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, connect = tls.connect)

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

const result = await resolveALPN({
	host: 'nghttp2.org',
	port: 443,
	ALPNProtocols: ['h2', 'http/1.1'],
	servername: 'nghttp2.org'
});

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

Note: While the servername option is not required in this case, many other servers do. It's best practice to set it anyway.

Note: If the socket times out, the promise will resolve and result.timeout will be set to true.

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',
	port: 443,
	ALPNProtocols: ['h2', 'http/1.1'],
	servername: 'nghttp2.org',
	resolveSocket: true
});

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

// Remember to destroy the socket if you don't use it!
result.socket.destroy();

connect

Type: Function<TLSSocket> | AsyncFunction<TLSSocket>
Default: tls.connect

Note: No matter which function is used (synchronous or asynchronous), it must accept a callback function as a second argument. The callback function gets executed when the socket has successfully connected.

License

MIT