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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;
}