dependency injection during boot time

[pgte]

Some libp2p modules require or would benefit from knowing the peerId and other values. It happens that, at the time the declarative options are created, the peerId is not yet known. As an example, libp2p-websocket-star would require the PeerId object to prevent spoofing. It happens that this value is not known before boot.

Here I propose a modules definition form that is backwards compatible and can be summed up to:

If a module is a function, libp2p assumes it is a constructor and executes that function, which should return a the module instance.

This would allow to declare config like this:

{
  modules: {
    transport: [
      wrtcStar // instance,
      ({peerId}) => new WSStar({id: peerId})
    ]
  }
}

[pgte]

One problem with this setting is the discovery. Usually, a discovery module is extracted from the transport module, something like this:

const wstar = new WRTCStar()
{
  modules: {
    transport: [
      wstar
    ],
    discovery: [ wstar.discovery ]
  }
}

One option to mitigate this would be to implicitely add the discovery module if the transport instance contains a .discovery attribute.

Another workaround would be to cache it like this:

let wsstar // caches the WSStar object instance
const createWSStar = ({peerId}) => (wsstar ? wsstar : wsstar = new WSStar({id: peerId}))

const libp2pOptions = {
  modules: {
    transport: [
      createWSStar
    ],
    discovery: [
      (options) => createWSStar(options).discovery
    ]
  }
}

Thoughts?

[pgte]

/cc @diasdavid @mkg20001

[pgte]

(Probably should replace peerId with peerInfo, but not really relevant for the overall discussion of the DI method here).

[dryajov]

Another approach might be passing an instance of swarm to the transport during initialization, the peerId/peerInfo can be extracted from it. We already do that for DHT and Circuit.

[daviddias]

Let's continue evaluating this, I need to think more about it but I am in the same page that we need DI.

[dryajov]

overall, 👍 for DI, should make things a lot more testable and such!

[mkg20001]

Currently I'm using a .setSwarm(swarm) function after transport creation to hack around this limitation in libp2p/js-libp2p-websocket-star#43
Something similar could be implemented. Like if (typeof transport._setSwarm === 'function') transport._setSwarm(swarm) after transport creation in libp2p.
Or even better: Just use the currently mostly-unused option object and add the swarm there