Why would an Overlapped call to recv return ERROR_NO_MORE_ITEMS(259)? - c++

Question

I did a few tests with an I/O-Completion port and winsock sockets.
I encountered, that sometimes after I received data from a connection and then adjacently call WSARecv again on that socket it returns immediately with the error 259 (ERROR_NO_MORE_ITEMS).
I am wondering why the system flags the overlapped transaction with this error instead of keeping the recv call blocking/waiting for incoming data.
Do You know what´s the sense of this ?
I would be glad to hear about your thoughts.
Edit: Code
do
{
OVERLAPPED* pOverlapped = nullptr;
DWORD dwBytes = 0; ULONG_PTR ulKey = 0;
//Dequeue a completion packet
if(!m_pIOCP->GetCompletionStatus(&dwBytes, &ulKey, &pOverlapped, INFINITE))
DebugBreak();
//Evaluate
switch(((MYOVERLAPPED*)pOverlapped)->WorkType)
{
case ACCEPT_OVERLAPPED_TYPE:
{
//cast
ACCEPT_OVERLAPPED* pAccept = (ACCEPT_OVERLAPPED*)pOverlapped;
//Associate the newly accepted connection with the IOCP
if(!m_pIOCP->AssociateHandle((HANDLE)(pAccept->pSockClient)->operator SOCKET(), 1))
{
//Association failed: close the socket and and delte the overlapped strucuture
}
//Call recv
RECV_OVERLAPPED* pRecvAction = new RECV_OVERLAPPED;
pRecvAction->pSockClient = pAccept->pSockClient;
short s = (pRecvAction->pSockClient)->Recv(pRecvAction->strBuf, pRecvAction->pWSABuf, 10, pRecvAction);
if(s == Inc::REMOTECONNECTION_CLOSED)
{
//Error stuff
}
//Call accept again (create a new ACCEPT_OVERLAPPED to ensure overlapped being zeroed out)
ACCEPT_OVERLAPPED *pNewAccept = new ACCEPT_OVERLAPPED;
pNewAccept->pSockListen = pAccept->pSockListen;
pNewAccept->pSockClient = new Inc::CSocket((pNewAccept->pSockListen)->Accept(nullptr, nullptr, pNewAccept));
//delete the old overlapped struct
delete pAccept;
}
break;
case RECV_OVERLAPPED_TYPE:
{
RECV_OVERLAPPED* pOldRecvAction = (RECV_OVERLAPPED*)pOverlapped;
if(!pOldRecvAction->InternalHigh)
{
//Connection has been closed: delete the socket(implicitly closes the socket)
Inc::CSocket::freewsabuf(pOldRecvAction->pWSABuf); //free the wsabuf
delete pOldRecvAction->pSockClient;
}
else
{
//Call recv again (create a new RECV_OVERLAPPED)
RECV_OVERLAPPED* pNewRecvAction = new RECV_OVERLAPPED;
pNewRecvAction->pSockClient = pOldRecvAction->pSockClient;
short sRet2 = (pNewRecvAction->pSockClient)->Recv(pNewRecvAction->strBuf, pNewRecvAction->pWSABuf, 10, pNewRecvAction);
//Free the old wsabuf
Inc::CSocket::freewsabuf(pOldRecvAction->pWSABuf);
delete pOldRecvAction;
}
Cutted error checkings...
The Recv-member-function is a simple wrapper around the WSARecv-call which creates the WSABUF and the receiving buffer itself (which needs to be cleaned up by the user via freewsabuf - just to mention)...

Answer 1

It looks like I was sending less data than was requested by the receiving side.
But since it´s an overlapped operation receiving a small junk of the requested bunch via the TCP-connection would trigger the completion indication with the error ERROR_NO_MORE_ITEMS, meaning there was nothing more to recv than what it already had.