Add Gossipsub direct peer support

[flcl42]

Summary

• add reciprocal direct-peer configuration and periodic reconnection
• forward valid subscribed-topic messages directly while excluding direct peers from mesh, fanout, and gossip selection
• reject direct-peer GRAFTs with PRUNE and cover delivery, mesh isolation, startup dialing, and configuration validation

Validation

• Pubsub protocol unit tests

[Copilot]

Pull request overview

Adds Gossipsub “direct peer” support to the pubsub router, enabling explicit peering (reciprocal direct connections) with special routing rules (direct forwarding + isolation from mesh/fanout/gossip).

Changes:

• Introduces direct-peer configuration (addresses + reconnect period) and validates configuration at router startup.
• Updates publish/forwarding logic to send subscribed-topic messages directly to configured direct peers while excluding them from mesh/fanout/gossip selection and graylisting behavior.
• Rejects direct-peer GRAFTs with PRUNE and adds unit tests covering delivery, mesh isolation, startup dialing, and configuration validation.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/libp2p/Libp2p.Protocols.Pubsub/PubSubSettings.cs	Adds DirectPeers + DirectConnectPeriod settings for explicit peering and reconnect cadence.
src/libp2p/Libp2p.Protocols.Pubsub/PubsubRouter.Topics.cs	Publishes directly to subscribed direct peers and excludes direct peers from fanout selection/publish paths.
src/libp2p/Libp2p.Protocols.Pubsub/PubsubRouter.Rpc.cs	Forwards valid messages to direct peers, skips graylist for direct peers, and rejects direct-peer GRAFT with PRUNE.
src/libp2p/Libp2p.Protocols.Pubsub/PubsubRouter.cs	Builds direct-peer map, discovers configured direct peers at startup, and periodically reconnects disconnected direct peers.
src/libp2p/Libp2p.Protocols.Pubsub.Tests/DirectPeersTests.cs	Adds tests for direct peer forwarding, mesh isolation, GRAFT rejection, startup dialing, and config validation.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Suppressed comments (1)

src/libp2p/Libp2p.Protocols.Pubsub/PubsubRouter.cs:177

• The ArgumentOutOfRangeException for DirectConnectPeriod uses nameof(settings) as the parameter name, which makes the exception less actionable for callers (it points at the whole settings object rather than the specific property).

        if (_settings.DirectConnectPeriod <= 0)
        {
            throw new ArgumentOutOfRangeException(nameof(settings), "DirectConnectPeriod must be positive.");
        }

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.

Suppressed comments (2)

Previously missed (2) — in code that hasn't changed since the last review.

src/libp2p/Libp2p.Protocols.Pubsub/PubSubSettings.cs:34

• The XML doc for DirectConnectPeriod doesn't state the units. Since the value is an int and used with AddMilliseconds(), it should explicitly document that this is milliseconds to avoid misconfiguration.

    /// <summary>
    /// Interval for reconnecting disconnected direct peers. Gossipsub recommends
    /// five minutes.
    /// </summary>
    public int DirectConnectPeriod { get; set; } = 5 * 60 * 1000;

src/libp2p/Libp2p.Protocols.Pubsub/PubsubRouter.cs:212

• Direct peer reconnect timing is currently driven by the LoopReconnect cadence (ReconnectionPeriod), which means DirectConnectPeriod won't be respected if ReconnectionPeriod is larger. Since ReconnectDirectPeers() already self-throttles via nextDirectConnectionAttempt, consider calling it from the heartbeat loop as well so the configured DirectConnectPeriod is honored independently.

        nextDirectConnectionAttempt = DateTime.UtcNow.AddMilliseconds(_settings.DirectConnectPeriod);

        _ = Task.Run(LoopHeartbeat, token);
        _ = Task.Run(LoopReconnect, token);

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.