Sample code that demonstrates uncollectible ClientRequests from keepAlive freeSockets

keepalive-leak.js

'use strict';
const heapdump=require('heapdump');
const assert = require('assert');
const http = require('http');
const PORT=8089;

const kMaxUsedSockets=10;
const kMaxFreeSockets=9;

const agent = new http.Agent({
  keepAlive: true,
  keepAliveMsecs: 1000,
  maxSockets: kMaxUsedSockets,
  maxFreeSockets: kMaxFreeSockets
});

var buffer=new Buffer(1000000);
buffer.fill('h');

const server = http.createServer(function(req, res) {
  res.write(buffer, () => res.end() );
});

function get(path, callback) {
  console.log(`Making request to ${path}`);
  return http.get({
    host: 'localhost',
    port: PORT,
    agent: agent,
    path: path
  }, callback);
}

const name = 'localhost:' + PORT + ':';

function checkSockets(used, free) {
  assert.equal(agent.sockets[name] ? agent.sockets[name].length : undefined, used);
  assert.equal(agent.freeSockets[name] ? agent.freeSockets[name].length : undefined, free);
}

function makeRequests(cb) {
  // Make kMaxUsedSOckets concurrent requests
  let initiated = 0;
  let freed = 0;
  let destroyed = 0;
  for (let i = 0; i < kMaxUsedSockets; ++i) {
    let reqNum = i;
    let req = get(`/buf?req=${reqNum}`, function(res) {
      res.data = '';
      assert.equal(res.statusCode, 200);
      res.on('data', body => res.data += body );
      res.on('end', function() {
        console.log(`Received response of size ${res.data.length} for req ${reqNum}`);
        let freeSock = agent.freeSockets[name] ? agent.freeSockets[name].length : agent.freeSockets[name];
        checkSockets(initiated-freed, freeSock);
      });
    });
    req.on('socket', s => {
      initiated++;
      s.once('free', (s) => {
        freed++;
        console.log('socket freed at ', Date.now());
        if (Math.min(kMaxFreeSockets,freed) + destroyed === kMaxUsedSockets) { cb(); }
      });
      s.once('close', (s) => {
        destroyed++;
        console.log('socket closed at ', Date.now());
        if (Math.min(kMaxFreeSockets,freed) + destroyed === kMaxUsedSockets) { cb(); }
      });

    });
  }
  checkSockets( kMaxUsedSockets, undefined );
}
      
server.listen(PORT, function() {
  // request first, and keep alive
  heapdump.writeSnapshot(function(err, fn) {
    console.log(`BEGIN: heapsnapshot written to ${fn}`);
  });
  makeRequests(() => {
    checkSockets( undefined, kMaxFreeSockets);
    heapdump.writeSnapshot(function(err, fn) {
      console.log(`END: heapsnapshot written to ${fn}`);
    });
  });
});