Using the net module

When your transaction test script needs to establish a TCP connection with a network target, you'll use the net module from ThousandEyes. The ThousandEyes runtime environment for transaction scripts includes the net module for creating raw TCP client sockets to servers on arbitrary ports.

Importing the Module

To use the net module, make sure to first import it within your transaction script:

import net from 'thousandeyes';

Creating a Connection

To create a client connection to a remote server, use the net.connect function:

await net.connect(<port>, '<host.ip.address>');

DNS Behavior for FQDN Targets

When you pass a fully qualified domain name (FQDN) to net.connect(), BrowserBot resolves both A (IPv4) and AAAA (IPv6) records. If either lookup times out, the script can fail during DNS resolution before it attempts the TCP connection. This behavior applies to raw TCP connections from the transaction script and is separate from Chromium page loading.

You can run dig A <FQDN> for IPv4 OR dig AAAA <FQDN> for IPv6 to check if either of the lookup times out. If either lookup times out, replace the hostname with the known working IP address:

const sock = await net.connect(21, '192.0.2.10');

Replace 192.0.2.10 with the IP address for your target. This behavior does not mean that every FQDN target must have both A and AAAA records. The failure occurs when a lookup times out.

Symptom	Likely cause	Recommended action
getaddrinfo EAI_AGAIN from net.connect() with an FQDN	An A (IPv4) or AAAA (IPv6) lookup timed out before the script attempted the raw TCP connection	Use the known working IP address directly, or verify that both lookups return cleanly
Direct IP connection works but FQDN connection fails	DNS resolution fails before the script attempts the raw TCP connection	Treat this as a DNS resolution issue, not proof that the TCP service is unavailable

If your transaction script fails with getaddrinfo EAI_AGAIN, first check whether the script calls net.connect() with a hostname. If the target works over IPv4 or IPv6 but the other lookup times out, update the script to use the working IP address instead of the hostname.

Sending Data

To send data over the socket connection, first assign the result of net.connect to a variable:

let socket = await net.connect(80, '1.1.1.1');

Then, use the write or writeAll methods to send data over the socket:

await socket.writeAll('GET / HTTP/1.1\r\n\r\n');

To read from the socket, use the read or readAll methods:

const response = await socket.readAll();

Example GET Request

In the following example, notice that first the net module is imported. Then, after net.connect is called, data is sent and received over the socket, using write and read:

import {net} from 'thousandeyes';

runScript();

async function runScript() {
   let host = 'newyork.wan.the-acme-corporation.net';
   let port = 80;
   let requestBody =
`GET / HTTP/1.1
Host: ${host}
User-Agent: thousandeyes-transaction
`

  let client = await net.connect(port, host);
  await client.write(requestBody);
  let response = await client.read();

  console.log(response.toString());
  
};

Advanced Examples

For additional examples, see the public repository of ThousandEyes transaction scripts.

Example: IMAP Login

In the following example, you establish a TCP connection; then send IMAP credentials over the connection you've created:

let host = 'box.the-acme-corporation.net';
   let port = 993;
   let imap_password = credentials.get('[e-mail]');

   const sock = await net.connectTls(port, host, {
       minVersion: 'TLSv1.2',
   });

   sock.setEncoding('utf8');

   let imap_commands = [
       `? LOGIN [e-mail] ${imap_password}\n`,
       `? SELECT Inbox\n`,
       `? FETCH 1:1 RFC822\n`,
   ]

   for(var i=0; i < imap_commands.length; i++){
       let command = imap_commands[i];
       await sock.writeAll(command);
     
       // Make driver sleep for .5 seconds
       await driver.sleep(500);
       console.log(command);
       let response = await sock.read();
       console.log(response);
   }