模拟一个简单的基于tcp的远程关机程序

最近在学习unix网络编程，现在正在学习tcp的通信。其实，只要建立起了tcp通信，操作远端的计算机就不是什么问题了。正向telnet一样，也是基于tcp/IP协议的。所以这个实验，也算是对telnet功能的一种简单的模拟。

但是，值得注意的问题是关机涉及到系统权限，所以要给运行在Server端的程序以足够的权限，这样才可以在接收到Client端的关机请求时，执行关机。

 

 

将会模拟如下执行过程：

1．执行 mytelnet 跟上参数telnet服务器 IP地址 127.0.0.1

2．输入login 向服务器请求登录，随之服务器会要求输入密码

3．输入一个错误的登录密码 123 

4．服务器验证不通过，所以返回Fail to login ,please check your password

5．再次输入密码，这次输入正确的密码123456

6．服务器验证通过，此时客户端可以执行基于telnet的远程操控

7．输入操控命令，例如关机命令shutdown 

8．服务器将会执行shutdown 操作。

 

 

在编译时使用如下的命令：

 

 

sudo gcc server.c -o server //足够的权限sudo chmod u+s server ./server 

 

gcc client.c -o mytelnet./mytelnet www.163.com 

 

Client端：

 

#include <stdio.h>#include <string.h>#include <arpa/inet.h>#include <netinet/in.h>#include <sys/socket.h>#define MAXLINE 4096void clientWork(FILE* fp , int sockfd){char sendline[MAXLINE],receiveline[MAXLINE];int n;while(fgets(sendline,MAXLINE,fp)!=NULL){write(sockfd,sendline,strlen(sendline));n=read(sockfd,receiveline,MAXLINE);receiveline[n]='/0';fputs(receiveline,stdout);if(strcmp(receiveline,"bye/n")==0) break;}}int main( int argc , char * * argv ){int sockfd , n ;char recvline[ MAXLINE + 1];struct sockaddr_in servaddr;if( ( sockfd = socket( AF_INET , SOCK_STREAM , 0 ) ) < 0 ) {printf( "socket error/n" );exit( 1 );}memset( &servaddr , 0 , sizeof( servaddr ) );servaddr.sin_family = AF_INET;servaddr.sin_port = htons( 2000 );//指定Server端的端口号char * serverAddress=argv[1];//判断指定的ip地址是否有错误if( inet_pton( AF_INET ,serverAddress , &servaddr.sin_addr ) <= 0 ) {printf( "inet_pton error for %s/n" , serverAddress );exit( 1 ); }if( connect( sockfd , (struct sockaddr *)&servaddr , sizeof( servaddr ) ) < 0 ) {printf( "connect error/n" );exit( 1 );}//从Terminal中读取用户输入的指令clientWork(stdin,sockfd);close(sockfd);return 0;} 

 

Server端：

 

#include <stdio.h>#include <string.h>#include <arpa/inet.h>#include <netinet/in.h>#include <sys/socket.h>#define MAXSIZE 1024#define LOGIN 1//登录Server#define BYE 2//离开Server#define PASS 3//合法登录#define DENY 4 //非法登录#define SHUTDOWN 5 //执行关机#define ERROR -1 //非法信息//记录状态信息static int STATE=0;int getClientChoice(char * clientmsg){if(strcmp(clientmsg,"login/n")==0) return LOGIN;if(STATE>0){if(strcmp(clientmsg,"bye/n")==0) return BYE;}if(STATE==LOGIN){//Default password is 123456if(strcmp(clientmsg,"123456/n")==0) return PASS;else return DENY;}if(STATE==PASS){if(strcmp(clientmsg,"shutdown/n")==0) return SHUTDOWN;else ERROR;}return ERROR;};//发送消息void sendMsg(int sockfd,char * buffer,char * msg){char buffer2[MAXSIZE];snprintf(buffer2,sizeof(buffer2),"%s",msg);write(sockfd,buffer2,sizeof(buffer2));}//定义关机函数void myshutdown(){//系统在一分钟后关机system("shutdown -t 1");}int main(int argc , char * * argv ){char buffer[MAXSIZE];int listenfd=socket(AF_INET,SOCK_STREAM,0);//定义socket，指向ipv4地址的字节流套接口struct sockaddr_in serverAddr;memset(&serverAddr,0,sizeof(serverAddr));//sockAddr_in 进行初始化serverAddr.sin_family=AF_INET;serverAddr.sin_addr.s_addr=htonl(INADDR_ANY);serverAddr.sin_port=htons(2000);if(bind(listenfd,(struct sockaddr *) &serverAddr,sizeof(serverAddr))==-1){printf("There is an error during binding/n");return -1;}else{printf("Bind successfully!!!/n");}//对listenfd进行监听，从最初建立时的主动套接口（用于进行connect的套接口）转化为被动套接口（接受连接）listen(listenfd,100);//第二个参数为套接口排队的最大连接个数int connectfd;socklen_t addrlen;struct sockaddr_in connectAddr;memset(&connectAddr,0,sizeof(connectAddr));printf("Be ready to accept a connection!/n");while(1){connectfd=accept(listenfd,(struct sockAddr * )&connectAddr,&addrlen);//接受client端一个请求的socketchar receivebuffer[MAXSIZE];int revbuflen;while(1){revbuflen = read(connectfd,receivebuffer,MAXSIZE);receivebuffer[revbuflen]='/0';//printf("%s",receivebuffer);int clientChoice=getClientChoice(receivebuffer);//模拟操作过程if(clientChoice==LOGIN){STATE=LOGIN;sendMsg(connectfd,buffer,"Please input your password :/n");}else if(clientChoice==PASS&&STATE==LOGIN){STATE=PASS;sendMsg(connectfd,buffer,"Welcome to my Telnet Server.../n");}else if(clientChoice==SHUTDOWN&&STATE==PASS){myshutdown();sendMsg(connectfd,buffer,"Remote computer is going to shutdown.../n");}else if (clientChoice==BYE){sendMsg(connectfd,buffer,"bye/n");break;}else if(clientChoice==DENY){sendMsg(connectfd,buffer,"Fail to login ,please check your password/n");}else if(clientChoice==ERROR){sendMsg(connectfd,buffer,"wrong,Check your input.../n");}}close(connectfd);}close(listenfd); //虽然因为上面有while（true），这行永远都执行不了，但是时刻注意关闭socket连接应该是个好习惯。 return 0;}