How to implement verification code verification function in nodejs

With the rapid development of the Internet, security issues have received widespread attention from users and developers. CAPTCHA technology is one of the most common defense mechanisms currently available. As an efficient server-side development language, Node.js can also implement verification code verification. The following introduces how Node.js implements verification code verification.

1. What is a verification code?

Verification code is a defense technology against automated programs, often used in web applications or computer systems. The verification code can be an image, a number or letter, or a simple math question. By filling out the correct verification code, the user can prove that they are a real person and not an automated program.

2. Steps to implement verification code verification in Node.js

1. Install the necessary npm package: We need to install an npm package named captcha-gen, which can help us generate Verification code image. You can use the following command to install:

npm install captcha-gen

2. Generate verification code images: It is very simple to use the captcha-gen package to generate verification code images. We just need to call require('captcha-gen'), and then use the function it returns as a middleware function. The following is the sample code:

const express = require('express');
const captcha = require('captcha-gen');

let app = express();

app.use((req, res, next) => {
    let cap = captcha.create({ width: 120, height: 50 });
    res.type('svg');
    res.send(cap.svg());
});

Here, we use the Express.js framework and return the verification code image generated by captcha-gen to the browser as SVG format.

3. Verify the verification code entered by the user: After receiving the verification code submission from the user, we need to verify whether the content entered is the same as the content in the verification code image. In Node.js, you can use the node-canvas npm package to achieve this. The following is the sample code:

const Canvas = require('canvas');

function verifyCode(code, userInput) {
    let c = new Canvas(100, 50);
    let ctx = c.getContext('2d');
    ctx.font = '30px Impact';
    ctx.fillStyle = '#fff';
    ctx.fillRect(0, 0, 100, 50);
    ctx.fillStyle = '#000';
    ctx.fillText(code, 10, 35);
    let imageData = ctx.getImageData(0, 0, 100, 50);
    let pixels = imageData.data;
    for (let i = 0; i < pixels.length; i += 4) {
        pixels[i] = pixels[i + 1] = pixels[i + 2] = (pixels[i] + pixels[i + 1] + pixels[i + 2]) / 3;
    }
    let sum = 0;
    for (let i = 0; i < pixels.length; i++) {
        sum += pixels[i];
    }
    sum = sum / pixels.length;
    let res = 0;
    for (let i = 0; i < userInput.length; i++) {
        res += userInput[i].charCodeAt(0);
    }
    return (sum - res) % 256 === 0;
}

In the above code, we use Canvas to create a 100*50 size canvas and draw the verification code image in it. Then use getImageData() to take out the data and perform a simple averaging process on the RGB value of each pixel. Finally, the verification code entered by the user is converted into an ASCII code and added together, and compared with the average pixel value. If they are the same, it means that the verification code entered by the user is correct.

3. Summary

Through the above method, we can implement verification code verification on the Node.js server side to improve the security and reliability of web applications. Although Node.js is not the best choice, it is a simple and efficient development language that can meet the needs of most small and medium-sized web applications.

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