接口判断客户端是否有某个具体权限，由于当前不支持自定义权限，因此只能校验当前系统所定义的权限。示例代码如下：

import { AppServiceExtensionAbility, Want } from '@kit.AbilityKit';
import { abilityAccessCtrl, bundleManager } from '@kit.AbilityKit';
import { rpc } from '@kit.IPCKit';
import { hilog } from '@kit.PerformanceAnalysisKit';
import { BusinessError } from '@kit.BasicServicesKit';

const TAG: string = '[AppServiceExtImpl]';
const DOMAIN_NUMBER: number = 0xFF00;

// 开发者需要在这个类里进行实现

class Stub extends rpc.RemoteObject {
  onRemoteMessageRequest(
    code: number,
    data: rpc.MessageSequence,
    reply: rpc.MessageSequence,
    options: rpc.MessageOption): boolean | Promise<boolean> {
    // 开发者自行实现业务逻辑
    hilog.info(DOMAIN_NUMBER, TAG, `onRemoteMessageRequest: ${data}`);
    let callerUid = rpc.IPCSkeleton.getCallingUid();
    bundleManager.getBundleNameByUid(callerUid).then((callerBundleName) => {
      hilog.info(DOMAIN_NUMBER, TAG, 'getBundleNameByUid: ' + callerBundleName);
      // 对客户端包名进行识别
      if (callerBundleName !== 'com.samples.stagemodelabilitydevelop') { // 识别不通过
        hilog.info(DOMAIN_NUMBER, TAG, 'The caller bundle is not in trustlist, reject');
        return;
      }
      // 识别通过，执行正常业务逻辑
    }).catch((err: BusinessError) => {
      hilog.error(DOMAIN_NUMBER, TAG, 'getBundleNameByUid failed: ' + err.message);
    });

    let callerTokenId = rpc.IPCSkeleton.getCallingTokenId();
    let accessManager = abilityAccessCtrl.createAtManager();
    // 所校验的具体权限由开发者自行选择，此处ohos.permission.GET_BUNDLE_INFO_PRIVILEGED只作为示例
    let grantStatus = accessManager.verifyAccessTokenSync(callerTokenId, 'ohos.permission.GET_BUNDLE_INFO_PRIVILEGED');
    if (grantStatus === abilityAccessCtrl.GrantStatus.PERMISSION_DENIED) {
      hilog.error(DOMAIN_NUMBER, TAG, 'PERMISSION_DENIED');
      return false;
    }
    hilog.info(DOMAIN_NUMBER, TAG, 'verify access token success.');
    return true;
  }
}

export default class MyAppServiceExtAbility extends AppServiceExtensionAbility {
  onConnect(want: Want): rpc.RemoteObject {
    return new Stub('test');
  }
  // 其他生命周期
}