如果需要使用UDP傳輸較大數(shù)據(jù)，例如傳輸10M的圖片，這突破了UDP的設(shè)計(jì)原則。UDP的設(shè)計(jì)是基于"datagram"，也就是它假設(shè)你發(fā)送的每個(gè)數(shù)據(jù)包都能包含在單一的包內(nèi)。并且設(shè)定UDP數(shù)據(jù)包的最大長(zhǎng)度受基礎(chǔ)網(wǎng)絡(luò)協(xié)議的限制。
UDP數(shù)據(jù)包的理論最大長(zhǎng)度限制是 65535 bytes，這包含 8 bytes 數(shù)據(jù)包頭和 65527 bytes 數(shù)據(jù)。但如果基于IPv4網(wǎng)絡(luò)傳輸，則還需減去 20 bytes 的IP數(shù)據(jù)包頭。
則單一的UDP數(shù)據(jù)包可傳輸?shù)臄?shù)據(jù)最大長(zhǎng)度為：
MaxUdpDataLength = 65535 - 8 - 20 = 65507 bytes
這就需要實(shí)現(xiàn)UDP包的分包傳輸和接收組包功能。
分包功能
1 /// <summary>
2 /// UDP數(shù)據(jù)包分割器
3 /// </summary>
4 public static class UdpPacketSplitter
5 {
6 /// <summary>
7 /// 分割UDP數(shù)據(jù)包
8 /// </summary>
9 /// <param name="sequence">UDP數(shù)據(jù)包所持有的序號(hào)</param>
10 /// <param name="datagram">被分割的UDP數(shù)據(jù)包</param>
11 /// <param name="chunkLength">分割塊的長(zhǎng)度</param>
12 /// <returns>
13 /// 分割后的UDP數(shù)據(jù)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 }發(fā)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 bytes
20 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 protocol
25 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 sending
34 udpClient.BeginSend(
35 udpPacketDatagram, udpPacketDatagram.Length,
36 packet.Destination.Address,
37 packet.Destination.Port,
38 SendCompleted, udpClient);
39 }
40 }
41 }
42 }
43 }接收組包功能
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 else
15 {
16 // rearrange packets to one packet
17 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 else
51 {
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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