UDP广播：一对多数据发送

一、怎么样进行UDP一对多数据发送？

1.很容易想到的一种方法是：如果一个client 要向其他其他100个server发送数据，那应该怎么办？如果我知道其他100个 server的ip地址 和 端口号就可以了，那么我们在一对一的进行发送就可以了。但是这种方法有点低效率了，接下来介绍高效的方式。

二、UDP通信中的广播

1.广播是向同一网络中的所有主机传输数据的方法

2.广播类型

        2.1 直接广播：IP地址中除网络地址外，其余主机地址均设置为1。比如：一个ip地址为：192.168.1.xxx 这个ip地址的前三个字节 192.168.1 为网络字节(net id)，后面一个字节xxx 为主机字节(host id)，这个时候需要把 xxx 设置成255(其余主机地址均设置为1)

        2.2 本地广播：无需要知道网络地址，使用 255.255.255.255 作为IP地址使用

3.区别：本地广播不经过路由器寻址，直接发送到本地主机

 

/* Put the current value for socket FD's option OPTNAME at protocol level LEVEL
   into OPTVAL (which is *OPTLEN bytes long), and set *OPTLEN to the value's
   actual length.  Returns 0 on success, -1 for errors.  */
extern int getsockopt (int __fd, int __level, int __optname,
               void *__restrict __optval,
               socklen_t *__restrict __optlen) __THROW;

/* Set socket FD's option OPTNAME at protocol level LEVEL
   to *OPTVAL (which is OPTLEN bytes long).
   Returns 0 on success, -1 for errors.  */
extern int setsockopt (int __fd, int __level, int __optname,
               const void *__optval, socklen_t __optlen) __THROW;

server.c

#include 
#include 
#include 
#include 
#include 
#include 
#include 

int main()
{
    int server = 0;
    struct sockaddr_in saddr = {0};
    int client = 0;
    struct sockaddr_in remote = {0};
    socklen_t asize = 0;
    int len = 0;
    char buf[32] = "Software";
    int r = 0;
    int brd = 1;

    server = socket(PF_INET, SOCK_DGRAM, 0);

    if( server == -1 )
    {
        printf("server socket error\n");
        return -1;
    }

    saddr.sin_family = AF_INET;
    saddr.sin_addr.s_addr = htonl(INADDR_ANY);
    saddr.sin_port = htons(8888);

    if( bind(server, (struct sockaddr*)&saddr, sizeof(saddr)) == -1 )
    {
        printf("udp server bind error\n");
        return -1;
    }

    printf("udp server start success\n");

    remote.sin_family = AF_INET;
    // remote.sin_addr.s_addr = inet_addr("192.168.3.255");
    remote.sin_addr.s_addr = 0xFFFFFFFF;
    remote.sin_port = htons(9000);

    // brd = 0;

    setsockopt(server, SOL_SOCKET, SO_BROADCAST, &brd, sizeof(brd));

    while( 1 )
    {
        len = sizeof(remote);

        r = strlen(buf);
        
        sendto(server, buf, r, 0, (struct sockaddr*)&remote, len);

        sleep(1);
    }
    
    close(server);

    return 0;
}

client.c

#include 
#include 
#include 
#include 
#include 
#include 
#include 

int main()
{
    int sock = 0;
    struct sockaddr_in addr = {0};
    struct sockaddr_in remote = {0};
    int len = 0;
    char buf[128] = {0};
    char input[32] = {0};
    int r = 0;

    sock = socket(PF_INET, SOCK_DGRAM, 0);

    if( sock == -1 )
    {
        printf("socket error\n");
        return -1;
    }

    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = htonl(INADDR_ANY);
    addr.sin_port = htons(9000);

    if( bind(sock, (struct sockaddr*)&addr, sizeof(addr)) == -1 )
    {
        printf("udp bind error\n");
        return -1;
    }

    remote.sin_family = AF_INET;
    remote.sin_addr.s_addr = inet_addr("127.0.0.1");
    remote.sin_port = htons(8888);

    while( 1 )
    {
        r = recvfrom(sock, buf, sizeof(buf), 0, (struct sockaddr*)&remote, &len);

        if( r > 0 )
        {
            buf[r] = 0;

            printf("Receive: %s\n", buf);
        }
        else
        {
            break;
        }
    }

    close(sock);

    return 0;
}