【Socket】linux广播技术

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１.mystery引入

１）本学期学的ARP协议和NTP协议都属于广播技术的实现，所以借此机会了解下广播技术的底层原理
２）在IP地址中，如果最后一个数字为255，则一定是一个广播地址
３）广播地址分为网络广播地址/受限广播地址/子网广播地址和全部子网广播地址
４）在设计广播程序时，要进行套接字的属性设置
５）广播通信要采用UDP的方式
６）广播套接字的属性为SO_BROADCAST
７）广播地址为INADDR_BROADCAST，同时也要指定发送的端口

２.实例操作

１）实现一个基于C/S模式的广播通信，服务器端程序负责创建广播组，并提供一个键盘输入接口，输入的信息向组内成员广播发送
２）客户端加入广播组，接收服务端的信息并显示，若发现信息中包含quit，则退出程序
３）源代码
服务器端：

//serverbroad.c
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <errno.h>
#define BUFFSIZE
#define PORT 5050
int main()
{
int serversocket;
struct sockaddr_in serveraddress,clientaddress;
int so_broadcast = 1;
socklen_t size;
if((serversocket=(socket(AF_INET,SOCK_DGRAM,0))) < 0)
{
perror("socket");
return 0;
}
if(setsockopt(serversocket,SOL_SOCKET,SO_BROADCAST,&so_broadcast,sizeof(so_broadcast)) < 0)
{
perror("setsockopt");
return 0;
}
serveraddress.sin_family=AF_INET;
serveraddress.sin_port=htons(INADDR_ANY);
serveraddress.sin_addr.s_addr= htonl(INADDR_BROADCAST);
if((bind(serversocket,(struct sockaddr *)&serveraddress, sizeof(struct sockaddr))) < 0)
{
perror("bind");
return 0;
}
clientaddress.sin_family=AF_INET;
clientaddress.sin_port=htons(PORT);
clientaddress.sin_addr.s_addr= htonl(INADDR_BROADCAST);
while (1)
{
char buf[200];
printf("please input your word:>");
scanf("%s",buf);
if((sendto(serversocket,buf,strlen(buf),0,(struct sockaddr *)&clientaddress,sizeof(clientaddress))) < 0)
{
perror("sendto error");
return 0;
}
else
printf("send msg %s\n",buf);
}
return 0;
}

客户端：

//clientbroad.c
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <errno.h>
int main()
{
int clientsocket;
struct sockaddr_in serveraddress,clientaddress;
clientsocket = socket(AF_INET, SOCK_DGRAM, 0);
serveraddress.sin_family = AF_INET;
serveraddress.sin_port = htons(5050);
serveraddress.sin_addr.s_addr = htonl(INADDR_ANY);
int opt = 1;
if(setsockopt(clientsocket, SOL_SOCKET, SO_REUSEADDR,&opt, sizeof(opt)) < 0)
{
perror("setsockopt:SO_REUSEADDR");
return 0;
}
if(bind(clientsocket,(struct sockaddr*)&serveraddress,sizeof(struct sockaddr)) != 0)
{
perror("bind");
return 0;
}
char buf[200];
while (1)
{
memset(buf,0,200);
int size = 0;
size = recvfrom(clientsocket,buf,200,0, (struct sockaddr *)&serveraddress,sizeof(serveraddress));
buf[size] = '\0';
printf("IP:%s msg:%s\n",inet_ntoa(serveraddress.sin_addr),buf);
if(strcmp(buf,"quit") == 0)
{
printf("system quit!!!!\n");
close(clientsocket);
return 0;
}
}
return 0;
}