net: fix readable event not emitted (fixes #25969)

[CGQAQ]

fix readable event not emitted after reconnect

Closes: #25969

[nodejs-github-bot]

Review requested:

• @nodejs/net

[mcollina]

Thanks for opening a PR! Can you please add a unit test?

[CGQAQ]

Thanks for opening a PR! Can you please add a unit test?

I'll add it later

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/52886/

[CGQAQ]

@mcollina I'm sorry, but I don't know how to test this, I have tested it locally, it works now.
I have two files, and I need to do the following

1. node server.js
2. node client.js
3. ctrl c node server.js
4. see client.js output
5. run node server.js again
6. see client.js output keep going

please help me.

client.js

const net = require('net');

const client = new net.Socket();
let connected = false;

client.on('error', (err) => console.error('client#error', err.message));

client.on('close', () =>
{
  console.log('client#close');
  
  connected = false;
  
  setTimeout(connect, 333);
});

client.on('connect', () =>
{
  console.log('client#connect');
  
  connected = true;
});

//client.on('data', (data) => console.log('client#data', data));
///*
client.on('readable', () =>
{
  const data = client.read();
  
  if (data)
  {
    console.log('client#readable', data);
  }
});
//*/

connect();

setInterval(() => 
{
  if (connected)
  {
    client.write(Buffer.from([0, 1, 2]));
  }
}, 333);

function connect()
{
  console.log('connecting...');
  
  client.connect(502, '127.0.0.1');
}

server.js

const net = require('net');

const server = net.createServer();

server.on('connection', (conn) =>
{
  console.log('server#connection');
  
  conn.on('error', (err) => console.error('conn#error', err.message));
  conn.on('close', (err) => console.log('conn#close'));
  conn.on('readable', () =>
  {
    const data = conn.read();
    
    if (data)
    {
      console.log('conn#readable', data);
      
      conn.write(data);
    }
  });
});

server.on('error', (err) => console.error(err.message));

server.on('close', () => console.log('server#close'));

server.on('listening', () => console.log('server#listening'));

server.listen(502);

[mcollina]

It might be passing, but it is now failing this test: https://github.com/nodejs/node/blob/main/test/parallel/test-net-connect-paused-connection.js.

---

As to write a test, you should combine your server and client into one file and place it inside test/parallel. Take a look at other tests too! Uou'll see that you need to add a require to ../common for example.

[CGQAQ]

I tried this, but client.on('end' wont trigger after server close, I didn't see any test failed @mcollina

test I tried

// Copyright Joyent, Inc. and other Node contributors.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to permit
// persons to whom the Software is furnished to do so, subject to the
// following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
// USE OR OTHER DEALINGS IN THE SOFTWARE.

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

const net = require('net');

const N = 50;
let client_recv_count = 0;
let client_end_count = 0;
let client_readable_count = 0;
let disconnect_count = 0;

const server = net.createServer(function(socket) {
  console.error('SERVER: got socket connection');
  
  console.error('SERVER connect, writing');
  socket.write('hello\r\n');

  socket.on('end', () => {
    console.error('SERVER socket end, calling end()');

    socket.end();
  });

  socket.on('close', (had_error) => {
    console.log(`SERVER had_error: ${JSON.stringify(had_error)}`);
    assert.strictEqual(had_error, false);
  });
});

server.listen(0, function() {
  console.log('SERVER listening');
  const client = net.createConnection(this.address().port);

  client.setEncoding('UTF8');

  client.on('connect', () => {
    console.error('CLIENT connected');
  });

  client.on("readable", () => {
    console.log('CLIENT readable');
    client_readable_count++;

    client_recv_count += 1;
    console.log(`client_recv_count ${client_recv_count}`);
    console.error('CLIENT: calling end');
    client.end(); 
  });

  client.on('end', () => {
    console.error('CLIENT end');
    client_end_count++;
  });

  client.on('close', (had_error) => {
    console.log('CLIENT disconnect');
    assert.strictEqual(had_error, false);
    if (disconnect_count++ < N)
      client.connect(server.address().port); // reconnect
    else
      server.close();
  });
});

process.on('exit', () => {
  assert.strictEqual(disconnect_count, N + 1);
  assert.strictEqual(client_recv_count, N + 1);
  assert.strictEqual(client_end_count, N + 1);
  assert.strictEqual(client_readable_count, N + 1);
});

Result(hangs on last line because client side close didn't trigger):

[ronag]

We should only resume if flowing? Or we might lose data when reconnecting a paused stream. @mcollina

[CGQAQ]

But flowing is always false after connected

[ronag]

The problem here is that if the socket is paused or never started, you will force it to start. Causing lost data for the user.

[ShogunPanda]

I agree with @ronag.
Could you just check if any data event is there (which implies flowing)?

Also please consider to add whatever solution you find here in internalConnectMultiple, otherwise it will fail with network family autoselection.

[ronag]

FWIW. I think the whole undestroy/reconnect flow for net.Socket is fundamentally flawed and I would personally prefer to just doc deprecate it and emit a warning to anyone that uses it. We should recommend creating a new socket instance instead.

[mcollina]

FWIW. I think the whole undestroy/reconnect flow for net.Socket is fundamentally flawed and I would personally prefer to just doc deprecate it and emit a warning to anyone that uses it. We should recommend creating a new socket instance instead.

I agree

[CGQAQ]

I think you guys are right