I wrote a chat software with timeout connect function

Hello everyone , I'm brother Tao .

lately , Wrote a simple chat software , Play very smoothly in the LAN , It's about network programming , One scenario is to implement timeout connect function . What does that mean ？ Let me give you an example , You'll see .

A boy wants to pursue a girl , But the girl didn't respond , The boy waited silently , Till the end of time . However , The reality is that , Many boys have limited patience , Wait up to three years , It doesn't wait until it expires .

Hand painted by Taoge

The same is true in network programming , By default , establish TCP Connected connect It's blocked , If the other person doesn't respond , Will wait . that , How can I give connect Action setting timeout ？

The train of thought is ： hold socket Instead of blocking socket, And then use select Function to monitor socket Related events . I have seen the implementation of many open source network modules , Basically in this way .

Windows Implementation of version

Let's see Windows Implementation of version , The complete code for the client is as follows , Please focus on connect Related code ：

#include <stdio.h>
#include <winsock2.h>
#pragma comment(lib, "ws2_32.lib")
 
int main()
{
  //  Network initialization 
  WORD wVersionRequested;
  WSADATA wsaData;
  wVersionRequested = MAKEWORD(2, 2);
  WSAStartup( wVersionRequested, &wsaData );
 
  //  Create client socket( The default is blocking socket)
  SOCKET sockClient = socket(AF_INET, SOCK_STREAM, 0);
 
  //  Set to non blocking socket
  int iMode = 1;
  ioctlsocket(sockClient, FIONBIO, (u_long FAR*)&iMode); 
 
  //  Define the server 
  SOCKADDR_IN addrSrv;
  addrSrv.sin_addr.S_un.S_addr = inet_addr("127.0.0.1");
  addrSrv.sin_family = AF_INET;
  addrSrv.sin_port = htons(8888);
 
  //  Timeout time 
  struct timeval tm;
  tm.tv_sec  = 3;
  tm.tv_usec = 0;
  int ret = -1;
  
 
  //  Try to connect to the server 
  if (-1 != connect(sockClient, (SOCKADDR*)&addrSrv, sizeof(SOCKADDR)))
  {
    ret = 1; //  Successful connection 
  }
  else
  {
    fd_set set;
    FD_ZERO(&set);
    FD_SET(sockClient, &set);
 
    if (select(-1, NULL, &set, NULL, &tm) <= 0)
    {
      ret = -1; //  Erroneous (select Error or timeout )
    }
    else
    {
      int error = -1;
      int optLen = sizeof(int);
      getsockopt(sockClient, SOL_SOCKET, SO_ERROR, (char*)&error, &optLen); 
      if (0 != error)
      {
        ret = -1; //  Erroneous 
      }
      else
      {
        ret = 1;  //  No mistake 
      }
    }
  }
 
  //  Set back to blocking socket
  iMode = 0;
  ioctlsocket(sockClient, FIONBIO, (u_long FAR*)&iMode); // Set to blocking mode 
 
  // connect state 
  printf("ret is %d\n", ret);
 
  //  Send data to the server to test 
  if(1 == ret)
  {
    send(sockClient, "hello world", strlen("hello world") + 1, 0);
  }
 
  //  Release the network connection 
  closesocket(sockClient);
  WSACleanup();
 
  return 0;
}

After testing , When the client connects to the server , If 3 No response in seconds , Then the client will timeout , No longer wait foolishly .

Linux Implementation of version

Next , Let's see Linux Implementation of version , The client code is ：

#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 main(int argc, char *argv[]) //  Note the input parameters ,  close ip and port
{
  int sockClient = socket(AF_INET, SOCK_STREAM, 0);
 
  struct sockaddr_in addrSrv;
  addrSrv.sin_addr.s_addr = inet_addr(argv[1]);
  addrSrv.sin_family = AF_INET;
  addrSrv.sin_port = htons(atoi(argv[2]));
 
  fcntl(sockClient, F_SETFL, fcntl(sockClient, F_GETFL, 0)|O_NONBLOCK);  
  
  int iRet = connect(sockClient, ( const struct sockaddr *)&addrSrv, sizeof(struct sockaddr_in));
  printf("connect iRet is %d, errmsg:%s\n", iRet, strerror(errno)); //  return -1 Not necessarily abnormal 
 
  if (iRet != 0)  
  {  
    if(errno != EINPROGRESS)
    {
      printf("connect error:%s\n", strerror(errno));  
    }
    else  
    {
      struct timeval tm = {3, 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);
      printf("time gap is %d\n", time2 - time1);
 
      if(n < 0)  
      {  
         printf("select error, n is %d\n", n);  
      }  
      else if(n == 0)  
      {  
         printf("connect time out\n");  
      }  
      else if (n == 1)  
      {
         if(FD_ISSET(sockClient, &wset))  
         {  
           printf("connect ok!\n");  
           fcntl(sockClient, F_SETFL, fcntl(sockClient, F_GETFL, 0) & ~O_NONBLOCK);  
         }  
         else  
         {  
           printf("unknow error:%s\n", strerror(errno));  
         }  
      }
      else
      {
        printf("oh, not care now, n is %d\n", n);
      }
    }  
  }  
 
  printf("I am here!\n");
  getchar();
  close(sockClient);
  return 0;
}

After testing , When the client connects to the server , If 3 No response in seconds , Then the client will timeout , No longer wait foolishly .

Divergent thinking and interpretation

We noticed that ,Linux The code is more concise , No annoying network initialization and cleanup operation . I love it more Linux.

There is an important problem to pay attention to ： stay Windows and Linux in ,select The meaning of the first parameter of the function is different .

stay Windows in , Generally, it is filled in by default -1 Just go ; And in the Linux in , I need to set to fdmax + 1, Why is that ？

see Linux select The meaning of the first parameter ： Total number of description sets to be tested , The description set to be tested is from 0,1,2 Start . 

If the descriptor you want to detect is 8,9,10, Then the system should actually monitor 0,1,2,3,4,5,6,7 These descriptors .

here , The number of descriptors to be tested is 11, That is to say max(8,9,10) + 1, therefore ,select The first parameter is ：fdmax + 1.

Computer network is a subject with strong practicality , When learning computer network and network programming , It is suggested to write more programs 、 Multi debugging 、 Grab more bags , Then compare it with the theory .

I'm familiar with the Internet , Wrote a lot of network programs , I've seen a lot of network open source code , I suggest you go and have a look when you are free Redis Source code , short , awesome .