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 8888int 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 8888int 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;}