app.js

// James Puleo (2018)
/*
  Node script to give Discord proxy servers the wrong image
  Their proxy server's aren't very identifiable based by their UA,
  but one thing that many of the servers had in common was that the
  response was from Firefox 38.0, which is highly deprecated. It seemed
  to never be from anything else. Not full-proof, but it works very successfully.
*/

var express = require("express");
var useragent = require("useragent");
var app = express();

app.all("*", (req, res, next) => {
  console.log("Got request!");
  console.log("Address: " + req.connection.remoteAddress);
  console.log("Port: " + req.connection.remotePort);
  console.log("user-agent: " + req.headers["user-agent"]);
  var agent = useragent.parse(req.headers["user-agent"]);
  console.log(
    `Using ${agent.family}, version ${agent.major}/${agent.minor}/${
      agent.patch
    }`
  );
  console.log("isDiscordProxy: " + isDiscordProxy(agent));
  next();
});

app.get("/", (req, res) => {
  var headersRet = "";
  res.send(
    "Your user agent is: <span style='font-family: Consolas'>" +
      req.headers["user-agent"] +
      "</span>"
  );
});

function isDiscordProxy(agent) {
  return (
    (agent.family.toUpperCase() === "FIREFOX" && parseInt(agent.major) <= 38) ||
    agent.family === "Discordbot"
  );
}

app.get("/a5jk3g.jpg", (req, res) => {
  var agent = useragent.parse(req.headers["user-agent"]);
  if (isDiscordProxy(agent)) {
    // This is a discord image proxy.
    res.sendFile("proxy_image.jpg", { root: "." });
  } else {
    // Probably not discord image proxy server.
    res.redirect("https://www.youtube.com/watch?v=6n3pFFPSlW4");
  }
});

app.listen(3000, "0.0.0.0");