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Last active September 23, 2025 07:02
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TCP echo server for Node.js
Raw
README.md

TCP echo server for Node.js

Usage

  1. Make sure you have a modern-ish version of Node.js installed.
  2. Type npx https://gist.github.com/kfox/1280c2f0ee8324067dba15300e0f2fd3
  3. Connect to it from a client, e.g. netcat or similar: nc localhost 9000
Raw
echo.mjs
#!/usr/bin/env node
import net from 'node:net'
const port = process.argv[2] || 9000
const server = net.createServer((connection) => {
const { address, port } = connection.address()
const socket = `${address}:${port}`
console.log(`${socket} - client connected`)
connection.on('data', (data) => {
console.log(`${socket} - client sent: %s`, String(data).trim())
connection.write(data)
})
connection.on('end', () => {
console.log(`${socket} - client disconnected`)
})
})
server.listen({ port }, () => {
const { address, port } = server.address()
console.log('listening on %s:%d', address, port)
})
Raw
package.json
{
"name": "tcp-echo-server",
"version": "1.0.0",
"bin": "./echo.mjs"
}
@renatoargh
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renatoargh commented Sep 13, 2023 •
edited
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Doesn't work from npx for me 😢

✗ npx https://gist.github.com/kfox/1280c2f0ee8324067dba15300e0f2fd3
Need to install the following packages:
  [email protected]
Ok to proceed? (y) y
/var/folders/zm/m0hqdgz50n3f3h5ccv2lb49r0000gn/T/npx69462768599.sh: line 2: tcp-echo-server: command not found

Also, npx -v === 8.13.2

@kfox
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Author

kfox commented Sep 13, 2023 •
edited
Loading

Doesn't work from npx for me 😢

✗ npx https://gist.github.com/kfox/1280c2f0ee8324067dba15300e0f2fd3
Need to install the following packages:
  [email protected]
Ok to proceed? (y) y
/var/folders/zm/m0hqdgz50n3f3h5ccv2lb49r0000gn/T/npx69462768599.sh: line 2: tcp-echo-server: command not found

Also, npx -v === 8.13.2

You need a newer version of node, which should also update npx. I'm not sure what the minimum version numbers for each binary are, but if you are running on a more recent version it should work. I have the following versions installed:

⮑  node -v
v20.6.1
⮑  npx -v
10.1.0
⮑  npx https://gist.github.com/kfox/1280c2f0ee8324067dba15300e0f2fd3
listening on :::9000

@renatoargh
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Amazing, it works now! Super cool idea, by the way

@guest271314
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Using WHATWG Streams

import { Server } from "node:net";
import { Duplex } from "node:stream";

const abortable = new AbortController();
const {
  signal,
} = abortable;

const connectionListener = async (socket) => {
  const { readable, writable } = Duplex.toWeb(socket);
  const writer = writable.getWriter();
  await readable.pipeTo(
    new WritableStream({
      async write(value, controller) {
        await writer.write(value);
      },
      close() {},
      abort(reason) {},
    }),
  ).catch(() => {});
};

const tcpserver = new Server({
  highWaterMark: 0,
  noDelay: true,
}, connectionListener);

tcpserver.listen({
  port: 8080,
  host: "127.0.0.1",
  signal,
});

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