版权声明:本文为博主原创文章,未经博主允许不得转载。 https://blog.csdn.net/chengqiuming/article/details/89428900
一 代码
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <assert.h>
#include <stdio.h>
#include <time.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <string.h>
#define BUFFER_SIZE 1023
int setnonblocking( int fd ) //设置套接字为非阻塞套接字
{
int old_option = fcntl( fd, F_GETFL );
int new_option = old_option | O_NONBLOCK;
fcntl( fd, F_SETFL, new_option );
return old_option;
}
int unblock_connect( const char* ip, int port, int time )
{
int ret = 0;
struct sockaddr_in address;
bzero( &address, sizeof( address ) );
address.sin_family = AF_INET;
inet_pton( AF_INET, ip, &address.sin_addr );
address.sin_port = htons( port );
int sockfd = socket( PF_INET, SOCK_STREAM, 0 );
int fdopt = setnonblocking( sockfd ); //套接字设置为非阻塞套接字
ret = connect( sockfd, ( struct sockaddr* )&address, sizeof( address ) );
printf("connect ret code = %d\n", ret);
if ( ret == 0 )
{
printf( "connect with server immediately\n" );
fcntl( sockfd, F_SETFL, fdopt ); //set old optional back
return sockfd;
}
//unblock mode --> connect return immediately! ret = -1 & errno=EINPROGRESS
else if ( errno != EINPROGRESS )
{
printf("ret = %d\n", ret);
printf( "unblock connect failed!\n" );
return -1;
}
else if (errno == EINPROGRESS)
{
printf( "unblock mode socket is connecting...\n" );
}
//use select to check write event, if the socket is writable, then
//connect is complete successfully!
fd_set readfds;
fd_set writefds;
struct timeval timeout;
FD_ZERO( &readfds );
FD_SET( sockfd, &writefds );
timeout.tv_sec = time; //我们设置超时时间为1秒,原来大概需要3秒
timeout.tv_usec = 0;
ret = select( sockfd + 1, NULL, &writefds, NULL, &timeout );
if ( ret <= 0 )
{
printf( "connection time out\n" );
close( sockfd );
return -1;
}
if ( ! FD_ISSET( sockfd, &writefds ) )
{
printf( "no events on sockfd found\n" );
close( sockfd );
return -1;
}
int error = 0;
socklen_t length = sizeof( error );
if( getsockopt( sockfd, SOL_SOCKET, SO_ERROR, &error, &length ) < 0 )
{
printf( "get socket option failed\n" );
close( sockfd );
return -1;
}
if( error != 0 )
{
printf( "connection failed after select with the error: %d \n", error );
close( sockfd );
return -1;
}
//connection successful!
printf( "connection ready after select with the socket: %d \n", sockfd );
fcntl( sockfd, F_SETFL, fdopt ); //set old optional back
return sockfd;
}
int main( int argc, char* argv[] )
{
if( argc <= 2 )
{
printf( "usage: %s ip_address port_number\n", basename( argv[0] ) );
return 1;
}
const char* ip = argv[1];
int port = atoi( argv[2] );
int sockfd = unblock_connect( ip, port, 1); //这个值可以修改为5秒作测试
if ( sockfd < 0 )
{
printf("sockfd error! return -1\n");
return 1;
}
//shutdown( sockfd, SHUT_WR ); //disable read and write
printf( "send data out\n" );
send( sockfd, "abc", 3, 0 );
shutdown( sockfd, SHUT_WR ); //disable read and write
close(sockfd);
return 0;
}
二 运行
[root@localhost test]# g++ test.cpp -o test
[root@localhost test]# ./test 192.168.0.111 11133 kkk //该IP不存在
connect ret code = -1
unblock mode socket is connecting...
connection time out
sockfd error! return -1
[root@localhost test]# ./test 192.168.0.110 11133 kkk //该IP是本机IP
connect ret code = -1
unblock mode socket is connecting...
connection failed after select with the error: 111
sockfd error! return -1
如果把超时时间修改为5秒
[root@localhost test]# ./test 192.168.0.112 11133 kkk
connect ret code = -1
unblock mode socket is connecting...
connection failed after select with the error: 113
sockfd error! return -1
三 说明
1 SO_ERROR参考
https://blog.csdn.net/feng973/article/details/53463750
2 常见SO_ERROR
#define ECONNREFUSED 111 /* Connection refused */
#define EHOSTDOWN 112 /* Host is down */
#define EHOSTUNREACH 113 /* No route to host */
3 代码中自定义函数setnonblocking,用于设置套接字为非阻塞套接字。然后定义一个函数unblock_connect用于连接,并且设置为1秒作为超时时间。而实际的超时返回是通过select函数来实现的。
192.168.0.111是Linux主机IP的同一网段的一个假IP,原来阻塞超时3秒作用,所以修改为1秒后,会走超时分支,说明我们自定义的超时生效了。
192.168.0.110是本机IP,它返回的错误码是111,拒绝连接。
192.168.0.111是Linux主机IP的同一网段的一个假IP,把代码的超时时间从1秒改为5秒,连接错误码是113,即没有路由到主机。