2020/2/22 Linux Socket编程 高级篇——基于UDP的广播实例

1. 服务端接收广播信号的程序

服务端receiver.c

#include <netdb.h>
#include <sys/socket.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <signal.h>
#include <time.h>
#include <arpa/inet.h>

int sockfd;

void sig_handler(int signo)//信号处理函数
{
	if(signo == SIGINT){
		printf("receiver will exited\n");
		close(sockfd);
		exit(1);
	}
}

int main(int argc, char *argv[])
{
	if(argc < 2){
		fprintf(stderr, "usage: %s port\n", argv[0]);
		exit(1);
	}
	if(signal(SIGINT, sig_handler) == SIG_ERR){//登记一个sigint信号，以及对应的sig_handler信号处理函数
		perror("signal sigint error");
		exit(1);
	}

	sockfd = socket(AF_INET, SOCK_DGRAM, 0);//创建socket，广播只能用在UDP中
	if(sockfd < 0){
		perror("socket error");
		exit(1);
	}
	struct sockaddr_in serveraddr;			//定义服务器地址结构体
	memset(&serveraddr, 0, sizeof(serveraddr));
	serveraddr.sin_family = AF_INET;
	serveraddr.sin_port = htons(atoi(argv[1]));
	serveraddr.sin_addr.s_addr = INADDR_ANY;//绑定服务器上所有地址；也可以专门绑定广播地址，但要把点分十进制转换成网络字节序
	if(bind(sockfd, (struct sockaddr*)&serveraddr, sizeof(serveraddr)) < 0){
		perror("bind error");
		exit(1);
	}

	char buffer[1024];
	struct sockaddr_in clientaddr;//定义客户端地址结构体，并创建缓存，用于保存接收广播信息
	socklen_t len = sizeof(clientaddr);
	while(1){
		memset(buffer, 0, sizeof(buffer));
		memset(&clientaddr, 0, sizeof(clientaddr));
		if(recvfrom(sockfd, buffer, sizeof(buffer), 0, (struct sockaddr*)&clientaddr, &len) < 0){
			perror("recvfrom error");
			exit(1);	
		}
		else{
			char ip[16];
			inet_ntop(AF_INET, &clientaddr.sin_addr.s_addr, ip, sizeof(ip));
			int port = ntohs(clientaddr.sin_port);
			printf("%s(%d): %s\n", ip, port, buffer);
		}

	}
	
	return 0;
}

2. 客户端发送广播信号的程序

客户端broadcast.c

#include <netdb.h>
#include <sys/socket.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <signal.h>
#include <time.h>
#include <arpa/inet.h>


int main(int argc, char *argv[])
{
	if(argc < 3){
		fprintf(stderr, "usage: %s ip port\n", argv[0]);
		exit(1);
	}

	int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
	if(sockfd < 0){
		perror("socket error");
		exit(1);
	}

	int opt = 1;
	//采用广播方式发送
	setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, &opt, sizeof(opt));

	struct sockaddr_in serveraddr;
	memset(&serveraddr, 0, sizeof(serveraddr));
	serveraddr.sin_family = AF_INET;
	serveraddr.sin_port = htons(atoi(argv[2]));
	inet_pton(AF_INET, argv[1], &serveraddr.sin_addr.s_addr);
	printf("I will broadcast...\n");
	char *info = "hello I'm client";
	size_t size = strlen(info) * sizeof(char);
	if(sendto(sockfd, info, size, 0, (struct sockaddr*)&serveraddr, sizeof(serveraddr)) < 0){
		perror("sendto error");
		exit(1);
	}
	else{
		printf("broadcast success\n");
	}
	close(sockfd);

	return 0;
}

3. 运行结果

如果在同一个网段中，另一台机器上也打开一个receiver，使用同样的端口8888， 也会收到这个广播信息。