wait-port

What is wait-port?

The wait-port npm package is a utility that allows you to wait for a port on a host to become open. This is particularly useful in scenarios where you need to ensure that a service is up and running before proceeding with the next steps in your application or script. It can be used programmatically within your Node.js applications or as a command-line tool.

What are wait-port's main functionalities?

Waiting for a port programmatically

This feature allows you to wait for a specific port on a host to become open by using the wait-port package programmatically within your Node.js application. The `waitPort` function returns a promise that resolves to a boolean indicating whether the port opened before the timeout.

const waitPort = require('wait-port');

const params = {
  host: 'localhost',
  port: 3000
};

waitPort(params).then((open) => {
  if(open) console.log('The port is now open!');
  else console.log('The port did not open before the timeout.');
});

Using wait-port as a CLI tool

wait-port can also be used as a command-line tool. This example demonstrates how to wait for port 3000 on localhost to become open by using wait-port in the terminal. It's useful for scripting and automation tasks outside of Node.js applications.

wait-port --host localhost --port 3000

Other packages similar to wait-port

wait-on

wait-on is a similar package that provides more general functionality for waiting on resources to become available. It supports waiting on file system paths, HTTP(S) resources, and TCP ports. Compared to wait-port, wait-on offers a broader range of features but with a similar core functionality of waiting for ports.

tcp-port-used

tcp-port-used is a package that allows you to check if a TCP port is already in use. It can be used to wait for a port to become free or to check if a port is currently occupied. While it offers similar functionality for checking port status, it doesn't provide a built-in mechanism to wait for a port to open, making it slightly less convenient for scenarios where waiting is required.

README

wait-port

Simple binary to wait for a port to open. Useful for docker-compose and general server side activities.

• Usage
  • Parameters
  • Error Codes
• API
• Developer Guide
  • Debugging
  • Testing
  • Testing the CLI
  • Releasing
  • Timeouts

Usage

To wait for a port to open, just use:

$ wait-port localhost:3000

To wait for a port to open, but limit to a certain timeout, use:

$ wait-port -t 10000 localhost:3000

Parameters

The following parameters are accepted:

Parameter	Usage
<target>	Required. The target to test for. Can be just a port, a colon and port (as one would use with httpie or host and port. Examples: 8080, :3000, 127.0.0.1:443.
--timeout, -t	Optional. Timeout (in milliseconds).

Error Codes

The following error codes are returned:

Code	Meaning
0	The specified port on the host is accepting connections.
1	A timeout occured waiting for the port to open.
2	Un unknown error occured waiting for the port to open. The program cannot establish whether the port is open or not.

API

You can use wait-port programmatically:

const waitPort = require('wait-port');

const params = {
  host: 'google.com',
  port: 443,
};

waitPort(params)
  .then((open) => {
    if (open) console.log('The port is now open!');
    else console.log('The port did not open before the timeout...');
  })
  .catch((err) => {
    console.err(`An unknown error occured while waiting for the port: ${err}`);
  });

The CLI is a very shallow wrapper around this function. The params object takes the following parameters:

CLI Parameter	API Parameter	Notes
<target>	host	Optional. Defaults to localhost.
<target>	port	Required. Port to wait for.
--timeout, -t	timeout	Optional. Defaults to 0. Timeout (in milliseconds). If 0, then the operation will never timeout.

Developer Guide

This module uses:

| Name | Usage | | commander.js | Utility for building commandline apps. | | debug | Utility for debug output. | R mocha / nyc | Test runner / coverage. |

Debugging

This module use debug for debug output. Set DEBUG=wait-port to see detailed diagnostic information:

DEBUG=wait-port wait-for -t 10000 localhost:6234

This will also work for any code which uses the API.

Testing

Run unit tests with npm test. Coverage is reported to artifacts/coverage.

Debug unit tests with npm run debug. Add a debugger statement to the line you are interested in, and consider limiting scope with .only.

Testing the CLI

Don't install the package to test the CLI. Instead, in the project folder run npm link. Now go to whatever folder you want to use the module in and run npm link wait-port. It will symlink the package and binary. See npm link for more details.

Releasing

Kick out a new release with:

npm version patch # or minor/major
git push --tags
npm publish

Timeouts

The timeout option for waitPort is used terminate attempts to open the socket after a certain amount of time has passed. Please note that operations can take significantly longer than the timeout. For example:

const promise = waitPort({ port: 9000, interval: 10000 }, 2000);

In this case, the socket will only attempt to connect every ten seconds. So on the first iteration, the timeout is not reached, then another iteration will be scheduled for after ten seconds, meaning the timeout will happen eight seconds later than one might expect.

The waitPort promise may take up to interval milliseconds greater than timeout to resolve.

TODO

Some more tasks to complete:

• Support validation of the timeout commandline parameter
• Add an interval commandline parameter
• Document how to use the API
• Package with pkg
• Diagnostic output with debug
• Finalise output format, colourise.
• Support output on the interval (with an -o option).
• NPM badge