今天在使用一套叫做 koahub-wemall 的现成商城源码的时候发生了一个诡异的报错，报错内容大概如下

Error: The session middleware not found
    at Koahub.loadMiddlewares (/home/snowfox/code/docker/koa-shop/koahub-wemall/node_modules/koahub/app/index.js:158:27)
    at Koahub.init (/home/snowfox/code/docker/koa-shop/koahub-wemall/node_modules/koahub/app/index.js:196:14)
    at new Koahub (/home/snowfox/code/docker/koa-shop/koahub-wemall/node_modules/koahub/app/index.js:28:14)                                                                                  
    at Object.<anonymous> (/home/snowfox/code/docker/koa-shop/koahub-wemall/app/index.js:13:13)                                                                                              
    at Module._compile (module.js:660:30)                                                                                                                                                    
    at Object.Module._extensions..js (module.js:671:10)                                                                                                                                      
    at Module.load (module.js:573:32)                                                                                                                                                        
    at tryModuleLoad (module.js:513:12)                                                                                                                                                      
    at Function.Module._load (module.js:505:3)
    at Function.Module.runMain (module.js:701:10)
    at startup (bootstrap_node.js:190:16)
    at bootstrap_node.js:662:3

在神奇的谷歌和坑爹的百度多番搜索无果，最后的解决办法如下：
打开项目下的 app/config/middleware.config.js

module.exports = {
    
    session: {
        key: 'koahub.js'
    },

    static: {
        dir: './www',
        dynamic: true
    }
}

替换成

module.exports = {

  'koa-session2': {
    key: 'koahub.js'
  },

  'koa-static-cache': {
    dir: './www',
    dynamic: true
  }
}

问题就解决了