happy-eyeballs

Happy Eyeballs

This package patches http(s).Agent to implement "happy eyeballs" (rfc8305), a standard published by the IETF.

It improves client performance and reliability by trying concurrently trying multiple ip addresses for a given host name. See Explanation for more detail.

$3

``
npm i --save-dev happy-eyeballs
`

`
yarn add --dev happy-eyeballs
`

$3

To use this library, simply import

`ts
import 'happy-eyeballs/eye-patch';
`

or

`js
require('happy-eyeballs/eye-patch')
`

to the top of your .js/.ts entry file.

Note: this will replace http.Agent.prototype.createConnection and https.Agent.prototype.createConnection, but it tries to preserve existing functionality as much as possible.

$3

If you want to be more explicit, you can explicitly patch the http(s).Agent:

`ts
import { patch } from 'happy-eyeballs';
import { Agent as HttpAgent } from 'http';
import { Agent as HttpsAgent } from 'https';

patch(HttpAgent, {delay: 300});
patch(HttpsAgent, {delay: 300});
`

Although, this is exactly what the import 'happy-eyeballs/eye-patch'; does anyway.

Note that delay refers to the delay before attempting the next addresses. This is the delay browsers use.

Later you can unpatch, which will undo the last patch:

`ts
unpatch([HttpsAgent, HttpAgent])
`

or reset to the original values of an agent:

`ts
reset([HttpsAgent, HttpAgent])
`

Also, note that the default is HttpAgent and HttpsAgent, so this has the same effect as

`ts
reset()
`

And that goes for patch and unpatch too.

You could also implement your own agent and replace the createConnection method:

`ts
import { createConnection } from 'happy-eyeballs';
import { Agent as HttpAgent } from 'http';
import { Agent as HttpsAgent } from 'https';

export class MyHttpAgent extends HttpAgent {
createConnection = createConnection;
delay = 250;
}

export class MyHttpsAgent extends HttpsAgent {
createConnection = createConnection;
delay = 250;
}
``

This does basically the same thing as the previous examples though.

$3

Essentially, the algorithm amounts to this:

1. Receive a hostname
2. Have we connected to this host before?
* If yes:
* Try the family (Ipv4 or IPv6) of last successful connection if we have connected to this host before
* If connection is not successful within 300ms, proceed to next step
* If no: proceed to next step.
3. Did the DNS lookup return both IPv4 and IPv6 addresses?
* If yes: try, both addresses concurrently until all have been tried
* If no: just try the address of the existent family
4. Proceed with each address in chain, trying both families concurrently until either:
*. A connection is made
*. All connection attempts time out
*. All connection attempt fail
5. If no connection was successful, return error of the first connection attempt or a "time out" error if all connections timed out