Introduction to Koa-body

Koa-body is an essential middleware for Koa.js framework that helps in dealing with the request body. It supports parsing JSON, URL-encoded, and multipart request bodies. Let’s dive into some of the useful APIs provided by Koa-body and understand how to integrate them.

Basic Setup

First, install koa-body:

  npm install koa-body

Then, use it in your Koa application:

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

  const app = new Koa();

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

Uploading Files

With koa-body, you can handle file uploads easily:

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

  const app = new Koa();

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

  app.use(async ctx => {
    const files = ctx.request.files.file; // File is the name you're uploading as
    ctx.body = `File uploaded: ${files.name}`;
  });

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

Handling JSON and URL-encoded Data

You can parse incoming JSON or URL-encoded data easily:

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

  const app = new Koa();

  app.use(koaBody());

  app.use(async ctx => {
    if (ctx.method === 'POST') {
      ctx.body = {
        message: 'Data received!',
        data: ctx.request.body
      };
    } else {
      ctx.body = 'Send a POST request with JSON or URL-encoded data';
    }
  });

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

Restricting File Upload Size

To limit the size of the files being uploaded:

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

  const app = new Koa();

  app.use(koaBody({
    multipart: true,
    formidable: {
      maxFileSize: 200 * 1024 * 1024 // 200 MB
    }
  }));

  app.use(async ctx => {
    const files = ctx.request.files.file;
    ctx.body = `File uploaded: ${files.name}`;
  });

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

Complete App Example

Here’s a complete app example combining the discussed functionalities:

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

  const app = new Koa();

  app.use(koaBody({
    multipart: true,
    formidable: {
      uploadDir: path.join(__dirname, 'uploads'),
      keepExtensions: true,
      maxFileSize: 200 * 1024 * 1024
    }
  }));

  app.use(async ctx => {
    if (ctx.method === 'POST') {
      const files = ctx.request.files.file;
      const data = ctx.request.body;

      ctx.body = {
        message: 'Data received!',
        data: data,
        fileInfo: files ? `File uploaded: ${files.name}` : 'No file uploaded'
      };
    } else {
      ctx.body = 'Send a POST request with JSON, URL-encoded data, or files';
    }
  });

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

Koa-body is a powerful middleware to handle various kinds of request bodies in a Koa.js application. Mastering its use can significantly enhance your API management capabilities.