[g175] multi: small G175 preparations

[ellemouton]

Here we:

• move the definition of the GossipVersion from the db package to the lnwire package.
• we also add a GossipMessage interface which all the gossip messages implement. This allows us to query the protocol that the message was gossiped on.
• we make our first use of this new interface in the discovery package in the rejectCache

[gemini-code-assist]

Summary of Changes

Hello @ellemouton, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces foundational changes to support multiple gossip protocol versions, specifically in preparation for the G175 update. It centralizes the definition of gossip protocol versions within the lnwire package and establishes a new GossipMessage interface. This interface is now implemented by all core gossip messages, enabling the system to differentiate and handle messages based on their protocol version. The discovery package's reject cache and the graph/db package's storage mechanisms have been updated to leverage this new versioning, ensuring proper segregation and processing of gossip data across different protocol iterations.

Highlights

• Gossip Version Centralization: The GossipVersion type and its associated constants (GossipVersion1, GossipVersion2) have been moved from the graph/db package to the lnwire package, centralizing the definition of gossip protocol versions.
• New GossipMessage Interface: A new GossipMessage interface has been introduced in lnwire, which includes a GossipVersion() method. All relevant gossip messages (AnnounceSignatures, ChannelAnnouncement, ChannelUpdate, NodeAnnouncement) now implement this interface, allowing for easy querying of the protocol version.
• Version-Aware Reject Cache: The rejectCache in the discovery package has been updated to include the GossipVersion in its keys. This ensures that rejected messages are distinguished by their protocol version, preventing a message rejected for one version from blocking a valid message for another.
• NodeAnnouncement Interface: A new NodeAnnouncement interface has been added to lnwire, and both NodeAnnouncement1 and NodeAnnouncement2 now implement it, along with the GossipMessage interface.
• Database Integration: All references to ProtocolV1 within the graph/db package (including migrations and the SQLStore) have been updated to use the new lnwire.GossipVersion1 constant, aligning the database layer with the centralized versioning.

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[gemini-code-assist]

Code Review

This pull request is a great step towards supporting G175. Moving GossipVersion to the lnwire package and introducing the GossipMessage interface are clean refactorings that will make it easier to handle multiple gossip protocol versions. The changes are applied consistently across the codebase. I have one suggestion to further improve the implementation in the discovery package to make it more robust for future protocol versions.

[bhandras]

LGTM 🎉🎉

[bitromortac]

LGTM ⚡