linux网络编程十五：I/O复用的应用－非阻塞connect

connect系统调用的man手册中描述了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，而连接又没建立时。

根据 man 文档解释，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上的错误。如果错误码是0，表示连接成功，否则连接失败。

1. 代码实现

#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 1024

int setnonblocking(int fd);
int unblock_connect(const char *ip, int port, int time);

int main(int argc, char **argv)
{
	if (argc != 3) {
		fprintf(stderr, "Usage: %s ip port\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;
	
	send( sockfd, "123abc", 6, 0 );	
	
	shutdown( sockfd, SHUT_WR );		//关闭sockfd的写功能，此选项将不允许sockfd进行写操作
	
	printf( "send data out\n" );
	ssize_t ret = send( sockfd, "abc", 3, 0 );	
	if (ret == -1) {
		printf("send failed\n");
	}
	
	
	return 0;
}

int 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;
	address.sin_port = htons(port);
	inet_pton(AF_INET, ip, &address.sin_addr);
	
	int sockfd = socket(PF_INET, SOCK_STREAM, 0);
	assert(sockfd);
	
	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, &readfds);
	
	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);
	
	//得到error的值,如果为零,则connect成功.
	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;
}

           

参考：《linux高性能服务器编程》