CODEWITHSUNDEEP
c++tcp
Eric.M.Zhu
Eric.M.Zhu

Reputation: 1

WSASend returns before sending data to device actually

Sorry for improper description of my question.

What my program do is that connect a server, send some data and close connection. I simplified my code as below:

WSAStartup(MAKEWORD(2, 2), &wsaData);
SOCKET s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

connect(s, (const sockaddr*)&dstAddr, sizeof(dstAddr));

send(s, (const char*)pBuffer, fileLen, 0);

shutdown(s, SD_SEND);
closesocket(s);

WSACleanup();

Only partial data was received by server before found a RST causing communication shutdown.

I wrote a simulate server program to accept connection and receive data, but the simulator could get all data. Because I couldn't access server's source code, I didn't know if something made wrong in it. Is there a way I can avoid this error by adding some code in client, or can I prove that there is something wrong in server program?

Setting socket's linger option can fix the bug. But I need to give a magic number for the value of linger time.

linger l;
l.l_onoff = 1;
l.l_linger = 30;
setsockopt(socket, SOL_SOCKET, SO_LINGER, (const char*)&l, sizeof(l));

Upvotes: 0

Views: 254

Answers (1)

user207421
user207421

Reputation: 310850

WSASend returns before sending data to device actually

Correct.

I created a non-blocking socket and tried to send data to server.

WSASocket(AF_INET, SOCK_STREAM, IPPROTO_TCP, NULL, 0, WSA_FLAG_OVERLAPPED)

No you didn't. You created an overlapped I/O socket.

After executed, returnValue was SOCKET_ERROR and WSAGetLastError() returned WSA_IO_PENDING. Then I called WSAWaitForMultipleEvents to wait for event being set. After it returned WSA_WAIT_EVENT_0, I called WSAGetOverlappedResult to get actual sent data length and it is the same value with I sent.

So all the data got transferred into the socket send buffer.

I called WSASocket first, then WSASend/WSAWaitForMultipleEvents/WSAGetOverlappedResult several times to send a bunch of data, and closesocket at the end.

So at the end of that process all the data and the close had been transferred to the socket send buffer.

But server couldn't receive all data, I used Wireshark to view tcp packets and found that client sent RST before all packet were sent out.

That could be for a number of reasons none of which is determinable without seeing some code.

If I slept 1 minute before calling closesocket, then server would receive all data.

Again this would depend on what else had happened in your code.

It seemed like that WSASend/WSAWaitForMultipleEvents/WSAGetOverlappedResult returned before sending data to server actually.

Correct.

The data were saved in buffer and waiting for being sent out.

Correct.

When I called closesocket, communication was shut down.

Correct.

They didn't work as my expectation.

So your expectation was wrong.

What did I go wrong? This problem only occurred in specific PCs, the application run well in others.

Impossible to answer without seeing some code. The usual reason for issuing an RST is that the peer had written data to a connection that you had already closed: in other words, an application protocol error; but there are other possibilities.

Upvotes: 1

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