Different socket connection behavior between Node.js v18 and v20/22 with keepAlive #5152

Node.js Version

v22

NPM Version

10.9.0

Operating System

Windows 11

Subsystem

Other

Description

Hi, I am encountering inconsistent socket connection behavior when migrating from Node.js v18 LTS to v22 LTS.

In v18, my TCP server using socket.setKeepAlive(true) maintains connections indefinitely as expected. However, in v22, the connections are being terminated unexpectedly after a specific idle period, even though keepAlive is explicitly enabled. I have verified that no firewall rules are changing.

Is this a known breaking change in the net module regarding keep-alive logic in recent versions? Or is there a new flag required to maintain legacy socket behavior?

Minimal Reproduction

const net = require('net');

const server = net.createServer((socket) => {
socket.setKeepAlive(true, 60000);
console.log('Client connected');

socket.on('data', (data) => {
socket.write(data);
});

socket.on('end', () => {
console.log('Client disconnected unexpectedly?');
});
});

server.listen(8080, () => {
console.log('Server listening on 8080');
});

Output

No specific error message is thrown. The server simply logs "Client disconnected unexpectedly?" after the idle period, whereas in v18 the connection remains open indefinitely.

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