Node.js server.keepAliveTimeout

README.md

A demo for the race condition that can happen with a short keepAliveTimeout

Start a server:

# Start a server with 3000 ms of keepAliveTimeout
node server.js 3000

Start a client to see the race condition

# Start a client that makes HTTP requests with 3000 ms of delay
node client.js 3000

client.js

const http = require("http");
const net = require("net");

const PORT = 8080;

const agent = new http.Agent({
  keepAlive: true,
  maxFreeSockets: Infinity
});

let delay = parseInt(process.argv[2], 10);
if (Number.isNaN(delay)) {
  delay = 100;
}
console.log("%d ms delay", delay);

function startClients() {
  for (let i = 0; i < 500; i++) {
    makeRequest(e => {
      if (e) {
        console.log(i, "error on first request", e);
        return;
      }
      setTimeout(() => {
        makeRequest(err => {
          if (err) {
            console.log(i, "error on second request", err);
          }
        });
      }, delay - 50 + Math.random() * 100);
    });
  }
}

function makeRequest(cb) {
  const req = http.request(
    {
      host: "localhost",
      port: PORT,
      agent
    },
    res => {
      res.on("error", cb);
      res.on("end", cb);
      res.resume();
    }
  );
  req.on("error", cb);
  req.end();
}

function countSockets(sockets) {
  return Object.values(sockets).reduce((total, socs) => total + socs.length, 0);
}

startClients();

setInterval(() => {
  console.log(
    "%d sockets, %d free sockets",
    countSockets(agent.sockets),
    countSockets(agent.freeSockets)
  );
}, 1000);

server.js

const http = require("http");

const PORT = 8080;

const keepAliveTimeout = parseInt(process.argv[2], 10);

const server = http.createServer((req, res) => {
  // req.resume();
  res.end("hello");
});

if (!Number.isNaN(keepAliveTimeout)) {
  console.log("keepAliveTimeout %d ms", keepAliveTimeout);
  server.keepAliveTimeout = keepAliveTimeout;
}

server.headersTimeout = 10 * 1000;

server.listen(PORT, () => {
  const { address, port } = server.address();
  console.log("Listening on %s:%d", address, port);

  let connections = 0;
  server.on("connection", socket => {
    connections += 1;
    socket.once("close", () => {
      connections -= 1;
    });
  });

  setInterval(() => {
    console.log("%d connections", connections);
  }, 1000);
});