带超时时间的telnet该怎么玩？------检测tcp是否可连接时经常用到（本文仅给出linux版本，之前博客也有Windows版本的）

        前面说过， 利用ping命令探测网络是否可通， 但很多时候， 服务端或者防火墙禁止了ping命令， 也就是说， ping不通， 不表示网络不通， 所以仍有可能能建立tcp连接。怎么检测tcp连接是否可通呢？ 用telnet命令就可以搞起， 但问题是， 很多时候（尤其是批量探测的时候）， 我们需要给telnet命令设置一个超时时间， 很遗憾， 这是telnet命令所不支持的。 那要怎么搞？ 还是自己写程序吧， 如下：

#include <unistd.h>#include <sys/types.h>#include <sys/socket.h>#include <netdb.h>#include <stdio.h>#include <stdlib.h>#include <string.h>#include <ctype.h>#include <errno.h>#include <malloc.h>#include <netinet/in.h>#include <arpa/inet.h>#include <sys/ioctl.h>#include <stdarg.h>#include <fcntl.h>#include <time.h>int telnetCheckTcp(const char *ip, int port, int tSecond){int sockClient = socket(AF_INET, SOCK_STREAM, 0);int iFinal = 0;struct sockaddr_in addrSrv;addrSrv.sin_addr.s_addr = inet_addr(ip);addrSrv.sin_family = AF_INET;addrSrv.sin_port = htons(port);fcntl(sockClient, F_SETFL, fcntl(sockClient, F_GETFL, 0)|O_NONBLOCK);  int iRet = connect(sockClient, ( const struct sockaddr *)&addrSrv, sizeof(struct sockaddr_in));  // 返回-1不一定是异常if (iRet != 0){  if(errno != EINPROGRESS){iFinal = -1;}else  {struct timeval tm = {tSecond, 0}; fd_set wset, rset;FD_ZERO(&wset); FD_ZERO(&rset); FD_SET(sockClient, &wset);FD_SET(sockClient, &rset); int time1 = time(NULL);int n = select(sockClient + 1, &rset, &wset, NULL, &tm);  int time2 = time(NULL);if(n < 0){      iFinal = -2;  }  else if(n == 0)  {      iFinal = -3;  }  else if (n == 1)  {   if(FD_ISSET(sockClient, &wset))   {     iFinal = 0;    fcntl(sockClient, F_SETFL, fcntl(sockClient, F_GETFL, 0) & ~O_NONBLOCK);     }     else     {     iFinal = -4;   }  }else{iFinal = -5;}}  }  close(sockClient);return iFinal;}int main(int argc, char *argv[]){if(argc != 4){printf("error\n");return -1;}int iFinal = telnetCheckTcp(argv[1], atoi(argv[2]), atoi(argv[3]));printf("iFinal is %d\n", iFinal);return 0;}

        来试下：

ubuntu@VM-0-13-ubuntu:~$ ./a.out 220.181.112.244 80 2iFinal is 0ubuntu@VM-0-13-ubuntu:~$ ./a.out 220.181.112.244 81 2iFinal is -3ubuntu@VM-0-13-ubuntu:~$ ./a.out 220.181.112.244 443 2iFinal is 0ubuntu@VM-0-13-ubuntu:~$ ./a.out 220.181.112.244 445 2iFinal is -3ubuntu@VM-0-13-ubuntu:~$ ./a.out 1.1.1.1 80 2iFinal is -3ubuntu@VM-0-13-ubuntu:~$ 

        

        批量探测怎么搞呢？ 来看看：

#include <unistd.h>#include <sys/types.h>#include <sys/socket.h>#include <netdb.h>#include <stdio.h>#include <stdlib.h>#include <string.h>#include <ctype.h>#include <errno.h>#include <malloc.h>#include <netinet/in.h>#include <arpa/inet.h>#include <sys/ioctl.h>#include <stdarg.h>#include <fcntl.h>#include <time.h>#include <iostream>#include <fstream>using namespace std;int telnetCheckTcp(const char *ip, int port, int tSecond){int sockClient = socket(AF_INET, SOCK_STREAM, 0);int iFinal = 0;struct sockaddr_in addrSrv;addrSrv.sin_addr.s_addr = inet_addr(ip);addrSrv.sin_family = AF_INET;addrSrv.sin_port = htons(port);fcntl(sockClient, F_SETFL, fcntl(sockClient, F_GETFL, 0)|O_NONBLOCK);  int iRet = connect(sockClient, ( const struct sockaddr *)&addrSrv, sizeof(struct sockaddr_in));  // 返回-1不一定是异常if (iRet != 0){  if(errno != EINPROGRESS){iFinal = -1;}else  {struct timeval tm = {tSecond, 0}; fd_set wset, rset;FD_ZERO(&wset); FD_ZERO(&rset); FD_SET(sockClient, &wset);FD_SET(sockClient, &rset); int time1 = time(NULL);int n = select(sockClient + 1, &rset, &wset, NULL, &tm);  int time2 = time(NULL);if(n < 0){      iFinal = -2;  }  else if(n == 0)  {      iFinal = -3;  }  else if (n == 1)  {   if(FD_ISSET(sockClient, &wset))   {     iFinal = 0;    fcntl(sockClient, F_SETFL, fcntl(sockClient, F_GETFL, 0) & ~O_NONBLOCK);     }     else     {     iFinal = -4;   }  }else{iFinal = -5;}}  }  close(sockClient);return iFinal;}int main(int argc, char *argv[])  // ./a.out ipfilename port timeout{if(argc != 4){cout << "error" << endl;return -1;}ifstream in(argv[1]);string filename;string line;unsigned int i = 0;if(in) // 有该文件{while (getline (in, line)) // line中不包括每行的换行符{// 这里最好做ip格式判断i++;int iFinal = telnetCheckTcp(line.c_str(), atoi(argv[2]), atoi(argv[3]));if(iFinal == 0){printf("iFinal is %d, ip is %s,  index is %d\n", iFinal, line.c_str(), i);}else{printf("iFinal is %d, cannot connect to %s, index is %d\n", iFinal, line.c_str(), i);}}}else // 没有该文件{cout <<"no such file" << endl;}return 0;}

       结果：

ubuntu@VM-0-13-ubuntu:~$ ./a.out a.txt 443 2iFinal is 0, ip is 220.181.112.244,  index is 1iFinal is -3, cannot connect to 1.1.1.1, index is 2ubuntu@VM-0-13-ubuntu:~$ ubuntu@VM-0-13-ubuntu:~$ ubuntu@VM-0-13-ubuntu:~$ ./a.out a.txt 80 2iFinal is 0, ip is 220.181.112.244,  index is 1iFinal is -3, cannot connect to 1.1.1.1, index is 2ubuntu@VM-0-13-ubuntu:~$ ubuntu@VM-0-13-ubuntu:~$ ubuntu@VM-0-13-ubuntu:~$ ./a.out a.txt 100 2iFinal is -3, cannot connect to 220.181.112.244, index is 1iFinal is -3, cannot connect to 1.1.1.1, index is 2ubuntu@VM-0-13-ubuntu:~$ 

        搞定。