UDP广播的客户端和服务器端的代码设计

实验环境

linux

注意：

使用UDP广播，是客户端发送广播消息，服务器端接收消息。实际上是客户端探测局域网中可用服务器的一种手段。客户端发送，服务器端接收，千万不能弄混淆！！！

为了避免混淆，本文不使用client、server字眼。而使用send，recv

构建send_broadcast.c。发送广播消息，并打印接收端的IP和端口，退出时发送"done"消息

流程：创建一个socket，并用setscokopt函数声明这是一个broadcast类型的socket，然后通过这个socket向INADDR_BROADCAST("255.255.255.255")发送消息。

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>

#define PORT 1234
#define BUFFER_SIZE 100

int32_t main()
{
    char msg[BUFFER_SIZE] = "I am a broadcast message";
    int32_t nb = ;
    struct sockaddr_in addrto;
    int32_t nlen=sizeof(addrto); 

    int32_t sockfd = -;
    if ((sockfd = socket(AF_INET, SOCK_DGRAM, )) == -)
    {
        perror("create socket failed\n");
        return -;
    }    

    const int opt = ;
    //设置该套接字为广播类型，
    nb = setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST | SO_REUSEADDR, &opt, sizeof(opt));
    if(nb == -)
    {
        perror("set socket error...\n");
        return -;
    }  

    /**< 接收者地址结构 */
    bzero(&addrto, sizeof(struct sockaddr_in));
    addrto.sin_family = AF_INET;
    addrto.sin_addr.s_addr = htonl(INADDR_BROADCAST);
    addrto.sin_port = htons(PORT);  

    int ret = sendto(sockfd, msg, BUFFER_SIZE, , (struct sockaddr*)&addrto, nlen);
    if (ret < )
    {
        perror("send error.\n");
    } 

    /**< 打印接收者的IP和端口号 */
    printf("recver's ip is %s, port is %d.\n", inet_ntoa(addrto.sin_addr), htons(addrto.sin_port));

    bzero(msg, BUFFER_SIZE);
    memcpy(msg, "done", );

    sendto(sockfd, msg, BUFFER_SIZE, , (struct sockaddr*)&addrto, nlen);

    printf("Done\n");
    return ;
}  

构建recv_broadcast.c 接收广播消息，打印发送端的IP和端口号，在接收到done后停止并退出

流程：创建一个socket并绑定INADDR_ANY的本地地址，接收消息

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define PORT 1234
#define BUFFER_SIZE 100

int32_t main()
{
    struct sockaddr_in addrto;

    struct sockaddr_in from;
    int32_t listenfd = -;
    int32_t len = sizeof(from);
    char recvbuf[BUFFER_SIZE];

    if ((listenfd = socket(AF_INET, SOCK_DGRAM, )) == -)
    {
        perror("create socket failed\n");
        return -;
    } 

    bzero(&addrto, sizeof(struct sockaddr_in));
    bzero(&from, sizeof(struct sockaddr_in));
    addrto.sin_family = AF_INET;
    addrto.sin_port = htons(PORT);
    addrto.sin_addr.s_addr = htonl(INADDR_ANY);  

    const int opt = ;
    int32_t nb = setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
    if(nb == -)
    {
        perror("set socket error...\n");
        return -;
    }  

    /**< 绑定自己的地址 */
    if (bind(listenfd, (struct sockaddr *)&addrto, len) == -)
    {
        perror("bind error\n");
        return -;
    }

    while ()
    {
        //从广播地址接收消息
        int ret = recvfrom(listenfd, recvbuf, BUFFER_SIZE, , (struct sockaddr*)&from, &len);
        if (ret > )
        {
            recvbuf[ret] = '\0';
            printf("receive messgse:%s\n", recvbuf);
            if (!strcmp("done", recvbuf))
            {
                break;
            }
        }
        else
        {
            perror("recv error.\n");  

        }
        bzero(recvbuf, BUFFER_SIZE);

        /**< 打印发送者的ip和端口号 */
        printf("sender's ip is %s, port is %d.\n", inet_ntoa(from.sin_addr), htons(from.sin_port));
    }

    close(listenfd);
    printf("Done\n");
    return ;
}  

Makefile

all:sender recver
sender:
    gcc send_broadcast.c -o sender

recver:
    gcc recv_broadcast.c -o recver

clean:
    rm -rf sender recver