Question

I’m writing a small application with a client and a server – the client sends a question and the server answers.

I managed to do the first part – the server gets the question from the client, do some work and sends back an answer. I just can’t figure out how to tell the client to wait for a response from the server.

This is my client code:

char* ipAddress = (char*)malloc(15);
wcstombs(ipAddress, (TCHAR*)argv[1], 15);
DWORD port = wcstod(argv[2], _T('\0'));
DWORD numOfThreads = wcstod(argv[3], _T('\0;'));
DWORD method = wcstod(argv[4], _T('\0;'));

//initialize windows sockets service
WSADATA wsaData;
int iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
assert(iResult==NO_ERROR);

//prepare server address
sockaddr_in server_addr;
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = inet_addr(ipAddress);
server_addr.sin_port = htons(port);

//create socket
SOCKET hClientSocket= socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
assert(hClientSocket!=INVALID_SOCKET);

//connect to server
int nRes=connect(hClientSocket, (SOCKADDR*)&server_addr, sizeof(server_addr));
assert(nRes!=SOCKET_ERROR);

char* buf = "GET /count.htm HTTP/1.1\r\nHost: 127.0.0.1:666\r\nAccept: text/html,application/xhtml+xml\r\nAccept-Language: en-us\r\nAccept-Encoding: gzip, deflate\r\nUser-Agent: Mozilla/5.0\r\n\r\n";

int nBytesToSend= strlen(buf);
int iPos=0;

while(nBytesToSend)
{
    int nSent=send(hClientSocket,buf,nBytesToSend,0);
    assert(nSent!=SOCKET_ERROR);

    nBytesToSend-=nSent;
    iPos+=nSent;
}

closesocket(hClientSocket);

int nLen = sizeof(server_addr);
SOCKET hRecvSocket=accept(hClientSocket,(SOCKADDR*)&server_addr, &nLen);
assert(hRecvSocket!=INVALID_SOCKET);

//prepare buffer for incoming data
char serverBuff[256];
int nLeft=sizeof(serverBuff);
iPos=0;

do //loop till there are no more data
{
    int nNumBytes=recv(hRecvSocket,serverBuff+iPos,nLeft,0);

    //check if cleint closed connection
    if(!nNumBytes)
        break;

    assert(nNumBytes!=SOCKET_ERROR);

    //update free space and pointer to next byte
    nLeft-=nNumBytes;
    iPos+=nNumBytes;

}while(1);

The assertion after the SOCKET hRecvSocket=accept(hClientSocket,(SOCKADDR*)&server_addr, &nLen); line fails.

Answer 1

The closesocket and accept call after your “send” loop – remove those calls. accept is for servers listening for incoming connections, not for clients that are already connected.

After your send() loop completes, go straight into your recv() loop. That should solve your immediate problem:

Also, your send loop is forgetting to referenece iPos on the buffer like I think you intended to. This is what you wanted:

int nSent=send(hClientSocket,buf+iPos,nBytesToSend,0);

In network programming, sockets will fail due to network conditions beyond your control. So “asserts” on network calls are not always appropriate. Better to just expect failure and be prepared to handle it. Typically, closing the socket and the active connection is the way to handle most errors.