server.js

const http = require('http')
const {createCanvas} = require('canvas')
const assert = require('assert')
const pdfjsLib = require('pdfjs-dist/es5/build/pdf.js')

const port = process.env.PDF2PNG_PORT || 3001

function NodeCanvasFactory() {
}

NodeCanvasFactory.prototype = {
    create: function NodeCanvasFactory_create(width, height) {
        assert(width > 0 && height > 0, 'Invalid canvas size');
        let canvas = createCanvas(width, height, 'png');
        let context = canvas.getContext('2d');
        return {
            canvas: canvas,
            context: context,
        };
    },

    reset: function NodeCanvasFactory_reset(canvasAndContext, width, height) {
        assert(canvasAndContext.canvas, 'Canvas is not specified');
        assert(width > 0 && height > 0, 'Invalid canvas size');
        canvasAndContext.canvas.width = width;
        canvasAndContext.canvas.height = height;
    },

    destroy: function NodeCanvasFactory_destroy(canvasAndContext) {
        assert(canvasAndContext.canvas, 'Canvas is not specified');

        // Zeroing the width and height cause Firefox to release graphics
        // resources immediately, which can greatly reduce memory consumption.
        canvasAndContext.canvas.width = 0;
        canvasAndContext.canvas.height = 0;
        canvasAndContext.canvas = null;
        canvasAndContext.context = null;
    },
};

http.createServer(function (req, res) {

    if (req.method !== 'POST') {
        res.writeHead(405, {'Content-Type': 'text/plain'});
        res.end('Method Not Allowed\n only POST requests are supported');
        console.error('http method not allowed: ' + req.method);

        return;
    }
    console.log((new Date()).toISOString() + ' incoming POST request');

    // read incoming POST data in chunks 
    let chunks = [];
    req.on('data', chunk => {
        chunks.push(chunk);
    });

    req.on('end', () => {
        // Read the PDF file into a typed array so PDF.js can load it.
        const rawData = new Uint8Array(Buffer.concat(chunks));
        // Load the PDF file.
        pdfjsLib.getDocument(rawData).promise.then(function (pdfDocument) {
            console.log((new Date()).toISOString() + ' PDF loaded (' + rawData.byteLength + ' Bytes)');

            // Get the first page.
            pdfDocument.getPage(1).then(function (page) {
                // Render the page on a Node canvas with 100% scale.
                const viewport = page.getViewport({ scale: 1, });
                const canvasFactory = new NodeCanvasFactory();
                const canvasAndContext = canvasFactory.create(viewport.width, viewport.height);
                const renderContext = {
                    canvasContext: canvasAndContext.context,
                    viewport: viewport,
                    canvasFactory: canvasFactory
                };

                page.render(renderContext).promise.then(function () {
                    console.log((new Date()).toISOString() + ' page rendered');
                    res.writeHead(200, {'Content-Type': 'image/png'});
                    // convert the canvas to a png stream.
                    canvasAndContext.canvas.createPNGStream({compressionLevel: 9}).pipe(res);
                    console.log((new Date()).toISOString() + ' PNG created');
                });
            });
        }).catch(function (reason) {
            res.writeHead(500, {'Content-Type': 'text/plain'});
            res.end('Error: ' + reason);
            console.log(reason);
        });

    });

}).listen(port, "0.0.0.0");

console.log('PDF2PNG Server listening on ' + port + ' waiting for PDF data via POST requests');