resolve-alpn

What is resolve-alpn?

The resolve-alpn npm package is designed to help Node.js applications determine the Application-Layer Protocol Negotiation (ALPN) protocol that a server supports. ALPN is a TLS extension used for negotiating which protocol should be performed over a secure connection. This is particularly useful for applications that need to decide between different protocols like HTTP/2 or HTTP/1.1 when connecting to a server.

What are resolve-alpn's main functionalities?

Determining ALPN protocol

This feature allows developers to programmatically determine the ALPN protocol supported by a server. The code sample demonstrates how to use the resolve-alpn package to check which ALPN protocol ('http/1.1', 'h2', etc.) a server supports by specifying the host and port.

const resolveAlpn = require('resolve-alpn');

resolveAlpn({
  host: 'example.com',
  port: 443
}).then((negotiatedProtocol) => {
  console.log(negotiatedProtocol);
}).catch((error) => {
  console.error(error);
});

Other packages similar to resolve-alpn

http2-wrapper

While not exclusively focused on ALPN negotiation, http2-wrapper includes functionality for automatically negotiating HTTP/2 connections using ALPN. It provides a higher-level API for making HTTP requests over either HTTP/1.1 or HTTP/2, depending on server support. This makes it a more comprehensive solution for HTTP communication compared to resolve-alpn, which is more narrowly focused on the ALPN negotiation process.

README

resolve-alpn

API

resolveALPN(options)

Returns an object with an alpnProtocol property. The socket property may be also present.

const result = await resolveALPN({
	host: 'nghttp2.org',
	ALPNProtocols: ['h2', 'http/1.1']
});

console.log(result); // {alpnProtocol: 'h2'}

options

Same as TLS options.

options.resolveSocket

By default, the socket gets destroyed and the promise resolves.
If you set this to true, it will return the socket in a socket property.

const result = await resolveALPN({
	host: 'nghttp2.org',
	ALPNProtocols: ['h2', 'http/1.1'],
	resolveSocket: true
});

console.log(result); // {alpnProtocol: 'h2', socket: tls.TLSSocket}

// Remember to close the socket!
result.socket.end();

License

MIT