C / C++ / MFC

while ( i = recv(buff, 3,..) )
{...}

bigdenny200 wrote:

you mention,
"a fixed-length "packet" scheme"

bigdenny200 wrote:

The server knows it should get 3 bytes at a time. So I have

while ( i = recv(buff, 3,..) )
{...}

    int BytesRemaining = # of expected bytes;
    BYTE *pCurBuf = start address of buffer to recv bytes into;

    while (BytesRemaining > 0)
    {
        int CurBytesReceived = ::recv(hSocket, (char*)pCurBuf, BytesRemaining, 0);

        if (CurBytesReceived == 0)
        {
            // connection was gracefully closed

            break;
        }
        else if (nCurBytesReceived == SOCKET_ERROR)
        {
            // Some error occurred!

            int rc = WSAGetLastError();

            if (rc != WSAEWOULDBLOCK)
            {
                break;
            }
        }
        else
        {
            // Some bytes were successfully received

            BytesRemaining -= CurBytesReceived;
            pCurBuf += CurBytesReceived;
        }
    }

bigdenny200 wrote:

what do you mean by: "a 4-byte int - don't forget byte order issues!"

Mark Salsbery
Microsoft MVP - Visual C++

bigdenny200 wrote:

I just prey

Mark Salsbery
Microsoft MVP - Visual C++

bigdenny200 wrote:

I am just using one recv(), so you mean that it is possible that I just get: "hell" and nothing else? Note, I am calling recv() only once.

JudyL_FL wrote:

There is no guarantee that a single recv call on one end of a connection will get all the data sent with a single send call on the other end.

Joergen Sigvardsson wrote:

It is possible with fixed sized messages

Mark Salsbery
Microsoft MVP - Visual C++

<font color="Green">//----------------------------------------------
// Listener/ receiver thread (started in CMYTestDlg::OnOK() below)</font>
<font color="Green">//----------------------------------------------
</font>UINT __cdecl TestThreadProc( LPVOID pParam )
{
    SOCKET ListenSocket;
    ListenSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (ListenSocket == INVALID_SOCKET) 
    {
        return 1;
    }

    sockaddr_in service;
    service.sin_family = AF_INET;
    service.sin_addr.s_addr = inet_addr("127.0.0.1");
    service.sin_port = htons(2460);

    if (bind( ListenSocket, (SOCKADDR*) &service, sizeof(service)) == SOCKET_ERROR) 
    {
        closesocket(ListenSocket);
        return 1;
    }

    if (listen( ListenSocket, 1 ) == SOCKET_ERROR) 
    {
        closesocket(ListenSocket);
        return 1;
    }

    SOCKET AcceptSocket;

    AcceptSocket = accept( ListenSocket, NULL, NULL );
    if (AcceptSocket == INVALID_SOCKET) 
    {
        closesocket(ListenSocket);
        return 1;
    } 


    BYTE *pBuf = new BYTE[512];
    BYTE *pCurBuf = pBuf;
    int BytesRemaining = 512;

    while (BytesRemaining > 0)
    {
        int CurBytesReceived = ::recv(AcceptSocket, (char*)pCurBuf, BytesRemaining, 0);

        if (CurBytesReceived == 0)  <font color="Red">//<-- put a breakpoint here - 256 bytes will be received</font>
        {
            // connection was gracefully closed

            break;
        }
        else if (CurBytesReceived == SOCKET_ERROR)
        {
            // Some error occurred!

            int rc = WSAGetLastError();

            if (rc != WSAEWOULDBLOCK)
            {
                break;
            }
        }
        else
        {
            // Some bytes were successfully received

            BytesRemaining -= CurBytesReceived;
            pCurBuf += CurBytesReceived;
        }
    }

    delete[] pBuf;


    closesocket(AcceptSocket);
    closesocket(ListenSocket);

    return 0;
}


<font color="Green">//----------------------------------------------
// Sender (on UI thread)
//----------------------------------------------</font>
void CMYTestDlg::OnOK()
{
    AfxBeginThread(&TestThreadProc, NULL);
    ::Sleep(1000); <font color="Red">//<--hehe DON'T DO THIS IN REAL LIFE - this is JUST A TEST LOL</font>


    SOCKET ConnectSocket;
    ConnectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (ConnectSocket == INVALID_SOCKET) 
    {
        return;
    }

    sockaddr_in clientService; 
    clientService.sin_family = AF_INET;
    clientService.sin_addr.s_addr = inet_addr( "127.0.0.1" );
    clientService.sin_port = htons( 2460 );

    if ( connect( ConnectSocket, (SOCKADDR*) &clientService, sizeof(clientService) ) == SOCKET_ERROR) 
    {
        return;
    }


    BYTE *pBuf = new BYTE[512];

    send(ConnectSocket, (const char *)pBuf, 256, 0);

    delete[] pBuf;


    ::MessageBox(*this, _T("Waiting for socket receive :-P"), _T("Waiting"), MB_OK);

    closesocket(ConnectSocket);

    return;
}

Mark Salsbery
Microsoft MVP - Visual C++

JudyL_FL wrote:

Can you try calling WSAGetLastError after you receive the partial bytes?

Mark Salsbery
Microsoft MVP - Visual C++

Mark Salsbery wrote:

WSAGetLastError() returns 0;

JudyL_FL wrote:

was curious - it was easier to have you check since you had working code.

JudyL_FL wrote:

How long does your recv sit before it returns?

JudyL_FL wrote:

I think we have our answer - always check the number of bytes received

Mark Salsbery
Microsoft MVP - Visual C++

Mark Salsbery wrote:

and it taught me to read the documentation thoroughly

Mark Salsbery
Microsoft MVP - Visual C++