Question

is it possible to send 2 consecutive TCP packets out as seen in this picture here:

I currently have set TCP_NODELAY to true and SO_SNDBUF to 0. I have also called send in my program 2x. This is the result I obtained:

The main issue here will be the delayed-ack causing the slow network performance in the 2nd screenshot.

The code for the server:

DWORD WINAPI ServerHandler(void *lp){
    //The port you want the server to listen on
    int host_port = 1852;

    //Initialize socket support WINDOWS ONLY!
    unsigned short wVersionRequested;
    WSADATA wsaData;
    int err;
    wVersionRequested = MAKEWORD( 2, 2 );
    err = WSAStartup( wVersionRequested, &wsaData );
    if ( err != 0 || ( LOBYTE( wsaData.wVersion ) != 2 || HIBYTE( wsaData.wVersion ) != 2 )) 
    {
        printf("Could not find useable sock dll %d\n",WSAGetLastError());
        return 0;
    }

    //Initialize sockets and set any options
    int hsock;
    BOOL bOptVal = true;
    int bOptLen = sizeof (BOOL);
    int iResult = 0;

    hsock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if(hsock == INVALID_SOCKET)
    {
        printf("Error initializing socket %d\n",WSAGetLastError());
        return 0;
    }

    iResult = setsockopt(hsock, SOL_SOCKET, SO_REUSEADDR, (char *) &bOptVal, bOptLen);
    if (iResult == SOCKET_ERROR)
        printf("setsockopt for SO_REUSEADDR failed with error: %d\n", WSAGetLastError());
    else
        printf("Set SO_REUSEADDR: ON\n");

    iResult = setsockopt(hsock, SOL_SOCKET, SO_KEEPALIVE, (char *) &bOptVal, bOptLen);
    if (iResult == SOCKET_ERROR)
        printf("setsockopt for SO_KEEPALIVE failed with error: %d\n", WSAGetLastError());
    else
        printf("Set SO_KEEPALIVE: ON\n");

    //Bind and listen
    struct sockaddr_in my_addr;

    my_addr.sin_family = AF_INET ;
    my_addr.sin_port = htons(host_port);

    memset(&(my_addr.sin_zero), 0, 8);
    my_addr.sin_addr.s_addr = INADDR_ANY ;

    if( bind( hsock, (struct sockaddr*)&my_addr, sizeof(my_addr)) == SOCKET_ERROR )
    {
        printf("Error binding to socket, make sure nothing else is listening on this port %d\n",WSAGetLastError());
        closesocket(hsock);
        return 0;
    }
    if( listen( hsock, MAXCONN) == SOCKET_ERROR )
    {
        printf("Error listening %d\n",WSAGetLastError());
        closesocket(hsock);
        return 0;
    }

    //Now lets to the server stuff

    int* csock;
    sockaddr_in sadr;
    int addr_size = sizeof(SOCKADDR);
    
    printf("waiting for a connection\n");

    while(true)
    {            
        csock = (int*)malloc(sizeof(int));
        if((*csock = accept( hsock, (SOCKADDR*)&sadr, &addr_size))!= INVALID_SOCKET )
        {
            printf("Received connection from %s, %u @ socket %d\n", inet_ntoa(sadr.sin_addr), sadr.sin_port, *csock);
            
            BOOL bOptVal = true;            
            int iResult = setsockopt(*csock, SOL_SOCKET, TCP_NODELAY, (char *) &bOptVal, sizeof(bOptVal));
            if (iResult == SOCKET_ERROR)
                printf("setsockopt for TCP_NODELAY failed with error: %d\n", WSAGetLastError());
            else
                printf("Set TCP_NODELAY: TRUE\n");

            int sendBuf = 0;
            iResult = setsockopt(*csock, SOL_SOCKET, SO_SNDBUF, (char *) &sendBuf, sizeof(sendBuf));
            if (iResult == SOCKET_ERROR)
                printf("setsockopt for SO_SNDBUF failed with error: %d\n", WSAGetLastError());
            else
                printf("Setsockopt for SO_SNDBUF set to 0\n");


            CreateThread(0,0,&SocketHandler, (void*)csock , 0,0);
        }
        else
        {
            printf("Error accepting %d\n",WSAGetLastError());
        }
    }
    WSACleanup();
}

The code I used for sending data:

int send_TCP_2(int cs, char responseLength[], char data[], int respond_length, int data_length)
{   
    int size = respond_length + data_length;
    int index = 0;

    // combined 10 byte response with data as 1 packet
    std::vector<char> packet(size);

    for(int i=0; i<respond_length; i++)
    {
        packet[index] = responseLength[i];
        index++;
    }

    for(int i=0; i<data_length; i++)
    {
        packet[index] = data[i];
        index++;
    }
    
    int status;
    char *data_ptr = &packet[0];
    while(size > 0)
    {
        status = send(cs, data_ptr, size, 0);
        if(status > 0)
        {
            data_ptr += status;
            size -= status;
        }
        else if (status == SOCKET_ERROR)
        {
            int error_code = WSAGetLastError();
            printf("send_TCP_2 failed with error code: %d\n", error_code);
            return 0;   // send failed
        }
    }
    return 1;   // send successful  
}

I have attached the screenshot when I do not disable Nagle and not touching SO_SNDBUF.

Answer 1

thanks for all the advise! Setting TCP_NODELAY to true will work as mentioned by most. I have made a silly mistake in setsockopt!

I should have put IPPROTO_TCP instead of SOL_SOCKET