{"componentChunkName":"component---src-templates-blog-detail-tsx","path":"/blog/2020-05-12-nodejs-runtime","result":{"data":{"currentBlog":{"id":"38503518-dfcb-58ff-8b5a-f545d5459e6b","frontmatter":{"thumbnail":"https://img.serverlesscloud.cn/2020518/1589791111276-node12%E5%89%AF%E6%9C%AC.jpg","authors":["Wes"],"categories":["guides-and-tutorials"],"date":"2020-05-12T00:00:00.000Z","title":"云函数 SCF Node.js Runtime 最佳实践","description":"如何使用腾讯云云函数来开发 Node.js 应用以及云函数的 Node.js runtime 实现原理","authorslink":["https://zhuanlan.zhihu.com/ServerlessGo"],"translators":null,"translatorslink":null,"tags":["Node.js","云函数"],"keywords":"Serverless,scf,Node.js","outdated":null},"wordCount":{"words":313,"sentences":54,"paragraphs":54},"fileAbsolutePath":"/opt/build/repo/content/blog/2020-05-12-nodejs-runtime.md","fields":{"slug":"/blog/2020-05-12-nodejs-runtime/","keywords":["java","serverless","spa","云函数","函数","异步","callback","返回","Node","event","context"]},"html":"

腾讯云云函数 SCF 最近新发布了 Node.js 12.16 的 runtime，也是国内首家支持 Node.js 12.x 的主流云服务商。

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Node.js 版本的升级带来了新的特性以及性能方面的提升，有兴趣的同学可以参考国外一博主总结的文章《Node.js 12: The future of server-side JavaScript》了解具体内容。

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其中比较重要的一点是启动速度提升，通过 v8 code cache 的支持，构建时提前为内置库生成代码缓存，提升 30% 的启动耗时。

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腾讯云云函数 SCF 为了让 Serverless 更加符合 Node.js 原生的使用体验，针对 Node.js runtime 做了针对性的优化。\n借这个机会，我想和大家分享一下如何使用腾讯云云函数来开发 Node.js 应用以及 scf 的 Node.js runtime 实现的原理。

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入口函数的参数

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首先我们看一下最基本的 Node.js 入口函数：

\n {\n console.log("Hello World");\n console.log(event);\n console.log(context);\n callback(null, event);\n};`, `37583914497687390000`)\"\n >\n \n 复制代码\n \n \n
exports.main_handler = (event, context, callback) => {\n  console.log(\"Hello World\");\n  console.log(event);\n  console.log(context);\n  callback(null, event);\n};
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runtime 会将三个参数传递到处理程序方法。

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第一个参数是 event，用来传递触发事件数据

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包含来自调用程序的信息。调用程序在调用时将该信息作为 JSON 格式字符串传递，事件结构因服务而异。

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{"headerParameters":{},"headers":{...},"httpMethod":"GET","path":"/params_log","pathParameters":{},"queryString":{},"queryStringParameters":{},"requestContext":{"httpMethod":"ANY","identity":{},"path":"/params_log","serviceId":"service-9khp96qy","sourceIp":"120.229.9.165","stage":"release"}}

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{"Records":[{"cos":{"cosBucket":{"appid":"1251133793","name":"test","region":"gz"},"cosNotificationId":"unkown","cosObject":{"key":"/1251133793/test/xxx.png","meta":{"Content-Type":"image/png","x-cos-request-id":"NWViNTZmMmFfOTJhODQwYV80MGZmXzI0Y2ZkYmM="},"size":6545739,"url":"...","vid":""},"cosSchemaVersion":"1.0"},"event":{"eventName":"cos:ObjectCreated:Put","eventQueue":"qcs:0:scf:ap-guangzhou:appid/1251133793:default.params_log.$DEFAULT","eventSource":"qcs::cos","eventTime":1588948779,"eventVersion":"1.0","reqid":1038862404,"requestParameters":{"requestHeaders":{"Authorization":"..."},"requestSourceIP":"120.229.9.165"},"reservedInfo":""}}]}

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第二个参数 context，函数运行时信息

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我们来看一下一个完整的 context 包含的内容：

\n\n \n 复制代码\n \n \n
callbackWaitsForEmptyEventLoop: true,\ngetRemainingTimeInMillis: 200,\nmemory_limit_in_mb: 128,\ntime_limit_in_ms: 3000,\nenvironment: \"{\"SCF_NAMESPACE\":\"demo\",\"TENCENTCLOUD_SECRETID\":\"...\",\"TENCENTCLOUD_SECRETKEY\":\"...\",\"TENCENTCLOUD_SESSIONTOKEN\":\"...\"}\"\nfunction_name: \"params\",\nfunction_version: \"$LATEST\",\nnamespace: \"demo\",\nrequest_id: \"ab42b693-8bfd-4dc1-b228-60360a63e06c\",\ntencentcloud_appid: \"...\",\ntencentcloud_region: \"ap-chengdu\",\ntencentcloud_uin: \"...\"
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从上面的内容可以看到，该对象包含的内容有：

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    \n
  • 函数配置信息，比如设置的内容大小，超时时间等
    • \n
  • 执行身份认证信息。如果设置了函数的运行角色（角色必须要包含对应操作的授权策略），在环境变量中会注入 secretId，secretKey，sessionToken，在访问第三方云服务，比如 cos、自定义监控数据上报时就可以使用这几个值直接调用云 api，而不用在代码里面去 hard code 各种密钥信息
    • \n
  • 环境变量：包括了用户自定义的环境变量以及一些系统环境变量
    • \n
  • 执行环境基本信息：包括了当前函数调用的地域，用户的 appId，uin
    • \n
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第三个参数 callback 是一个可选参数，在非异步函数中返回执行结果

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回调函数采用两个参数：一个 Error 和一个返回。返回对象必须与 JSON.stringify 兼容。异步函数将忽略 callback 的返回，必须通过 return、throw exception 或者 promise 来处理返回或错误

\n {\n callback(null, res.statusCode)\n }).on('error', (e) => {\n callback(Error(e))\n })\n}`, `86882909659537560000`)\"\n >\n \n 复制代码\n \n \n
const https = require('https')\nlet url = \"https://cloud.tencent.com/\"\n\nexports.main_handler = function(event, context, callback) {\n  https.get(url, (res) => {\n    callback(null, res.statusCode)\n  }).on('error', (e) => {\n    callback(Error(e))\n  })\n}
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函数返回

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我们来看一下，针对异步场景（async 函数）和非异步场景，云函数怎么把返回值传递出去

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异步函数

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对于异步函数，可以使用 return 和 throw 来发送返回或错误。函数必须使用 async 关键字。在异步函数中，第三个参数 callback 没有定义

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示例：异步函数

\n {\n const promise = new Promise(function(resolve, reject) {\n https\n .get(url, res => {\n resolve(res.statusCode)\n })\n .on('error', e => {\n reject(Error(e))\n })\n })\n return promise\n}\n\nexports.handler = async function(event, context) {\n try{\n const result = await httpRequest(url)\n // 在async函数中callback未定义\n // callback(null, result)\n return result\n }catch(e) {\n throw e\n }\n}`, `11176975998930815000`)\"\n >\n \n 复制代码\n \n \n
const https = require('https')\nlet url = \"https://cloud.tencent.com/\"\n\nconst httpRequest = url => {\n  const promise = new Promise(function(resolve, reject) {\n    https\n      .get(url, res => {\n        resolve(res.statusCode)\n      })\n      .on('error', e => {\n        reject(Error(e))\n      })\n  })\n  return promise\n}\n\nexports.handler =  async function(event, context) {\n  try{\n    const result = await httpRequest(url)\n    // 在async函数中callback未定义\n    // callback(null, result)\n    return result\n  }catch(e) {\n    throw e\n  }\n}
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同步函数

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还是上面的例子，发起一个 http 请求，如果用同步函数实现，参照以下示例

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示例：同步函数，callback 返回

\n {\n // 只能通过callback返回，return会被忽略\n callback(null, res.statusCode)\n }).on('error', (e) => {\n callback(Error(e))\n })\n}`, `18244431053465182000`)\"\n >\n \n 复制代码\n \n \n
const https = require('https')\nlet url = \"https://cloud.tencent.com/\"\n\nexports.handler = function(event, context, callback) {\n  https.get(url, (res) => {\n    // 只能通过callback返回，return会被忽略\n    callback(null, res.statusCode)\n  }).on('error', (e) => {\n    callback(Error(e))\n  })\n}
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返回的时机

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正常的 Node.js web framework 在 response 返回后，异步逻辑还是继续在执行的。而 Serverless 场景下，由于机制和 framework的差别，对于已经返回 responese 的情况，一种是等着异步都处理完再来返回，这样保证了一次调用的完整性。另外一种就是在返回后就直接结束当次调用，直接挂起异步处理。

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腾讯云云函数针对 Node.js 的异步场景，实现了返回和结束分离的特殊机制。

\n

\n
    \n
  • 入口函数的同步执行过程完成及返回后，云函数的调用将立刻返回，并将代码的返回信息返回给函数调用方
    • \n
  • 同步流程处理并返回后，代码中的异步逻辑可以继续执行和处理，直到异步事件执行完成后，云函数的实际执行过程才完成和退出。
    • \n
\n

默认情况下，函数执行会等待所有异步执行结束才算一次调用结束，但也给用户提供了关闭事件循环等待的选项，用户可以关闭事件循环等待来自行控制函数的返回时机。通过在 callback 回调执行前设置 context.callbackWaitsForEmptyEventLoop = false，可以使云函数在执行返回后立刻冻结进程，不再等待异步循环内的事件

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比如一下示例代码，代码里面发起了一个异步 http 请求，另外有一个 2s 后执行的 setTimeout

\n {\n const promise = new Promise(function(resolve, reject) {\n https\n .get(url, res => {\n resolve(res.statusCode)\n })\n .on('error', e => {\n reject(Error(e))\n })\n })\n return promise\n}\n\nexports.main_handler = async function(event, context) {\n // 设置该选项为false会不等待异步队列执行完，而是在返回后直接冻结process\n //context.callbackWaitsForEmptyEventLoop = false\n try{\n const result = await httpRequest(url)\n setTimeout(() => {\n console.log('timeout log')\n }, 2000)\n return result\n }catch(e) {\n throw e\n }\n}`, `69109614256747640000`)\"\n >\n \n 复制代码\n \n \n
const https = require('https')\nlet url = \"https://cloud.tencent.com/\"\n\nconst httpRequest = url => {\n  const promise = new Promise(function(resolve, reject) {\n    https\n      .get(url, res => {\n        resolve(res.statusCode)\n      })\n      .on('error', e => {\n        reject(Error(e))\n      })\n  })\n  return promise\n}\n\nexports.main_handler =  async function(event, context) {\n  // 设置该选项为false会不等待异步队列执行完，而是在返回后直接冻结process\n  //context.callbackWaitsForEmptyEventLoop = false\n  try{\n    const result = await httpRequest(url)\n    setTimeout(() => {\n        console.log('timeout log')\n    }, 2000)\n    return result\n  }catch(e) {\n    throw e\n  }\n}
\n

在 http 请求完成后，会立即返回给调用方，不会等待 setTimeout 的异步实践执行完。而在返回后，程序会继续执行，直到 setTimeout 的事件执行完才算本次调用结束。

\n

在设置了 context.callbackWaitsForEmptyEventLoop = false 后，在 return 后进程会被冻结，setTimeout 里面的执行逻辑会被挂起

\n

完整流程图

\n

以下是单实例内 runtime 运行的完整流程图

\n

\"流程图\"

\n

针对 Node.js应用，有以下几个实践建议：

\n
    \n
  • 日志：runtime重写了 console 的几个主要方法，而且是在 require 用户文件之后，所以用户自定义日志选项会无效
    • \n
  • 缓存复用：在入口函数外可以定义变量，存储可以复用的缓存对象，比如数据库的连接等\nNode.js 的模块实现逻辑中，如果一个 module 被 require 过，该模块就会被 cache 到内存中，再次被 require时不会重新初始化。针对这一特性，如果实例一直再复用，那么在入口文件中，入口函数外定义的变量都不会被销毁，可以达到复用的效果
    • \n
  • 内置部分 npm 包，可以直接使用，具体参照文档。部署云函数代码时推荐 npm install --production，减少代码包的体积，提升上传速度和执行速度
    • \n
  • 执行角色：配置执行角色，从 context 中可以获取临时的密钥信息，可以用了访问有相应权限的第三方服务，而不用在代码内写死密钥信息
    • \n
\n
\n

回放：点击观看 Tencent Serverless Hours 线上分享会第一期

\n
\n
\n
\n
\n
\n

传送门：

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\n

欢迎访问：Serverless 中文网，您可以在 最佳实践 里体验更多关于 Serverless 应用的开发！

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也将进一步拓展层功能的使用","authorslink":["https://zhuanlan.zhihu.com/ServerlessGo"],"translators":null,"translatorslink":null,"tags":["Serverless","layer"],"keywords":"Serverless 全局变量组件,Serverless 单独部署组件,Serverless 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