非阻塞connect
非阻塞connect
connect系统调用的man手册中一段话描述了connect出错时的一种errno值：EINPROGRESS。这种错误发生在对非阻塞的socket调用connect，而连接又没有立即建立时。根据man文档的解释，在这种情况下，我们可以调用select，poll等函数来监听这个连接失败的socket上的可写事件。当select，poll等函数返回后，在利用getsockopt来读取错误码并清除该socket上的错误。如果错误码为0，表示连接成功建立，否则连接失败。
代码为：
#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 1023int setnonblocking( int fd )
{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 );ret = connect( sockfd, ( struct sockaddr* )&address, sizeof( address ) );if ( ret == 0 ){printf( "connect with server immediately\n" );fcntl( sockfd, F_SETFL, fdopt );return sockfd;}else if ( errno != EINPROGRESS ){printf( "unblock connect not support\n" );return -1;}fd_set readfds;fd_set writefds;struct timeval timeout;FD_ZERO( &readfds );FD_SET( sockfd, &writefds );timeout.tv_sec = time;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;}printf( "connection ready after select with the socket: %d \n", sockfd );fcntl( sockfd, F_SETFL, fdopt );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, 10 );if ( sockfd < 0 ){return 1;}shutdown( sockfd, SHUT_WR );sleep( 200 );printf( "send data out\n" );send( sockfd, "abc", 3, 0 );//sleep( 600 );return 0;
}