Interplay between reservationConcurrency and discoverRelays

[2color]

While experimenting with circuitRelayTransport configuration, I found that js-libp2p will not to create a reservation with the following configuration, even though the peer is already connected to circuit relay peer:

circuitRelayTransport({
    discoverRelays: 0,
    reservationConcurrency: 1
}),

Only setting discoverPeers to 1, results in a reservation.

circuitRelayTransport({
    discoverRelays: 1,
    reservationConcurrency: 1
}),

What's weird is if I connect to two relays manually (via a bootstrap list), set discoverRelays: 2 and reservationConcurrency: 1, the browser peer will get a reservations with both. So the logic seems to be the "highest of the two values":

const libp2p = await createLibp2p({
    metrics: devToolsMetrics(),
    addresses: {
      listen: [
        // 👇 Listen for webRTC connection
        '/webrtc',
      ],
    },
    transports: [
      webSockets({
        // Allow all WebSocket connections inclusing without TLS
        filter: filters.all,
      }),
      webTransport(),
      webRTC(),
      // // 👇 Required to create circuit relay reservations in order to hole punch browser-to-browser WebRTC connections
      circuitRelayTransport({
        discoverRelays: 2,
        reservationConcurrency: 1
      }),
    ],
    connectionEncryption: [noise()],
    streamMuxers: [yamux()],
    connectionGater: {
      // Allow private addresses for local testing
      denyDialMultiaddr: async () => false,
    },
    peerDiscovery: [
      bootstrap({
        list: [
          '/ip4/127.0.0.1/tcp/9001/ws/p2p/12D3KooWA7QLGSgDNB3NdYmHEdEDU3FHv3PzjW9mHsEJst4e2Rqi',
          '/ip4/127.0.0.1/tcp/9003/ws/p2p/12D3KooWDJ9J5PVyxgqKg93wqaA7azr525YWakQGeYS9hRvZyCK6'
        ],
      }),
    ],
    services: {
      pubsub: gossipsub(),
      identify: identify(),
    },
  })

---

Is this a bug? or expected behaviour? It seems to me that setting reservationConcurrency: 1 should limit the reservations.

[achingbrain]

These settings control different things.

discoverRelays means "Make reservations on this many relays". So setting it to 0 means you won't make any reservations, setting it to 100 means you'll make 100 reservations.

reservationConcurrency means "Try to make this many reservations at the same time". So setting it to 1 will make reservations on relays sequentially (bad if you encounter a relay that's slow to respond), setting it to a greater number will make that many reservation attempts in parallel, but the total number of reservations you'll make is still controlled by discoverRelays.