[英]send succeeds even when the connection is no longer available?
What am I missing? 我想念什么?
I have very simple client and server. 我有非常简单的客户端和服务器。 The server uses recv
with timeout (using select
) for 3 seconds. 服务器使用带有超时的recv
(使用select
)持续3秒钟。 Then it shutdown
s and close
s the sockets and exits. 然后shutdown
并close
套接字,然后退出。
The client connects to the server, sleeps 30 seconds and sends very short message. 客户端连接到服务器,睡眠30秒并发送非常短的消息。 The sending is about 27seconds after the server has closed the sockets and exited. 服务器关闭套接字并退出后,发送大约需要27秒。
And send
does not fail..? 并且send
不会失败..? Why? 为什么? Why it does not return -1
for error? 为什么它不为错误返回-1
?
Please note: I cut all checks for return codes and removed all logs, to make this as short as I can. 请注意:我削减了所有检查返回码的内容,并删除了所有日志,以使之尽可能短。 Also, I removed all includes, to make this shorter. 另外,我删除了所有包含项,以使其更短。 But it IS a real code. 但这是一个真实的代码。
client code: 客户代码:
int main( int argc, char* argv[] )
{
addrinfo hints;
memset(&hints, 0, sizeof hints); // make sure the struct is empty
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM; // TCP stream sockets
addrinfo *res;
getaddrinfo( "127.0.0.1", "1313", &hints, &res );
int nSocketFD = socket( res->ai_family, res->ai_socktype, res->ai_protocol );
assert( -1 != connect( nSocketFD, res->ai_addr, res->ai_addrlen) );
freeaddrinfo( res ); // free the linked-list, we don't need it anymore
sleep( 30 );
if( send( nSocketFD, "bla", 4, 0 ) > 0 )
{
printf( "Message successfully sent!\n" );
}
close( nSocketFD );
return 0;
}
and server: 和服务器:
int main()
{
addrinfo hints;
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE;
addrinfo *res; // will point to the results
getaddrinfo( NULL, "1313", &hints, &res );
int nSocketFD = socket( res->ai_family, res->ai_socktype, res->ai_protocol );
bind( nSocketFD, res->ai_addr, res->ai_addrlen );
freeaddrinfo( res ); // free the linked-list
listen( nSocketFD, 1 );
sockaddr_storage their_addr;
socklen_t addr_size = sizeof( sockaddr_storage );
int nAcceptedSocket = accept( nSocketFD, (sockaddr*)&their_addr, &addr_size );
assert( -1 != nAcceptedSocket );
fd_set fds;
FD_ZERO( &fds );
FD_SET( nAcceptedSocket, &fds );
timeval tv;
tv.tv_sec = 3;
tv.tv_usec = 0;
if( 0 == select( nAcceptedSocket + 1, &fds, NULL, NULL, &tv) )
{
printf( "recv timeout! Exiting..\n" );
shutdown( nSocketFD, SHUT_RDWR );
close( nSocketFD );
shutdown( nAcceptedSocket, SHUT_RDWR );
close( nAcceptedSocket );
return 1;
}
assert( false );
return 0;
}
When I execute it, I see the messages for recv
timeout and for successful sent message. 当我执行它时,我看到recv
超时和成功发送消息的消息。
Sorry for the long and probably stupid question. 很抱歉这个长期的,可能是愚蠢的问题。
In general you need to read from a socket to get it to notice that the remote end has closed the connection. 通常,您需要读取套接字以获取它,以注意远端已关闭连接。
From the manual page of send
(which is just write
but with flags): 在send
的手册页中(只是write
但带有标志):
No indication of failure to deliver is implicit in a send(). Locally
detected errors are indicated by a return value of -1.
You didnt not close the socket in your client - so this a valid socket. 您没有在客户端中关闭套接字-因此这是有效的套接字。 From send()'s man page 从send()的手册页中
No indication of failure to deliver is implicit in a send(). Locally detected errors are indicated by a return value of -1.
We have this issue with some of our software - if network hardware fails somewhere along the line and it is brought back up again - then either end still thinks the socket is valid - and without keepalives probes - it will stay this way. 我们的某些软件存在此问题-如果网络硬件沿线某处发生故障并再次恢复运行-那么任一端仍然认为套接字有效-并且没有keepalives探针-它将保持这种状态。
ADDING: Have a look at socket options (man setsockopt and man tcp) SO_KEEPALIVE 添加:看一下套接字选项(man setsockopt和man tcp)SO_KEEPALIVE
From TCP man page tcp_keepalive_intvl (integer; default: 75; since Linux 2.4) The number of seconds between TCP keep-alive probes. 从TCP手册页tcp_keepalive_intvl(整数;默认值:75;从Linux 2.4开始),两次TCP保持活动探测之间的秒数。
tcp_keepalive_probes (integer; default: 9; since Linux 2.2)
The maximum number of TCP keep-alive probes to send before giving up and killing the connection if no response is obtained from the other end.
tcp_keepalive_time (integer; default: 7200; since Linux 2.2)
The number of seconds a connection needs to be idle before TCP begins sending out keep-alive probes. Keep-alives are only sent when the SO_KEEPALIVE socket option is enabled. The default value is 7200 seconds (2 hours). An idle connection is terminated after approximately an additional 11 minutes (9 probes an interval of 75 seconds apart) when keep-alive is enabled.
Note that underlying connection tracking mechanisms and application timeouts may be much shorter.
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.