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 2
iFinal is 0
ubuntu@VM-0-13-ubuntu:~$ ./a.out 220.181.112.244 81 2
iFinal is -3
ubuntu@VM-0-13-ubuntu:~$ ./a.out 220.181.112.244 443 2
iFinal is 0
ubuntu@VM-0-13-ubuntu:~$ ./a.out 220.181.112.244 445 2
iFinal is -3
ubuntu@VM-0-13-ubuntu:~$ ./a.out 1.1.1.1 80 2
iFinal is -3
ubuntu@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 2
iFinal is 0, ip is 220.181.112.244,  index is 1
iFinal is -3, cannot connect to 1.1.1.1, index is 2
ubuntu@VM-0-13-ubuntu:~$
ubuntu@VM-0-13-ubuntu:~$
ubuntu@VM-0-13-ubuntu:~$ ./a.out a.txt 80 2
iFinal is 0, ip is 220.181.112.244,  index is 1
iFinal is -3, cannot connect to 1.1.1.1, index is 2
ubuntu@VM-0-13-ubuntu:~$
ubuntu@VM-0-13-ubuntu:~$
ubuntu@VM-0-13-ubuntu:~$ ./a.out a.txt 100 2
iFinal is -3, cannot connect to 220.181.112.244, index is 1
iFinal is -3, cannot connect to 1.1.1.1, index is 2
ubuntu@VM-0-13-ubuntu:~$

        搞定。