React Node app crashing while downloading file - node.js

Question

I am creating an app using Node and react as part of my learning process. The which covert HTTP, https links to torrent. The problem is, I need to download the file first to convert it to torrent. The app working fine when it comes to small files. But if it is a large file like One GB it fails and app crash.
here is my project link:-
https://github.com/savadks95/FireBit/blob/master/server.js
Can anyone please tell me how to fix this. And I also want to show the download in progress.
var http = require("http");
var webtorrentify = require("webtorrentify-link");
var fs = require("fs");
var url = require("url");
var path = require("path");
var validUrl = require("valid-url");
var express = require("express");
var getUrls = require("get-urls");
var remote = require("remote-file-size");
var app = express();
var downloadLink;
var fileName;
var fileSize;
var server;
var parsed;
var param;
var link;
var port;
port = process.env.PORT || 80;
app.get("/favicon.ico", function(req, res) {
console.log("favicon request recived");
});
app.get("*", function(req, res) {
if (req.url === "/") {
//app.use('/public/html', express.static(path.join(__dirname)));
fs.readFile("public/html/index.html", function(err, data) {
res.write(data);
});
} else if (req.url === "/l?thelink=") {
fs.readFile("public/html/emptyRequest.html", function(err, data) {
res.write(data);
res.end();
});
} else {
//---------Reciving Url--------------------
console.log(req.query.thelink);
downloadLink = req.query.thelink;
//-----------------------------------------
//------------checking for valid url-------
if (validUrl.isUri(downloadLink)) {
console.log("Looks like an URI");
//-----------------------------------------
//----------Extracting filename-------------
parsed = url.parse(downloadLink);
fileName = path.basename(parsed.pathname);
console.log(path.basename(parsed.pathname));
//-------------------------------------------
//----------Finding File size----------------
remote(downloadLink, function(err, o) {
fileSize = o / 1024 / 1024;
console.log("size of " + fileName + " = " + fileSize + " MB");
//-------------------------------------------
if (fileSize < 501) {
///////////////Creating Torrent////////////////////
webtorrentify(downloadLink).then(function(buffer) {
console.log("creating the torrent");
//res.send('what is');
//-------------------------------------------
res.setHeader("Content-Type", "application/x-bittorrent");
res.setHeader(
"Content-Disposition",
`inline; filename="${fileName}.torrent"`
);
res.setHeader("Cache-Control", "public, max-age=2592000"); // 30 days
res.send(buffer);
console.log(fileName + ".torrent created");
res.end();
//-------------------------------------------
});
////////////////////////////////////////////////
} else {
console.log("More than 500 MB");
res.send("<h4> More than 500 MB or invalid URL </h4>");
}
});
} else {
console.log("not url");
fs.readFile("public/html/404.html", function(err, data) {
res.write(data);
res.end();
});
}
}
});
app.listen(port);