linux网络编程（组播）

组播

1. 分组

每个D类IP地址就是一个组，组播实现原理:

接收 -- 加入一个组

发送 -- 向一个组(目标IP地址为组播地址)发送数据包

2. 组播地址(IP地址和网卡地址)

IP地址: D类地址 ，高位固定为1110，范围: 224.0.0.0-239.255.255.255

网卡地址: 前24bit固定为01-00-5e, 最后23bit是D类IP地址的后23bit直接映射下来 -- 仅仅正对于以太网

3. 接收流程

(1) 创建套接字

sockfd = socket(AF_INET, SOCK_DGRAM, 0);

(2) 加入组

struct ip_mreq mreq;

mreq.imr_multiaddr.s_addr = inet_addr(argv[1]); // "224.10.10.1"

mreq.imr_interface.s_addr = INADDR_ANY;

ret = setsockopt(sockfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));

(3) 绑定IP地址和端口

struct sockaddr_in addr;

bzero(&addr, sizeof(addr));

addr.sin_family = AF_INET;

addr.sin_port = htons(port);

addr.sin_addr.s_addr = inet_addr(ip);

// addr.sin_addr.s_addr = INADDR_ANY;

ret = bind(sockfd, (struct sockaddr *)&addr, sizeof(addr));

(4) 接收

struct sockaddr_in peer_addr;

socklen_t addrlen = sizeof(peer_addr);

ret = recvfrom(sockfd, buf, sizeof(buf), 0, (struct sockaddr *)&peer_addr, &addrlen);

(3) 关闭

close(sockfd);

4. 发送流程

(1) 创建套接字

sockfd = socket(AF_INET, SOCK_DGRAM, 0);

(2) 发送

struct sockaddr_in muticast_addr;

bzero(&muticast_addr, sizeof(muticast_addr));

muticast_addr.sin_family = AF_INET;

muticast_addr.sin_port = htons(port);

muticast_addr.sin_addr.s_addr = inet_addr(一定填多播(224.10.10.1));

ret = sendto(sockfd, buf, len, 0, (struct sockaddr *)&broad_addr, sizeof(broad_addr));

(3) 关闭

close(sockfd);

组播（代码）

一、发送端

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <strings.h>

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

// ./send 224.0.0.1 8888
int main(int argc, const char *argv[])
{
int ret;
int sockfd;
char packet[1024];
struct sockaddr_in muti_addr;

if (argc < 3){
fprintf(stderr, "Usage: %s <broadcast ip> <port>\n", argv[0]);
exit(EXIT_FAILURE);
}

// 1. 创建报文套接字
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (-1 == sockfd){
perror("Fail to socket.");
exit(EXIT_FAILURE);
}

// 2. 通过多播地址发送数据包到指定端口
bzero(&muti_addr, sizeof(muti_addr));
muti_addr.sin_family = AF_INET;
muti_addr.sin_port = htons(atoi(argv[2]));
muti_addr.sin_addr.s_addr = inet_addr(argv[1]);

while (1){
putchar('\n');
putchar('>');
fgets(packet, sizeof(packet), stdin);
packet[strlen(packet) - 1] = '\0';

ret = sendto(sockfd, packet, strlen(packet), 0, (struct sockaddr *)&muti_addr, sizeof(muti_addr));
if (-1 == ret){
perror("Fail to sendto.");
break;
}

if (strcmp(packet, "quit") == 0){
break;
}
}

// 3. 关闭套接字
close(sockfd);

return 0;
}

二、接收端

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <strings.h>

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

// ./recv 192.168.2.255 8888
int main(int argc, const char *argv[])
{
int ret;
int sockfd;
char packet[1024];
struct sockaddr_in addr;
struct ip_mreq mreq;
struct sockaddr_in peer_addr;
socklen_t addrlen = sizeof(peer_addr);

if (argc < 3){
fprintf(stderr, "Usage: %s <broadcast ip> <port>\n", argv[0]);
exit(EXIT_FAILURE);
}

// 1. 创建报文套接字
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (-1 == sockfd){
perror("Fail to socket.");
exit(EXIT_FAILURE);
}
//加入组
mreq.imr_multiaddr.s_addr = inet_addr(argv[1]);
mreq.imr_interface.s_addr = INADDR_ANY;
ret = setsockopt(sockfd,IPPROTO_IP,IP_ADD_MEMBERSHIP,&mreq,sizeof(mreq));
if(-1 == ret){
perror("fail to setsockopt");
exit(EXIT_FAILURE);
}
// 2. 绑定广播地址和端口
bzero(&addr, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(atoi(argv[2]));
// broad_addr.sin_addr.s_addr = inet_addr(argv[1]);
addr.sin_addr.s_addr = INADDR_ANY;

ret = bind(sockfd, (struct sockaddr *)&addr, sizeof(addr));
if (-1 == ret){
perror("Fail to bind.");
exit(EXIT_FAILURE);
}

while (1){
// 3. 接收
ret = recvfrom(sockfd, packet, sizeof(packet), 0, (struct sockaddr *)&peer_addr, &addrlen);
if (-1 == ret){
perror("Fail to recvfrom.");
break;
}
packet[ret] = '\0';

printf("---------------------------------------\n");
printf("ip       : %s\n", inet_ntoa(peer_addr.sin_addr));
printf("port     : %d\n", ntohs(peer_addr.sin_port));
printf("recv(%d)  : %s\n", ret, packet);
printf("---------------------------------------\n");
if (strcmp(packet, "quit") == 0){
break;
}
}

// 4. 关闭套接字
close(sockfd);

return 0;
}