超时阻塞：Linux下connect超时处理（总结）

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>     /* See NOTES */
#include <sys/socket.h>
#include <netinet/in.h>
#include <fcntl.h>
#include <errno.h>
int main(int argc, char **argv)
{
  if (argc < 3) {
    printf("please input ip and port, for example ./main 120.12.34.56 80.\n");
    return -1;
  }
  
  char *ipaddr = argv[1];
  unsigned int port = atoi(argv[2]);
  int fd = 0;
  struct sockaddr_in addr;
  fd_set fdr, fdw;
  struct timeval timeout;
  int err = 0;
  int errlen = sizeof(err);
  fd = socket(AF_INET,SOCK_STREAM,0);
  if (fd < 0) {
    fprintf(stderr, "create socket failed,error:%s.\n", strerror(errno));
    return -1;
  }
  bzero(&addr, sizeof(addr));
  addr.sin_family = AF_INET;
  addr.sin_port = htons(port);
  inet_pton(AF_INET, ipaddr, &addr.sin_addr);
  /*设置套接字为非阻塞*/
  int flags = fcntl(fd, F_GETFL, 0);
  if (flags < 0) {
    fprintf(stderr, "Get flags error:%s\n", strerror(errno));
    close(fd);
    return -1;
  }
  flags |= O_NONBLOCK;
  if (fcntl(fd, F_SETFL, flags) < 0) {
    fprintf(stderr, "Set flags error:%s\n", strerror(errno));
    close(fd);
    return -1;
  }
  /*阻塞情况下linux系统默认超时时间为75s*/
  int rc = connect(fd, (struct sockaddr*)&addr, sizeof(addr));
  if (rc != 0) {
    if (errno == EINPROGRESS) {
      printf("Doing connection.\n");
      /*正在处理连接*/
      FD_ZERO(&fdr);
      FD_ZERO(&fdw);
      FD_SET(fd, &fdr);
      FD_SET(fd, &fdw);
      timeout.tv_sec = 10;
      timeout.tv_usec = 0;
      rc = select(fd + 1, &fdr, &fdw, NULL, &timeout);
      printf("rc is: %d\n", rc);
      /*select调用失败*/
      if (rc < 0) {
        fprintf(stderr, "connect error:%s\n", strerror(errno));
        close(fd);
        return -1;
      }
      
      /*连接超时*/
      if (rc == 0) {
        fprintf(stderr, "Connect timeout.\n");
        close(fd);
        return -1;
      }
      /*[1] 当连接成功建立时，描述符变成可写,rc=1*/
      if (rc == 1 && FD_ISSET(fd, &fdw)) {
        printf("Connect success\n");
        close(fd);
        return 0;
      }
      /*[2] 当连接建立遇到错误时，描述符变为即可读，也可写，rc=2 遇到这种情况，可调用getsockopt函数*/
      if (rc == 2) {
        if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &err, &errlen) == -1) {
          fprintf(stderr, "getsockopt(SO_ERROR): %s", strerror(errno));
          close(fd);
          return -1;
        }
        if (err) {
          errno = err;
          fprintf(stderr, "connect error:%s\n", strerror(errno));
          close(fd);
          return -1;
        }
      }
    } 
    fprintf(stderr, "connect failed, error:%s.\n", strerror(errno));
    return -1;
  } 
  return 0;
}