chore: Improve peer persistence and bootnode loading

[s-h-ubham]

Title

network/server: persist only active peers to last_peers.json; server: load custom bootnodes from genesis params and merge with external sources

Context

Two related issues were observed in production-like setups:

• Some nodes occasionally persisted inactive peers to last_peers.json, causing them to try reconnecting to dead addresses after restart.
• For custom networks, even if params.bootnodes were present in genesis.json, the node required an adjacent bootnode.json or --bootnodes file to start. Operators expected params.bootnodes in custom genesis to be honored, similar to mainnet/testnet.

Changes

1. Persist only active peers to last_peers.json

• Problem: Peers() returned all entries in the in-memory s.peers map without checking whether they’re still connected. During shutdown or disconnect races, stale entries could be written to last_peers.json.
• Fix: Peers() now filters by live connectedness (network.Connected) before returning the list used by Close() for persistence.
• Impact: last_peers.json now contains only peers confirmed to be connected at persistence time, preventing invalid reconnect attempts after restart.

2. Load bootnodes from custom genesis params and merge

• Previous behavior:
  • mainnet/testnet: bootnodes loaded from the embedded chain config (works).
  • custom: ignored params.bootnodes in genesis.json; only looked for adjacent bootnode.json (node.p2p.staticNodes) or --bootnodes <file>.
• New behavior for custom networks:
  • Also read genesis.params.bootnodes (if present).
  • Merge order (deduped):
    • genesis.params.bootnodes
    • adjacent bootnode.json (node.p2p.staticNodes)
    • --bootnodes <file> with schema { "bootnodes": ["..."] }
  • If, after merging, no bootnodes are found, the error message now clearly suggests all accepted sources.
• Impact: Operators can embed bootnodes directly in custom genesis.json without needing a separate file or flag. External sources still work and are merged.

Files Touched

• network/server.go
  • Filter peers by live connectedness in Peers() before persisting.
• command/server/init.go
  • In getBootnodeConfig(), for custom networks, include genesis.Params.Bootnodes and merge with adjacent bootnode.json and --bootnodes file. Improved error message.

Why This Is Safe

• The connectedness check is a fast state lookup; locking semantics unchanged.
• Bootnode merging is additive and deduplicated. Existing mainnet/testnet behavior is preserved.
• Error messaging now guides operators to all valid sources.

Testing

• Peers persistence:
  • Start 5 nodes; establish connections.
  • Stop a peer; quickly stop another node to induce a tight window.
  • Inspect libp2p/last_peers.json on the stopped node:
    • Before: could include the disconnected peer.
    • After: contains only peers with Connected state at the time of persistence.
  • Restart using last_peers.json and verify successful reconnects.
• Bootnodes loading (custom):
  • Case A: only params.bootnodes in genesis.json → node starts and dials bootnodes.
  • Case B: only adjacent bootnode.json (staticNodes) → node starts and dials bootnodes.
  • Case C: both → merged set (no duplicates) is used.
  • Case D: --bootnodes file provided → merged with above (no duplicates).
  • Case E: none available → clear error instructs accepted sources.

Backward Compatibility

• No breaking flags or config changes.
• mainnet/testnet flows unchanged.
• Custom networks gain support for params.bootnodes while keeping existing external file/flag paths.

Operational Guidance

• For custom networks, you can now:
  • Embed bootnodes in genesis.json under params.bootnodes, and/or
  • Keep using adjacent bootnode.json and/or --bootnodes <file> at runtime.
• For built-in networks (mainnet/testnet), continue using the embedded list, optionally extending via --bootnodes <file> if needed.