feat: dispatcher _buildConnector() method

[zdm]

This relates to...

#3486

Rationale

This patch allows to access buildConnector options in the DispatcherBase subclasses.
This will allows to create custom connect function in subclasses using buiildConnector options.

Changes

1. _buildConnector() protected method added to DispatcherBase.
2. buildConnector calls changed from direct use to use this._buildConnector() method.
3. helper function configureSocket() added. It sets socket no delay and keep alive based on passed options.

Features

It is too hard to make connect callback receive full list of connect options.
At least I have no idea how to implement it on current code base without deep refactoring.
This patch helps to solve this problem in dispatcher subclasses, that will be enough for most of developers.

Use case:

import Client from 'undici/dispatcher/client'
import { configureSocket } from 'undici/core/connect'

export default class extends Client {

  _buildConnector (buildOptions) {

    // create custom connector
    if (this.proxy) {
      return async (options, callback) => {
        const socket = await this._createSocket(buildOptions, options)

        callback(configureSocket(socket))
      }

    // or fallback to the default behavior
    } else {
      return super._buildConnector(buildOptions)
    }
  }
}

Bug Fixes

#3486

Breaking Changes and Deprecations

Status

• [x ] I have read and agreed to the Developer's Certificate of Origin
• Tested
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

[mcollina]

why is this needed?

[zdm]

This is needed if I want to create custom dispatcher and get access to buildConnector options (with resolved default values), please look at related issue.

[ronag]

I don't think this is a good idea...

[zdm]

Why nor? Do you have arguments?
"buildConnector" is used in subclasses constructor, why not provide this standard functionality as private method?
I think this is obvious