Linux平台C语言Socket编程练习之UDP套接字

c, c语言, socket programming, socket编程练习, udp socket, udp套接字

0x00 要求

实现一个基于UDP协议的服务器-客户端程序，要求完成以下功能:

服务端

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接收客户的连接请求，并发送欢迎信息，显示客户的IP地址和端口号；
 
循环接收接收客户传来的字符串，反转后传递给客户；

客户端

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从命令行读入服务器的IP地址；并连接到服务器；
 
循环从命令行读入一行字符串，并传递给服务器，由服务器对字符串反转，并将结果返回客户程序，如果用户输入的是quit，则关闭连接；
 
客户程序显示反转后的字符串；

0x01 代码

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define PORT 1234
#define MAXDATASIZE 100
int main()
{
    int sockfd;
    socklen_t client_len;
    ssize_t recv_num,send_num;
    struct sockaddr_in server;
    struct sockaddr_in client;
    char recv_buf[MAXDATASIZE];
    char send_buf[MAXDATASIZE];
    char response[MAXDATASIZE];
    char wel_msg[]="[!] Welcome,I can return your input,you can input 'quit' to exit:)";
    if((sockfd = socket(AF_INET,SOCK_DGRAM,0))==-1)
    {
        perror("socket() failed.");
        exit(1);
    }
    bzero(&server,sizeof(server));
    server.sin_family=AF_INET;
    server.sin_port=htons(PORT);
    server.sin_addr.s_addr=htonl(INADDR_ANY);
    client_len=sizeof(client);
    if((bind(sockfd,(struct sockaddr *)&server,sizeof(server)))==-1)
    {
        perror("bind() failed.");
        exit(1);
    }
    if((recvfrom(sockfd,response,MAXDATASIZE,0,(struct sockaddr *)&client,&client_len))==-1)
    {
        perror("recvfrom() failed.");
        exit(1);
    }
    printf("[!] You got a connection: message <%s> client ip <%s> port <%d>\n",response,inet_ntoa(client.sin_addr),ntohs(client.sin_port));
    if((sendto(sockfd,wel_msg,sizeof(wel_msg),0,(const struct sockaddr *)&client,client_len))==-1)
    {
        perror("sendto() failed");
        exit(1);
    }
    while(1)
    {
        if((recv_num=recvfrom(sockfd,recv_buf,MAXDATASIZE,0,(struct sockaddr *)&client,&client_len))==-1)
        {
            perror("recvfrom() failed.");
            exit(1);
        }
        recv_buf[recv_num]='\0';
        printf("[>] Receive client inputed string:%s\n",recv_buf);
        printf("[*] Return client inputed string:%s\n",recv_buf);
        strcpy(send_buf,recv_buf);
        if((send_num=(sendto(sockfd,send_buf,sizeof(send_buf),0,(struct sockaddr *)&client,client_len)))==-1)
        {
            perror("sendto() failed");
            exit(1);
        }
        if(!strcmp(recv_buf,"quit"))
        {
            printf("[!] Client request to exit.\n");
            close(sockfd);
            exit(1);
        }
    }
    close(sockfd);
    return 0;
}

客户端

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#define PORT 1234
#define MAXDATASIZE 100
int main(int argc,char *argv[])
{
    int sockfd;
    ssize_t recv_num,send_num;
    socklen_t server_len;
    char recv_buf[MAXDATASIZE];
    char send_buf[MAXDATASIZE];
    char request[]="hello";
    struct hostent *remote_host;
    struct sockaddr_in server;
    if(argc!=2)
    {
        printf("Usage:%s <IP Address>\n",argv[0]);
        exit(1);
    }
    if((remote_host=gethostbyname(argv[1]))==NULL)
    {
        printf("gethostbyname() failed.");
        exit(1);
    }
    if((sockfd=socket(AF_INET,SOCK_DGRAM,0))==-1)
    {
        perror("socket() failed.");
        exit(1);
    }
    bzero(&server,sizeof(server));
    server.sin_family=AF_INET;
    server.sin_port=htons(PORT);
    server.sin_addr=*((struct in_addr *)remote_host->h_addr);
    server_len=sizeof(server);
    if(sendto(sockfd,request,sizeof(request),0,(struct sockaddr *)&server,sizeof(server))==-1)
    {
        perror("sendto() failed.");
        exit(1);
    }
    if((recv_num=recvfrom(sockfd,recv_buf,MAXDATASIZE,0,(struct sockaddr*)&server,&server_len))==-1)
    {
        perror("recvfrom() failed.");
        exit(1);
    }
    printf("%s\n",recv_buf);
    while(1)
    {
        printf("[*] Please input ASCII string:");
        scanf("%s",send_buf);
        send_buf[strlen(send_buf)]='\0';
        if((send_num=sendto(sockfd,send_buf,strlen(send_buf),0,(struct sockaddr *)&server,sizeof(server)))==-1)
        {
            perror("sendto() failed.");
            exit(1);
        }
        if((recv_num=recvfrom(sockfd,recv_buf,MAXDATASIZE,0,(struct sockaddr*)&server,&server_len))==-1)
        {
            perror("recvfrom() failed.");
            exit(1);
        }
        printf("[>] Server return string:%s\n",recv_buf);
        if(!strcmp(recv_buf,"quit"))
        {
            printf("[!] You inputed 'quit' to exit.\n");
            close(sockfd);
            exit(1);
        }
    }
    close(sockfd);
    return 0;
}

0x02 演示

服务端

UDP 服务端.gif

客服端

UDP 客户端.gif

0x03 心得

UDP使用recvfrom函数接收数据，使用sendto函数发送数据，注意它们的传输的参数。