Add some comments of P2P

src/neo/Network/P2P/LocalNode.cs

@@ -64,6 +64,10 @@ private void BroadcastMessage(MessageCommand command, ISerializable payload = nu
             BroadcastMessage(Message.Create(command, payload));
         }
 
+        /// <summary>
+        /// Broadcast a message to all connected nodes.
+        /// </summary>
+        /// <param name="message">The message to be broadcasted.</param>
         private void BroadcastMessage(Message message)
         {
             Connections.Tell(message);
@@ -127,6 +131,7 @@ public IEnumerable<IPEndPoint> GetUnconnectedPeers()
         /// Performs a BroadcastMessage with the command `MessageCommand.GetAddr`, which, eventually, tells all known connections
         /// If there are no connected peers it will try with the default, respecting MaxCountFromSeedList limit
         /// </summary>
+        /// <param name="count">The count of peers required</param>
         protected override void NeedMorePeers(int count)
         {
             count = Math.Max(count, MaxCountFromSeedList);
@@ -164,6 +169,12 @@ protected override void OnReceive(object message)
             }
         }
 
+        /// <summary>
+        /// There are three implementations of IInventory. Block, ConsensusPayload and Transaction.
+        /// For Transaction, it will tell Transaction to the actor of Consensus.
+        /// Otherwise, tell the inventory to the actor of Blockchain.
+        /// </summary>
+        /// <param name="inventory">The inventory to be relayed.</param>
         private void OnRelay(IInventory inventory)
         {
             if (inventory is Transaction transaction)

src/neo/Network/P2P/Message.cs

@@ -13,6 +13,10 @@ public class Message : ISerializable
         private const int CompressionMinSize = 128;
         private const int CompressionThreshold = 64;
 
+        /// <summary>
+        /// Flags that represents whether a message is compressed.
+        /// 0 for None, 1 for Compressed.
+        /// </summary>
         public MessageFlags Flags;
         public MessageCommand Command;
         public ISerializable Payload;

src/neo/Network/P2P/Peer.cs

@@ -37,8 +37,19 @@ private class WsConnected { public WebSocket Socket; public IPEndPoint Remote; p
 
         private static readonly HashSet<IPAddress> localAddresses = new HashSet<IPAddress>();
         private readonly Dictionary<IPAddress, int> ConnectedAddresses = new Dictionary<IPAddress, int>();
+        /// <summary>
+        /// A dictionary that stores the connected nodes.
+        /// </summary>
         protected readonly ConcurrentDictionary<IActorRef, IPEndPoint> ConnectedPeers = new ConcurrentDictionary<IActorRef, IPEndPoint>();
+        /// <summary>
+        /// A ImmutableHashSet that stores the Peers received from other nodes.
+        /// If the number of desired connections is not enough, first try to connect with the peers in UnconnectedPeers.
+        /// </summary>
         protected ImmutableHashSet<IPEndPoint> UnconnectedPeers = ImmutableHashSet<IPEndPoint>.Empty;
+        /// <summary>
+        /// When a TCP connection request is sent to a peer, the peer will be added to the ImmutableHashSet.
+        /// If a Tcp.Connected or a Tcp.CommandFailed is received, the related peer will be removed.
+        /// </summary>
         protected ImmutableHashSet<IPEndPoint> ConnectingPeers = ImmutableHashSet<IPEndPoint>.Empty;
         protected HashSet<IPAddress> TrustedIpAddresses { get; } = new HashSet<IPAddress>();
 
@@ -65,7 +76,7 @@ static Peer()
         }
 
         /// <summary>
-        /// Tries to add a set ff peers to an immutable hashset of UnconnectedPeers
+        /// Tries to add a set of peers to an immutable hashset of UnconnectedPeers
         /// </summary>
         /// <param name="peers">Peers that the method will try to add (union) to (with) UnconnectedPeers</param>
         protected void AddPeers(IEnumerable<IPEndPoint> peers)
@@ -86,6 +97,7 @@ protected void ConnectToPeer(IPEndPoint endPoint, bool isTrusted = false)
             if (endPoint.Port == ListenerTcpPort && localAddresses.Contains(endPoint.Address)) return;
 
             if (isTrusted) TrustedIpAddresses.Add(endPoint.Address);
+            // If connections with the peer greater than or equal to MaxConnectionsPerAddress, return.
             if (ConnectedAddresses.TryGetValue(endPoint.Address, out int count) && count >= MaxConnectionsPerAddress)
                 return;
             if (ConnectedPeers.Values.Contains(endPoint)) return;
@@ -189,6 +201,13 @@ private void OnStart(ChannelsConfig config)
             }
         }
 
+        /// <summary>
+        /// Will be triggered when a Tcp.Connected message is received.
+        /// If the conditions are met, the remote endpoint will be removed from ConnectingPeers and added to ConnectedPeers.
+        /// Increase the connection number with the remote endpoint by one.
+        /// </summary>
+        /// <param name="remote">The remote endpoint of TCP connection</param>
+        /// <param name="local">The local endpoint of TCP connection</param>
         private void OnTcpConnected(IPEndPoint remote, IPEndPoint local)
         {
             ImmutableInterlocked.Update(ref ConnectingPeers, p => p.Remove(remote));
@@ -197,7 +216,7 @@ private void OnTcpConnected(IPEndPoint remote, IPEndPoint local)
                 Sender.Tell(Tcp.Abort.Instance);
                 return;
             }
-
+            // If connections with the peer greater than or equal to MaxConnectionsPerAddress, abort the TCP connection.
             ConnectedAddresses.TryGetValue(remote.Address, out int count);
             if (count >= MaxConnectionsPerAddress)
             {
@@ -206,13 +225,19 @@ private void OnTcpConnected(IPEndPoint remote, IPEndPoint local)
             else
             {
                 ConnectedAddresses[remote.Address] = count + 1;
+                // An actor reference of the connection.
                 IActorRef connection = Context.ActorOf(ProtocolProps(Sender, remote, local), $"connection_{Guid.NewGuid()}");
                 Context.Watch(connection);
                 Sender.Tell(new Tcp.Register(connection));
                 ConnectedPeers.TryAdd(connection, remote);
             }
         }
 
+        /// <summary>
+        /// Will be triggered when a Tcp.CommandFailed message is received.
+        /// If it's a Tcp.Connect command, remove the related endpoint from ConnectingPeers.
+        /// </summary>
+        /// <param name="cmd"></param>
         private void OnTcpCommandFailed(Tcp.Command cmd)
         {
             switch (cmd)

src/neo/Network/P2P/ProtocolHandler.cs

@@ -145,6 +145,10 @@ private void OnFilterLoadMessageReceived(FilterLoadPayload payload)
             Context.Parent.Tell(new SetFilter { Filter = bloom_filter });
         }
 
+        /// <summary>
+        /// Will be triggered when a MessageCommand.GetAddr message is received.
+        /// Randomly select nodes from the local RemoteNodes, package and tell to RemoteNode actor as MessageCommand.Addr Message.
+        /// </summary>
         private void OnGetAddrMessageReceived()
         {
             Random rand = new Random();
@@ -158,9 +162,15 @@ private void OnGetAddrMessageReceived()
             Context.Parent.Tell(Message.Create(MessageCommand.Addr, AddrPayload.Create(networkAddresses)));
         }
 
+        /// <summary>
+        /// Will be triggered when a MessageCommand.GetBlocks message is received.
+        /// Tell the specified number of blocks' hashes starting with the requested HashStart to RemoteNode actor as MessageCommand.Inv Message.
+        /// </summary>
+        /// <param name="payload">Getsblockpayload, including start block Hash and number of blocks requested</param>
         private void OnGetBlocksMessageReceived(GetBlocksPayload payload)
         {
             UInt256 hash = payload.HashStart;
+            // The default value of payload.Count is -1
             int count = payload.Count < 0 || payload.Count > InvPayload.MaxHashesCount ? InvPayload.MaxHashesCount : payload.Count;
             TrimmedBlock state = Blockchain.Singleton.View.Blocks.TryGet(hash);
             if (state == null) return;
@@ -198,6 +208,12 @@ private void OnGetBlockDataMessageReceived(GetBlockDataPayload payload)
             }
         }
 
+        /// <summary>
+        /// Will be triggered when a MessageCommand.GetData message is received.
+        /// The payload includes a array of hash values.
+        /// For different payload.Type (Tx, Block, Consensus), get the corresponding (Tx, Block, Consensus) and tell it to RemoteNode actor.
+        /// </summary>
+        /// <param name="payload">The payload containing the request information</param>
         private void OnGetDataMessageReceived(InvPayload payload)
         {
             UInt256[] hashes = payload.Hashes.Where(p => sentHashes.Add(p)).ToArray();
@@ -233,6 +249,11 @@ private void OnGetDataMessageReceived(InvPayload payload)
             }
         }
 
+        /// <summary>
+        /// Will be triggered when a MessageCommand.GetHeaders message is received.
+        /// Tell the specified number of blocks' headers starting with the requested HashStart to RemoteNode actor.
+        /// </summary>
+        /// <param name="payload">Getsblockpayload, including start block Hash and number of blocks' headers requested</param>
         private void OnGetHeadersMessageReceived(GetBlocksPayload payload)
         {
             UInt256 hash = payload.HashStart;

src/neo/Network/P2P/RemoteNode.cs

@@ -50,6 +50,12 @@ public RemoteNode(NeoSystem system, object connection, IPEndPoint remote, IPEndP
             SendMessage(Message.Create(MessageCommand.Version, VersionPayload.Create(LocalNode.Nonce, LocalNode.UserAgent, capabilities.ToArray())));
         }
 
+        /// <summary>
+        /// Check the message queue.
+        /// If the high-priority message queue is not empty, choose the high-priority message queue,.
+        /// Otherwise, choose the low-priority message queue.
+        /// Send the first message of the queue.
+        /// </summary>
         private void CheckMessageQueue()
         {
             if (!verack || !ack) return;
@@ -67,6 +73,10 @@ private void EnqueueMessage(MessageCommand command, ISerializable payload = null
             EnqueueMessage(Message.Create(command, payload));
         }
 
+        /// <summary>
+        /// Add message to high priority queue or low priority queue depending on the message type.
+        /// </summary>
+        /// <param name="message">The message to be added</param>
         private void EnqueueMessage(Message message)
         {
             bool is_single = false;

src/neo/Network/P2P/TaskManager.cs

@@ -25,6 +25,9 @@ private class Timer { }
 
         private readonly NeoSystem system;
         private const int MaxConncurrentTasks = 3;
+        /// <summary>
+        /// The hashes corresponding to the completed tasks.
+        /// </summary>
         private readonly FIFOSet<UInt256> knownHashes;
         private readonly Dictionary<UInt256, int> globalTasks = new Dictionary<UInt256, int>();
         private readonly Dictionary<IActorRef, TaskSession> sessions = new Dictionary<IActorRef, TaskSession>();
@@ -228,6 +231,7 @@ private void RequestTasks(TaskSession session)
                     return;
                 }
             }
+            // When the number of AvailableTasks is no more than 0, processing the task of getting the headers and blocks.
             if ((!HasHeaderTask || globalTasks[HeaderTaskHash] < MaxConncurrentTasks) && Blockchain.Singleton.HeaderHeight < session.StartHeight)
             {
                 session.Tasks[HeaderTaskHash] = DateTime.UtcNow;