[Add] Neo N3 P2P peer session: framing, handshake, connect, and keep-alive

[cschuchardt88]

Summary

Adds a Neo N3–compatible P2P session layer so this platform can speak the same TCP wire protocol as neo-project/neo Network/P2P: message framing, node capabilities, Version/Verack handshake, listen + outbound connect, and Ping/Pong with idle timeouts.

Also wires store/backup config defaults into the hosting environment provider and adds RandomNumberFactory as a public SDK utility (used for nonces and available to consumers).

Motivation

Node hosting needs real peer connectivity. This PR lands the connection + handshake foundation (aligned with Neo’s Message, RemoteNode handshake, and capability layout) without implementing full chain sync yet.

What’s included

1. Protocol framing (ProtocolMessage)

Wire layout matches Neo N3:

[Flags:1][Command:1][VarSize length][payload]

API	Behavior
TryRead	Returns 0 if incomplete, byte count if complete, throws if payload > PayloadMaxSize (0x02000000)
Create	Builds outbound frames; LZ4 compress only for Neo-allowed commands when savings ≥ 64 bytes and payload > 128
ToArray(allowCompression)	Can force uncompressed send (pre-handshake / remote disable-compression)

2. Version & capabilities

• VersionMessage — network, version, timestamp, nonce, user agent, capabilities
• Capability hierarchy with single type-byte ownership (DeserializeFrom + DeserializeWithoutType / SerializeWithoutType), matching Neo
• Types: TcpServer (port), FullNode (start height), ArchivalNode, DisableCompression
• Duplicate capability check by type; max 32 capabilities
• Fix: array GetSerializedSize now sums sizes correctly (no length × sum)

3. Peer connection (NodeConnection)

• Socket → Pipe → frame parse loop (TryReadFrame)
• ConnectAsync outbound factory
• WaitForHandshakeAsync
• SendAsync with optional compression
• Events: HandshakeCompleted, MessageReceived (post-handshake), Disconnected
• LocalBlockIndex / RemoteLastBlockIndex for Ping/Pong height

4. Handshake (NodeHandshake)

Pure state machine (testable without I/O):

WaitingForVersion → (Version OK) → send Verack → WaitingForVerack → Ready

Rejects: wrong command order, network mismatch, self-nonce, handshake messages after Ready.

5. Listener (NodeServerListener)

• TCP accept with ReuseAddress, default backlog 128
• No named mutex (OS bind exclusivity only)
• Shared node nonce + local capabilities (FullNode + TcpServer)
• Tracks inbound and outbound peers; removes on Disconnected
• ConnectAsync for outbound dial using this node’s identity

6. Keep-alive (Neo-style)

Timer	Value	Action
Handshake	10s	Close if not Ready
Receive idle	60s	Close
Keep-alive tick	30s	Evaluate timeouts / ping
Send idle	1 min	Send Ping

• Auto Pong on Ping (same nonce, local height)
• PingMessage payload: LastBlockIndex, Timestamp, Nonce

7. Hosting / config

• BlockchainStoreNames config keys
• Env defaults for store path, create-if-missing, backup path/max backups
• RandomNumberFactory public SDK surface

8. Tests

Area	Coverage
UT_ProtocolMessage	Incomplete frames, trailing bytes, VarSize, Create/compress round-trip
UT_NodeCapabilityMessage	Per-capability serialize/deserialize
UT_VersionMessage	Capabilities, duplicates, Version inside ProtocolMessage
UT_NodeHandshake	Happy path + protocol violations
UT_NodeConnection	Frame consumption on sequences
UT_NodeConnectionConnect / UT_NodeServerListener	Loopback accept, outbound connect, client cleanup, Ping/Pong
UT_PingMessage	Payload + frame round-trip
TestUtilities	GetFreeTcpPort, WaitForAsync

Commits

1. Added environment variables
2. Added Version Network Message Class
3. Fixed Version Message tests
4. Added Node Server and Node Connection Classes
5. Add Neo N3 P2P framing, handshake, and keep-alive for node connections

Out of scope (follow-ups)

• Peer discovery (GetAddr / Addr, seed list)
• Sync messages (GetHeaders, Headers, Inv, GetData, Block, Tx, …)
• Max peers / connect queue / per-IP limits
• Relay, mempool, bloom filters
• Live smoke test against a public Neo seed

Test plan

• dotnet test tests/Neo.Core.Tests/Neo.Core.Tests.csproj --filter "FullyQualifiedName~Net"
• Framing incomplete/complete/oversize behavior
• Capability type byte not double-read
• Listen + accept + disconnect tracking
• Outbound connect
• Version/Verack
• Ping/Pong + idle timeouts
• Full protocol / chain sync (future PRs)

Compatibility notes

• Intended to interoperate with Neo N3 P2P framing + handshake + ping
• Compression policy matches Neo’s command list and thresholds
• Until remote Version is known (or peer disables compression), sends uncompressed frames

[cschuchardt88]

Reopening to resync head after CI flake-fix push (fork tip 17b69f9; PR was stuck on 52e5aa8).