C#实现UDP数据包大文件分包传输和接收组包

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 ///

2 /// UDP数据包分割器 3 /// 4 public static class UdpPacketSplitter 6 /// 7 /// 分割UDP数据包 8 /// 9 ///

UDP数据包所持有的序号10 ///

被分割的UDP数据包11 ///

分割块的长度12 /// 13 /// 分割后的UDP数据包列表14 /// 15 public static ICollection Split(long sequence, byte[] datagram, int chunkLength)17 if (datagram == null)18 throw new ArgumentNullException("datagram");20 List packets = new List();22 int chunks = datagram.Length / chunkLength;23 int remainder = datagram.Length % chunkLength;24 int total = chunks;25 if (remainder > 0) total++;27 for (int i = 1; i 0)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));41 return packets;43 }

发送分包

1 private void WorkThread()

2 { 3 while (IsRunning) 5 waiter.WaitOne(); 6 waiter.Reset(); 8 while (queue.Count > 0)10 StreamPacket packet = null;11 if (queue.TryDequeue(out packet))13 RtpPacket rtpPacket = RtpPacket.FromImage(14 RtpPayloadType.JPEG, 15 packet.SequenceNumber, 16 (long)Epoch.GetDateTimeTotalMillisecondsByYesterday(packet.Timestamp),17 packet.Frame);19 // max UDP packet length limited to 65,535 bytes20 byte[] datagram = rtpPacket.ToArray(); 21 packet.Frame.Dispose();23 // split udp packet to many packets 24 // to reduce the size to 65507 limit by underlying IPv4 protocol25 ICollection udpPackets 26 = UdpPacketSplitter.Split(27 packet.SequenceNumber, 28 datagram, 29 65507 - UdpPacket.HeaderSize);30 foreach (var udpPacket in udpPackets)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);43 }

接收组包功能

1 private void OnDatagramReceived(object sender, UdpDatagramReceivedEventArgs e)

2 { 3 try 5 UdpPacket udpPacket = UdpPacket.FromArray(e.Datagram); 7 if (udpPacket.Total == 1) 9 RtpPacket packet = new RtpPacket(udpPacket.Payload, udpPacket.PayloadSize);10 Bitmap bitmap = packet.ToBitmap();11 RaiseNewFrameEvent(12 bitmap, Epoch.GetDateTimeByYesterdayTotalMilliseconds(packet.Timestamp));14 else16 // rearrange packets to one packet17 if (packetCache.ContainsKey(udpPacket.Sequence))19 List udpPackets = null;20 if (packetCache.TryGetValue(udpPacket.Sequence, out udpPackets))22 udpPackets.Add(udpPacket);24 if (udpPackets.Count == udpPacket.Total)26 packetCache.TryRemove(udpPacket.Sequence, out udpPackets);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();32 byte[] rtpPacket = new byte[rtpPacketLength];33 foreach (var item in udpPackets)35 Buffer.BlockCopy(36 item.Payload, 0, rtpPacket, 37 (item.Order - 1) * maxPacketLength, item.PayloadSize);40 RtpPacket packet = new RtpPacket(rtpPacket, rtpPacket.Length);41 Bitmap bitmap = packet.ToBitmap();42 RaiseNewFrameEvent(43 bitmap, 44 Epoch.GetDateTimeByYesterdayTotalMilliseconds(packet.Timestamp));46 packetCache.Clear();50 else52 List udpPackets = new List();53 udpPackets.Add(udpPacket);54 packetCache.AddOrUpdate(55 udpPacket.Sequence, 56 udpPackets, (k, v) => { return udpPackets; });60 catch (Exception ex)62 RaiseVideoSourceExceptionEvent(ex.Message);64 } 实现,UDP,数据,包大,文件,分包,传输,和,接收,