粘包/半包及解决方案

一、粘包/半包介绍

1：粘包

粘包（Packet Concatenation）通常发生在基于流式传输协议（如 TCP）的通信中，因为 TCP 是面向流的传输协议，它不保证数据包的边界，而是将数据视为连续的字节流，它表示客户端发送多条消息，服务端只收到了一条消息

2：半包

半包（Half Packet）与粘包问题相反。在半包问题中，接收端接收到的数据包不完整，即接收到的数据包只是完整数据包的一部分，无法完整地解析和处理。

3：原因

①网络延迟/阻塞

②发送方连续发送数据

③接收端缓冲区大小限制

④数据包丢失

二、粘包/半包解决方案

1：长度信息法

在每个数据包前面加上长度信息，每次接收数据后，先读取长度，如果缓冲区数据长度大于要取的字节数，则取出相应字节，否则等待下一次接收,举个例子

①客户端第一次发送包含长度信息的内容

②客户端第二次发送包含长度信息的内容

③服务端第一次接收到了4个字节，存入缓冲区，但是这时候并不处理，因为收到了10，所以要等到11个字节完整再处理

④服务端等到客户端发送剩下的7个字节，但是第二次接收到了9个字节，服务端把之前的6个字节再读取，然后拼接，把10helloworld进行处理，读取到标志长度4，等待下次处理

⑤服务端最后一次收到ove，就把之前的l一起拼接，返回完整的4love

*一般的游戏是16位的整型数来存放长度信息

2：固定长度法

每次都发送相同长度的数据，一次不足的数据用.来补充，.位补充字符，没有实际意义

如果接收到的字符数大于10，就只提取前10个字符

3：结束符号法

规定一个结束符号作为消息的分隔符，比如Hello$World就是两条信息

三、代码示例

1：发送数据

        byte[] bodyBytes = System.Text.Encoding.Default.GetBytes(SendStr);Int16 len = (Int16)bodyBytes.Length;//把长度转化为Int16byte[] lenBytes = BitConverter.GetBytes(len);//此时SendBytes包含长度字符串和内容字符串byte[] sendBytes = lenBytes.Concat(bodyBytes).ToArray();

2：接收数据

定义一个接收缓冲区和接收缓冲区长度。缓冲区会保存尚未处理的数据

    //接收缓冲区byte[] readBuff = new byte[1024];//接收缓冲区长度int buffCount = 0;

之前的BeginReceive函数原型如下：

public IAsyncResult BeginReceive (  byte[] buffer,  int offset,  int size,  SocketFlags socketFlags,  AsyncCallback callback, object state )

现在的参数应该写成这个样子：

socket.BeginReceive(readBuff, buffCount 1024-buffCount, 0,  ReceiveCallback, socket);

readBuff 是缓冲区

buffCount 是开始读取的位置

1024 - buffCount 是剩余多少可读取的大小

3：处理数据

public void OnReceiveData(){//消息长度小于2，直接返回等待下一次接收if(buffCount <= 2)return;//消息的长度Int16 bodyLength = BitConverter.ToInt16(readBuff, 0);//消息体//如果消息长度小于我消息内容和长度的字节，就返回继续读取if(buffCount < 2+bodyLength)return;//如果长度够用，就转化为string类型string s = System.Text.Encoding.UTF8.GetString(readBuff, 2,buffCount);//更新缓冲区int start = 2 + bodyLength;int count = buffCount - start;//Copy函数把缓冲区后面的内容提到前面Array.Copy(readBuff, start, readBuff, 0, count);buffCount -= start;//继续读取消息if(readBuff.length > 2){OnReceiveData();}
}

Copy的原型函数如下：

public static void Copy(Array sourceArray,//源数组long sourceIndex,//目标数据Array destinationArray,//目标数组long destinationIndex,//目标数组起始位置long length//复制消息的长度
)

四、完整示例

1：客户端

using System;
using System.Linq;
using System.Net.Sockets;
using UnityEngine;
using UnityEngine.UI;public class SendScr : MonoBehaviour
{Socket socket;public InputField inputField;public Text text;byte[] readBuff = new byte[1024];int buffCount = 0;//缓冲区数据长度string recvStr = "";public void Connection(){socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);socket.Connect("127.0.0.1", 8888);socket.BeginReceive(readBuff, buffCount, 1024 - buffCount, 0, ReceiveCallback, socket);}private void ReceiveCallback(IAsyncResult ar){try{Socket socket = (Socket)ar.AsyncState;//获取接收数据长度int count = socket.EndReceive(ar);buffCount += count;//处理二进制消息OnReceiveData();//继续接收数据socket.BeginReceive(readBuff, buffCount, 1024 - buffCount, 0, ReceiveCallback, socket);}catch (SocketException ex){Debug.Log("Socket Receive fail" + ex.ToString());}}private void OnReceiveData(){Debug.Log("[Recv 1] buffCount = " + buffCount);Debug.Log("[Recv 2] readbuff = " + BitConverter.ToString(readBuff));if (buffCount <= 2) return;Int16 bodyLength = BitConverter.ToInt16(readBuff, 0);Debug.Log("[Recv 3] bodyLength=" + bodyLength);//消息体if (buffCount < 2 + bodyLength) return;string s = System.Text.Encoding.UTF8.GetString(readBuff, 2, buffCount);Debug.Log("[Recv 4] s=" + s);//更新缓冲区int start = 2 + bodyLength;int count = buffCount - start;Array.Copy(readBuff, start, readBuff, 0, count);buffCount -= start;Debug.Log("[Recv 5] buffCount=" + buffCount);//消息处理recvStr = s + "\n" + recvStr;//继续读取消息OnReceiveData();}public void Send(){string sendStr = inputField.text;byte[] bodyBytes = System.Text.Encoding.Default.GetBytes(sendStr);Int16 len = (Int16)bodyBytes.Length;byte[] lenBytes = BitConverter.GetBytes(len);//此时SendBytes包含长度字符串和内容字符串byte[] sendBytes = lenBytes.Concat(bodyBytes).ToArray();socket.Send(sendBytes);Debug.Log("[Send]" + BitConverter.ToString(sendBytes));}private void Update(){text.text = recvStr;}}

捋一下客户端的功能：

当进入场景点击Connection，创建新的Socket连接，绑定服务端口，开始接收信息

这里的BeginReceive就是我们接受消息的函数，它传入我们的缓冲区readBuff，缓冲区长度buffCount，1024 - buffCount表示我们还剩多少字节数据，然后进入回调函数

Receive回调函数中创建新的Socket对象来解析获取到的socket对象，count用于跟踪每次异步接收操作实际接收到的数据长度，然后把count加到buffCount上，这样更新了缓冲区的长度

然后使用OnReceiveData处理数据，继续读取数据，点击发送就调用Send()

2：服务端

using System.Net.Sockets;
using System.Net;
internal class ClientState
{public Socket socket;public byte[] readBuff = new byte[1024];
}
class Class
{static Socket listenfd;static Dictionary<Socket, ClientState> clients = new Dictionary<Socket, ClientState>();public static void Main(string[] args){listenfd = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);IPAddress ipAdr = IPAddress.Parse("127.0.0.1");IPEndPoint ipEp = new IPEndPoint(ipAdr, 8888);listenfd.Bind(ipEp);listenfd.Listen(0);Console.WriteLine("[服务器]启动成功");List<Socket> checkRead = new List<Socket>();while (true){//填充checkRead列表checkRead.Clear();checkRead.Add(listenfd);foreach (ClientState s in clients.Values){checkRead.Add(s.socket);}//selectSocket.Select(checkRead, null, null, 1000);//检查可读对象foreach (Socket s in checkRead){if (s == listenfd){ReadListenfd(s);}else{ReadClientfd(s);}}}}public static void ReadListenfd(Socket listenfd){Console.WriteLine("Accept");Socket clientfd = listenfd.Accept();ClientState state = new ClientState();state.socket = clientfd;clients.Add(clientfd, state);}public static bool ReadClientfd(Socket clientfd){ClientState state = clients[clientfd];//接收int count = clientfd.Receive(state.readBuff);if (count == 0){clientfd.Close();clients.Remove(clientfd);Console.WriteLine("Socket Close");return false;}//广播string recvStr = System.Text.Encoding.Default.GetString(state.readBuff, 2, count - 2);Console.WriteLine("Receive" + recvStr);byte[] sendBytes = new byte[count];Array.Copy(state.readBuff, 0, sendBytes, 0, count);foreach (ClientState cs in clients.Values){cs.socket.Send(sendBytes);}return true;}
}

这里的服务端代码和Select部分的代码基本相同

3：测试

打开服务器，客户端连接后输入UNITY

①客户端反馈

Recv1的buffCount就是接收到服务端所返回的消息，服务端所返回的信息是客户端发送的拼接数组，就是UNITY+lenBytes，就是7

Rec2的readbuff就是缓冲区存储的内容

Recv3是当消息没有接受完整的时候的消息本体长度

Recv4是完整的消息内容

Recv5是接受完成UNITY后更新后的新buffCount新长度，因为没有后续的，所以是0

②服务端反馈

服务端接受到的消息

四、模拟粘包

客户端修改

using System;
using System.Linq;
using System.Net.Sockets;
using UnityEngine;
using UnityEngine.UI;public class SendScr : MonoBehaviour
{Socket socket;public InputField inputField;public Text text;byte[] readBuff = new byte[1024];int buffCount = 0;//缓冲区数据长度string recvStr = "";public void Connection(){socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);socket.Connect("127.0.0.1", 8888);socket.BeginReceive(readBuff, buffCount, 1024 - buffCount, 0, ReceiveCallback, socket);}private void ReceiveCallback(IAsyncResult ar){try{Socket socket = (Socket)ar.AsyncState;//获取接收数据长度int count = socket.EndReceive(ar);buffCount += count;//处理二进制消息OnReceiveData();System.Threading.Thread.Sleep(1000*30);//继续接收数据socket.BeginReceive(readBuff, buffCount, 1024 - buffCount, 0, ReceiveCallback, socket);}catch (SocketException ex){Debug.Log("Socket Receive fail" + ex.ToString());}}private void OnReceiveData(){Debug.Log("[Recv 1] buffCount = " + buffCount);Debug.Log("[Recv 2] readbuff = " + BitConverter.ToString(readBuff));if (buffCount <= 2) return;Int16 bodyLength = BitConverter.ToInt16(readBuff, 0);Debug.Log("[Recv 3] bodyLength=" + bodyLength);//消息体if (buffCount < 2 + bodyLength) return;string s = System.Text.Encoding.UTF8.GetString(readBuff, 2, buffCount);Debug.Log("[Recv 4] s=" + s);//更新缓冲区int start = 2 + bodyLength;int count = buffCount - start;Array.Copy(readBuff, start, readBuff, 0, count);buffCount -= start;Debug.Log("[Recv 5] buffCount=" + buffCount);//消息处理recvStr = s + "\n" + recvStr;//继续读取消息OnReceiveData();}public void Send(){string sendStr = inputField.text;byte[] bodyBytes = System.Text.Encoding.Default.GetBytes(sendStr);Int16 len = (Int16)bodyBytes.Length;byte[] lenBytes = BitConverter.GetBytes(len);//此时SendBytes包含长度字符串和内容字符串byte[] sendBytes = lenBytes.Concat(bodyBytes).ToArray();socket.Send(sendBytes);Debug.Log("[Send]" + BitConverter.ToString(sendBytes));}private void Update(){text.text = recvStr;}}

*在接收数据的时候，强制等待30s再进行下一次接收，ReceiveCallback是在子线程执行，调用Sleep函数并不会卡住主线程，客户端不会被卡住，在30s内多次发送数据，经由服务端转发，再次调用BeginReceive的时候，缓冲区有很多数据，会产生粘包。

客户端快速发送三条消息，发送不会堵塞，每次接收都会等待30s，但是接收到的消息不是在一起的，而是分开的