Support Gossipsub partial messages

[flcl42]

Summary

• provide an opt-in application API for the Gossipsub v1.3 Partial Messages extension
• advertise capabilities only on v1.3 streams and honor each peer's subscription flags
• forward application-defined partial payloads without retaining peer-initiated state
• replace eligible IHAVE gossip with application callbacks for partial-message recipients

Validation

• Pubsub protocol unit tests

[Copilot]

Pull request overview

This PR adds opt-in support for the Gossipsub v1.3 Partial Messages extension to the Pubsub router, exposing a topic-level application API to send/receive partial payloads and integrating capability advertisement and per-peer gating into subscription handling and gossip flow.

Changes:

• Introduces IPartialMessagesTopic + PartialMessage/PartialMessagesTopicOptions and wires partial-message delivery through Topic/PubsubRouter.
• Adds router support for advertising/processing the Partial Messages extension (including per-topic subscription flags and a new OnPartialGossip callback path).
• Adds unit tests covering opt-in requirements and basic advertisement/gating behavior.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/libp2p/Libp2p.Protocols.Pubsub/Topic.cs	Implements IPartialMessagesTopic, wires partial-message events, adds publish/send APIs for partial payloads.
src/libp2p/Libp2p.Protocols.Pubsub/PubSubSettings.cs	Adds EnablePartialMessages opt-in setting.
src/libp2p/Libp2p.Protocols.Pubsub/PubsubRouter.Topics.cs	Adds GetPartialMessagesTopic, subscription capability flags, and partial publish/send routing APIs.
src/libp2p/Libp2p.Protocols.Pubsub/PubsubRouter.Rpc.cs	Parses incoming partial-message extension payloads and tracks per-peer partial subscription flags.
src/libp2p/Libp2p.Protocols.Pubsub/PubsubRouter.cs	Adds extension advertisement and heartbeat logic to swap some IHAVE gossip for OnPartialGossip callbacks.
src/libp2p/Libp2p.Protocols.Pubsub/PartialMessage.cs	Adds PartialMessage and PartialMessagesTopicOptions public API types.
src/libp2p/Libp2p.Protocols.Pubsub/IPartialMessagesTopic.cs	Adds the public partial-messages topic interface.
src/libp2p/Libp2p.Protocols.Pubsub.Tests/PartialMessagesTests.cs	Adds unit tests for opt-in, advertisement, and per-peer gating.

Suppressed comments (1)

src/libp2p/Libp2p.Protocols.Pubsub/Topic.cs:82

• Topic.Unsubscribe() currently calls router.Unsubscribe() only when IsSubscribed is false, which prevents unsubscribing when the topic is actually subscribed and can cause subscription state to get stuck.

    public void Unsubscribe()
    {
        if (!IsSubscribed) router.Unsubscribe(topicName);
    }

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[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Suppressed comments (3)

src/libp2p/Libp2p.Protocols.Pubsub/Topic.cs:82

• Topic.Unsubscribe() currently calls router.Unsubscribe(topicName) only when the topic is not subscribed, which makes Unsubscribe a no-op for subscribed topics (and can trigger an unnecessary unsubscribe call when already unsubscribed). Flip the condition so subscribed topics are actually unsubscribed.

    public void Unsubscribe()
    {
        if (!IsSubscribed) router.Unsubscribe(topicName);
    }

src/libp2p/Libp2p.Protocols.Pubsub/PubsubRouter.Topics.cs:64

• CreateSubscription() sets RequestsPartial/SupportsSendingPartial whenever partial messages are enabled and the local Topic has flags, but the resulting SubOpts are sent to all peers (including non-v1.3 streams) via OutboundConnection() and AnnounceSubscription(). This contradicts the PR description constraint to advertise capabilities only on v1.3 streams. Consider constructing per-peer subscription updates so these fields are only populated when sending over Gossipsub v1.3 (SupportsExtensions), otherwise leave them unset/false.

    private Rpc.Types.SubOpts CreateSubscription(string topicId, bool subscribe)
    {
        Rpc.Types.SubOpts subscription = new() { Subscribe = subscribe, Topicid = topicId };
        if (subscribe && _settings.EnablePartialMessages && topicState.TryGetValue(topicId, out Topic? topic))
        {
            subscription.RequestsPartial = topic.RequestsPartialMessages;
            subscription.SupportsSendingPartial = topic.SupportsSendingPartialMessages;
        }

src/libp2p/Libp2p.Protocols.Pubsub/PartialMessage.cs:42

• PartialMessagesTopicOptions uses the name SupportSendingPartialMessages, while other related APIs use SupportsSendingPartialMessages (plural) (e.g., IPartialMessagesTopic.SupportsSendingPartialMessages). This inconsistency makes the public API harder to discover and can lead to confusion. Consider renaming the option to SupportsSendingPartialMessages while the API is still new.

    /// <summary>
    /// Signals that this topic can send partial data and receive parts metadata.
    /// </summary>
    public bool SupportSendingPartialMessages { get; init; }

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Suppressed comments (2)

Previously missed (1) — in code that hasn't changed since the last review.

src/libp2p/Libp2p.Protocols.Pubsub/Topic.cs:82

• Topic.Unsubscribe() calls router.Unsubscribe() when IsSubscribed is false. This is inverted logic and can trigger KeyNotFoundException in PubsubRouter.Unsubscribe(topicId) (it indexes fPeers[topicId]) when called on an already-unsubscribed topic.

    public void Unsubscribe()
    {
        if (!IsSubscribed) router.Unsubscribe(topicName);
    }

src/libp2p/Libp2p.Protocols.Pubsub/PubsubRouter.Rpc.cs:254

• Partial-messages subscription flags are not being honored as sent by the peer: SupportsSendingPartialMessages is stored as (RequestsPartial || SupportsSendingPartial). This causes the router to treat a peer that only set RequestsPartial as also supporting the metadata flow, and may send PartsMetadata contrary to the peer's advertised capability.

                if (_settings.EnablePartialMessages && state.SupportsPartialMessagesExtension)
                {
                    bool requestsPartialMessages = sub.RequestsPartial;
                    state.UpdatePartialMessagesSubscription(
                        sub.Topicid,
                        requestsPartialMessages,
                        sub.SupportsSendingPartial);
                }

[Copilot]

Pull request overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Suppressed comments (1)

src/libp2p/Libp2p.Protocols.Pubsub/Topic.cs:37

• OnRouterPartialMessage forwards partial payloads even when the topic is not subscribed and even when the topic was never configured for partial messages. This makes partial-message delivery inconsistent with OnRouterMessage and undermines the intended opt-in behavior (topics created via GetTopic can still receive partial messages if the event is hooked via an interface cast). Gate partial-message delivery on IsSubscribed and on the topic having partial-message capabilities enabled.

    private void OnRouterPartialMessage(string topicName, PeerId peerId, PartialMessage message)
    {
        if (this.topicName != topicName)
        {
            return;
        }