Koa-Body: Introduction and Comprehensive API Guide

Koa-body is a popular middleware for Koa, a next-generation web framework for Node.js. It seamlessly handles the parsing of request bodies, making it a versatile tool for developers. This article provides an in-depth look at the Koa-body API with numerous code snippets to help you get started quickly.

1. Basic Usage

Install koa-body via npm:

  
    npm install koa-body
  

2. Importing and Configuring Koa-Body

  
    const Koa = require('koa');
    const koaBody = require('koa-body');

    const app = new Koa();

    app.use(koaBody());
  

3. Example API: Parsing JSON Body

Simple JSON body parsing:

  
    app.use(async (ctx) => {
      if (ctx.method === 'POST') {
        ctx.body = ctx.request.body;
      } else {
        ctx.body = 'Send a POST request with a JSON body';
      }
    });

    // curl -X POST http://localhost:3000 -H "Content-Type: application/json" -d '{"name": "John Doe"}'
  

4. Example API: Parsing Form Data

Handling URL-encoded form data:

  
    app.use(async (ctx) => {
      if (ctx.method === 'POST') {
        ctx.body = ctx.request.body;
      } else {
        ctx.body = 'Send a POST request with form data';
      }
    });

    // curl -X POST http://localhost:3000 -H "Content-Type: application/x-www-form-urlencoded" -d "name=John Doe"
  

5. Example API: Parsing Multi-Part Form Data

Handling file uploads with multi-part form data:

  
    app.use(koaBody({
      multipart: true,
      formidable: {
        uploadDir: './uploads',
        keepExtensions: true
      }
    }));

    app.use(async (ctx) => {
      if (ctx.method === 'POST') {
        ctx.body = ctx.request.files;
      } else {
        ctx.body = 'Send a POST request with multi-part form data';
      }
    });

    // curl -X POST http://localhost:3000 -F "file=@/path/to/file"
  

6. Additional Options

Koa-body includes additional configuration options:

  
    app.use(koaBody({
      text: true,
      urlencoded: true,
      multipart: true,
      encoding: 'gzip',
      formLimit: '1mb',
      jsonLimit: '1mb',
      strict: true,
      onError: (err, ctx) => {
        ctx.throw('body parse error', 422);
      }
    }));
  

7. Full Application Example

Here’s a complete example using several Koa-body features:

  
    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,
      urlencoded: true,
      multipart: true
    }));

    router.post('/upload', async (ctx) => {
      ctx.body = ctx.request.files;
    });

    router.post('/json', async (ctx) => {
      ctx.body = ctx.request.body;
    });

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

    app.listen(3000, () => {
      console.log('Server is running on port 3000');
    });
  

With these examples and configurations, you are now well-equipped to use Koa-body in your next Koa project! Happy coding!

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