socket编程——C实现服务端与客户端间通信实现大小写转换

编译环境：VIM (Ubuntu 16.04)

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更新：1）程序加上了对错误的处理
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常用函数笔记：Socket编程——常用函数

程序包括服务端（server.c）和客户端（client.c），客户端实现从shell中输入小写字母，通过socket也就是套接字将数据发给服务端，服务端实现小写->大写，再将转换好的数据发回客户端。、

执行顺序：server ----> client
结束顺序：client  ----> server

如果先终止server的话会导致server绑定的端口不能及时被释放，下次再执行server的时候可能会报错。

server.c
——

#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <ctype.h>
#include <string.h>

#define SERV_IP "127.0.0.1"
#define SERV_PORT 6666

int main()
{
    int lfd,cfd;
    struct sockaddr_in serv_addr, clie_addr;
    socklen_t clie_addr_len;
    char buf[BUFSIZ], clie_IP[BUFSIZ];
    int n, i, ret;

    lfd = socket(AF_INET, SOCK_STREAM, 0);//IPV4,TCP
    if(lfd == -1){
        perror("socket error");
        exit(1);
    } 
    serv_addr.sin_family = AF_INET;//IPV4 与socket()的参数相同
    serv_addr.sin_port = htons(SERV_PORT);//本地字节序(小端)->网络字节序(大端)
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);//INADDR_ANY:本地任意IP(点分十进制类型)

    ret = bind(lfd ,(struct sockaddr *)&serv_addr, sizeof(serv_addr)); //绑定
    if(ret == -1){
        perror("bind error");
        exit(1);
    } 
    ret = listen(lfd, 128);//设定最大同时连接数，default:128 
    if(ret == -1){
        perror("listen error");
        exit(1);
    } 
    clie_addr_len = sizeof(clie_addr);
    cfd = accept(lfd,(struct sockaddr *)&clie_addr, &clie_addr_len);//accept():接收一个连接
    if(cfd == -1){
        perror("accept error");
        exit(1);
    } 
    printf("client IP:%s, client Port:%d
", 
            inet_ntop(AF_INET, &clie_addr.sin_addr.s_addr, clie_IP, sizeof(clie_IP)),ntohs(clie_addr.sin_port));
    while(1)
    {
        memset(buf,0,sizeof(buf));
        n = read(cfd, buf, sizeof(buf)); //服务器程序阻塞在这，从客户端读取
        if(strcmp(buf, "q
") == 0) break;
        for(i = 0; i < n; i++)
            buf[i] = toupper(buf[i]);    //小写 -> 大写
        write(cfd, buf, n);              //写回客户端
    }
    close(lfd);
    close(cfd);

    return 0;
}

client.c
——

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <string.h>

#define SERV_IP "127.0.0.1"
#define SERV_PORT 6666
int main()
{
    int cfd, n, ret;
    struct sockaddr_in serv_addr;
    char buf[BUFSIZ];
    cfd = socket(AF_INET, SOCK_STREAM, 0);
    if(cfd == -1){
        perror("socket error");
        exit(1);
    }    
    memset(&serv_addr,0,sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(SERV_PORT);
    inet_pton(AF_INET, SERV_IP, &serv_addr.sin_addr); //字符串"127.0.0.1" ---> 网络端格式

    ret = connect(cfd, (struct sockaddr *)&serv_addr, (socklen_t)sizeof(serv_addr)); //连接
    if(ret == -1){
        perror("socket error");
        exit(1);
    }    

    while(1)
    {
     fgets(buf,sizeof(buf),stdin); //hello world -- fgets  --->"hello world
"
     write(cfd,buf,strlen(buf));
     n = read(cfd,buf,sizeof(buf));      
     write(STDOUT_FILENO,buf,n);
    }
    close(cfd);
    return 0;
}