【转】C#实现UDP数据包大文件分包传输和接收组包

来源：互联网发布：长镜头知乎编辑：程序博客网时间：2024/06/06 15:50

转自：http://www.cr173.com/html/19884_1.html

如果需要使用UDP传输较大数据，例如传输10M的图片，这突破了UDP的设计原则。UDP的设计是基于"datagram"，也就是它假设你发送的每个数据包都能包含在单一的包内。并且设定UDP数据包的最大长度受基础网络协议的限制。

UDP数据包的理论最大长度限制是 65535 bytes，这包含 8 bytes 数据包头和 65527 bytes 数据。但如果基于IPv4网络传输，则还需减去 20 bytes 的IP数据包头。
则单一的UDP数据包可传输的数据最大长度为：

MaxUdpDataLength = 65535 - 8 - 20 = 65507 bytes

这就需要实现UDP包的分包传输和接收组包功能。

分包功能

1 /// <summary>

 2   /// UDP数据包分割器 3   /// </summary> 4   public static class UdpPacketSplitter 5   { 6     /// <summary> 7     /// 分割UDP数据包 8     /// </summary> 9     /// <param name="sequence">UDP数据包所持有的序号</param>10     /// <param name="datagram">被分割的UDP数据包</param>11     /// <param name="chunkLength">分割块的长度</param>12     /// <returns>13     /// 分割后的UDP数据包列表14     /// </returns>15     public static ICollection<UdpPacket> Split(long sequence, byte[] datagram, int chunkLength)16     {17       if (datagram == null)18         throw new ArgumentNullException("datagram");19 20       List<UdpPacket> packets = new List<UdpPacket>();21 22       int chunks = datagram.Length / chunkLength;23       int remainder = datagram.Length % chunkLength;24       int total = chunks;25       if (remainder > 0) total++;26 27       for (int i = 1; i <= chunks; i++)28       {29         byte[] chunk = new byte[chunkLength];30         Buffer.BlockCopy(datagram, (i - 1) * chunkLength, chunk, 0, chunkLength);31         packets.Add(new UdpPacket(sequence, total, i, chunk, chunkLength));32       }33       if (remainder > 0)34       {35         int length = datagram.Length - (chunkLength * chunks);36         byte[] chunk = new byte[length];37         Buffer.BlockCopy(datagram, chunkLength * chunks, chunk, 0, length);38         packets.Add(new UdpPacket(sequence, total, total, chunk, length));39       }40 41       return packets;42     }43   }

发送分包

1 private void WorkThread()

 2 { 3   while (IsRunning) 4   { 5     waiter.WaitOne(); 6     waiter.Reset(); 7  8     while (queue.Count > 0) 9     {10       StreamPacket packet = null;11       if (queue.TryDequeue(out packet))12       {13         RtpPacket rtpPacket = RtpPacket.FromImage(14           RtpPayloadType.JPEG, 15           packet.SequenceNumber, 16           (long)Epoch.GetDateTimeTotalMillisecondsByYesterday(packet.Timestamp),17           packet.Frame);18 19         // max UDP packet length limited to 65,535 bytes20         byte[] datagram = rtpPacket.ToArray(); 21         packet.Frame.Dispose();22 23         // split udp packet to many packets 24         // to reduce the size to 65507 limit by underlying IPv4 protocol25         ICollection<UdpPacket> udpPackets 26           = UdpPacketSplitter.Split(27             packet.SequenceNumber, 28             datagram, 29             65507 - UdpPacket.HeaderSize);30         foreach (var udpPacket in udpPackets)31         {32           byte[] udpPacketDatagram = udpPacket.ToArray();33           // async sending34           udpClient.BeginSend(35             udpPacketDatagram, udpPacketDatagram.Length,36             packet.Destination.Address,37             packet.Destination.Port,38             SendCompleted, udpClient);39         }40       }41     }42   }43 }

接收组包功能

1 private void OnDatagramReceived(object sender, UdpDatagramReceivedEventArgs<byte[]> e)

 2     { 3       try 4       { 5         UdpPacket udpPacket = UdpPacket.FromArray(e.Datagram); 6  7         if (udpPacket.Total == 1) 8         { 9           RtpPacket packet = new RtpPacket(udpPacket.Payload, udpPacket.PayloadSize);10           Bitmap bitmap = packet.ToBitmap();11           RaiseNewFrameEvent(12             bitmap, Epoch.GetDateTimeByYesterdayTotalMilliseconds(packet.Timestamp));13         }14         else15         {16           // rearrange packets to one packet17           if (packetCache.ContainsKey(udpPacket.Sequence))18           {19             List<UdpPacket> udpPackets = null;20             if (packetCache.TryGetValue(udpPacket.Sequence, out udpPackets))21             {22               udpPackets.Add(udpPacket);23 24               if (udpPackets.Count == udpPacket.Total)25               {26                 packetCache.TryRemove(udpPacket.Sequence, out udpPackets);27 28                 udpPackets = udpPackets.OrderBy(u => u.Order).ToList();29                 int rtpPacketLength = udpPackets.Sum(u => u.PayloadSize);30                 int maxPacketLength = udpPackets.Select(u => u.PayloadSize).Max();31 32                 byte[] rtpPacket = new byte[rtpPacketLength];33                 foreach (var item in udpPackets)34                 {35                   Buffer.BlockCopy(36                     item.Payload, 0, rtpPacket, 37                     (item.Order - 1) * maxPacketLength, item.PayloadSize);38                 }39 40                 RtpPacket packet = new RtpPacket(rtpPacket, rtpPacket.Length);41                 Bitmap bitmap = packet.ToBitmap();42                 RaiseNewFrameEvent(43                   bitmap, 44                   Epoch.GetDateTimeByYesterdayTotalMilliseconds(packet.Timestamp));45 46                 packetCache.Clear();47               }48             }49           }50           else51           {52             List<UdpPacket> udpPackets = new List<UdpPacket>();53             udpPackets.Add(udpPacket);54             packetCache.AddOrUpdate(55               udpPacket.Sequence, 56               udpPackets, (k, v) => { return udpPackets; });57           }58         }59       }60       catch (Exception ex)61       {62         RaiseVideoSourceExceptionEvent(ex.Message);63       }64     }

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