C# 网络编程之UDP

C# 网络编程之UDP

什么是UDP

UDP是一个无连接的传输协议，它不保证可靠传输和数据的顺序，但是其传输速度很快，适合于传输实时性要求高的数据。

UDP的使用场景

由于UDP不需要建立连接，所以适合于一对多或多对多的广播传输。比如实现网络游戏的消息传输，实时视频传输等。

UDP编程实现

发送端实现

UDP发送方需要绑定发送端口，然后指定目标地址和目标端口，将要发送的数据包发送出去。

示例1：发送一个简单的字符串。

using System.Net;
using System.Net.Sockets;
using System.Text;

class Sender {
  static void Main() {
    var endPoint = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 12345);
    using (var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp)) {
      byte[] data = Encoding.UTF8.GetBytes("Hello World!");
      socket.SendTo(data, endPoint);
    }
  }
}

示例2：发送一个自定义的数据包。

using System;
using System.Net;
using System.Net.Sockets;

struct CustomPacket {
  public int id;
  public float x;
  public float y;
  public float z;
}

class Sender {
  static void Main() {
    var endPoint = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 12345);
    using (var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp)) {
      var packet = new CustomPacket {
        id = 123,
        x = 1.0f,
        y = 2.0f,
        z = 3.0f
      };
      byte[] data = Serialize(packet);
      socket.SendTo(data, endPoint);
    }
  }

  // 自定义的序列化方法
  static byte[] Serialize<T>(T obj) {
    int size = System.Runtime.InteropServices.Marshal.SizeOf(typeof(T));
    byte[] data = new byte[size];
    var ptr = System.Runtime.InteropServices.Marshal.AllocHGlobal(size);
    System.Runtime.InteropServices.Marshal.StructureToPtr(obj, ptr, true);
    System.Runtime.InteropServices.Marshal.Copy(ptr, data, 0, size);
    System.Runtime.InteropServices.Marshal.FreeHGlobal(ptr);
    return data;
  }
}

接收端实现

UDP接收方需要绑定监听端口，然后不断从网络中读取数据包。

示例1：接收简单的字符串。

using System.Net;
using System.Net.Sockets;
using System.Text;

class Receiver {
  static void Main() {
    var endPoint = new IPEndPoint(IPAddress.Any, 12345);
    using (var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp)) {
      socket.Bind(endPoint);
      byte[] buffer = new byte[1024];
      int size = socket.Receive(buffer);
      string message = Encoding.UTF8.GetString(buffer, 0, size);
      Console.WriteLine(message);
    }
  }
}

示例2：接收自定义的数据包。

using System;
using System.Net;
using System.Net.Sockets;

struct CustomPacket {
  public int id;
  public float x;
  public float y;
  public float z;
}

class Receiver {
  static void Main() {
    var endPoint = new IPEndPoint(IPAddress.Any, 12345);
    using (var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp)) {
      socket.Bind(endPoint);
      byte[] buffer = new byte[1024];
      int size = socket.Receive(buffer);
      var packet = Deserialize<CustomPacket>(buffer, size);
      Console.WriteLine(packet.id);
      Console.WriteLine(packet.x);
      Console.WriteLine(packet.y);
      Console.WriteLine(packet.z);
    }
  }

  // 自定义的反序列化方法
  static T Deserialize<T>(byte[] buffer, int size) {
    T obj = default(T);
    int objSize = System.Runtime.InteropServices.Marshal.SizeOf(typeof(T));
    if (size == objSize) {
      var ptr = System.Runtime.InteropServices.Marshal.AllocHGlobal(objSize);
      System.Runtime.InteropServices.Marshal.Copy(buffer, 0, ptr, objSize);
      obj = (T)System.Runtime.InteropServices.Marshal.PtrToStructure(ptr, typeof(T));
      System.Runtime.InteropServices.Marshal.FreeHGlobal(ptr);
    }
    return obj;
  }
}

UDP总结

UDP是一个高速传输的无连接协议，适合于实时性要求高的数据传输。使用UDP需要我们手动处理数据包的组装和拆解，同时对于丢包和乱序等问题需要自行处理。