Node.js Image Conversion Services over HTTP

img-server.js

// receive POST to /convert, with POST fields:
// svg - SVG image data
// format - format to convert image to (see switch below)
// width - width of converted image in pixels
// height - height of converted image in pixels
const express = require('express');
const multer = require('multer');
const upload = multer({ limits:{fieldSize: 25 * 1024 * 1024} });
const sharp = require("sharp");

const host = 'localhost';
const port = 3000;   // no need to open in firewall if accessed locally only
const defaultWidth = 500;  // adjust to suit, these are for DrawShield
const defaultHeight = 600;
const debug = false;

const app = express();

app.get("/", (req, res) => {
    res.sendFile(__dirname + "/index.html");  // Suggested contents, usage instructions?
});

app.post('/convert', upload.none(), (req, res) => {
    if (debug) {console.log(req.body);}
    let format = req.body.format;
    let width = Number(req.body.width);
    let height = Number(req.body.height);
    let options = {};
    switch(format.toLowerCase()) {
        case 'jpeg':
        case 'jpg':
            format = 'jpeg';
            options = { quality: 90 };
            break;
        case 'webp':
            format = 'webp';
            options = { lossless: true };
            break;
        case false: // i.e. undefined
        case 'png':
            format = 'png';
            break;
        default:
            res.setHeader("Content-Type", "text/plain");
            res.writeHead(500);
            res.end("Unknown conversion format");
            return;
    }
    if (!width) {
        width = defaultWidth;
    } else if (width < 50) {
        width = 50;
    }
    if (!height) {
        height = defaultHeight;
    } else if (height < 50) {
        height = 50;
    }
    let svg = req.body.svg;
    // just a dummy box if for some reason we get nothing.
    if (!svg) {
        svg = '<svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="236" height="120" viewBox="0 0 236 120"><rect x="14" y="23" width="200" height="50" fill="#55FF55" stroke="black" stroke-width="1" /></svg>';
    }
    const buf = Buffer.from(svg, "utf-8");
    if (debug) {console.log(`Converting to ${format} with width ${width} & heigth ${height}`);}
    sharp(buf)
        .resize(width,height)
        .toFormat(format, options)
        .toBuffer((err, data, info) => {
            if(err) {
                if (debug) {console.log("Error code");}
                res.setHeader("Content-Type", "text/plain");
                res.writeHead(500);
                res.end(err);
            } else {
                if (debug) {console.log("Success!");}
                res.setHeader("Content-Type", "image/png");
                res.setHeader("Content-Transfer-Encoding", "binary");
                res.writeHead(200);
                res.end(data);
            }
        })
});

console.log(`Img Server launched on http://${host}:${port}`);
app.listen(port);