# Android AB升级（三） – update engine架构概述

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原文：https://www.dandroid.cn/archives/21294
Canonical：https://www.dandroid.cn/archives/21294
作者：admin
发布日期：2023-09-26
最后更新：2023-09-26 15:25
分类：Android移植核心库 / Android系统开发
内容类型：post
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## 正文

update engine是通过AIDL对上层client端和server端分离，实现跨进程。上层提供服务绑定接口，以及升级触发和回调接口，底层实现升级的具体逻辑。本篇只是简单梳理下流程流转的过程。

1. 应用升级接口相关文件

1.framework层应用接口（systemApi）

frameworks/base/core/java/android/os/UpdateEngineCallback.java

frameworks/base/core/java/android/os/UpdateEngine.java

2.AIDL接口文件：

system/update_engine/binder_bindings/android/os/IUpdateEngine.aidl

system/update_engine/binder_bindings/android/os/IUpdateEngineCallback.aidl

3.服务端接口文件：

继承BnUpdateEngine： system/update_engine/binder_service_android.h

继承BnUpdateEngineCallback： system/update_engine/update_engine_client_android.cc

1.1. UpdateEngine类接口

UpdateEngine类（@SystemApi）主要提供bind和applyPayload接口给应用

1.1.1. 代码流程（bind和applyPayload）

1.UpdateEngine.java

bind(final UpdateEngineCallback callback, final Handler handler) 主要接受UpdateEngineCallback对象，同步代码块中会实现callback的两个接口，获取升级服务的状态码和结果错误码

applyPayload传递升级包路径大小等信息，并会传递到服务端进行实际逻辑的操作

//frameworks/base/core/java/android/os/UpdateEngine.java
 //传递升级包信息
 public void applyPayload(String url, long offset, long size, String[] headerKeyValuePairs) {
 try {
 mUpdateEngine.applyPayload(url, offset, size, headerKeyValuePairs);
 } catch (RemoteException e) {
 throw e.rethrowFromSystemServer();
 }
 }

 public boolean bind(final UpdateEngineCallback callback, final Handler handler) {
 synchronized (mUpdateEngineCallbackLock) {
 //IUpdateEngineCallback对象
 mUpdateEngineCallback = new IUpdateEngineCallback.Stub() {
 //重写回调类的接口，其中会调用到服务端的对应实现接口
 @Override
 public void onStatusUpdate(final int status, final float percent) {
 if (handler != null) {
 handler.post(new Runnable() {
 @Override
 public void run() {
 callback.onStatusUpdate(status, percent);
 }
 });
 } else {
 callback.onStatusUpdate(status, percent);
 }
 }

 @Override
 public void onPayloadApplicationComplete(final int errorCode) {
 if (handler != null) {
 handler.post(new Runnable() {
 @Override
 public void run() {
 callback.onPayloadApplicationComplete(errorCode);
 }
 });
 } else {
 callback.onPayloadApplicationComplete(errorCode);
 }
 }
 };

 try {
 return mUpdateEngine.bind(mUpdateEngineCallback);
 } catch (RemoteException e) {
 throw e.rethrowFromSystemServer();
 }
 }
 }

2.AIDL接口

interface IUpdateEngine {
 /** @hide */
 void applyPayload(String url,
 in long payload_offset,
 in long payload_size,
 in String[] headerKeyValuePairs);
 /** @hide */
 boolean bind(IUpdateEngineCallback callback);
 ....

3.服务端接口

//system/update_engine/binder_service_android.h
class BinderUpdateEngineAndroidService : public android::os::BnUpdateEngine,
 public ServiceObserverInterface {
 ...

//system/update_engine/binder_service_android.cc
Status BinderUpdateEngineAndroidService::applyPayload(
 const android::String16& url,
 int64_t payload_offset,
 int64_t payload_size,
 const std::vector<:string16>& header_kv_pairs) {
 const std::string payload_url{android::String8{url}.string()};
 std::vector<:string> str_headers;
 str_headers.reserve(header_kv_pairs.size());
 for (const auto& header : header_kv_pairs) {
 str_headers.emplace_back(android::String8{header}.string());
 }

 brillo::ErrorPtr error;
 //调用system/update_engine/update_attempter_android.cc的接口
 if (!service_delegate_->ApplyPayload(
 payload_url, payload_offset, payload_size, str_headers, &error)) {
 return ErrorPtrToStatus(error);
 }
 return Status::ok();
}

Status BinderUpdateEngineAndroidService::bind(
 const android::sp& callback, bool* return_value) {
 callbacks_.emplace_back(callback);

 const android::sp& callback_binder =
 IUpdateEngineCallback::asBinder(callback);
 auto binder_wrapper = android::BinderWrapper::Get();
 binder_wrapper->RegisterForDeathNotifications(
 callback_binder,
 base::Bind(
 base::IgnoreResult(&BinderUpdateEngineAndroidService::UnbindCallback),
 base::Unretained(this),
 base::Unretained(callback_binder.get())));

 // Send an status update on connection (except when no update sent so far),
 // since the status update is oneway and we don't need to wait for the
 // response.
 if (last_status_ != -1)
 callback->onStatusUpdate(last_status_, last_progress_);

 *return_value = true;
 return Status::ok();
}</:string></:string16>

1.2. UpdateEngineCallback类接口

主要是onStatusUpdate和onPayloadApplicationComplete接口

1.2.1. 代码流程（onStatusUpdate和onPayloadApplicationComplete）

1.抽象类，实现在UpdateEngine的bind方法中：

//frameworks/base/core/java/android/os/UpdateEngineCallback.java
@SystemApi
public abstract class UpdateEngineCallback {
 public abstract void onStatusUpdate(int status, float percent);
 public abstract void onPayloadApplicationComplete(int errorCode);
}

2.AIDL接口：

//system/update_engine/binder_bindings/android/os/IUpdateEngineCallback.aidl
oneway interface IUpdateEngineCallback {
 /** @hide */
 void onStatusUpdate(int status_code, float percentage);
 /** @hide */
 void onPayloadApplicationComplete(int error_code);
}

3.服务端接口：

//system/update_engine/update_engine_client_android.cc
private:
 class UECallback : public android::os::BnUpdateEngineCallback {
 public:
 explicit UECallback(UpdateEngineClientAndroid* client) : client_(client) {}

 // android::os::BnUpdateEngineCallback overrides.
 Status onStatusUpdate(int status_code, float progress) override;
 Status onPayloadApplicationComplete(int error_code) override;

 private:
 UpdateEngineClientAndroid* client_;
 };
...
 android::sp<:os::iupdateengine> service_;
 android::sp<:os::bnupdateenginecallback> callback_;
};
//升级过程中会打印这两个接口的日志
Status UpdateEngineClientAndroid::UECallback::onStatusUpdate(int status_code,
 float progress) {
 update_engine::UpdateStatus status =
 static_cast<:updatestatus>(status_code);
 LOG(INFO) << "onStatusUpdate(" << UpdateStatusToString(status) << " ("
 << status_code << "), " << progress << ")";
 return Status::ok();
}

Status UpdateEngineClientAndroid::UECallback::onPayloadApplicationComplete(
 int error_code) {
 ErrorCode code = static_cast(error_code);
 LOG(INFO) << "onPayloadApplicationComplete(" << utils::ErrorCodeToString(code)
 << " (" << error_code << "))";
 client_->ExitWhenIdle(
 (code == ErrorCode::kSuccess || code == ErrorCode::kUpdatedButNotActive)
 ? EX_OK
 : 1);
 return Status::ok();
}</:updatestatus></:os::bnupdateenginecallback></:os::iupdateengine>

2. 解析升级包payload.bin工具

payload dumper

使用payload dumper对升级包patload.bin文件进行解析，可以生成对应升级的image镜像文件

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