Play the connect function with timeout under linux

In the previous article, we played the game with timeout under Windows, in this article we played it under linux. In an interview, was also met this question, interesting.

Directly to 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[]) //  Notice the input parameters ,  take 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 Don't 1 This is abnormal 
 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;
}

The server-side code, which we have written several times, will not be written in this article.

After testing, the above procedures OK, tcpdump to catch the package, can also learn a lot of things, such as SYN package retransmission, RST package, etc. It's kind of interesting.

conclusion