Allow changing the tracker mode dynamically at runtime

[josecelano]

Relates to: #488

Recently I was working on this issue:

• Overhaul tracker keys in torrents and magnet links #488

I assumed that the Tracker mode can't be changed at runtime. Currently, the tracker mode can only be changed when the services are deployed.

Changing the tracker mode when the services are deployed

• Both services the Tracker and the Index are deployed at the same time.
• The Index depends on the Tracker, so the Tracker must be deployed first.
• The Tracker configuration is manually added to the Index when it's deployed and not changed dynamically.
• The only way to change the Tracker mode is to restart both services simultaneously. This means restarting the tracker with the new mode and restarting the index with the new tracker configuration.

It'd be nice to allow changing the tracker mode at runtime without restarting the Index.

Changing the tracker mode dynamically at runtime

• The tracker mode option is removed from the tracker configuration in the index.
• The Index uses a tracker endpoint to get its mode.
• The index can use a cached value for the tracker mode (expiration could be configurable).
• The tracker can change its mode manually or dynamically without the need to restart manually the Index.

TrackeMode struct:

pub enum TrackerMode {
    // todo: use https://crates.io/crates/torrust-tracker-primitives
    /// Will track every new info hash and serve every peer.
    Public,
    /// Will only serve authenticated peers.
    Private,
    /// Will only track whitelisted info hashes.
    Whitelisted,
    /// Will only track whitelisted info hashes and serve authenticated peers.
    PrivateWhitelisted,
}

Index config file:

[tracker]
url = "udp://localhost:6969"
mode = "Public"
api_url = "http://localhost:1212"
token = "MyAccessToken"
token_valid_seconds = 7257600

For both whitelisted modes (Whitelisted, Whitelisted) there is no problem because the Index always whitelist the torrent when a new torrent is uploaded regardless of the tracker mode. And it's removed from the whitelist when the torrent is deleted.

Changing from private modes (Private and PrivateWhitelisted) to public modes (Public and Whitelisted) is not a problem. If the user downloads a torrent with a tracker key and the tracker is public, the tracker just will ignore the key.

The problem is when the Tracker switches from public (open) to private (close) modes. In that case, some downloaded torrents may not work if they are downloaded before the Index detects that the tracker configuration has changed.

I do not know how useful would be this feature. I guess most Index steak to one mode. And even if the mode changes I don't think that would be very often.

What do you think @da2ce7 @WarmBeer?

Maybe It could make sense if we allow more than one associated tracker or tracker can be associated dinamically.

cc @torrust/torrustaceans

[josecelano]

I'm not going to include this feature in the roadmap because it hasn't received any feedback.