Summary

Add support for running both discv4 and discv5 discovery protocols simultaneously, sharing a single unified PeerTable.

Motivation

• discv5 is the newer discovery protocol with better security and features
• Transitioning requires supporting both protocols during the migration period
• A unified PeerTable allows peers discovered via either protocol to be used interchangeably

Proposed Changes

Architecture

• Two separate discovery servers sharing one unified PeerTable
• Separate UDP ports: discv4 on 30303 (default), discv5 on 30304 (default)
• Runtime control via CLI flags (not just compile-time feature flags)

New CLI Options

--discovery.discv4       Enable discv4 (default: true)
--discovery.discv5       Enable discv5 (default: false)
--discovery.discv5-port  UDP port for discv5 (default: 30304)

Unified PeerTable

• Merge discv4/peer_table.rs and discv5/peer_table.rs into a single peer_table.rs
• Use generic pending_ping_id: Option<Bytes> instead of protocol-specific fields
• Keep session: Option<Session> for discv5 encryption sessions

Files to Modify

• crates/networking/p2p/peer_table.rs - CREATE unified module
• crates/networking/p2p/network.rs - spawn servers based on config
• crates/networking/p2p/discv4/server.rs - use unified peer_table
• crates/networking/p2p/discv5/server.rs - use unified peer_table
• cmd/ethrex/cli.rs - add discovery CLI flags

Testing

• cargo build -p ethrex-p2p - builds with discv4 only
• cargo build -p ethrex-p2p --features experimental-discv5 - builds with both
• cargo test -p ethrex-p2p - run existing tests
• Manual: start node with both protocols, verify peer discovery works

Related

• Builds on discv5 handshake handling work (current branch: discv5-server-handshake-handling)