TypeScript Backend -- 孙雷

backend/.env

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+MONGO_CONNECTION_STRING=
+PORT=5000
+LOG_PATH=log
+HOST_HTTPS=false
+HOST_DOMAIN=localhost:5000
+
+RATE_LIMIT_URL_GET=10
+RATE_LIMIT_URL_GET_WINDOW_SEC=60
+RATE_LIMIT_URL_POST=5
+RATE_LIMIT_URL_POST_WINDOW_SEC=60

backend/.eslintrc.json

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+{
+    "env": {
+        "node": true,
+        "commonjs": true,
+        "es2021": true
+    },
+    "extends": [
+        "eslint:recommended",
+        "plugin:@typescript-eslint/recommended"
+    ],
+    "parser": "@typescript-eslint/parser",
+    "parserOptions": {
+        "ecmaVersion": "latest"
+    },
+    "plugins": [
+        "@typescript-eslint"
+    ],
+    "rules": {
+    }
+}

backend/.gitignore

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+# Logs
+logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+lerna-debug.log*
+.pnpm-debug.log*
+
+# Diagnostic reports (https://nodejs.org/api/report.html)
+report.[0-9]*.[0-9]*.[0-9]*.[0-9]*.json
+
+# Runtime data
+pids
+*.pid
+*.seed
+*.pid.lock
+
+# Directory for instrumented libs generated by jscoverage/JSCover
+lib-cov
+
+# Coverage directory used by tools like istanbul
+coverage
+*.lcov
+
+# nyc test coverage
+.nyc_output
+
+# Grunt intermediate storage (https://gruntjs.com/creating-plugins#storing-task-files)
+.grunt
+
+# Bower dependency directory (https://bower.io/)
+bower_components
+
+# node-waf configuration
+.lock-wscript
+
+# Compiled binary addons (https://nodejs.org/api/addons.html)
+build/Release
+
+# Dependency directories
+node_modules/
+jspm_packages/
+
+# Snowpack dependency directory (https://snowpack.dev/)
+web_modules/
+
+# TypeScript cache
+*.tsbuildinfo
+
+# Optional npm cache directory
+.npm
+
+# Optional eslint cache
+.eslintcache
+
+# Optional stylelint cache
+.stylelintcache
+
+# Microbundle cache
+.rpt2_cache/
+.rts2_cache_cjs/
+.rts2_cache_es/
+.rts2_cache_umd/
+
+# Optional REPL history
+.node_repl_history
+
+# Output of 'npm pack'
+*.tgz
+
+# Yarn Integrity file
+.yarn-integrity
+
+# dotenv environment variable files
+# .env
+.env.development.local
+.env.test.local
+.env.production.local
+.env.local
+
+# parcel-bundler cache (https://parceljs.org/)
+.cache
+.parcel-cache
+
+# Next.js build output
+.next
+out
+
+# Nuxt.js build / generate output
+.nuxt
+dist
+
+# Gatsby files
+.cache/
+# Comment in the public line in if your project uses Gatsby and not Next.js
+# https://nextjs.org/blog/next-9-1#public-directory-support
+# public
+
+# vuepress build output
+.vuepress/dist
+
+# vuepress v2.x temp and cache directory
+.temp
+.cache
+
+# Docusaurus cache and generated files
+.docusaurus
+
+# Serverless directories
+.serverless/
+
+# FuseBox cache
+.fusebox/
+
+# DynamoDB Local files
+.dynamodb/
+
+# TernJS port file
+.tern-port
+
+# Stores VSCode versions used for testing VSCode extensions
+.vscode-test
+
+# yarn v2
+.yarn/cache
+.yarn/unplugged
+.yarn/build-state.yml
+.yarn/install-state.gz
+.pnp.*
+
+# log
+log/

backend/README.md

@@ -1,4 +1,141 @@
+
+[toc]
+
 # TypeScript Backend Engineer Assignment
+## 设计
+### 假设与估算
+#### 假设
+用户量： 100,000  
+单用户每天创建链接数：3  
+单用户每天获取链接数：30
+
+长链接平均长度：30
+#### 估算
+QPS峰值：`100,000 * 33 / 24 / 3600 * 4 = 152 query/sec`
+> 4为峰值估算的系数，平均值为38  
+
+存储量：`100,000 * 3 * (30 + 8 + 32) * 365 = 7665MB/year`   
+服务器数量：2，分布在不同可用区
+
+### Database Schema
+#### urls
+链接记录表
+| Field | Type | Index |  Description | Validate |
+| --- | --- | --- | --- | --- |
+| shortenUrl | string | unique | 短链 | 最长8位字符 |
+| originUrl | string | - | 原始链 | 最长512位字符 |
+| description | string | - | 描述信息 | 最长256位字符 |
+| creator | string | - | 原始链 | 最长32位字符 |
+| expires | Date | - | 过期时间 | - |
+| status | string | - | "o": open，可用 "c": close，不可用 | - |
+| createdAt | Date | - | 创建时间 | - |
+| updatedAt | Date | - | 更新时间 | - |
+#### systems
+系统数据项表，name="id"的记录，为短链id生成器
+| Field | Type | Index |  Description | Validate |
+| --- | --- | --- | --- | --- |
+| id | BigInt | unique | 短链生成器 | - |
+| name | string | unique | 系统数据项name | 取值只有"id" |
+### 架构图
+#### 生成短链：  
+Request --> Load Balancer --> RateLimiter --> Sequencer --> Database(Mongodb)  
+> RateLimiter: [ratelimiter.ts](./src/middleware/ratelimiter.ts)为避免大量无效流量影响系统性能，对流量采用了基于IP的时间窗口限流策略
+
+> Sequencer: 短链生成算法原理[url.ts/newUrl](src/data/url.ts)是，基于mongodb的findOneAndUpdate的$inc原子操作[id.ts](./src/data/id.ts)，采用base58编码[base58.ts](./src/util/base58.ts)，生成链接
+##### 
+#### 获取原始链接：   
+Request --> Load Balancer --> RateLimiter --> Cache(Memory) --missed,read through--> Database(Mongodb)    
+> 选择的缓存策略是read through模式[url.ts/getOriginUrlFromCache](src/data/url.ts)，辅助策略是miss保护位（分别对应db miss和数据失效的情况，避免缓存穿透）
+### API
+#### 生成链接
+`POST /url`  
+##### Request
+Request Json Body
+```
+interface NewUrlRequest {
+    originUrl: string,
+    description: string,
+    creator: string,
+    expires?: Date,
+}
+```
+##### Response
+```
+{
+    "bizErrorCode": "0",
+    "message": "",
+    "data": {
+        "url": "http://localhost:5000/url/0000000p",
+        "originUrl": "https://bing.com",
+        "description": "bing search engine",
+        "creator": "Simon",
+        "expires": null,
+        "createdAt": "2023-09-12T02:59:05.309Z"
+    }
+}
+```
+| bizErrorCode | message |
+| --- | --- |
+| 0 | ok |
+| 20000 | id system config is not created yet |
+| 20001 | max id exceed |
+| 30000 | short url should be provided |
+| 30001 | origin url not found |
+| 30012 | creator should be provided |
+| 30013 | originUrl should be provided |
+| 30014 | description should be provided |
+| 30015 | creator too long |
+| 30016 | originUrl too long |
+| 30017 | description too long |
+
+#### 获取原始链接
+`GET /url/:shortUrl`  
+##### Response
+1. HTTP STATUS CODE 302, HTTP HEADER Location: originUrl
+2. HTTP STATUS CODE 404, Response Json Body
+```
+{
+    "bizErrorCode": "0",
+    "message": "no such url"
+}
+```
+
+### 后续扩展完善
+1. 添加监控报警功能
+2. 观察数据量以及缓存命中率，可扩展缓存为redis，可扩展服务器数量
+3. 添加数据埋点，挖掘用户行为的数据价值
+
+## 单元测试代码以及单元测试覆盖率
+#### 单元测试代码
+使用jest框架进行单元测试，100%覆盖率  
+对于复杂逻辑的测试，利用jest的mock功能实现每个代码分支的测试，  
+
+例如：  
+[./src/data/url.test.ts](./src/data/url.test.ts)  中，url数据的读取采用了read-through的缓存策略，测试代码分别用mock功能模拟相应接口，实现了以下分支覆盖:  
+1. 缓存miss;数据库exists
+2. 缓存miss;数据库miss
+3. 缓存exists
+#### 单元测试覆盖率
+![单元测试覆盖率](./images/test_coverage.png)
+## 集成测试
+#### 集成测试代码
+> [postman数据](./test/api_integration/hongshan.api.integration.test.json)    
+
+采用postman编写集成测试代码:
+1. 调用api POST /url 创建短链
+2. 调用api GET /url/:shortUrl 访问上一步创建的短链
+
+异常情况：
+1. 输入值不合法
+2. 读取不存在的短链
+#### 集成测试结果
+![API 集成测试案例](./images/api_integration.png)
+
+
+---
+---
+
+
 
 ### Typescript 实现短域名服务（细节可以百度/谷歌）
 

backend/jest.config.js

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+/** @type {import('ts-jest').JestConfigWithTsJest} */
+module.exports = {
+  preset: 'ts-jest',
+  testEnvironment: 'node',
+  setupFiles: ['dotenv/config'],
+  testEnvironment: 'node',
+};