unix网络编程笔记---15.UDP的C/S之2回射客户端并启动echo服务

1. 利用现成的echo服务端与自己写的client端进行udp通信
2. 代码

cong@msi:/work/test/tcpip/14udp/client$ cat client.c
#include "utils.h"

//#define TIME_SERV_ADDR "192.168.4.98"
#define TIME_SERV_ADDR "127.0.0.1"

char * sock_ntop(const struct sockaddr *sa, socklen_t salen)
{
    char        portstr[8];
    static char str[128]; /* Unix domain is largest */
    struct sockaddr_in *sin = (struct sockaddr_in *) sa;
    //只处理AF_INET 协议族
    if (inet_ntop(AF_INET, &sin->sin_addr, str, sizeof(str)) == NULL)
        return(NULL);
    if (ntohs(sin->sin_port) != 0) {
        snprintf(portstr, sizeof(portstr), ":%d", ntohs(sin->sin_port));
        strcat(str, portstr);
    }
    return(str);
}

void dg_cli(FILE* fp, int sockfd, const struct sockaddr* pservaddr, socklen_t servlen)
{
    int n;
    char sendline[MAXLINE], recvline[MAXLINE];
    socklen_t len;
    struct sockaddr* preply_addr;
    preply_addr = malloc(servlen);
    while(fgets(sendline, MAXLINE, fp) != NULL)
    {
        //write(sockfd, sendline, strlen(sendline));
        sendto(sockfd, sendline, strlen(sendline), 0, pservaddr, servlen);

        len = servlen;
        n = recvfrom(sockfd, recvline, MAXLINE, 0, preply_addr, &len);
        if( (len!=servlen) || (memcmp(pservaddr, preply_addr, len)!= 0))
        {
            dbmsg("reply from %s (ignored)",sock_ntop(preply_addr,len));
            continue;
        }
        recvline[n] = 0;
        fputs(recvline, stdout);
    }
}

int main ( int argc, char *argv[] )
{
    int sockfd, n;
    struct sockaddr_in servaddr;
    char recvline[1024];
    //sockfd = socket(AF_INET, SOCK_STREAM, 0);
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if(sockfd < 0)
        return -1;
    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(7);
    inet_pton(AF_INET, TIME_SERV_ADDR, &servaddr.sin_addr);

    //connect(sockfd, (const struct sockaddr*)&servaddr, sizeof(servaddr));
    dbmsg("next dg_cli");
    dg_cli(stdin, sockfd, (const struct sockaddr*)&servaddr, sizeof(servaddr));
    return EXIT_SUCCESS;
}

3.错误分析
client端没有收到回复的原因是本机的echo服务没有打开
本机配置一下:

cong@msi:/tmp$ sudo apt-get install xinetd
cong@msi:/tmp$ sudo vi /etc/inetd.conf
   echo dgram udp  wait    root    internal       -->配置echo服务是udp
   #echo stream    tcp nowait  root    internal   -->配置echo服务是tcp
cong@msi:/tmp$ sudo /etc/init.d/xinetd restart
cong@msi:/tmp$ netstat -nlp                -->查看端口
   tcp        0      0 0.0.0.0:7               0.0.0.0:* LISTEN -       -->配置echo服务是tcp就会出现这一行
   udp        0      0 0.0.0.0:7               0.0.0.0:* -              -->配置echo服务是udp,就会出现这一行

netstat -nlp查看时出现
udp 0 0 0.0.0.0:7 0.0.0.0:* -   -->出现这一行就是我们需要的
client.rar (下载后改名为client.tar.gz)