多播

• 多播（Multicast）方式的資料傳輸時基於UDP完成的。
• TTL(time of live)，是決定“資料包傳遞距離”的主要因素。用整數表示，每經過一個路由器就減1，變為0時，資料包無法再傳遞，只能銷燬。

news_sender

//
//  main.c
//  news_sender
//
//  Created by lee on 15/10/26.
//  Copyright (c) 2015年 . All rights reserved.
//

#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);

int main(int argc, const char * argv[])
{
    int send_sock;
    struct sockaddr_in mul_adr;
    int time_live = TTL;
    FILE *fp;
    char buf[BUF_SIZE];

    if
 
 (argc != 4) {
        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]);
    mul_adr.sin_port = htons(atoi(argv[2
 
]));

    //設定TTL的方法
    setsockopt(send_sock, IPPROTO_IP, IP_MULTICAST_TTL, (void *)&time_live, sizeof(time_live));
    if ((fp = fopen(argv[3], "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;
}


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

    exit(1);
}

news_receiver

//
//  main.c
//  news_receiver
//
//  Created by lee on 15/10/26.
//  Copyright (c) 2015年 . All rights reserved.
//

#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);

int main(int argc, const 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]));

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

    //加入多播組通過設定套接字選項完成
    //多播組地址資訊
    join_adr.imr_multiaddr.s_addr = inet_addr(argv[1]);
    //加入多播組的主機地址資訊
    join_adr.imr_interface.s_addr = htonl(INADDR_ANY);

    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;
}


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

    exit(1);
}