目录

1--多播

2--多播代码实例

3--广播

4--广播代码实例

1--多播

// 与 TTL 相关的协议层是 IPPROTO_IP，选项名为IP_MULTICAST_TTL
// 以下伪代码将 TTL 设置为 64
int send_sock;
int time_live = 64;
send_sock = socket(PF_INET, SOCK_DGRAM, 0);
setsockopt(send_sock, IPPROTO_IP, IP_MULTICAST, (void*) &time_live, sizeof(time_live));

// 与加入多播组相关的协议层是 IPPROTO_IP，选项名为IP_ADD_MEMBERSHIP
// 以下伪代码实现加入多播组
int recv_sock;
struct ip_mreq join_adr;
...
recv_sock = socket(PFINET, SOCK_DGRAM, 0);
...
join_adr.imr_multiaddr.s_addr = "多播组地址信息";
join_adr.imr_interface.s_addr = "加入多播组的主机地址信息";
setsockopt(recv_sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (void*)& join_adr, sizeof(join_adr));
...

struct ip_mreq{
    struct in_addr imr_multiaddr; // 表示加入的多播组IP地址
    struct in_addr imr_interface; // socket所属主机的IP地址，可以使用 INADDR_ANY
} 

2--多播代码实例

发送端：

// gcc news_sender.c -o news_sender
// ./news_sender 224.1.1.2 9190

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>

#define TTL 64
#define BUF_SIZE 30

void error_handling(char *message){
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}

int main(int argc, char* argv[]){
    int send_sock;
    struct sockaddr_in mul_adr;
    int time_live = TTL; // 初始化 TTL 大小
    FILE* fp;
    char buf[BUF_SIZE];
    if(argc != 3){
        printf("Usage: %s <GroupIP> <PORT>\n", argv[0]);
        exit(1);
    }

    send_sock = socket(PF_INET, SOCK_DGRAM, 0);
    memset(&mul_adr, 0, sizeof(mul_adr));
    mul_adr.sin_family = AF_INET;
    mul_adr.sin_addr.s_addr = inet_addr(argv[1]); // 多播IP
    mul_adr.sin_port = htons(atoi(argv[2])); // 多播端口

    setsockopt(send_sock, IPPROTO_IP, IP_MULTICAST_TTL, (void*)&time_live, sizeof(time_live));
    if((fp = fopen("news.txt", "r")) == NULL){
        error_handling("fopen() error");
    }

    while(!feof(fp)){
        fgets(buf, BUF_SIZE, fp);
        sendto(send_sock, buf, strlen(buf), 0, (struct sockaddr*)&mul_adr, sizeof(mul_adr));
        sleep(2);
    }
    fclose(fp);
    close(send_sock);
    return 0;
}

接收端：

// gcc news_receiver.c -o news_receiver
// ./news_receiver 224.1.1.2 9190
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>

#define BUF_SIZE 30

void error_handling(char *message){
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}

int main(int argc, char* argv[]){
    int recv_sock;
    int str_len;
    char buf[BUF_SIZE];
    struct sockaddr_in adr;
    struct ip_mreq join_adr;

    if(argc != 3){
        printf("Usage: %s <GroupIP> <PORT>\n", argv[0]);
        exit(1);
    }

    recv_sock = socket(PF_INET, SOCK_DGRAM, 0);
    memset(&adr, 0, sizeof(adr));
    adr.sin_family = AF_INET;
    adr.sin_addr.s_addr = htonl(INADDR_ANY);
    adr.sin_port = htons(atoi(argv[2])); // 多播端口

    if(bind(recv_sock, (struct sockaddr*) &adr, sizeof(adr)) == -1){
        error_handling("bind() error");
    }

    join_adr.imr_multiaddr.s_addr = inet_addr(argv[1]); // 设置接收的多播地址
    join_adr.imr_interface.s_addr = htonl(INADDR_ANY); // 设置本机地址

    // 设置 IP_ADD_MEMBERSHIP 可选项，允许加入多播组
    setsockopt(recv_sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (void*)&join_adr, sizeof(join_adr));

    while(1){
        str_len = recvfrom(recv_sock, buf, BUF_SIZE-1, 0, NULL, 0);
        if(str_len < 0){
            break;
        }
        buf[str_len] = 0;
        fputs(buf, stdout);
    }
    close(recv_sock);
    return 0;
}

3--广播

// 数据通信中使用的 IP 地址是与 UDP 示例的唯一区别
// 默认生成的 socket 会阻止广播，因此需要使用以下伪代码更改默认设置
// 调用 setsockopt() 函数，将 SO_BROADCAST 选项设置为 bcast 变量中的值 1
int send_sock;
int bcast = 1;
...
send_sock = socket(PF_INET, SOCK_DGRAM, 0);
...
setsockopt(send_sock, SOL_SOCKET, SO_BROADCAST, (void*)& bcast, sizeof(bcast));
...

4--广播代码实例

发送端：

// gcc news_sender_brd.c -o news_sender_brd
// ./news_sender_brd 255.255.255.255 9190

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>

#define BUF_SIZE 30

void error_handling(char *message){
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}

int main(int argc, char* argv[]){
    int send_sock;
    struct sockaddr_in broad_adr;
    FILE* fp;
    char buf[BUF_SIZE];
    int so_brd = 1;
    if(argc != 3){
        printf("Usage: %s <Broadcast_IP> <PORT>\n", argv[0]);
        exit(1);
    }

    send_sock = socket(PF_INET, SOCK_DGRAM, 0);
    memset(&broad_adr, 0, sizeof(broad_adr));
    broad_adr.sin_family = AF_INET;
    broad_adr.sin_addr.s_addr = inet_addr(argv[1]); // 广播IP
    broad_adr.sin_port = htons(atoi(argv[2])); // 广播端口

    // 允许数据广播
    setsockopt(send_sock, SOL_SOCKET, SO_BROADCAST, (void*)&so_brd, sizeof(so_brd));
    if((fp = fopen("news.txt", "r")) == NULL){
        error_handling("fopen() error");
    }

    while(!feof(fp)){
        fgets(buf, BUF_SIZE, fp);
        sendto(send_sock, buf, strlen(buf), 0, (struct sockaddr*)&broad_adr, sizeof(broad_adr));
        sleep(2);
    }
    close(send_sock);
    return 0;
}

接收端：

// gcc news_receiver_brd.c -o news_receiver_brd
// ./news_receiver_brd 9190
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>

#define BUF_SIZE 30

void error_handling(char *message){
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}

int main(int argc, char* argv[]){
    int recv_sock;
    struct sockaddr_in adr;
    int str_len;
    char buf[BUF_SIZE];

    if(argc != 2){
        printf("Usage: %s <PORT>\n", argv[0]);
        exit(1);
    }

    recv_sock = socket(PF_INET, SOCK_DGRAM, 0);
    memset(&adr, 0, sizeof(adr));
    adr.sin_family = AF_INET;
    adr.sin_addr.s_addr = htonl(INADDR_ANY);
    adr.sin_port = htons(atoi(argv[1])); // 接收的广播端口

    if(bind(recv_sock, (struct sockaddr*) &adr, sizeof(adr)) == -1){
        error_handling("bind() error");
    }

    while(1){
        str_len = recvfrom(recv_sock, buf, BUF_SIZE-1, 0, NULL, 0);
        if(str_len < 0){
            break;
        }
        buf[str_len] = 0;
        fputs(buf, stdout);
    }
    close(recv_sock);
    return 0;
}