freeptcha/routes.js

const sharp = require('sharp');
const canvas = require('canvas');
const crypto = require('crypto');
const randint = (min, max) => { return crypto.randomInt(max) + min };

/** @param {import('fastify').FastifyRequest} req */
const getSettings = (req) => {
    const q = req.query;
    const settings = {
        // Width and height are ratio numbers; actual width & height is calculated from text length & padding
        width: q.width ?? 3,
        height: q.height ?? 1,
        padding: q.padding ?? 20,
        format: q.format ?? 'png',
        dpi: q.dpi ?? 250
    };
    for (const key in settings) {
        if (['format'].indexOf(key) !== -1) continue;
        settings[key] = parseInt(settings[key]);
    }
    return settings;
}

const get_size = (ratio, dpi, txtlen, padding) => {
    return {
        width: Math.floor((ratio[0] * dpi * 0.12) + (txtlen * dpi * 0.08)) + (padding * 2),
        height: Math.floor(ratio[1] * dpi * 0.2) + (padding * 2)
    }
}

const createImage = async (width, height, bg = 'white', options = {}) => {
    return sharp({
        create: {
            width: width,
            height: height,
            channels: 3,
            background: bg,
            ...options
        }
    })
}
const drawText = (pic, text, dpi, blend, options = {}) => {
    return pic.composite([{
        input: {
            text: {
                text,
                font: 'Open Sans',
                dpi,
                rgba: true,
                ...options
            }
        },
        blend
    }])
}

/** @param {import('fastify').FastifyInstance} fastify */
module.exports = (fastify) => {
    fastify.get('/captcha/v1/:text', async (req, res) => {

        const text = req.params.text;

        const settings = getSettings(req);
        const size = get_size([settings.width, settings.height], settings.dpi, text.length, settings.padding);

        console.log(size)
        console.log(settings)

        let pic = await createImage(size.width, size.height);

        drawText(pic, text, settings.dpi, 'over');

        const textpic = await pic
            .ensureAlpha()
            .toFormat('png', { compressionLevel: 0 })
            .toBuffer();

        const draw = canvas.createCanvas(size.width, size.height);
        const ctx = draw.getContext('2d');
        ctx.drawImage(await canvas.loadImage(textpic), 0, 0, size.width, size.height);

        const strokes = randint(25, 40);
        for (let i = 0; i < strokes; i++) {
            ctx.strokeStyle = `rgba(0,0,0,${10})`;
            ctx.beginPath();
            ctx.bezierCurveTo(randint(0, size.width), randint(0, size.height), randint(0, size.width), randint(0, size.height), randint(0, size.width), randint(0, size.height));
            ctx.stroke();
        }

        res.header('Content-Type', 'png');
        return draw.toBuffer();
    })
}