Why wont a simple socket to the localhost connect?

Question

I am following a tutorial that teaches me how to use win32 sockets(winsock2). I am attempting to create a simple socket that connects to the "localhost" but my program is failing when I attempt to connect to the local host(at the function connect()).

Do I need admin privileges to connect to the localhost? Maybe thats why it fails? Maybe theres a problem with my code? I have tried the ports 8888 & 8000 & they both fail.

Also if I change the port to 80 & connect to www.google.com I can connect BUT I get no response back. Is that because I haven't sent a HTTP request or am I meant to get some response back?

Here's my code (with the includes removed):

// Constants & Globals //
typedef unsigned long IPNumber;    // IP number typedef for IPv4
const int SOCK_VER    = 2;
const int SERVER_PORT = 8888;  // 8888
SOCKET mSocket        = INVALID_SOCKET;
SOCKADDR_IN sockAddr  = {0};
WSADATA wsaData;
HOSTENT* hostent;


int _tmain(int argc, _TCHAR* argv[])
{
    // Initialise winsock version 2.2
    if (WSAStartup(MAKEWORD(SOCK_VER,2), &wsaData) != 0)
    {
        printf("Failed to initialise winsock\n");
        WSACleanup();
        system("PAUSE");
        return 0;
    }

    if (LOBYTE(wsaData.wVersion) != SOCK_VER || HIBYTE(wsaData.wVersion) != 2)
    {
        printf("Failed to load the correct winsock version\n");
        WSACleanup();
        system("PAUSE");
        return 0;
    }

    // Create socket
    mSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (mSocket == INVALID_SOCKET)
    {
        printf("Failed to create TCP socket\n");
        WSACleanup();
        system("PAUSE");
        return 0;
    }


    // Get IP Address of website by the domain name, we do this by contacting(??) the Domain Name Server
    if ((hostent = gethostbyname("localhost")) == NULL)  // "localhost"  www.google.com
    {
        printf("Failed to resolve website name to an ip address\n");
        WSACleanup();
        system("PAUSE");
        return 0;
    }

    sockAddr.sin_port             = htons(SERVER_PORT);
    sockAddr.sin_family           = AF_INET;
    sockAddr.sin_addr.S_un.S_addr = (*reinterpret_cast <IPNumber*> (hostent->h_addr_list[0]));
    // sockAddr.sin_addr.s_addr=*((unsigned long*)hostent->h_addr);  // Can also do this

    // ERROR OCCURS ON NEXT LINE: Connect to server
    if (connect(mSocket, (SOCKADDR*)(&sockAddr), sizeof(sockAddr)) != 0)
    {
        printf("Failed to connect to server\n");
        WSACleanup();
        system("PAUSE");
        return 0;
    }

    printf("Got to here\r\n");
    // Display message from server
    char buffer[1000];
    memset(buffer,0,999);
    int inDataLength=recv(mSocket,buffer,1000,0);
    printf("Response: %s\r\n", buffer);

    // Shutdown our socket
    shutdown(mSocket, SD_SEND);

    // Close our socket entirely
    closesocket(mSocket);

    // Cleanup Winsock
    WSACleanup();

    system("pause");
    return 0;
}

Solution 1

Someone should be listening in the port you are connecting to. Try writing a small server program that will listen for incoming connections. If connect succeeds obviously you are connected to google but you need to send a HTTP request (from C? - that would be difficult).

Solution 2

As you're willing to use the TCP-Protocol wich is connection based you will need a communication counterpart such as an application listening on port 8888 to respond to your connection initiation request (SYN-Packet in TCP Terms)

You could use the unix tool netcat (which is also availibla for other OS') to do so without the need of admin privileges...

nc -l 8888

... wich opens a listening socket on port 8888 on your local machine

However, on unix systems you aren't allowed to listen on so called well known ports without admin privileges.

For more information read about the TCP Connection Life-Cycle