I am writing a small server-client-stuff using an I/O-Completion Port.
I get the server and client connected successfully via AcceptEx over my completion port.
After the client has connected the client socket is associated with the completion port and an overlapped call to WSARecv on that socket is invoked.
Everything works just fine, until I close the client test program.
GetQueuedCompletionStatus() returns FALSE and GetLastError returns
ERROR_NETNAME_DELETED
, which makes sense to me (after I read the description on the MSDN).
But my problem is, that I thought the call to GetQueuedCompletionStatus would return me a packet indicating the failure due to closure of the socket, because WSARecv would return the apropriate return value.
Since this is not the case I don´t know which clients´ socket caused the error and cant act the way i need to (freeing structures , cleanup for this particular connection, etc)...
Any suggestion on how to solve this, Or hints?
Thanks:)
EDIT: http://codepad.org/WeYINasO <- the code responsible... the "error" occures at the first functions beginning of the while-loop (the call to GetCompletionStatus() which is only a wrapper for GetQueuedCompletionStatus() working fine in other cases) [Did post it there, because it looks shitty & messy in here]
Here are the scenarios that you need to watch for when calling GetQueuedCompletionStatus:
GetQueuedCompletionStatus returns TRUE: A successful completion packet has been received, all the out parameters have been populated.
GetQueuedCompletionStatus returns FALSE, lpOverlapped == NULL: No packet was dequeued. The other out parameters contain indeterminate values.
GetQueuedCompletionStatus returns FALSE, lpOverlapped != NULL: The function has dequeued a failed completion packet. The error code is available via GetLastError.
To answer your question, when GetQueuedCompletionStatus returns FALSE and lpOverlapped != NULL, there was a failed I/O completion. It's the value of lpOverlapped that you need to be concerned about.
I know this is an old question, but I found this page while fruitlessly googling for details about ERROR_NETNAME_DELETED. It is an error which I get while doing an overlapped Readfile().
After some debugging it turned out that the problem was caused by a program which was writing to a socket but forgetting to call closesocket() before using ExitProcess() (due to garbage collection issues). Calling CloseHandle() did not prevent the error, nor did adding WSACleanup() before ExitProcess(). However, adding a short sleep before the client exited did prevent the error. Maybe avoiding ExitProcess() would have prevented the problem also.
So I suspect your problem is caused by the program exiting without closing down the socket properly.
I don't think this would be an issue on Unix where sockets are just ordinary file descriptors.
Related
I'm curious about the behavior of the SO_ERROR socket option used with getsockopt() after a successful socket operation
The Open Group specification:
SO_ERROR
Reports information about error status and clears it. This option shall store an int value.
Usually I see SO_ERROR used after a socket operation returns -1, but what happens if the previous socket operation succeeded (thus not returning -1). Does the getsockopt() call fail? Does it return 0 as the int value?
It's ok for non-blocking connect, see connect(2)
The socket is nonblocking and the connection cannot be completed immediately. It is possible to select(2) or poll(2) for completion by selecting the socket for writing. After select(2) indicates writability, use getsockopt(2) to read the SO_ERROR option at level SOL_SOCKET to determine whether connect() completed successfully (SO_ERROR is zero) or unsuccessfully (SO_ERROR is one of the usual error codes listed here, explaining the reason for the failure).
other is undefined.
It's undefined. You should only call this option when you already know that there has been an error. Not as a means to discover whether there was one.
I've learned more about SO_ERROR in Unix Networking Programmig Vol 1, it's become clear to me. SO_ERROR is used to report asynchronous errors that are the result of events within the network stack and not synchronous errors that are the result of a library call (send/recv/connect). Synchronous results are reported via errno.
Calling getsockopt() with SO_ERROR after a library call returns -1 is incorrect from the POSIX implementation.
Learning of the non-blocking connect result via select is an example of discovering when the asynchronous result is ready (which can then be retrieved via SO_ERROR)
I am attempting to run MOOS-IvP on a Beaglebone Black
On attempting to run the MOOS database it continuously throws the exception
"Exception Thrown in listen loop: Error Listening To Socket. Operation not supported"
This software runs on a Raspberry Pi
Any ideas what might be the issue?
I have found the problem and fixed it.
When the socket is created it needs to be TCP. However when getprotobyname(_sName) is called in the XPCGetProtocol class to lookup the correct protocol number in /etc/protocols it returns the value of the previous time it was called, which was when a UDP socket was setup.
To fix it I simply called the function twice, the second time it returns the correct value.
I am not sure why it would return incorrect the first time but this works!
I also encountered this error while working with a BeagleBone Black running Ubuntu 14.04. However, the solution of running the request twice did not work. More troubleshooting led me to determine that the one that was supposed to be a TCP socket was opened after another process had opened a UDP socket. The structure returned by getprotobyname() is a pointer to a static location that does not change from call to call, but does get updated with the protocol details (see here although for another Unix os). Therefore, the second call by another process overwrites the original details.
This then gets tested during socket creation in the constructor of XPCSocket, and results in creation of a UDP socket where it should have been a TCP socket. This could probably be fixed by adding a lock to this function, but I took the non-blocking approach to initialize the requested protocol using the string the constructor was called with (_sProtocol) instead of the one returned in the socketProtocol structure. In addition, I modified the XPCGetProtocol class to store the protocol number in a member variable that would not be changed upon subsequent calls to getprotobyname().
My modifications can be found here.
I am using pseudo-synchronous sockets in a Windows Phone 7 application. My socket code is based on the sample from http://msdn.microsoft.com/en-us/library/hh202858(v=vs.92).aspx.
The server's sending pattern is somewhat unpredictable. It starts with a fixed-size header that contains the length of the rest of the message. I first read in this header, and then I read the specified number of bytes from the socket.
Since I need to send messages to the server as well, and my attempts at duplexing the socket with a thread for receiving and another thread for sending caused lots of problems, I have a loop like this in my code:
while (KeepConnectionGoing)
{
byte[] Rcvd;
Rcvd = Socket.Receive();//Returns null if no message received in 50 ms
if (Rcvd != null)
{
ParseMessage(Rcvd);
}
if (HasMessageThatNeedsToBeSent())
{
byte[] Message = GetMessageToSend();
Socket.Send(Message);
}
}
This works fine for the majority of the time, but strange things happen when the message is null.
Because the timeout in the Receive method (see the linked sample) uses a ManualResetEvent, the receive request on the socket is never actually cancels. Even though the method returns, that request waits around somewhere, and when data is available on the socket, chomps up the header. The event handler has nothing to do with the data it received (since the method has returned and the variables in the method will never be used again), the data basically disappears. The read request I expect to return the header skips reads the bytes after the header, and I have no idea how long the message is.
I'd like to be able to cancel all outstanding requests if the socket times out. I am using anonymous methods like in the sample since it simplifies everything and prevents me from having to write all the state transfer code myself. Thus, I cannot unhook the event handler. I think though, that even if I were using a method as the event handler, but unhooking before the asynchronous operation is done, the callback method would still be called. (I haven't tested this, it's just my understanding)
Right now, the only solution I can see is hacking together some static byte arrays (ie. having a static byte[] Header and if it is null, I read the header, otherwise I read the message), but that seems like a really inelegant solution and very prone to race conditions.
Is there a better way?
Thanks
It appears there really is no good way to do this. A poll method would be nice, but Silverlight doesn't have it. I hacked together a solution using static flags to tell me what state I am in (Has the header been requested, has the message been requested), a static int for the length and a static buffer.
At the beginning of the method, either the header or the body can be requested. If the header has already been requested, the thread waits until a valid body length is available. If this wait times out, that means that the header receive operation is still pending, but there really is no message available. Otherwise, it reads in that length of a message.
If the header has not been requested, receive the header. In the event handler, after completion, check to see if the control flow has already continued (i.e. the receive operation took too long, so the function returned already, but is now actually done). Update the length, then request the body unless it timed out.
I've a select based server. Sockets are in blocking mode,but for select() function I'm using 250 ms. timeout.
Basically my server accepts only one client and sending data to that client.
It is working for weeks without problem if I just send data from server to client.
But I realized that if client sends data to server after 3-4 hours at the select() line it gives stack overflow exception (0xC00000FD).
I red dozens of times MSDN page of Select(), but nothing mentioned related to this.
I'm really stuck. Any help will be appreciated.
By the way, I found on the net, example;
http://tangentsoft.net/wskfaq/examples/basics/select-server.cpp
here after accepting client connection, he is setting it to nonblocking mode.
And it is commented that;
// Mark the socket as non-blocking, for safety.
What does "safety" means above?
So do you think is this my problem? Because in my implementation, connected ones are in blocking mode?
Thanks in advance
An exception means there is a bug in your code. Since you are getting a stack overflow, you likely have a recursive loop in your code that is running too long, eating up stack space on each call until there no more stack space left. Under normal conditions, select() returns an error code when it fails, so you have to be messing up your program's memory somewhere to be getting an exception.
I'm currently maintaining some web server software and I need to perform a lot of I/O operations. The read(), write(), close() and shutdown() calls, when used on a socket, may sometimes raise an ENOTCONN error. What exactly does this error mean? What are the conditions that would trigger it? I can never seem to reproduce it locally but there are users who can.
Right now I just ignore ENOTCONN when raised by close() and shutdown() because it seems harmless, but I'm not entirely sure.
EDIT:
I am absolutely sure that the connect() call succeeded. I check for its return value.
ENOTCONN is most often raised by close() and shutdown(). I've only very rarely seen a read() and write() raising ENOTCONN.
If you are sure that nothing on your side of the TCP connection is closing the connection, then it sounds to me like the remote side is closing the connection.
ENOTCONN, as others have pointed out, simply means that the socket is not connected. This doesn't necessarily mean that connect failed. The socket may well have been connected previously, it just wasn't at the time of the call that resulted in ENOTCONN.
This differs from:
ECONNRESET: the other end of the connection sent a TCP reset packet. This can happen if the other end is refusing a connection, or doesn't acknowledge that it is already connected, among other things.
ETIMEDOUT: this generally applies only to connect. This can happen if the connection attempt is not successful within a system-dependent amount of time.
EPIPE can sometimes be returned by some socket-related system calls under conditions that are more or less the same as ENOTCONN. For example, on some systems, EPIPE and ENOTCONN are synonymous when returned by send.
While it's not unusual for shutdown to return ENOTCONN, since this function is supposed to tear down the TCP connection, I would be surprised to see close return ENOTCONN. It really should never do that.
Finally, as dwc mentioned, EBADF shouldn't apply in your scenario unless you are attempting some operation on a file descriptor that has already been closed. Having a socket get disconnected (i.e. the TCP connection has broken) is not the same as closing the file descriptor associated with that socket.
It's because, at the moment of shutting() the socket, you have data in the socket's buffer waiting to be delivered to the remote party which has closed() or shutted down() its receiving socket.
I don't finish understanding how sockets work, I am rather a noob, and I've failed to even find the files where this "shutdown" function is implemented, but seeing that there's practically no user manual for the whole sockets thing I started trying all possibilities until I got the error in a "controlled" environment. It could be something else, but after much trying these are the explanations I settled for:
If you sent data after the remote side closed the connection, when you shutdown(), you get the error.
If you sent data before the remote side closed the connection but it didn't get received() on the other end, you can shutdown() once, the next time you try to shutdown(), you get the error.
If you didn't send any data, you can shutdown all the times you want, as long as the remote side doesn't shutdown(); once the remote side has shutdown(), if you try to shutdown() and the socket was already shutdown(), you get the error.
I believe ENOTCONN is returned, because shutdown() is not supposed to return ECONNRESET or other more accurate errors.
It is wrong to assume that the other side “just” closed the connection. On the TCP-level, the other side can only half-close a connection (or abort it). The connection is ordinary fully closed if both sides do a shutdown() (or close()). If both side do that, shutdown() actually succeeds for both of them!
The problem is that shutdown() did not succeed in ordinary (half-)closing the connection, neither as the first one to close it, nor as the second one. – From the errors listed in the POSIX docs for shutdown(), ENOTCONN is the least inappropriate, because the others indicate problems with arguments passed to shutdown() (or local resource problems to handle the request).
So what happened? These days, a NAT device somewhere between the two parties involved might have dropped the association and sends out RESET packets as a reaction. Reset connections are so common for IPv4, that you will get them anywhere in your code, even masked as ENOTCONN in shutdown().
A coding bug might also be the reason. On a non-blocking socket, for example, a connect() can return 0 without indicating a successful connection yet.
Transport endpoint is not connected
The socket is associated with a connection-oriented protocol and has not been connected. This is usually a programming flaw.
From: http://www.wlug.org.nz/ENOTCONN
If you're sure you've connected properly in the first place, ENOTCONN is most likely to be caused by either the fd being closed on your end (perhaps in another thread?) while you're in the middle of a request, or by the connection dropping while you're in the middle of the request.
In any case, it means that the socket is not connected. Go ahead and clean up that socket. It's dead. No problem calling close() or shutdown() on it.