How to upload file using Koa? - node.js

Question

I am setting up a new server and want to support advanced upload function. Firstly I need to validate file (filetype, filesize, maxcount), and finally upload it to some destination. I tried something with koa-multer but I cannot get multer validation errors.
multer.js
const multer = require('koa-multer')
const storage = multer.diskStorage({
destination: function (req, file, cb) {
cb(null, './public/uploads/')
},
filename: function (req, file, cb) {
var fileFormat = (file.originalname).split('.')
cb(null, file.fieldname + '_' + Date.now() + '.' + fileFormat[fileFormat.length - 1])
}
})
const fileFilter = (req, file, cb) => {
if (file.mimetype === 'image/jpeg' || file.mimetype === 'image/png') {
cb(null, true)
} else {
cb(new Error('This is not image file type'), false)
}
}
const upload = multer({
storage: storage,
limits: {
fileSize: 1024 * 1024 * 1,
files: 5
},
fileFilter: fileFilter
})
module.exports = upload
router.js
const Router = require('koa-router')
const multer = require('../middlewares/multer')
const auth = require('../middlewares/auth')
const controller = require('../controllers').userController
const schemas = require('../schemas/joi_schemas')
const validation = require('../middlewares/validation')
const router = new Router()
const BASE_URL = `/users`
router.post(BASE_URL, auth , validation(schemas.uPOST, 'body'), controller.
addUser)
router.put(`${BASE_URL}/:id`, auth , multer.single('logo')(ctx, (err) => {
if (err) {
ctx.body = {
success: false,
message: 'This is not image file'
}
}
}), controller.editUser)
router.delete(`${BASE_URL}/:id`, auth , controller.deleteUser)
module.exports = router.routes()
How can I solve upload problem this in best way for long term maintain of code?

Answer 1

The simplest approach for uploading files is the following (assume the form has a file upload field called avatar:
const Koa = require('koa')
const mime = require('mime-types')
const Router = require('koa-router')
const koaBody = require('koa-body')({multipart: true, uploadDir: '.'})
const router = new Router()
router.post('/register', koaBody, async ctx => {
try {
const {path, name, type} = ctx.request.files.avatar
const fileExtension = mime.extension(type)
console.log(`path: ${path}`)
console.log(`filename: ${name}`)
console.log(`type: ${type}`)
console.log(`fileExtension: ${fileExtension}`)
await fs.copy(path, `public/avatars/${name}`)
ctx.redirect('/')
} catch(err) {
console.log(`error ${err.message}`)
await ctx.render('error', {message: err.message})
}
})
Notice that this example uses Async Functions which allows for clean code with a standard try-catch block to handle exceptions.

Answer 2

koa middleware is like a nested callback, you should catch "next()" not after multer
router.put(`${BASE_URL}/:id`, auth , async (ctx, next) => {
try{
await next()
} catch(err) {
ctx.body = {
success: false,
message: 'This is not image file'
}
}
}, multer.single('logo'), controller.editUser)
but you do this, it will catch controller.editUser errors too which not been caught by controller itself.

Answer 3

You can use one of two options:
The first is by adding callback function to the end of the route.
const multer = require('#koa/multer')
//Options to limit file size and file extension
const upload = multer({
dest: '../avatars',
limits: {
fileSize: 1024*1024
},
fileFilter(ctx, file, cb) {
if (!file.originalname.match(/\.(jpg|jpeg|png)$/)) {
return cb(new Error('Please upload a World document'))
}
cb(undefined, true)
}
})
//The last callback should handle the error from multer
router
.post('/upload', upload.single('upload'), async (ctx) => {
ctx.status = 200
}, (error, ctx) => {
ctx.status = 400
ctx.body = error.message
})
})
The second option is by adding try/ catch before calling multer middleware:
router
.post('/upload', async (ctx, next) => {
try {
await next()
ctx.status = 200
} catch (error) {
ctx.status = 400
ctx.body = error.message
}
}, upload.single('upload'), async ctx => {ctx.status = 200})
In last case if exception will thrown in multer, it will be handled by try/catch in previous await next()