recv function blocks with keep-alive (HTTP)

Question

I'm learning about sockets in Windows, also HTTP protocol. So I was doing some tests with keep-alive but for some reason recv hangs for about 5 seconds, here it's:

VOID TestWinsock()
{
    WSADATA WsaData;
    addrinfo hints;
    addrinfo* hResult;
    SOCKET hsocket;
    int Result;

    WSAStartup(MAKEWORD(2, 2), &WsaData);
    RtlZeroMemory(&hints, sizeof(hints));

    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;
    Result = getaddrinfo("localhost", "80", &hints, &hResult);
    if (Result != 0)
    {
        return;
    }

    hsocket = socket(hResult->ai_family, hResult->ai_socktype, hResult->ai_protocol);
    if (hsocket == INVALID_SOCKET)
    {
        return;
    }

    Result = connect(hsocket, hResult->ai_addr, (int)hResult->ai_addrlen);
    if (Result == SOCKET_ERROR)
    {
        return;
    }

    char* POSTContent;
    char HTTPRequestBuffer[1024];
    char RecvBuffer[1024];

    char* HTTPRequest =
        "POST %s HTTP/1.0\r\n"
        "Host: %s\r\n"
        "connection: keep-alive\r\n"
        "Content-type: application/x-www-form-urlencoded\r\n"
        "Content-Length: %u\r\n"
        "\r\n"
        "%s"
        "\r\n"
        "\r\n";

    POSTContent = "variable1=10";
    wsprintfA(
        HTTPRequestBuffer,
        HTTPRequest,
        "/tests/test.php",
        "127.0.0.1",
        strlen(POSTContent),
        POSTContent
        );

    int sent = send(hsocket, HTTPRequestBuffer, strlen(HTTPRequestBuffer), 0);
    RtlZeroMemory(RecvBuffer, sizeof(RecvBuffer));

    // here recv blocks for about 5 seconds, yeah, it reads only 100 bytes, tried with something like sizeof(RecvBuffer) as well.
    recv(hsocket, RecvBuffer, 100, 0);

    ....
}

I want to know how to solve this problem or which is the proper way to use keep-alive.

Answer 1

In your HTTP request, you send an additional \\r\\n\\r\\n which you do not include in your Content-Length , thus the data and and the length announced does not match. The HTTP standard says that :

When a Content-Length is given in a message where a message-body is allowed, its field value MUST exactly match the number of OCTETs in the message-body.

The MUST is important, it means the server is totally in its right to reject your request. The fact that you specified keep-alive can also mean that the server waits for a next, valid request. Since you only send 4 bytes, the server end up closing the connection anyway after 5s, and probably sends an error (this part is only speculation about what actually happens).