linux socket怎么检测断开 怎样判断socket断开并自动重连

linux socket\u600e\u4e48\u68c0\u6d4b\u65ad\u5f00

/* Net check Make sure you have not used OUT OF BAND DATA AND YOU CAN use OOB */int netcheck(int fd) { int buf_size = 1024; char buf[buf_size]; //clear OOB DATA recv(fd, buf, buf_size); if(send(fd, (void *)"\0", 1, MSG_OOB) < 0 ) { fprintf(stderr, "Connection[%d] send OOB failed, %s", fd, strerror(errno)); return -1; } return 0;}/* Net check Make sure you have not used OUT OF BAND DATA AND YOU CAN use OOB */int netcheck(int fd) { int buf_size = 1024; char buf[buf_size]; //clear OOB DATA recv(fd, buf, buf_size); if(send(fd, (void *)"\0", 1, MSG_OOB) < 0 ) { fprintf(stderr, "Connection[%d] send OOB failed, %s", fd, strerror(errno)); return -1; } return 0;}

1. \u6839\u636eERRNO\u548crecv\u7ed3\u679c\u8fdb\u884c\u5224\u65ad
\u5728UNIX/LINUX\u4e0b\uff0c\u975e\u963b\u585e\u6a21\u5f0fSOCKET\u53ef\u4ee5\u91c7\u7528recv+MSG_PEEK\u7684\u65b9\u5f0f\u8fdb\u884c\u5224\u65ad\uff0c\u5176\u4e2dMSG_PEEK\u4fdd\u8bc1\u4e86\u4ec5\u4ec5\u8fdb\u884c\u72b6\u6001\u5224\u65ad\uff0c\u800c\u4e0d\u5f71\u54cd\u6570\u636e\u63a5\u6536
\u5bf9\u4e8e\u4e3b\u52a8\u5173\u95ed\u7684SOCKET, recv\u8fd4\u56de-1\uff0c\u800c\u4e14errno\u88ab\u7f6e\u4e3a9\uff08#define EBADF 9 /* Bad file number */\uff09\u6216104 \uff08#define ECONNRESET 104 /* Connection reset by peer */\uff09
\u5bf9\u4e8e\u88ab\u52a8\u5173\u95ed\u7684SOCKET,recv\u8fd4\u56de0\uff0c\u800c\u4e14errno\u88ab\u7f6e\u4e3a11\uff08#define EWOULDBLOCK EAGAIN /* Operation would block */\uff09
\u5bf9\u6b63\u5e38\u7684SOCKET, \u5982\u679c\u6709\u63a5\u6536\u6570\u636e\uff0c\u5219\u8fd4\u56de>0, \u5426\u5219\u8fd4\u56de-1\uff0c\u800c\u4e14errno\u88ab\u7f6e\u4e3a11\uff08#define EWOULDBLOCK EAGAIN /* Operation would block */\uff09

\u56e0\u6b64\u5bf9\u4e8e\u7b80\u5355\u7684\u72b6\u6001\u5224\u65ad\uff08\u4e0d\u8fc7\u591a\u8003\u8651\u5f02\u5e38\u60c5\u51b5\uff09\uff1a
recv\u8fd4\u56de>0\uff0c \u6b63\u5e38

我想通过recv和send的返回值来判断是否连接异常，但是不成功，下面是我的测试代码，连接成功后如果我断开客户端，那么服务端不会打印错误信息而是等待几秒后直接终止；如果断开服务端，客户端的recv不再阻塞，而且返回值一直是0,请高手指点。

C/C++ code//服务端
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/wait.h>
#define MYPORT 3490 /*定义用户连接端口*/
#define BACKLOG 10 /*多少等待连接控制*/
int main(int argc, char *argv[])
{
int sockfd, new_fd;/* listen on sock_fd, new connection on new_fd*/
struct sockaddr_in my_addr; /* my address information */
struct sockaddr_in their_addr; /* connector's address information */
int sin_size;
if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
perror("socket");
exit(1);
}

int opt = 1;
int len = sizeof(opt);
setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &opt, len);

my_addr.sin_family = AF_INET; /* host byte order */
my_addr.sin_port = htons(MYPORT); /* short, network byte order */
my_addr.sin_addr.s_addr = INADDR_ANY; /* auto-fill with my IP */
bzero(&(my_addr.sin_zero),0); /* zero the rest of the struct */

if (bind(sockfd, (struct sockaddr *)&my_addr, sizeof(struct sockaddr))== -1)
{
perror("bind");
exit(1);
}
if (listen(sockfd, BACKLOG) == -1) {
perror("listen");
exit(1);
}

while(1) { /* main accept() loop */
sin_size = sizeof(struct sockaddr_in);
printf("while\n");
if ((new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size)) == -1)
{
perror("accept");
continue;
}
printf("server: got connection from %s\n", inet_ntoa(their_addr.sin_addr));

while(1)
{
usleep(10000000);
if (send(new_fd, "Hello, world!\n", 14, 0) == -1)
perror("send");
}
close(new_fd);
exit(0);

}
return 0;
}

C/C++ code//客户端
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <netdb.h>
#define PORT 3490 /* 客户机连接远程主机的端口 */
#define MAXDATASIZE 100 /* 每次可以接收的最大字节 */
int main(int argc, char *argv[])
{
int sockfd, numbytes;
char buf[MAXDATASIZE];
struct hostent *he;
struct sockaddr_in their_addr; /* connector's address information */
if (argc != 2)
{
fprintf(stderr,"usage: client hostname\n");
exit(1);
}
if ((he=gethostbyname(argv[1])) == NULL)
{ /* get the host info */
herror("gethostbyname");
exit(1);
}

if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
perror("socket");
exit(1);
}

their_addr.sin_family = AF_INET; /* host byte order */
their_addr.sin_port = htons(PORT); /* short, network byte order */
their_addr.sin_addr = *((struct in_addr *)(he->h_addr));
bzero(&(their_addr.sin_zero),0); /* zero the rest of the struct */
if (connect(sockfd, (struct sockaddr *)&their_addr,sizeof(struct sockaddr)) == -1)
{
perror("connect");
exit(1);
}
while(1)
{
printf("receiving......\n");
if ((numbytes=recv(sockfd, buf, MAXDATASIZE, 0)) == -1)
{
perror("recv");
exit(1);
}
buf[numbytes] = '\0';
printf("Received: %s\n",buf);
}
close(sockfd);
return 0;
}

另外，在网上看到一种利用TCP协议栈中的KeepAlive探测的方法，下面是我从网上找的用的比较多的一段代码，这里应该只是设置了一些属性参数，但不知具体怎样在通信中检测断开，请高手赐教。
C/C++ code#include
……
////KeepAlive实现
//下面代码要求有ACE,如果没有包含ACE,则请把用到的ACE函数改成linux相应的接口
int keepAlive = 1;//设定KeepAlive
int keepIdle = 5;//开始首次KeepAlive探测前的TCP空闭时间
int keepInterval = 5;//两次KeepAlive探测间的时间间隔
int keepCount = 3;//判定断开前的KeepAlive探测次数

if(setsockopt(s,SOL_SOCKET,SO_KEEPALIVE,(void*)&keepAlive,sizeof(keepAlive)) == -1)
{
ACE_DEBUG ((LM_INFO,
ACE_TEXT ("(%P|%t) setsockopt SO_KEEPALIVE error!\n")));

}

if(setsockopt(s,SOL_TCP,TCP_KEEPIDLE,(void *)&keepIdle,sizeof(keepIdle)) == -1)
{
ACE_DEBUG ((LM_INFO,
ACE_TEXT ("(%P|%t) setsockopt TCP_KEEPIDLE error!\n")));
}

if(setsockopt(s,SOL_TCP,TCP_KEEPINTVL,(void *)&keepInterval,sizeof(keepInterval)) == -1)
{
ACE_DEBUG ((LM_INFO,
ACE_TEXT ("(%P|%t) setsockopt TCP_KEEPINTVL error!\n")));
}

if(setsockopt(s,SOL_TCP,TCP_KEEPCNT,(void *)&keepCount,sizeof(keepCount)) == -1)
{
ACE_DEBUG ((LM_INFO,
ACE_TEXT ("(%P|%t)setsockopt TCP_KEEPCNT error!\n")));
}

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