Nodejs implements image verification code

With the development of Internet technology, graphical verification codes (CAPTCHA) are widely used in website login, registration, password retrieval and other places where user identity needs to be verified. It graphically displays some questions and answers, numbers, letters, etc. for users to judge, thereby preventing robots from registering and violently cracking passwords. This article will introduce how to implement image verification code using Node.js.

1. Installation dependencies

There are many third-party modules in Node.js that can be used to generate graphical verification codes. This article will use the svg-captcha module , which can generate verification code images in SVG format. Execute the following command in the terminal to install it:

npm install svg-captcha

2. Create a basic project structure

Create a app.js file in the working directory and public folder, public folder is used to store verification code images. The following is the directory structure:

- app.js
- public
    - captcha.svg

In the app.js file, introduce the svg-captcha module and create an Express instance:

const express = require('express')
const svgCaptcha = require('svg-captcha')

const app = express()

// 其他代码

3. Create route

In order to implement the image verification code, you need to create a route to generate the verification code image. Create a route /captcha in the app.js file:

app.get('/captcha', (req, res) => {
  const captcha = svgCaptcha.create()
  res.type('svg')
  res.status(200)
  res.send(captcha.data)
})

In this route, call the svgCaptcha.create() function Generate a random verification code string and corresponding SVG image, and then send it to the client.

4. Add logic

In order for the generated verification code to match the verification code returned by the client, the generated verification code string needs to be saved in the session and Validation occurs when the client submits the form. Add the following logic in the route:

app.get('/captcha', (req, res) => {
  const captcha = svgCaptcha.create()
  req.session.captcha = captcha.text
  res.type('svg')
  res.status(200)
  res.send(captcha.data)
})

app.post('/login', (req, res) => {
  const { username, password, captcha } = req.body
  const expectedCaptcha = req.session.captcha
  if (expectedCaptcha === captcha) {
    // 验证码正确，进行登录操作
  } else {
    // 验证码错误，返回错误提示
  }
})

Save the generated verification code string in the session in the /captcha route, and then compare the verification code string with the one when the user submits the form The verification codes entered by the user are compared. If they are the same, it is judged that the verification is successful and subsequent operations are performed.

5. Start the server

After completing the above steps, execute the following command to start the server:

node app.js

Then access http in the browser: //localhost:3000/captcha, you should be able to see the generated verification code image. Enter the verification code in the login form and submit the form for subsequent operations.

Summary

It is not difficult to implement image verification code using Node.js. It only requires a third-party module to complete. However, in order to improve the security of the verification code, you need to pay attention to the following points:

1. The generated verification code string should be complex enough and try to contain uppercase and lowercase letters, numbers, and special characters.
2. The validity period of the verification code should be limited, usually about 5 minutes, to prevent the attacker from saving the verification code and trying continuously during the validity period.
3. Verification codes should be randomly generated to avoid prediction and copying.
4. Session should be used to save the verification code string, and the verification code should not be stored directly in the client or server cache.

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