本文介绍如何使用 Koa2 创建一个简单的文件上传接口，然后介绍使用 Postman 对其进行测试的详细步骤。

准备工作

• 已安装 Node.js
• 具有 JavaScript 和 Node.js 的基本知识
• 已安装 Postman 用于测试

第 1 步：建立项目

创建一个新目录，并进入该目录：

mkdir koa-file-upload
cd koa-file-upload

初始化一个新的 Node.js 项目：

npm init -y

安装 koa 和 koa-body（用于解析请求体和文件的中间件）：

npm install koa koa-router koa-body --save

第 2 步：创建 Koa 服务器

创建一个名为 app.js 的文件：

touch app.js

在 app.js 中，设置一个基本的 Koa 服务器：

const Koa = require('koa');
const Router = require('koa-router');
const { koaBody } = require('koa-body');

const app = new Koa();
const router = new Router();

app.use(koaBody({ multipart: true }));

// 在这里定义路由

app.use(router.routes()).use(router.allowedMethods());

const PORT = 3000;
app.listen(PORT, () => {
  console.log(`服务器正在运行于 http://localhost:${PORT}`);
});

第 3 步：创建文件上传端点

在 app.js 中添加以下代码，创建一个文件上传端点：

router.post('/upload', async (ctx) => {
    const file = ctx.request.files.file; // 从请求中获取文件
    const reader = fs.createReadStream(file.filepath); // 创建一个读取文件的流
    const stream = fs.createWriteStream(path.join(__dirname, 'uploads', file.originalFilename)); // 创建一个写入文件的流
    reader.pipe(stream); // 将读取流导向写入流
    console.log('正在上传 %s -> %s', file.originalFilename, stream.path);

    ctx.body = '文件成功上传';
});

确保在项目根目录中创建一个 uploads 目录来存储上传的文件：

mkdir uploads

第 4 步：启动服务器

运行 Koa 服务器：

node app.js

第 5 步：使用 Postman 进行测试

打开 Postman，按照以下步骤测试文件上传 API：

1. 点击 'New' 按钮并选择 'Request' 来创建一个新请求。
2. 将请求方法设置为 'POST'。
3. 输入 URL http://localhost:3000/upload。
4. 转到 'Body' 选项卡，选择 'form-data'。
5. 在 'Key' 下，将类型改为 'File'。
6. 输入 'file' 作为键，并从您的系统中选择要上传的文件。
7. 点击 'Send' 按钮执行请求。

如果此次数据交换成功，则客户端收到 '文件成功上传' 的响应，文件现在应该在后端项目的 uploads 目录中。

额外提示

• 在生产代码中始终处理错误情况。
• 为了安全起见，实施文件类型和大小验证。
• 在实际应用中确保有适当的流事件错误处理。

基于此基本文件上传服务，并已经使用 Postman 进行了测试。您可以通过添加更多功能，如文件类型检查、存储服务集成和更健全的错误处理，来扩展这个服务。

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English version

Creating a File Upload API with Koa2 and Testing with Postman

This guide will walk you through setting up a simple file upload API using Koa2 and testing it using Postman.

Prerequisites

• Node.js installed
• Basic knowledge of JavaScript and Node.js
• Postman installed for testing

Step 1: Set Up Your Project

First, create a new directory for your project and navigate into it:

mkdir koa-file-upload
cd koa-file-upload

Initialize a new Node.js project:

npm init -y

Install koa and koa-body (middleware to parse the body and files):

npm install koa koa-router koa-body --save

Step 2: Create the Koa Server

Create a file named app.js:

touch app.js

Inside app.js, set up a basic Koa server:

const Koa = require('koa');
const Router = require('koa-router');
const { koaBody } = require('koa-body');

const app = new Koa();
const router = new Router();

app.use(koaBody({ multipart: true }));

// Define routes here

app.use(router.routes()).use(router.allowedMethods());

const PORT = 3000;
app.listen(PORT, () => {
  console.log(`Server is running on http://localhost:${PORT}`);
});

Step 3: Create File Upload Endpoint

Add the following code to app.js to create a file upload endpoint:

router.post('/upload', async (ctx) => {
  const file = ctx.request.files.file; // Get the file from the request
  const reader = fs.createReadStream(file.filepath); // Create a stream to read the file
  const stream = fs.createWriteStream(path.join(__dirname, 'uploads', file.originalFilename)); // Create a stream to write the file
  reader.pipe(stream); // Pipe the read stream to the write stream
  console.log('uploading %s -> %s', file.originalFilename, stream.path);

  ctx.body = 'File uploaded successfully';
});

Make sure to create an uploads directory in the root of your project to store the uploaded files:

mkdir uploads

Step 4: Start the Server

Run your Koa server by executing:

node app.js

Step 5: Test with Postman

Open Postman and follow these steps to test your file upload API:

1. Create a new request by clicking the 'New' button and selecting 'Request'.
2. Set the request method to 'POST'.
3. Enter the URL `http://localhost:

3000/upload`. 4. Go to the 'Body' tab and select 'form-data'. 5. Under 'Key', change the type to 'File'. 6. Enter 'file' as the key and select the file you want to upload from your system. 7. Click the 'Send' button to execute the request.

You should receive a response that says 'File uploaded successfully', and the file should now be in the uploads directory of your project.

Additional Tips

• Always handle error cases in your production code.
• Implement file type and size validation for security purposes.
• Make sure to have proper error handling for stream events in real-world applications.

Now, you have a basic file upload service running with Koa2 and have tested it with Postman. You can expand upon this by adding more features like file type checks, storage service integration, and more robust error handling.