Play with the connect function with timeout in Linux

Play with the connect function with timeout in Linux

In the previous article, we played with timeouts under Windows. In this article, we will play with Linux. I encountered this question in an interview, which is interesting.

Directly on the client code:

#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[]) // Pay attention to the input parameters, bring 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)); // Returning -1 is not necessarily an exception if (iRet != 0) 
 { 
   if (errno != EINPROGRESS)
 {
  printf("connect error:%s\n", strerror(errno)); 
 }
   else 
 {
  struct timeval tm = {5, 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;
}

We have written the server code many times, so we will not write it in this article.

After testing, the above program is OK. You can also learn a lot by using tcpdump to capture packets, such as SYN packet retransmission, RST packet, etc. Quite interesting.

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