修复cache.cfg丢时缓存映射错误

[fanmingyi]

问题描述

近期我司产品有用户反馈发送的表情和预期不符.如发送一个哭的表情变为笑.

说明

缺陷 1

假设缓存关系如下:
http://hello.pag -> 1.bin
http://world.pag -> 2.bin
cache.cfg 被回收删除但是缓存文件依旧存在时,我们重启 app .我们调用readFile函数,传入 http://world.pag .

std::shared_ptr<tgfx::Data> DiskCache::readFile(const std::string& key) {
  std::lock_guard<std::mutex> autoLock(locker);
  if (cacheFolder.empty() || key.empty()) {
    return nullptr;
  }
  //由于缓存配置文件丢失这里重新从 1 开始自增,所以http://world.pag  返回 fileID 为 1
  auto fileID = getFileID(key);
  //重新映射文件路径.得到/sdcard/android/data/org.libpag.pagviewer/cache/files/1.bin
  auto filePath = fileIDToPath(fileID);
  //由于 1.bin 存储实际为http://hello.pag 对象.导致读取错误
  auto stream = tgfx::Stream::MakeFromFile(filePath);
  if (stream == nullptr) {
    return nullptr;
  }
  tgfx::Buffer buffer(stream->size());
  auto readLength = stream->read(buffer.data(), buffer.size());
  if (readLength != buffer.size()) {
    return nullptr;
  }
  return buffer.release();
}

缺陷 2

调用saveConfig 时被强制中断,会导致cache.cfg 丢失.从而导致缓存错误

void DiskCache::saveConfig() {
  Directory::CreateRecursively(Directory::GetParentDirectory(configPath));
  //wb 写入方式会重写文件.如果这时候文件读写中断会导致配置丢失
  auto file = fopen(configPath.c_str(), "wb");
//....
}

问题模拟复现

插入以下代码,在休眠期间强制停止

void DiskCache::saveConfig() {
    LOGE("fmy invoke saveConfig");
  Directory::CreateRecursively(Directory::GetParentDirectory(configPath));
  auto file = fopen(configPath.c_str(), "wb");
  if (file == nullptr) {
      LOGE("fmy invoke saveConfig file is nullptr");
    return;
  }
    LOGE("fmy invoke saveConfig start sleep");
    //模拟高耗时操作,然后在休眠期间 Android app 强制停止
    std::this_thread::sleep_for(std::chrono::seconds(15));
    LOGE("fmy invoke saveConfig end sleep");
    size_t bufferSize = 0;
  //...略
}

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 28.57143% with 5 lines in your changes missing coverage. Please review.

Project coverage is 77.33%. Comparing base (c77c593) to head (d345a1c).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/rendering/caches/DiskCache.cpp	28.57%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2527   +/-   ##
=======================================
  Coverage   77.32%   77.33%           
=======================================
  Files         420      420           
  Lines       22457    22460    +3     
  Branches     6325     6346   +21     
=======================================
+ Hits        17365    17369    +4     
- Misses       3818     3819    +1     
+ Partials     1274     1272    -2     

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[domchen]

removeRedundancyCache存在很多 readConfig里已经写过的重复代码，可以给 readConfig() 加个返回值，如果读取配置失败（不存在文件或者文件size为0）就返回false：然后判断返回值即可：
if (!readConfig()) { Directory::VisitFiles(cacheFolder, [&](const std::string& path, size_t) { remove(path.c_str()); }); }

[fanmingyi]

确实这样更优雅我改改

[domchen]

变量命名要避免使用缩写ret，可以直接用if(!readConfig())，或者起个有明确含义的变量名