node/test/parallel/test-http-agent-destroyed-socket.js

'use strict';
require('../common');
const assert = require('assert');
const http = require('http');

const server = http.createServer(function(req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n');
}).listen(0, function() {
  const agent = new http.Agent({maxSockets: 1});

  agent.on('free', function(socket, host, port) {
    console.log('freeing socket. destroyed? ', socket.destroyed);
  });

  const requestOptions = {
    agent: agent,
    host: 'localhost',
    port: this.address().port,
    path: '/'
  };

  const request1 = http.get(requestOptions, function(response) {
    // assert request2 is queued in the agent
    const key = agent.getName(requestOptions);
    assert.strictEqual(agent.requests[key].length, 1);
    console.log('got response1');
    request1.socket.on('close', function() {
      console.log('request1 socket closed');
    });
    response.pipe(process.stdout);
    response.on('end', function() {
      console.log('response1 done');
      /////////////////////////////////
      //
      // THE IMPORTANT PART
      //
      // It is possible for the socket to get destroyed and other work
      // to run before the 'close' event fires because it happens on
      // nextTick. This example is contrived because it destroys the
      // socket manually at just the right time, but at Voxer we have
      // seen cases where the socket is destroyed by non-user code
      // then handed out again by an agent *before* the 'close' event
      // is triggered.
      request1.socket.destroy();

      response.once('close', function() {
        // assert request2 was removed from the queue
        assert(!agent.requests[key]);
        console.log("waiting for request2.onSocket's nextTick");
        process.nextTick(function() {
          // assert that the same socket was not assigned to request2,
          // since it was destroyed.
          assert.notStrictEqual(request1.socket, request2.socket);
          assert(!request2.socket.destroyed, 'the socket is destroyed');
        });
      });
    });
  });

  const request2 = http.get(requestOptions, function(response) {
    assert(!request2.socket.destroyed);
    assert(request1.socket.destroyed);
    // assert not reusing the same socket, since it was destroyed.
    assert.notStrictEqual(request1.socket, request2.socket);
    console.log('got response2');
    let gotClose = false;
    let gotResponseEnd = false;
    request2.socket.on('close', function() {
      console.log('request2 socket closed');
      gotClose = true;
      done();
    });
    response.pipe(process.stdout);
    response.on('end', function() {
      console.log('response2 done');
      gotResponseEnd = true;
      done();
    });

    function done() {
      if (gotResponseEnd && gotClose)
        server.close();
    }
  });
});