How to validate if input in input field has base64 encoded string using express-validator ?

Last Updated : 08 Jan, 2025

In HTML forms, we often required validation of different types. Validate existing email, validate password length, validate confirm password, validate to allow only integer inputs, these are some examples of validation. If In a certain input field only base 64 encoded string are allowed i.e there not allowed any other form of string which not constitute base64 encoded string. We can also validate these input fields to accept only base 64 encoded string using express-validator middleware.

Command to install express-validator:

npm install express-validator

Steps to use express-validator to implement the logic:

Install express-validator middleware.
Create a validator.js file to code all the validation logic.
Validate input by validateInputField: check(input field name) and chain on the validation isBase64() with ‘ . ‘
Use the validation name(validateInputField) in the routes as a middleware as an array of validations.
Destructure ‘validationResult’ function from express-validator to use it to find any errors.
If error occurs redirect to the same page passing the error information.
If error list is empty, give access to the user for the subsequent request.

Note: Here we use local or custom database to implement the logic, the same steps can be followed to implement the logic in a regular database like MongoDB or MySql.

Example: This example illustrates how to validate a input field to accept only base 64 encoded string.

Filename – index.js

javascript

const express = require('express')
const bodyParser = require('body-parser')
const {validationResult} = require('express-validator')
const repo = require('./repository')
const { validateBase64Data } = require('./validator')
const formTemplet = require('./form')

const app = express()
const port = process.env.PORT || 3000

// The body-parser middleware to parse form data
app.use(bodyParser.urlencoded({extended : true}))

// Get route to display HTML form
app.get('/', (req, res) => {
  res.send(formTemplet({}))
})

// Post route to handle form submission logic and 
app.post(
  '/data',
  [validateBase64Data],
  async (req, res) => {
    const errors = validationResult(req)
    if(!errors.isEmpty()){
      return res.send(formTemplet({errors}))
    }
    const {name, base64data} = req.body
    await repo.create({
      name,
      base64data
    })

 res.send('<h2>Base 64 data decoded and '
  + 'Stored successfully in the database</h2>')
})

// Server setup
app.listen(port, () => {
  console.log(`Server start on port ${port}`)
})

Filename – repository.js: This file contains all the logic to create a local database and interact with it.

javascript

// Importing node.js file system module 
const fs = require('fs')
const { base64decode } = require('nodejs-base64');

class Repository {
  constructor(filename) {

    // The filename where datas are going to store
    if(!filename) {
      throw new Error(
'Filename is required to create a datastore!')
    }

    this.filename = filename

    try {
      fs.accessSync(this.filename)
    } catch(err) {

      // If file not exist it is created
      // with empty array
      fs.writeFileSync(this.filename, '[]')
    }
  }

  // Get all existing records
  async getAll(){
    return JSON.parse(
      await fs.promises.readFile(this.filename, {
        encoding : 'utf8'
      })
    )
  }
  
  // Create new record
  async create(attrs){
    // Fetch all existing records
    const records = await this.getAll()
    // Decode base64 encoded data
    const data = base64decode(attrs.base64data)
    // New record
    const record = {
      name:attrs.name,
      data
    }

    // All the existing records with 
    // new record push back to database
    records.push(record)
    await fs.promises.writeFile(
      this.filename,
      JSON.stringify(records, null, 2)   
    )
    return record
  }
}

// The 'datastore.json' file created at runtime 
// and all the information provided via signup form
// store in this file in JSON format.
module.exports = new Repository('datastore.json')

Filename – form.js: This file contains logic to show HTML form.

javascript

const getError = (errors, prop) => {
  try {
    return errors.mapped()[prop].msg
  } catch (error) {
    return ''
  } 
}

module.exports = ({errors}) => {
  return `
    <!DOCTYPE html>
    <html>
      <head>
        <link rel='stylesheet' 
href='https://cdnjs.cloudflare.com/ajax/libs/bulma/0.9.0/css/bulma.min.css'>
        <style>
          div.columns{
            margin-top: 100px;
          }
          .button{
            margin-top : 10px
          }
        </style>
      </head>
      <body>
        <div class='container'>
          <div class='columns is-centered'>
            <div class='column is-5'>
              <form action='/data' method='POST'>            
                <div>
                  <div>
                    <label class='label' id='name'>
                      Name
                    </label>
                  </div>
                  <input class='input' type='text'
                         name='name' 
                         placeholder='Submitted By' 
                         for='name'>
                </div>
                <div>
                  <div>
                    <label class='label' id='base64data'>
                      Base 64 data
                    </label>
                  </div>
                  <input class='input' type='text' 
                         name='base64data' 
                         placeholder='Base 64 Encode data'
                         for='base64data'>
                  <p class="help is-danger">
                    ${getError(errors, 'base64data')}
                  </p>


                </div>
                <div>
                  <button class='button is-primary'>
                    Submit
                   </button>
                </div>
              </form>
            </div>
          </div>
        </div>
      </body>
    </html>   
  `
}

Filename – validator.js: This file contain all the validation logic(Logic to validate a input field to accept only base encoded 64 string)

javascript

const {check} = require('express-validator')
const repo = require('./repository')
module.exports = {
  
  validateBase64Data : check('base64data')
    // To delete leading and trailing space
    .trim()
    // Validate input field to accept only base32 string
    .isBase64()
    // Custom message
    .withMessage('Must be a Base 64 encoded string')
}