很抱歉上传这么大的一段代码，但我想这很清楚地解释了事情是如何工作的，并且可能真的很有用。如果您对此代码有任何疑问，请告诉我。
笔记：
- 这只是草稿
- （重要）你必须用你的本地端点通知服务器。如果您不这样做，您将无法在一个 NAT 后面的两个对等方之间进行通信（例如，在一台本地计算机上），即使服务器不在 NAT 中
- 您必须关闭“puncher”客户端（至少，在我这样做之前我没有收到任何数据包）。稍后您将能够使用其他服务器与服务器
UdpClient通信
- 当然它不适用于对称 NAT
- 如果您发现此代码中的某些内容是“糟糕的做法”，请告诉我，我不是网络专家 :)
服务器.cs
using System;
using System.Collections.Generic;
using System.Net;
using System.Net.Sockets;
using HolePunching.Common;
namespace HolePunching.Server
{
class Server
{
private static bool _isRunning;
private static UdpClient _udpClient;
private static readonly Dictionary<byte, PeerContext> Contexts = new Dictionary<byte, PeerContext>();
private static readonly Dictionary<byte, byte> Mappings = new Dictionary<byte, byte>
{
{1, 2},
{2, 1},
};
static void Main()
{
_udpClient = new UdpClient( Consts.UdpPort );
ListenUdp();
Console.ReadLine();
_isRunning = false;
}
private static async void ListenUdp()
{
_isRunning = true;
while ( _isRunning )
{
try
{
var receivedResults = await _udpClient.ReceiveAsync();
if ( !_isRunning )
{
break;
}
ProcessUdpMessage( receivedResults.Buffer, receivedResults.RemoteEndPoint );
}
catch ( Exception ex )
{
Console.WriteLine( $"Error: {ex.Message}" );
}
}
}
private static void ProcessUdpMessage( byte[] buffer, IPEndPoint remoteEndPoint )
{
if ( !UdpProtocol.UdpInfoMessage.TryParse( buffer, out UdpProtocol.UdpInfoMessage message ) )
{
Console.WriteLine( $" >>> Got shitty UDP [ {remoteEndPoint.Address} : {remoteEndPoint.Port} ]" );
_udpClient.Send( new byte[] { 1 }, 1, remoteEndPoint );
return;
}
Console.WriteLine( $" >>> Got UDP from {message.Id}. [ {remoteEndPoint.Address} : {remoteEndPoint.Port} ]" );
if ( !Contexts.TryGetValue( message.Id, out PeerContext context ) )
{
context = new PeerContext
{
PeerId = message.Id,
PublicUdpEndPoint = remoteEndPoint,
LocalUdpEndPoint = new IPEndPoint( message.LocalIp, message.LocalPort ),
};
Contexts.Add( context.PeerId, context );
}
byte partnerId = Mappings[context.PeerId];
if ( !Contexts.TryGetValue( partnerId, out context ) )
{
_udpClient.Send( new byte[] { 1 }, 1, remoteEndPoint );
return;
}
var response = UdpProtocol.PeerAddressMessage.GetMessage(
partnerId,
context.PublicUdpEndPoint.Address,
context.PublicUdpEndPoint.Port,
context.LocalUdpEndPoint.Address,
context.LocalUdpEndPoint.Port );
_udpClient.Send( response.Data, response.Data.Length, remoteEndPoint );
Console.WriteLine( $" <<< Responsed to {message.Id}" );
}
}
public class PeerContext
{
public byte PeerId { get; set; }
public IPEndPoint PublicUdpEndPoint { get; set; }
public IPEndPoint LocalUdpEndPoint { get; set; }
}
}
客户端.cs
using System;
namespace HolePunching.Client
{
class Client
{
public const string ServerIp = "your.server.public.address";
static void Main()
{
byte id = ReadIdFromConsole();
// you need some smarter :)
int localPort = id == 1 ? 61043 : 59912;
var x = new Demo( ServerIp, id, localPort );
x.Start();
}
private static byte ReadIdFromConsole()
{
Console.Write( "Peer id (1 or 2): " );
var id = byte.Parse( Console.ReadLine() );
Console.Title = $"Peer {id}";
return id;
}
}
}
演示.cs
using HolePunching.Common;
using System;
using System.Collections.Generic;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.Threading.Tasks;
namespace HolePunching.Client
{
public class Demo
{
private static bool _isRunning;
private static UdpClient _udpPuncher;
private static UdpClient _udpClient;
private static UdpClient _extraUdpClient;
private static bool _extraUdpClientConnected;
private static byte _id;
private static IPEndPoint _localEndPoint;
private static IPEndPoint _serverUdpEndPoint;
private static IPEndPoint _partnerPublicUdpEndPoint;
private static IPEndPoint _partnerLocalUdpEndPoint;
private static string GetLocalIp()
{
var host = Dns.GetHostEntry( Dns.GetHostName() );
foreach ( var ip in host.AddressList )
{
if ( ip.AddressFamily == AddressFamily.InterNetwork )
{
return ip.ToString();
}
}
throw new Exception( "Failed to get local IP" );
}
public Demo( string serverIp, byte id, int localPort )
{
_serverUdpEndPoint = new IPEndPoint( IPAddress.Parse( serverIp ), Consts.UdpPort );
_id = id;
// we have to bind all our UdpClients to this endpoint
_localEndPoint = new IPEndPoint( IPAddress.Parse( GetLocalIp() ), localPort );
}
public void Start( )
{
_udpPuncher = new UdpClient(); // this guy is just for punching
_udpClient = new UdpClient(); // this will keep hole alive, and also can send data
_extraUdpClient = new UdpClient(); // i think, this guy is the best option for sending data (explained below)
InitUdpClients( new[] { _udpPuncher, _udpClient, _extraUdpClient }, _localEndPoint );
Task.Run( (Action) SendUdpMessages );
Task.Run( (Action) ListenUdp );
Console.ReadLine();
_isRunning = false;
}
private void InitUdpClients(IEnumerable<UdpClient> clients, EndPoint localEndPoint)
{
// if you don't want to use explicit localPort, you should create here one more UdpClient (X) and send something to server (it will automatically bind X to free port). then bind all clients to this port and close X
foreach ( var udpClient in clients )
{
udpClient.ExclusiveAddressUse = false;
udpClient.Client.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true );
udpClient.Client.Bind( localEndPoint );
}
}
private void SendUdpMessages()
{
_isRunning = true;
var messageToServer = UdpProtocol.UdpInfoMessage.GetMessage( _id, _localEndPoint.Address, _localEndPoint.Port );
var messageToPeer = UdpProtocol.P2PKeepAliveMessage.GetMessage();
while ( _isRunning )
{
// while we dont have partner's address, we will send messages to server
if ( _partnerPublicUdpEndPoint == null && _partnerLocalUdpEndPoint == null )
{
_udpPuncher.Send( messageToServer.Data, messageToServer.Data.Length, _serverUdpEndPoint );
Console.WriteLine( $" >>> Sent UDP to server [ {_serverUdpEndPoint.Address} : {_serverUdpEndPoint.Port} ]" );
}
else
{
// you can skip it. just demonstration, that you still can send messages to server
_udpClient.Send( messageToServer.Data, messageToServer.Data.Length, _serverUdpEndPoint );
Console.WriteLine( $" >>> Sent UDP to server [ {_serverUdpEndPoint.Address} : {_serverUdpEndPoint.Port} ]" );
// THIS is how we punching hole! very first this message should be dropped by partner's NAT, but it's ok.
// i suppose that this is good idea to send this "keep-alive" messages to peer even if you are connected already,
// because AFAIK "hole" for UDP lives ~2 minutes on NAT. so "we will let it die? NEVER!" (c)
_udpClient.Send( messageToPeer.Data, messageToPeer.Data.Length, _partnerPublicUdpEndPoint );
_udpClient.Send( messageToPeer.Data, messageToPeer.Data.Length, _partnerLocalUdpEndPoint );
Console.WriteLine( $" >>> Sent UDP to peer.public [ {_partnerPublicUdpEndPoint.Address} : {_partnerPublicUdpEndPoint.Port} ]" );
Console.WriteLine( $" >>> Sent UDP to peer.local [ {_partnerLocalUdpEndPoint.Address} : {_partnerLocalUdpEndPoint.Port} ]" );
// "connected" UdpClient sends data much faster,
// so if you have something that your partner cant wait for (voice, for example), send it this way
if ( _extraUdpClientConnected )
{
_extraUdpClient.Send( messageToPeer.Data, messageToPeer.Data.Length );
Console.WriteLine( $" >>> Sent UDP to peer.received EP" );
}
}
Thread.Sleep( 3000 );
}
}
private async void ListenUdp()
{
_isRunning = true;
while ( _isRunning )
{
try
{
// also important thing!
// when you did not punched hole yet, you must listen incoming packets using "puncher" (later we will close it).
// where you already have p2p connection (and "puncher" closed), use "non-puncher"
UdpClient udpClient = _partnerPublicUdpEndPoint == null ? _udpPuncher : _udpClient;
var receivedResults = await udpClient.ReceiveAsync();
if ( !_isRunning )
{
break;
}
ProcessUdpMessage( receivedResults.Buffer, receivedResults.RemoteEndPoint );
}
catch ( SocketException ex )
{
// do something here...
}
catch ( Exception ex )
{
Console.WriteLine( $"Error: {ex.Message}" );
}
}
}
private static void ProcessUdpMessage( byte[] buffer, IPEndPoint remoteEndPoint )
{
// if server sent partner's endpoinps, we will store it and (IMPORTANT) close "puncher"
if ( UdpProtocol.PeerAddressMessage.TryParse( buffer, out UdpProtocol.PeerAddressMessage peerAddressMessage ) )
{
Console.WriteLine( " <<< Got response from server" );
_partnerPublicUdpEndPoint = new IPEndPoint( peerAddressMessage.PublicIp, peerAddressMessage.PublicPort );
_partnerLocalUdpEndPoint = new IPEndPoint( peerAddressMessage.LocalIp, peerAddressMessage.LocalPort );
_udpPuncher.Close();
}
// since we got this message we know partner's endpoint for sure,
// and we can "connect" UdpClient to it, so it will work faster
else if ( UdpProtocol.P2PKeepAliveMessage.TryParse( buffer ) )
{
Console.WriteLine( $" IT WORKS!!! WOW!!! [ {remoteEndPoint.Address} : {remoteEndPoint.Port} ]" );
_extraUdpClientConnected = true;
_extraUdpClient.Connect( remoteEndPoint );
}
else
{
Console.WriteLine( "???" );
}
}
}
}
协议.cs
我不确定这种方法有多好，也许像 protobuf 这样的东西可以做得更好
using System;
using System.Linq;
using System.Net;
using System.Text;
namespace HolePunching.Common
{
public static class UdpProtocol
{
public static readonly int GuidLength = 16;
public static readonly int PeerIdLength = 1;
public static readonly int IpLength = 4;
public static readonly int IntLength = 4;
public static readonly byte[] Prefix = { 12, 23, 34, 45 };
private static byte[] JoinBytes( params byte[][] bytes )
{
var result = new byte[bytes.Sum( x => x.Length )];
int pos = 0;
for ( int i = 0; i < bytes.Length; i++ )
{
for ( int j = 0; j < bytes[i].Length; j++, pos++ )
{
result[pos] = bytes[i][j];
}
}
return result;
}
#region Helper extensions
private static bool StartsWith( this byte[] @this, byte[] value, int offset = 0 )
{
if ( @this == null || value == null || @this.Length < offset + value.Length )
{
return false;
}
for ( int i = 0; i < value.Length; i++ )
{
if ( @this[i + offset] < value[i] )
{
return false;
}
}
return true;
}
private static byte[] ToUnicodeBytes( this string @this )
{
return Encoding.Unicode.GetBytes( @this );
}
private static byte[] Take( this byte[] @this, int offset, int length )
{
return @this.Skip( offset ).Take( length ).ToArray();
}
public static bool IsSuitableUdpMessage( this byte[] @this )
{
return @this.StartsWith( Prefix );
}
public static int GetInt( this byte[] @this )
{
if ( @this.Length != 4 )
throw new ArgumentException( "Byte array must be exactly 4 bytes to be convertible to uint." );
return ( ( ( @this[0] << 8 ) + @this[1] << 8 ) + @this[2] << 8 ) + @this[3];
}
public static byte[] ToByteArray( this int value )
{
return new[]
{
(byte)(value >> 24),
(byte)(value >> 16),
(byte)(value >> 8),
(byte)value
};
}
#endregion
#region Messages
public abstract class UdpMessage
{
public byte[] Data { get; }
protected UdpMessage( byte[] data )
{
Data = data;
}
}
public class UdpInfoMessage : UdpMessage
{
private static readonly byte[] MessagePrefix = { 41, 57 };
private static readonly int MessageLength = Prefix.Length + MessagePrefix.Length + PeerIdLength + IpLength + IntLength;
public byte Id { get; }
public IPAddress LocalIp { get; }
public int LocalPort { get; }
private UdpInfoMessage( byte[] data, byte id, IPAddress localIp, int localPort )
: base( data )
{
Id = id;
LocalIp = localIp;
LocalPort = localPort;
}
public static UdpInfoMessage GetMessage( byte id, IPAddress localIp, int localPort )
{
var data = JoinBytes( Prefix, MessagePrefix, new[] { id }, localIp.GetAddressBytes(), localPort.ToByteArray() );
return new UdpInfoMessage( data, id, localIp, localPort );
}
public static bool TryParse( byte[] data, out UdpInfoMessage message )
{
message = null;
if ( !data.StartsWith( Prefix ) )
return false;
if ( !data.StartsWith( MessagePrefix, Prefix.Length ) )
return false;
if ( data.Length != MessageLength )
return false;
int index = Prefix.Length + MessagePrefix.Length;
byte id = data[index];
index += PeerIdLength;
byte[] localIpBytes = data.Take( index, IpLength );
var localIp = new IPAddress( localIpBytes );
index += IpLength;
byte[] localPortBytes = data.Take( index, IntLength );
int localPort = localPortBytes.GetInt();
message = new UdpInfoMessage( data, id, localIp, localPort );
return true;
}
}
public class PeerAddressMessage : UdpMessage
{
private static readonly byte[] MessagePrefix = { 36, 49 };
private static readonly int MessageLength = Prefix.Length + MessagePrefix.Length + PeerIdLength + ( IpLength + IntLength ) * 2;
public byte Id { get; }
public IPAddress PublicIp { get; }
public int PublicPort { get; }
public IPAddress LocalIp { get; }
public int LocalPort { get; }
private PeerAddressMessage( byte[] data, byte id, IPAddress publicIp, int publicPort, IPAddress localIp, int localPort )
: base( data )
{
Id = id;
PublicIp = publicIp;
PublicPort = publicPort;
LocalIp = localIp;
LocalPort = localPort;
}
public static PeerAddressMessage GetMessage( byte id, IPAddress publicIp, int publicPort, IPAddress localIp, int localPort )
{
var data = JoinBytes( Prefix, MessagePrefix, new[] { id },
publicIp.GetAddressBytes(), publicPort.ToByteArray(),
localIp.GetAddressBytes(), localPort.ToByteArray() );
return new PeerAddressMessage( data, id, publicIp, publicPort, localIp, localPort );
}
public static bool TryParse( byte[] data, out PeerAddressMessage message )
{
message = null;
if ( !data.StartsWith( Prefix ) )
return false;
if ( !data.StartsWith( MessagePrefix, Prefix.Length ) )
return false;
if ( data.Length != MessageLength )
return false;
int index = Prefix.Length + MessagePrefix.Length;
byte id = data[index];
index += PeerIdLength;
byte[] publicIpBytes = data.Take( index, IpLength );
var publicIp = new IPAddress( publicIpBytes );
index += IpLength;
byte[] publicPortBytes = data.Take( index, IntLength );
int publicPort = publicPortBytes.GetInt();
index += IntLength;
byte[] localIpBytes = data.Take( index, IpLength );
var localIp = new IPAddress( localIpBytes );
index += IpLength;
byte[] localPortBytes = data.Take( index, IntLength );
int localPort = localPortBytes.GetInt();
message = new PeerAddressMessage( data, id, publicIp, publicPort, localIp, localPort );
return true;
}
}
public class P2PKeepAliveMessage : UdpMessage
{
private static readonly byte[] MessagePrefix = { 11, 19 };
private static P2PKeepAliveMessage _message;
private P2PKeepAliveMessage( byte[] data )
: base( data )
{
}
public static bool TryParse( byte[] data )
{
if ( !data.StartsWith( Prefix ) )
return false;
if ( !data.StartsWith( MessagePrefix, Prefix.Length ) )
return false;
return true;
}
public static P2PKeepAliveMessage GetMessage()
{
if ( _message == null )
{
var data = JoinBytes( Prefix, MessagePrefix );
_message = new P2PKeepAliveMessage( data );
}
return _message;
}
}
#endregion
}
}