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简介

UDP协议与TCP协议一样用于处理数据包，在OSI模型中，两者都位于传输层，处于IP协议的上一层。UDP有不提供数据包分组、组装和不能对数据包进行排序的缺点，也就是说，当报文发送之后，是无法得知其是否安全完整到达的。

代码实现

#ifndef _SOCKET_HPP_
#define _SOCKET_HPP_

#include <iostream>
#include <sstream>
#include <exception>
#include <string>
#include <stdlib.h>

#include <arpa/inet.h>

#define MAX_BUFFER 1024

using namespace std;

namespace Socket
{ 
   
    typedef int Socket;
    typedef string Ip;
    typedef unsigned int Port;
    typedef string Data;
    
    typedef struct
    { 
   
        Ip ip;
        Port port;
    }Address;
    
    typedef struct
    { 
   
        Address address;
        Data data;
    }Datagram;
    
    struct sockaddr_in* to_sockaddr(Address* a)
    { 
      struct sockaddr_in* ret;

        ret=(struct sockaddr_in*) malloc (sizeof(struct sockaddr_in));
        ret->sin_family = AF_INET;
        inet_aton(a->ip.c_str(),&(ret->sin_addr));
        ret->sin_port=htons(a->port);
            
        return ret;
    }

    Address* from_sockaddr(struct sockaddr_in* address)
    { 
      Address* ret;

        ret=(Address*)malloc(sizeof(Address));
        ret->ip = inet_ntoa(address->sin_addr);
        ret->port = ntohs(address->sin_port);
        
        return ret;
    }

    class Exception
    { 
   
    private:
        string _message;
    public:
        Exception(string error) { 
    this->_message = error; }
        virtual const char* what() { 
    return this->_message.c_str(); }
    };

    class UDP
    { 
   
    private:
        
        Socket _socket_id;
        bool _binded;
        
    public:
        
        UDP(void);
        ~UDP(void);
        void close(void);
        void bind(Port port);
        void send(Ip ip, Port port, Data data);
        Datagram receive();
    };

    UDP::UDP(void)
        { 
   
            this->_socket_id = socket(AF_INET, SOCK_DGRAM, 0);   
            if (this->_socket_id == -1) throw Exception("[Constructor] Cannot create socket");           
            this->_binded = false;
        }

    UDP::~UDP(void)
        { 
   
        }
        
    void UDP::close(void)
        { 
   
            shutdown(this->_socket_id, SHUT_RDWR);
        }
        
    void UDP::bind(Port port)
        { 
   
            struct sockaddr_in address;
            address.sin_family = AF_INET;
            address.sin_addr.s_addr=htonl(INADDR_ANY);
            address.sin_port=htons(port);
            
            if (this->_binded)
            { 
   
                this->close();
                this->_socket_id = socket(AF_INET, SOCK_DGRAM, 0);
            }
            // ::bind() calls the function bind() from <arpa/inet.h> (outside the namespace) 
            if (::bind(this->_socket_id, (struct sockaddr*)&address, sizeof(struct sockaddr_in)) == -1)
            { 
   
                stringstream error;
                error << "[listen_on_port] with [port=" << port << "] Cannot bind socket";
                throw Exception(error.str());
            }
            
            this->_binded = true;
        }
        
    void UDP::send(Ip ip, Port port, Data data)
        { 
   
            struct sockaddr_in address;
            address.sin_family = AF_INET;
            address.sin_port = htons(port);
            inet_aton(ip.c_str(), &address.sin_addr);
            
            if (sendto(this->_socket_id, (void*)data.c_str(), data.length() + 1, 0, (struct sockaddr*)&address, sizeof(struct sockaddr_in)) == -1)
            { 
   
                stringstream error;
                error << "[send] with [ip=" << ip << "] [port=" << port << "] [data=" << data << "] Cannot send";
                throw Exception(error.str());
            }
        }
        
    Datagram UDP::receive()
        { 
   
            int size = sizeof(struct sockaddr_in);
            char *buffer = (char*)malloc(sizeof(char) * MAX_BUFFER);
            struct sockaddr_in address;
            Datagram ret;
            
            if (recvfrom(this->_socket_id, (void*)buffer, MAX_BUFFER, 0, (struct sockaddr*)&address, (socklen_t*)&size) == -1) throw Exception("[receive] Cannot receive");
            
            ret.data = buffer;
            ret.address.ip = inet_ntoa(address.sin_addr);
            ret.address.port = ntohs(address.sin_port);
            
            free(buffer);
            
            return ret;
        }
}

#endif // _SOCKET_HPP_

使用示例

UDP server

#include <iostream>
#include "Socket.hpp"

using namespace std;

int main(void)
{ 
   
    try
    { 
   
        Socket::UDP sock;
        
        sock.bind(2000);
        
        Socket::Datagram received = sock.receive();
        
        cout << received.data << endl;
        
        sock.send("127.0.0.1", 3000, "response");
        
        sock.close();
    }
    catch (Socket::Exception &e)
    { 
   
        cout << e.what() << endl;
    }
    
    return 0;
}

UDP client

#include <iostream>
#include "Socket.hpp"

using namespace std;

int main(void)
{ 
   
    try
    { 
   
        Socket::UDP sock;
        
        sock.bind(3000);
        
        sock.send("127.0.0.1", 2000, "request");
        
        Socket::Datagram received = sock.receive();
        
        cout << received.data << endl;
        
        sock.close();
    }
    catch (Socket::Exception &e)
    { 
   
        cout << e.what() << endl;
    }
    
    return 0;
}