UDP服务器

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


#define SERV_PORT      9877
#define BUF_MAX_SIZE   1024


int main()
{
    int lis_sock_fd, con_sock_fd;
    int ret;
    struct sockaddr_in serv_addr, cli_addr;
    socklen_t cli_addr_len;
    char buffer[BUF_MAX_SIZE] = {0};
    ssize_t nread_bytes, nwrite_bytes;
    int i;


    lis_sock_fd = socket(AF_INET, SOCK_DGRAM, 0);   //创建 socket  返回 socket 描述符
    if (-1 == lis_sock_fd)
    {
perror("socket");
exit(EXIT_FAILURE);
    }


    memset((struct sockaddr_in*)&serv_addr, 0, sizeof(struct sockaddr_in));


    serv_addr.sin_family = AF_INET;                     //指定 socket 域
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);      //指定 IP 地址
    serv_addr.sin_port = htons(SERV_PORT);              //指定 端口号


    ret = bind(lis_sock_fd, (struct sockaddr *)&serv_addr, (socklen_t)sizeof(serv_addr)); //命名 socket
    if (-1 == ret)
    {
perror("bind");
exit(EXIT_FAILURE);
    }


    while (1)
    {
cli_addr_len = sizeof(cli_addr);
printf("Waiting for client...\n");


while(nread_bytes = recvfrom(lis_sock_fd, buffer, BUF_MAX_SIZE, 0, (struct sockaddr *)&cli_addr, &cli_addr_len))
{
if (-1 == nread_bytes)
{
perror("recvfrom");
return;
}


printf("Connection from %s\n", inet_ntoa(cli_addr.sin_addr));

for (i = 0; i < strlen(buffer); i++)
{
buffer[i] += 'a' - 'A';
} 


nwrite_bytes = sendto(lis_sock_fd, buffer, nread_bytes, 0, (struct sockaddr *)&cli_addr, cli_addr_len);
if (-1 == nwrite_bytes)
{
perror("sendto");
return;
}
}
    }


    close(con_sock_fd);
    exit(EXIT_SUCCESS);
}